Question: Which of the following organisms is the decomposer in this food web?

Choices:
A. sea otter
B. black rockfish
C. kelp bass
D. bat star

Below is a food web from an ocean ecosystem in Monterey Bay, off the coast of California.
A food web models how the matter eaten by organisms moves through an ecosystem. The arrows in a food web represent how matter moves between organisms in an ecosystem.

A food web is a model.
A food web shows where organisms in an ecosystem get their food. Models can make things in nature easier to understand because models can represent complex things in a simpler way. If a food web showed every organism in an ecosystem, the food web would be hard to understand. So, each food web shows how some organisms in an ecosystem can get their food.
Arrows show how matter moves.
A food web has arrows that point from one organism to another. Each arrow shows the direction that matter moves when one organism eats another organism. An arrow starts from the organism that is eaten. The arrow points to the organism that is doing the eating.
An organism in a food web can have more than one arrow pointing from it. This shows that the organism is eaten by more than one other organism in the food web.
An organism in a food web can also have more than one arrow pointing to it. This shows that the organism eats more than one other organism in the food web.

Decomposers help break down dead organisms into simpler matter, such as nutrients. These nutrients can then help plants and other organisms grow. In a food web, there is an arrow pointing from another organism to a decomposer. There are no arrows pointing from a decomposer to another organism.
The bat star does not have arrows pointing from it to other organisms. So, the bat star is a decomposer.
The sea otter has an arrow pointing from it. So, the sea otter is not a decomposer.
The kelp bass has an arrow pointing from it. So, the kelp bass is not a decomposer.
The sea cucumber does not have arrows pointing from it to other organisms. So, the sea cucumber is a decomposer.
The black rockfish has an arrow pointing from it. So, the black rockfish is not a decomposer.

natural science


Question: Select the bird.

Choices:
A. piranha
B. box turtle
C. sea otter
D. emu

Birds have feathers, two wings, and a beak.

An emu is a bird. It has feathers, two wings, and a beak.
Emus cannot fly, but they can run very fast. They run to avoid predators.
A box turtle is a reptile. It has scaly, waterproof skin.
Box turtles can live to be over 100 years old!
A sea otter is a mammal. It has fur and feeds its young milk.
Sea otters have very thick fur. Their fur keeps them warm in cold water.
A piranha is a fish. It lives underwater. It has fins, not limbs.
Piranhas have sharp teeth. Piranhas hunt in groups. A group of piranhas can eat a large animal.

natural science

Identify mammals, birds, fish, reptiles, and amphibians

local parquet snapshot does not include README/license metadata; verify upstream before public upload


Question:
What do these two changes have in common?
water evaporating from a puddle
dust settling out of the air

Choices:
A. Both are caused by cooling.
B. Both are only physical changes.
C. Both are chemical changes.
D. Both are caused by heating.

Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.
In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.
In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Water evaporating from a puddle is a change of state. So, it is a physical change. The liquid changes into a gas, but a different type of matter is not formed.
Dust settling out of the air is a physical change. As the dust settles, or falls, it might land on furniture or the ground. This separates dust particles from the air, but does not form a different type of matter.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are physical changes. No new matter is created.
Both are chemical changes.
Both changes are physical changes. They are not chemical changes.
Both are caused by heating.
Water evaporating is caused by heating. But dust settling out of the air is not.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: What is the expected ratio of offspring with black fur to offspring with brown fur? Choose the most likely ratio.

Choices:
A. 4:0
B. 2:2
C. 1:3
D. 3:1
E. 0:4

In a group of rabbits, some individuals have black fur and others have brown fur. In this group, the gene for the fur color trait has two alleles. The allele for brown fur (f) is recessive to the allele for black fur (F).
This Punnett square shows a cross between two rabbits.

Offspring phenotypes: dominant or recessive?
How do you determine an organism's phenotype for a trait? Look at the combination of alleles in the organism's genotype for the gene that affects that trait. Some alleles have types called dominant and recessive. These two types can cause different versions of the trait to appear as the organism's phenotype.
If an organism's genotype has at least one dominant allele for a gene, the organism's phenotype will be the dominant allele's version of the gene's trait.
If an organism's genotype has only recessive alleles for a gene, the organism's phenotype will be the recessive allele's version of the gene's trait.
A Punnett square shows what types of offspring a cross can produce. The expected ratio of offspring types compares how often the cross produces each type of offspring, on average. To write this ratio, count the number of boxes in the Punnett square representing each type.
For example, consider the Punnett square below.
 | F | f
F | FF | Ff
f | Ff | ff
There is 1 box with the genotype FF and 2 boxes with the genotype Ff. So, the expected ratio of offspring with the genotype FF to those with Ff is 1:2.

To determine how many boxes in the Punnett square represent offspring with black fur or brown fur, consider whether each phenotype is the dominant or recessive allele's version of the fur color trait. The question tells you that the f allele, which is for brown fur, is recessive to the F allele, which is for black fur.
Black fur is the dominant allele's version of the fur color trait. A rabbit with the dominant version of the fur color trait must have at least one dominant allele for the fur color gene. So, offspring with black fur must have the genotype FF or Ff.
There are 3 boxes in the Punnett square with the genotype FF or Ff. These boxes are highlighted below.
Brown fur is the recessive allele's version of the fur color trait. A rabbit with the recessive version of the fur color trait must have only recessive alleles for the fur color gene. So, offspring with brown fur must have the genotype ff.
There is 1 box in the Punnett square with the genotype ff. This box is highlighted below.
So, the expected ratio of offspring with black fur to offspring with brown fur is 3:1. This means that, on average, this cross will produce 3 offspring with black fur for every 1 offspring with brown fur.

natural science

Use Punnett squares to calculate ratios of offspring types


Question:
What do these two changes have in common?
water evaporating from a lake
stretching a rubber band

Choices:
A. Both are chemical changes.
B. Both are caused by heating.
C. Both are only physical changes.
D. Both are caused by cooling.

Chemical changes and physical changes are two common ways matter can change.
In a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it reacts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.
In a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Water evaporating from a lake is a change of state. So, it is a physical change. The liquid changes into a gas, but a different type of matter is not formed.
Stretching a rubber band is a physical change. The rubber band gets longer. But it is still made of the same type of matter as before.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are physical changes. No new matter is created.
Both are chemical changes.
Both changes are physical changes. They are not chemical changes.
Both are caused by heating.
Water evaporating is caused by heating. But stretching a rubber band is not.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: How long is the Red Sea?

Choices:
A. 2,240 centimeters
B. 2,240 millimeters
C. 2,240 kilometers
D. 2,240 meters

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using metric units, length can be written with units of millimeters, centimeters, meters, or kilometers. One meter contains 100 centimeters or 1,000 millimeters. So, 1 meter is larger than 1 centimeter, and 1 centimeter is larger than 1 millimeter.
The tip of the pencil shown here is only 1 millimeter wide, but the pencil is about 16 centimeters long.
A red fox is about 1 meter long. The Sydney Harbour Bridge in Australia is about 1,000 meters, or 1 kilometer, in length.

The best estimate for the length of the Red Sea is 2,240 kilometers.
2,240 millimeters, 2,240 centimeters, and 2,240 meters are all too short.

natural science

Choose metric units of distance, mass, and volume


Question: How long is an adult great white shark?

Choices:
A. 5 millimeters
B. 5 centimeters
C. 5 meters
D. 5 kilometers

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using metric units, length can be written with units of millimeters, centimeters, meters, or kilometers. One meter contains 100 centimeters or 1,000 millimeters. So, 1 meter is larger than 1 centimeter, and 1 centimeter is larger than 1 millimeter.
The tip of the pencil shown here is only 1 millimeter wide, but the pencil is about 16 centimeters long.
A red fox is about 1 meter long. The Sydney Harbour Bridge in Australia is about 1,000 meters, or 1 kilometer, in length.

The best estimate for the length of an adult great white shark is 5 meters.
5 millimeters and 5 centimeters are too short. 5 kilometers is too long.

natural science


Question: How long is a tennis racket?

Choices:
A. 55 meters
B. 55 centimeters
C. 55 kilometers
D. 55 millimeters

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using metric units, length can be written with units of millimeters, centimeters, meters, or kilometers. One meter contains 100 centimeters or 1,000 millimeters. So, 1 meter is larger than 1 centimeter, and 1 centimeter is larger than 1 millimeter.
The tip of the pencil shown here is only 1 millimeter wide, but the pencil is about 16 centimeters long.
A red fox is about 1 meter long. The Sydney Harbour Bridge in Australia is about 1,000 meters, or 1 kilometer, in length.

The best estimate for the length of a tennis racket is 55 centimeters.
55 millimeters is too short. 55 meters and 55 kilometers are too long.

natural science


Question: Select the mammal below.

Choices:
A. red kangaroo
B. red crowned crane
C. great white shark
D. brown tree frog

Mammals have hair or fur and feed their young milk.
Mammals are warm-blooded. Warm-blooded animals can control their body temperature.
A koala is an example of a mammal.

Birds, mammals, fish, reptiles, and amphibians are groups of animals. Scientists sort animals into each group based on traits they have in common. This process is called classification.
Classification helps scientists learn about how animals live. Classification also helps scientists compare similar animals.

A brown tree frog is an amphibian. It has moist skin and begins its life in water.
There are many kinds of tree frogs. Most tree frogs are very small. They can walk on thin branches.
A great white shark is a fish. It lives underwater. It has fins, not limbs.
Great white sharks can live for up to 70 years.
A red crowned crane is a bird. It has feathers, two wings, and a beak.
Cranes wade in shallow water to look for food. Cranes eat insects, worms, and plants.
A red kangaroo is a mammal. It has fur and feeds its young milk.
Kangaroos hop to move around. They use their large tails for balance while hopping.

natural science


Question: Select the vertebrate.

Choices:
A. fire salamander
B. ladybug
C. metallic tarantula
D. peacock mantis shrimp

Hint: Mammals, birds, fish, reptiles, and amphibians are vertebrates.

Vertebrates and invertebrates are both groups of animals.
A vertebrate has a backbone. The backbone is made of many bones in an animal's back. A vertebrate's backbone helps connect the different parts of its body. In the drawings below, each vertebrate's backbone is colored orange.
An invertebrate does not have a backbone. In fact, invertebrates do not have any bones! Some invertebrates have an outer cover on their body called an exoskeleton. Other invertebrates have a soft body.

A ladybug is an insect. Like other insects, a ladybug is an invertebrate. It does not have a backbone. It has an exoskeleton.
A fire salamander is an amphibian. Like other amphibians, a fire salamander is a vertebrate. It has a backbone.
Like other tarantulas, a metallic tarantula is an invertebrate. It does not have a backbone. It has an exoskeleton.
A peacock mantis shrimp is a crustacean. Like other crustaceans, a peacock mantis shrimp is an invertebrate. It does not have a backbone. It has an exoskeleton.

natural science


Question: In this food web, which organism contains matter that eventually moves to the earthworm?

Choices:
A. parasitic jaeger
B. grizzly bear
C. mushroom
D. barren-ground caribou
E. lichen

Below is a food web from a tundra ecosystem in Nunavut, a territory in Northern Canada.
A food web models how the matter eaten by organisms moves through an ecosystem. The arrows in a food web represent how matter moves between organisms in an ecosystem.

A food web is a model.
A food web shows where organisms in an ecosystem get their food. Models can make things in nature easier to understand because models can represent complex things in a simpler way. If a food web showed every organism in an ecosystem, the food web would be hard to understand. So, each food web shows how some organisms in an ecosystem can get their food.
Arrows show how matter moves.
A food web has arrows that point from one organism to another. Each arrow shows the direction that matter moves when one organism eats another organism. An arrow starts from the organism that is eaten. The arrow points to the organism that is doing the eating.
An organism in a food web can have more than one arrow pointing from it. This shows that the organism is eaten by more than one other organism in the food web.
An organism in a food web can also have more than one arrow pointing to it. This shows that the organism eats more than one other organism in the food web.

Use the arrows to follow how matter moves through this food web. For each answer choice, try to find a path of arrows to the earthworm.
No arrows point from the mushroom to any other organisms. So, in this food web, matter does not move from the mushroom to the earthworm.
The only arrow pointing from the lichen leads to the barren-ground caribou. There are two arrows pointing from the barren-ground caribou to other organisms. One arrow points to the grizzly bear. The only arrow pointing from the grizzly bear leads to the mushroom. The other arrow pointing from the barren-ground caribou leads to the mushroom. No arrows point from the mushroom to any other organisms. So, in this food web, matter does not move from the lichen to the earthworm.
There are two arrows pointing from the barren-ground caribou to other organisms. One arrow points to the grizzly bear. The only arrow pointing from the grizzly bear leads to the mushroom. The other arrow pointing from the barren-ground caribou leads to the mushroom. No arrows point from the mushroom to any other organisms. So, in this food web, matter does not move from the barren-ground caribou to the earthworm.
The only arrow pointing from the grizzly bear leads to the mushroom. No arrows point from the mushroom to any other organisms. So, in this food web, matter does not move from the grizzly bear to the earthworm.There is one path matter can take from the parasitic jaeger to the earthworm: parasitic jaeger->rough-legged hawk->earthworm.

natural science


Question: How long is a long-distance running race?

Choices:
A. 15 miles
B. 15 yards
C. 15 feet
D. 15 inches

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using customary units, length may be written with units of inches, feet, yards, or miles.
There are 12 inches in 1 foot, and 3 feet in 1 yard. There are 5,280 feet in 1 mile.
A football is about 1 foot long. A football field is 100 yards long.

The best estimate for the length of a long-distance running race is 15 miles.
15 inches, 15 feet, and 15 yards are all too short.

natural science

Choose customary units of distance, mass, and volume


Question:
What do these two changes have in common?
a penny tarnishing
an old sandwich rotting in a trashcan

Choices:
A. Both are only physical changes.
B. Both are chemical changes.
C. Both are caused by cooling.
D. Both are caused by heating.

Chemical changes and physical changes are two common ways matter can change.
In a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it reacts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.
In a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Metal turning less shiny over time is called tarnishing. A penny tarnishing is a chemical change. When air touches the penny, the surface of the penny changes into a different type of matter. This matter makes the penny dull.
A sandwich rotting is a chemical change. The matter in the sandwich breaks down and slowly turns into a different type of matter.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are chemical changes. They are not physical changes.
Both are chemical changes.
Both changes are chemical changes. The type of matter before and after each change is different.
Both are caused by heating.
Neither change is caused by heating.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: Select the liquid.

Choices:
A. book
B. water from a faucet
C. arrowhead
D. stone statue

Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.
When matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.
Some solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.
When matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.
Some liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.
When matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.
Many gases are invisible. Air is a gas.

An arrowhead is a solid. A solid has a size and shape of its own. An arrowhead is made of rock.
The water from a faucet is a liquid. A liquid takes the shape of any container it is in. If you put water from a faucet into a container, the water will take the shape of that container. But the water will still take up the same amount of space.
A book is a solid. When you read a book, you bend the spine and turn the pages. But the book still has a shape of its own.
A stone statue is a solid. A solid has a size and shape of its own. Stone statues are made of one or more pieces of rock. Each piece of rock has a size and shape of its own.

natural science


Question: Select the mammal.

Choices:
A. fire salamander
B. ostrich
C. elephant seal
D. parrotfish

Mammals have hair or fur and feed their young milk.

A parrotfish is a fish. It lives underwater. It has fins, not limbs.
Parrotfish have fins and live underwater near coral reefs. They get their name from their bird-like beak!
An elephant seal is a mammal. It has hair and feeds its young milk.
Seals have flippers instead of arms! They use their flippers to swim underwater or to crawl on the beach.
A fire salamander is an amphibian. It has moist skin and begins its life in water.
Fire salamanders can release poison from their skin. This poison helps protect them from predators.
An ostrich is a bird. It has feathers, two wings, and a beak.
The ostrich is the largest bird alive today. Ostriches cannot fly, but they can run very fast.

natural science


Question: Select the invertebrate.

Choices:
A. carp
B. toucan
C. luna moth
D. koala

Hint: Insects, spiders, and worms are invertebrates.

Vertebrates and invertebrates are both groups of animals.
A vertebrate has a backbone. The backbone is made of many bones in an animal's back. A vertebrate's backbone helps connect the different parts of its body. In the drawings below, each vertebrate's backbone is colored orange.
An invertebrate does not have a backbone. In fact, invertebrates do not have any bones! Some invertebrates have an outer cover on their body called an exoskeleton. Other invertebrates have a soft body.

A carp is a fish. Like other fish, a carp is a vertebrate. It has a backbone.
A koala is a mammal. Like other mammals, a koala is a vertebrate. It has a backbone.
A luna moth is an insect. Like other insects, a luna moth is an invertebrate. It does not have a backbone. It has an exoskeleton.
A toucan is a bird. Like other birds, a toucan is a vertebrate. It has a backbone.

natural science


Question: Select the animal.

Choices:
A. Orcas swim in the ocean.
B. Walnut trees have many green leaves.
C. Dandelions can grow small yellow flowers.
D. Lavender bushes have many purple flowers.

Plants and animals are living things. Living things are called organisms.
Plants come in many shapes and sizes. Most plants grow in the ground. They might grow leaves, flowers, and fruit. Plants cannot move around on their own like animals can.
Animals also come in many shapes and sizes. Most animals can move around. Animals might run, swim, jump, or fly. Animals eat plants or other organisms for food.

An orca is an animal. It swims in the ocean.
Orcas are also called killer whales. They hunt fish and other animals that live in the ocean.
A walnut tree is a plant. It has many green leaves.
People pick and eat walnuts from walnut trees. Walnuts are the tree's seeds!
A dandelion is a plant. It can grow small yellow flowers.
Dandelion seeds can be blown long distances by the wind.
A lavender bush is a plant. It has many purple flowers.
Lavender has a sweet smell. Some people use the oil from lavender bushes for perfume.

natural science


Question:
What do these two changes have in common?
mixing chocolate syrup into milk
stapling an envelope shut

Choices:
A. Both are only physical changes.
B. Both are caused by cooling.
C. Both are caused by heating.
D. Both are chemical changes.

Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.
In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.
In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Mixing chocolate syrup into milk is a physical change. The chocolate syrup and milk make a mixture. Making a mixture does not form a different type of matter.
Stapling an envelope shut is a physical change. The envelope and the staple get new shapes. Both are still made of the same type of matter.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are physical changes. No new matter is created.
Both are chemical changes.
Both changes are physical changes. They are not chemical changes.
Both are caused by heating.
Neither change is caused by heating.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: Select the living thing.

Choices:
A. rabbit
B. ice cube
C. scarecrow
D. rain

All living things are made up of cells. Plants, animals, and some fungi have many cells. Other living things are made up of just one cell.
All living things need food and water. Water helps living things break down food and remove waste. Food gives living things energy. They use energy from food to grow and change.
All living things sense changes in their environment. Living things might sense changes by seeing, smelling, hearing, or feeling. Living things can respond to the changes they sense.

A scarecrow is not a living thing.
A scarecrow does not have all the traits of a living thing. It is shaped like a person, but it does not grow. It does not need food or water.
Rain is not a living thing.
Rain is made of water. It helps living things survive. But it does not have all the traits of a living thing. Rain does not grow or need food.
A rabbit is a living thing.
Rabbits grow and respond to their environment. They need food and water. Rabbits are made up of many cells.
An ice cube is not a living thing.
An ice cube can change. It will melt in warm weather! But it does not have all the traits of a living thing. It does not need food.

natural science


Question: What is the probability that a muskmelon plant produced by this cross will be homozygous recessive for the fruit taste gene?

Choices:
A. 0/4
B. 3/4
C. 2/4
D. 1/4
E. 4/4

In a group of muskmelon plants, some individuals have sour fruit and others have sweet fruit. In this group, the gene for the fruit taste trait has two alleles. The allele for sweet fruit (f) is recessive to the allele for sour fruit (F).
This Punnett square shows a cross between two muskmelon plants.

Offspring genotypes: homozygous or heterozygous?
How do you determine whether an organism is homozygous or heterozygous for a gene? Look at the alleles in the organism's genotype for that gene.
An organism with two identical alleles for a gene is homozygous for that gene.
If both alleles are dominant, the organism is homozygous dominant for the gene.
If both alleles are recessive, the organism is homozygous recessive for the gene.
An organism with two different alleles for a gene is heterozygous for that gene.
In a Punnett square, each box represents a different outcome, or result. Each of the four outcomes is equally likely to happen. Each box represents one way the parents' alleles can combine to form an offspring's genotype.
Because there are four boxes in the Punnett square, there are four possible outcomes.
An event is a set of one or more outcomes. The probability of an event is a measure of how likely the event is to happen. This probability is a number between 0 and 1, and it can be written as a fraction:
probability of an event = number of ways the event can happen / number of equally likely outcomes
You can use a Punnett square to calculate the probability that a cross will produce certain offspring. For example, the Punnett square below has two boxes with the genotype Ff. It has one box with the genotype FF and one box with the genotype ff. This means there are two ways the parents' alleles can combine to form Ff. There is one way they can combine to form FF and one way they can combine to form ff.
 | F | f
F | FF | Ff
f | Ff | ff
Consider an event in which this cross produces an offspring with the genotype ff. The probability of this event is given by the following fraction:
number of ways the event can happen / number of equally likely outcomes = number of boxes with the genotype ff / total number of boxes = 1 / 4

natural science

Use Punnett squares to calculate probabilities of offspring types


Question: Which of the following organisms is the primary consumer in this food web?

Choices:
A. sea urchin
B. phytoplankton
C. orca
D. black rockfish

Below is a food web from an ocean ecosystem in Monterey Bay, off the coast of California.
A food web models how the matter eaten by organisms moves through an ecosystem. The arrows in a food web represent how matter moves between organisms in an ecosystem.

A food web is a model.
A food web shows where organisms in an ecosystem get their food. Models can make things in nature easier to understand because models can represent complex things in a simpler way. If a food web showed every organism in an ecosystem, the food web would be hard to understand. So, each food web shows how some organisms in an ecosystem can get their food.
Arrows show how matter moves.
A food web has arrows that point from one organism to another. Each arrow shows the direction that matter moves when one organism eats another organism. An arrow starts from the organism that is eaten. The arrow points to the organism that is doing the eating.
An organism in a food web can have more than one arrow pointing from it. This shows that the organism is eaten by more than one other organism in the food web.
An organism in a food web can also have more than one arrow pointing to it. This shows that the organism eats more than one other organism in the food web.

Primary consumers eat producers. So, in a food web, primary consumers have arrows pointing to them from producers.
The black rockfish has an arrow pointing to it from the zooplankton. The zooplankton is not a producer. So, the black rockfish is not a primary consumer.
The phytoplankton does not have any arrows pointing to it. So, the phytoplankton is not a primary consumer.
The orca has an arrow pointing to it from the sea otter. The sea otter is not a producer. So, the orca is not a primary consumer.
The sea urchin has an arrow pointing to it from the kelp. The kelp is a producer, so the sea urchin is a primary consumer.
The kelp bass has an arrow pointing to it from the kelp. The kelp is a producer, so the kelp bass is a primary consumer.

natural science


Question: Select the mammal below.

Choices:
A. Banggai cardinalfish
B. gray crowned crane
C. snowy owl
D. black howler

Mammals have hair or fur and feed their young milk.
Mammals are warm-blooded. Warm-blooded animals can control their body temperature.
A red kangaroo is an example of a mammal.

Birds, mammals, fish, reptiles, and amphibians are groups of animals. Scientists sort animals into each group based on traits they have in common. This process is called classification.
Classification helps scientists learn about how animals live. Classification also helps scientists compare similar animals.

A snowy owl is a bird. It has feathers, two wings, and a beak.
Snowy owls live in cold places. Even their feet have feathers to keep warm!
A gray crowned crane is a bird. It has feathers, two wings, and a beak.
Cranes wade in shallow water to look for food. Cranes eat insects, worms, and plants.
A black howler is a mammal. It has hair and feeds its young milk.
Howler monkeys have loud calls, or howls. Their calls can be heard over three miles away!
A Banggai cardinalfish is a fish. It lives underwater. It has fins, not limbs.
Cardinalfish often live near coral reefs. They are nocturnal, which means that they are active mostly at night.

natural science


Question:
What do these two changes have in common?
baking an apple pie
plants making food from sunlight, air, and water

Choices:
A. Both are caused by heating.
B. Both are caused by cooling.
C. Both are only physical changes.
D. Both are chemical changes.

Chemical changes and physical changes are two common ways matter can change.
In a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it reacts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.
In a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Baking an apple pie is a chemical change. The type of matter in the pie changes. The apples become soft, and the crust turns brown.
Plants making food is a chemical change. Plants use energy from sunlight to change air and water into food. The food is sugar. Sugar is a different type of matter than air or water.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are chemical changes. They are not physical changes.
Both are chemical changes.
Both changes are chemical changes. The type of matter before and after each change is different.
Both are caused by heating.
Baking is caused by heating. But plants making food is not.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: How long is a pen?

Choices:
A. 18 kilometers
B. 18 centimeters
C. 18 meters
D. 18 millimeters

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using metric units, length can be written with units of millimeters, centimeters, meters, or kilometers. One meter contains 100 centimeters or 1,000 millimeters. So, 1 meter is larger than 1 centimeter, and 1 centimeter is larger than 1 millimeter.
The tip of the pencil shown here is only 1 millimeter wide, but the pencil is about 16 centimeters long.
A red fox is about 1 meter long. The Sydney Harbour Bridge in Australia is about 1,000 meters, or 1 kilometer, in length.

The best estimate for the length of a pen is 18 centimeters.
18 millimeters is too short. 18 meters and 18 kilometers are too long.

natural science


Question: Select the liquid.

Choices:
A. water in a waterfall
B. air from a hair dryer
C. chair
D. baseball

Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.
When matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.
Some solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.
When matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.
Some liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.
When matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.
Many gases are invisible. Air is a gas.

A baseball is a solid. A solid has a size and shape of its own. If you hit a baseball with a bat, the baseball will still have a size and shape of its own.
The air from a hair dryer is a gas. A gas expands to fill a space. A hair dryer uses a fan to blow warm air out. When the air leaves the hair dryer, the air expands to fill a much large space.
The water in a waterfall is a liquid. A liquid can change shape. But it still takes up the same amount of space. As water flows down a waterfall, the water changes shape.
A chair is a solid. A solid has a size and shape of its own. When you sit on a chair, it keeps its shape.

natural science


Question: How long is a bench?

Choices:
A. 11 inches
B. 11 feet
C. 11 yards
D. 11 miles

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using customary units, length may be written with units of inches, feet, yards, or miles.
There are 12 inches in 1 foot, and 3 feet in 1 yard. There are 5,280 feet in 1 mile.
A football is about 1 foot long. A football field is 100 yards long.

The best estimate for the length of a bench is 11 feet.
11 inches is too short. 11 yards and 11 miles are too long.

natural science


Question: What is the expected ratio of offspring with yellow pods to offspring with green pods? Choose the most likely ratio.

Choices:
A. 1:3
B. 3:1
C. 2:2
D. 0:4
E. 4:0

In a group of pea plants, some individuals have green pods and others have yellow pods. In this group, the gene for the pod color trait has two alleles. The allele for yellow pods (d) is recessive to the allele for green pods (D).
This Punnett square shows a cross between two pea plants.

Offspring phenotypes: dominant or recessive?
How do you determine an organism's phenotype for a trait? Look at the combination of alleles in the organism's genotype for the gene that affects that trait. Some alleles have types called dominant and recessive. These two types can cause different versions of the trait to appear as the organism's phenotype.
If an organism's genotype has at least one dominant allele for a gene, the organism's phenotype will be the dominant allele's version of the gene's trait.
If an organism's genotype has only recessive alleles for a gene, the organism's phenotype will be the recessive allele's version of the gene's trait.
A Punnett square shows what types of offspring a cross can produce. The expected ratio of offspring types compares how often the cross produces each type of offspring, on average. To write this ratio, count the number of boxes in the Punnett square representing each type.
For example, consider the Punnett square below.
 | F | f
F | FF | Ff
f | Ff | ff
There is 1 box with the genotype FF and 2 boxes with the genotype Ff. So, the expected ratio of offspring with the genotype FF to those with Ff is 1:2.

To determine how many boxes in the Punnett square represent offspring with yellow pods or green pods, consider whether each phenotype is the dominant or recessive allele's version of the pod color trait. The question tells you that the d allele, which is for yellow pods, is recessive to the D allele, which is for green pods.
Yellow pods is the recessive allele's version of the pod color trait. A pea plant with the recessive version of the pod color trait must have only recessive alleles for the pod color gene. So, offspring with yellow pods must have the genotype dd.
There are 0 boxes in the Punnett square with the genotype dd.
Green pods is the dominant allele's version of the pod color trait. A pea plant with the dominant version of the pod color trait must have at least one dominant allele for the pod color gene. So, offspring with green pods must have the genotype DD or Dd.
All 4 boxes in the Punnett square have the genotype DD or Dd.
So, the expected ratio of offspring with yellow pods to offspring with green pods is 0:4. This means that, based on the Punnett square, this cross will never produce offspring with yellow pods. Instead, this cross is expected to always produce offspring with green pods.

natural science


Question: What can seeds look like?

Choices:
A. Seeds are always small.
B. Seeds can be many shapes, colors, and sizes.
C. Seeds are always black or white.
D. Seeds are always round or oval-shaped.

Seeds can be many shapes, colors, and sizes.

Many plants have flowers. These plants can use their flowers to reproduce, or make new plants like themselves. How do plants use their flowers to reproduce?
First, the male part of the flower makes pollen, and the female part makes eggs. Animals, wind, or water can move pollen. Pollination is what happens when pollen is moved to the female part of the flower.
After pollination, sperm from the pollen can combine with the eggs. This is called fertilization. The fertilized eggs grow into seeds. The fruit grows around the seeds. Later, a seed can fall out of the fruit. It can germinate, or start to grow into a new plant.

Seeds can be big or small. This coconut seed is big.
Seeds can be many different shapes. These maple seeds are long and flat.
Seeds can be more than one color. These pistachio seeds are green and brown.

natural science

Describe and construct flowering plant life cycles


Question:
What do these two changes have in common?
tearing a piece of paper
stapling an envelope shut

Choices:
A. Both are chemical changes.
B. Both are caused by cooling.
C. Both are caused by heating.
D. Both are only physical changes.

Chemical changes and physical changes are two common ways matter can change.
In a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it reacts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.
In a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Tearing a piece of paper is a physical change. The paper tears into pieces. But each piece is still made of paper.
Stapling an envelope shut is a physical change. The envelope and the staple get new shapes. Both are still made of the same type of matter.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are physical changes. No new matter is created.
Both are chemical changes.
Both changes are physical changes. They are not chemical changes.
Both are caused by heating.
Neither change is caused by heating.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: How long is an ice skate?

Choices:
A. 12 inches
B. 12 feet
C. 12 yards
D. 12 miles

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using customary units, length may be written with units of inches, feet, yards, or miles.
There are 12 inches in 1 foot, and 3 feet in 1 yard. There are 5,280 feet in 1 mile.
A football is about 1 foot long. A football field is 100 yards long.

The best estimate for the length of an ice skate is 12 inches.
12 feet, 12 yards, and 12 miles are all too long.

natural science


Question: Select the mammal below.

Choices:
A. barn owl
B. wombat
C. ocean sunfish
D. flamingo

Mammals have hair or fur and feed their young milk.
Mammals are warm-blooded. Warm-blooded animals can control their body temperature.
A rabbit is an example of a mammal.

Birds, mammals, fish, reptiles, and amphibians are groups of animals. Scientists sort animals into each group based on traits they have in common. This process is called classification.
Classification helps scientists learn about how animals live. Classification also helps scientists compare similar animals.

A wombat is a mammal. It has fur and feeds its young milk.
Wombats have strong claws on their front feet. They use their claws to dig underground holes called burrows.
A barn owl is a bird. It has feathers, two wings, and a beak.
Barn owls live on every continent except Antarctica.
A flamingo is a bird. It has feathers, two wings, and a beak.
Flamingos live in large groups. These groups are called flocks.
An ocean sunfish is a fish. It lives underwater. It has fins, not limbs.
Ocean sunfish have a flat body and wide fins. They sometimes swim to the ocean's surface to rest in the sun.

natural science


Question: Select the living thing.

Choices:
A. toy car
B. ferris wheel
C. hedge maze
D. crayon

All living things are made up of cells. Plants, animals, and some fungi have many cells. Other living things are made up of just one cell.
All living things need food and water. Water helps living things break down food and remove waste. Food gives living things energy. They use energy from food to grow and change.
All living things sense changes in their environment. Living things might sense changes by seeing, smelling, hearing, or feeling. Living things can respond to the changes they sense.

A toy car is not a living thing.
If this toy car is wound up, it will roll forward. But toy cars do not have all of the traits of living things. They do not grow. They do not need food or water.
A hedge maze is a living thing.
Hedge mazes grow and respond to their environment. They need food and water. Hedge mazes are made up of many cells.
Hedge mazes are made from shrubs. People cut the shrubs into shapes that form a maze.
A ferris wheel is not a living thing.
A ferris wheel does not have all the traits of a living thing. It moves in a circle, but it does not grow. It does not need food or water.
A crayon is not a living thing.
Crayons do not have all of the traits of living things. They do not grow or respond to their environment. They do not need food or water.

natural science


Question:
What do these two changes have in common?
bleaching clothes
a piece of apple turning brown

Choices:
A. Both are caused by heating.
B. Both are caused by cooling.
C. Both are chemical changes.
D. Both are only physical changes.

Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.
In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.
In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Bleaching clothes is a chemical change. The bleach reacts with dark stains on the clothes. The reaction changes the stains into different types of matter that wash away easily.
A piece of apple turning brown is a chemical change. The apple reacts with oxygen in the air and turns into a different type of matter.
If you scrape off the brown layer of the apple, the inside is still white. The inside hasn't touched the air. So the chemical change didn't happen to that part of the apple.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are chemical changes. They are not physical changes.
Both are chemical changes.
Both changes are chemical changes. The type of matter before and after each change is different.
Both are caused by heating.
Neither change is caused by heating.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: What is the probability that a horse produced by this cross will have a reddish-brown coat?

Choices:
A. 0/4
B. 4/4
C. 1/4
D. 2/4
E. 3/4

In a group of horses, some individuals have a black coat and others have a reddish-brown coat. In this group, the gene for the coat color trait has two alleles. The allele for a black coat (L) is dominant over the allele for a reddish-brown coat (l).
This Punnett square shows a cross between two horses.

Offspring phenotypes: dominant or recessive?
How do you determine an organism's phenotype for a trait? Look at the combination of alleles in the organism's genotype for the gene that affects that trait. Some alleles have types called dominant and recessive. These two types can cause different versions of the trait to appear as the organism's phenotype.
If an organism's genotype has at least one dominant allele for a gene, the organism's phenotype will be the dominant allele's version of the gene's trait.
If an organism's genotype has only recessive alleles for a gene, the organism's phenotype will be the recessive allele's version of the gene's trait.
In a Punnett square, each box represents a different outcome, or result. Each of the four outcomes is equally likely to happen. Each box represents one way the parents' alleles can combine to form an offspring's genotype. Because there are four boxes in the Punnett square, there are four possible outcomes.
An event is a set of one or more outcomes. The probability of an event is a measure of how likely the event is to happen. This probability is a number between 0 and 1, and it can be written as a fraction:
probability of an event = number of ways the event can happen / number of equally likely outcomes
You can use a Punnett square to calculate the probability that a cross will produce certain offspring. For example, the Punnett square below has two boxes with the genotype Ff. It has one box with the genotype FF and one box with the genotype ff. This means there are two ways the parents' alleles can combine to form Ff. There is one way they can combine to form FF and one way they can combine to form ff.
 | F | f
F | FF | Ff
f | Ff | ff
Consider an event in which this cross produces an offspring with the genotype ff. The probability of this event is given by the following fraction:
number of ways the event can happen / number of equally likely outcomes = number of boxes with the genotype ff / total number of boxes = 1 / 4.

natural science


Question: What is the probability that a rabbit produced by this cross will have brown fur?

Choices:
A. 0/4
B. 3/4
C. 1/4
D. 2/4
E. 4/4

In a group of rabbits, some individuals have black fur and others have brown fur. In this group, the gene for the fur color trait has two alleles. The allele for brown fur (f) is recessive to the allele for black fur (F).
This Punnett square shows a cross between two rabbits.

Offspring phenotypes: dominant or recessive?
How do you determine an organism's phenotype for a trait? Look at the combination of alleles in the organism's genotype for the gene that affects that trait. Some alleles have types called dominant and recessive. These two types can cause different versions of the trait to appear as the organism's phenotype.
If an organism's genotype has at least one dominant allele for a gene, the organism's phenotype will be the dominant allele's version of the gene's trait.
If an organism's genotype has only recessive alleles for a gene, the organism's phenotype will be the recessive allele's version of the gene's trait.
In a Punnett square, each box represents a different outcome, or result. Each of the four outcomes is equally likely to happen. Each box represents one way the parents' alleles can combine to form an offspring's genotype. Because there are four boxes in the Punnett square, there are four possible outcomes.
An event is a set of one or more outcomes. The probability of an event is a measure of how likely the event is to happen. This probability is a number between 0 and 1, and it can be written as a fraction:
probability of an event = number of ways the event can happen / number of equally likely outcomes
You can use a Punnett square to calculate the probability that a cross will produce certain offspring. For example, the Punnett square below has two boxes with the genotype Ff. It has one box with the genotype FF and one box with the genotype ff. This means there are two ways the parents' alleles can combine to form Ff. There is one way they can combine to form FF and one way they can combine to form ff.
 | F | f
F | FF | Ff
f | Ff | ff
Consider an event in which this cross produces an offspring with the genotype ff. The probability of this event is given by the following fraction:
number of ways the event can happen / number of equally likely outcomes = number of boxes with the genotype ff / total number of boxes = 1 / 4.

natural science


Question:
What do these two changes have in common?
a piece of pizza rotting in a trashcan
cooking an egg

Choices:
A. Both are only physical changes.
B. Both are caused by cooling.
C. Both are caused by heating.
D. Both are chemical changes.

Chemical changes and physical changes are two common ways matter can change.
In a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it reacts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.
In a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
A piece of pizza rotting is a chemical change. The matter in the pizza breaks down and slowly turns into a different type of matter.
Cooking an egg is a chemical change. The heat causes the matter in the egg to change. Cooked eggs and raw eggs are made of different types of matter.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are chemical changes. They are not physical changes.
Both are chemical changes.
Both changes are chemical changes. The type of matter before and after each change is different.
Both are caused by heating.
Cooking is caused by heating. But a piece of pizza rotting is not.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: Select the chemical formula for this molecule.

Choices:
A. CH2O2
B. He2O2
C. H2O2
D. HO3

Every substance around you is made up of atoms. Atoms can link together to form molecules. The links between atoms in a molecule are called chemical bonds. Different molecules are made up of different chemical elements, or types of atoms, bonded together.
Scientists use both ball-and-stick models and chemical formulas to represent molecules.
A ball-and-stick model of a molecule is shown below.
The balls represent atoms. The sticks represent the chemical bonds between the atoms.
Notice how each ball is labeled with a symbol made of one or more letters. The symbol is an abbreviation for a chemical element. The ball represents one atom of that element.
Every chemical element is represented by its own symbol. For some elements, that symbol is one capital letter. For other elements, it is one capital letter followed by one lowercase letter. For example, the symbol for the element boron is B and the symbol for the element chlorine is Cl.
The molecule shown above has one boron atom and three chlorine atoms. A chemical bond links each chlorine atom to the boron atom.
The chemical formula for a molecule contains the symbol for each chemical element in the molecule. Many chemical formulas use subscripts. A subscript is text that is smaller and placed lower than the normal line of text.
In chemical formulas, the subscripts are numbers. The subscript is always written after the symbol for an element. The subscript tells you how many atoms that symbol represents. If the symbol represents just one atom, then no subscript is included.
The symbols in the chemical formula for a molecule match the symbols in the ball-and-stick model for that molecule. The ball-and-stick model shown before and the chemical formula shown above represent the same substance.

H is the symbol for hydrogen. O is the symbol for oxygen. This ball-and-stick model shows a molecule with two hydrogen atoms and two oxygen atoms.
The chemical formula will contain the symbols H and O. There are two hydrogen atoms, so H will have a subscript of 2. There are two oxygen atoms, so O will have a subscript of 2.
The correct formula is H2 O2.
The diagram below shows how each part of the chemical formula matches with each part of the model above.

natural science

Match chemical formulas to ball-and-stick models


Question: Select the living thing.

Choices:
A. pebble
B. television
C. ferris wheel
D. cabbage in a field

All living things are made up of cells. Plants, animals, and some fungi have many cells. Other living things are made up of just one cell.
All living things need food and water. Water helps living things break down food and remove waste. Food gives living things energy. They use energy from food to grow and change.
All living things sense changes in their environment. Living things might sense changes by seeing, smelling, hearing, or feeling. Living things can respond to the changes they sense.

A ferris wheel is not a living thing.
A ferris wheel does not have all the traits of a living thing. It moves in a circle, but it does not grow. It does not need food or water.
A pebble is not a living thing.
Pebbles do not have all of the traits of living things. They do not grow or respond to their environment. They do not need food or water.
Cabbage in a field is a living thing.
Cabbage in a field grows and responds to its environment. It needs food and water. It is made up of many cells.
Cabbage plants grow and change. They need food and water. Cabbage plants use water, air, and energy from sunlight to make food.
A television is not a living thing.
A television does not have all the traits of a living thing. It responds to the world around it, but it does not grow. It does not need food or water.

natural science


Question: Which of the following organisms is the secondary consumer in this food web?

Choices:
A. orca
B. kelp
C. sea urchin
D. kelp bass

Below is a food web from an ocean ecosystem in Monterey Bay, off the coast of California.
A food web models how the matter eaten by organisms moves through an ecosystem. The arrows in a food web represent how matter moves between organisms in an ecosystem.

A food web is a model.
A food web shows where organisms in an ecosystem get their food. Models can make things in nature easier to understand because models can represent complex things in a simpler way. If a food web showed every organism in an ecosystem, the food web would be hard to understand. So, each food web shows how some organisms in an ecosystem can get their food.
Arrows show how matter moves.
A food web has arrows that point from one organism to another. Each arrow shows the direction that matter moves when one organism eats another organism. An arrow starts from the organism that is eaten. The arrow points to the organism that is doing the eating.
An organism in a food web can have more than one arrow pointing from it. This shows that the organism is eaten by more than one other organism in the food web.
An organism in a food web can also have more than one arrow pointing to it. This shows that the organism eats more than one other organism in the food web.

Secondary consumers eat primary consumers, and primary consumers eat producers. So, in a food web, secondary consumers have arrows pointing to them from primary consumers. Primary consumers have arrows pointing to them from producers.
The kelp does not have any arrows pointing to it. So, the kelp is not a secondary consumer.
The orca has an arrow pointing to it from the sea otter. The sea otter is not a primary consumer. So, the orca is not a secondary consumer.
The kelp bass has arrows pointing to it from the zooplankton and the plainfin midshipman. The zooplankton and the plainfin midshipman are primary consumers, so the kelp bass is a secondary consumer.
The black rockfish has an arrow pointing to it from the zooplankton. The zooplankton is a primary consumer, so the black rockfish is a secondary consumer.
The sea urchin has an arrow pointing to it from the kelp. The kelp is not a primary consumer. So, the sea urchin is not a secondary consumer.

natural science


Question: Select the vertebrate.

Choices:
A. crown jellyfish
B. chameleon
C. blue crab
D. dung beetle

Hint: Mammals, birds, fish, reptiles, and amphibians are vertebrates.

Vertebrates and invertebrates are both groups of animals.
A vertebrate has a backbone. The backbone is made of many bones in an animal's back. A vertebrate's backbone helps connect the different parts of its body. In the drawings below, each vertebrate's backbone is colored orange.
An invertebrate does not have a backbone. In fact, invertebrates do not have any bones! Some invertebrates have an outer cover on their body called an exoskeleton. Other invertebrates have a soft body.

A chameleon is a reptile. Like other reptiles, a chameleon is a vertebrate. It has a backbone.
Like other jellyfishes, a crown jellyfish is an invertebrate. It does not have a backbone. It has a soft body.
A dung beetle is an insect. Like other insects, a dung beetle is an invertebrate. It does not have a backbone. It has an exoskeleton.
Like other crabs, a blue crab is an invertebrate. It does not have a backbone. It has an exoskeleton.

natural science


Question:
What do these two changes have in common?
baking cookies
a piece of avocado turning brown

Choices:
A. Both are caused by cooling.
B. Both are caused by heating.
C. Both are chemical changes.
D. Both are only physical changes.

Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.
In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.
In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Baking cookies is a chemical change. The type of matter in the cookie dough changes when it is baked. The cookie dough turns into cookies!
A piece of avocado turning brown is a chemical change. The avocado reacts with oxygen in the air to form a different type of matter.
If you scrape off the brown part of the avocado, the inside will still be green. The inside hasn't touched the air. So the chemical change hasn't happened to that part of the avocado.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are chemical changes. They are not physical changes.
Both are chemical changes.
Both changes are chemical changes. The type of matter before and after each change is different.
Both are caused by heating.
Baking is caused by heating. But a piece of avocado turning brown is not.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: Select the fish below.

Choices:
A. wombat
B. piranha
C. bison
D. emerald tree boa

Fish live underwater. They have fins, not limbs.
Fish are cold-blooded. The body temperature of cold-blooded animals depends on their environment.
A goldfish is an example of a fish.

Birds, mammals, fish, reptiles, and amphibians are groups of animals. Scientists sort animals into each group based on traits they have in common. This process is called classification.
Classification helps scientists learn about how animals live. Classification also helps scientists compare similar animals.

A bison is a mammal. It has fur and feeds its young milk.
Male bison have horns. They can use their horns to defend themselves.
A wombat is a mammal. It has fur and feeds its young milk.
Wombats have strong claws on their front feet. They use their claws to dig underground holes called burrows.
A piranha is a fish. It lives underwater. It has fins, not limbs.
Piranhas have sharp teeth. Piranhas hunt in groups. A group of piranhas can eat a large animal.
An emerald tree boa is a reptile. It has scaly, waterproof skin.
Tree boas eat small mammals, birds, lizards, and frogs. Tree boas only need to eat once every few months!

natural science


Question: Which of the following organisms is the producer in this food web?

Choices:
A. beaver
B. gray fox
C. silver maple
D. pine vole

Below is a food web from Shenandoah National Park, a forest ecosystem in Virginia.
A food web models how the matter eaten by organisms moves through an ecosystem. The arrows in a food web represent how matter moves between organisms in an ecosystem.

A food web is a model.
A food web shows where organisms in an ecosystem get their food. Models can make things in nature easier to understand because models can represent complex things in a simpler way. If a food web showed every organism in an ecosystem, the food web would be hard to understand. So, each food web shows how some organisms in an ecosystem can get their food.
Arrows show how matter moves.
A food web has arrows that point from one organism to another. Each arrow shows the direction that matter moves when one organism eats another organism. An arrow starts from the organism that is eaten. The arrow points to the organism that is doing the eating.
An organism in a food web can have more than one arrow pointing from it. This shows that the organism is eaten by more than one other organism in the food web.
An organism in a food web can also have more than one arrow pointing to it. This shows that the organism eats more than one other organism in the food web.

Producers do not eat other organisms. So, in a food web, producers do not have arrows pointing to them from other organisms.
The persimmon tree does not have any arrows pointing to it. So, the persimmon tree is a producer.
The gray fox has arrows pointing to it, so it is not a producer.
The silver maple does not have any arrows pointing to it. So, the silver maple is a producer.
The beaver has an arrow pointing to it, so it is not a producer.
The pine vole has arrows pointing to it, so it is not a producer.

natural science


Question:
What do these two changes have in common?
an antacid tablet reacting with water
burning food on a stove

Choices:
A. Both are chemical changes.
B. Both are only physical changes.
C. Both are caused by cooling.
D. Both are caused by heating.

Chemical changes and physical changes are two common ways matter can change.
In a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it reacts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.
In a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
An antacid tablet reacting with water is a chemical change. When the tablet touches water, the type of matter in the tablet changes and carbon dioxide gas is released. This gas makes the water fizz.
Burning food on a stove is a chemical change. When the food burns, the type of matter in it changes. The food turns black and gives off smoke.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are chemical changes. They are not physical changes.
Both are chemical changes.
Both changes are chemical changes. The type of matter before and after each change is different.
Both are caused by heating.
Burning is caused by heating. But an antacid tablet reacting with water is not.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question:
What do these two changes have in common?
carving a piece of wood
sewing an apron

Choices:
A. Both are caused by cooling.
B. Both are only physical changes.
C. Both are caused by heating.
D. Both are chemical changes.

Chemical changes and physical changes are two common ways matter can change.
In a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it reacts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.
In a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Carving a piece of wood is a physical change. The wood changes shape, but it is still made of the same type of matter.
Sewing an apron is a physical change. The fabric and thread that make up the apron get a new shape, but the type of matter in each of them does not change.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are physical changes. No new matter is created.
Both are chemical changes.
Both changes are physical changes. They are not chemical changes.
Both are caused by heating.
Neither change is caused by heating.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: Select the fish below.

Choices:
A. tiger shark
B. Hermann's tortoise
C. leaf-tailed gecko
D. dwarf crocodile

Fish live underwater. They have fins, not limbs.
Fish are cold-blooded. The body temperature of cold-blooded animals depends on their environment.
A manta ray is an example of a fish.

Birds, mammals, fish, reptiles, and amphibians are groups of animals. Scientists sort animals into each group based on traits they have in common. This process is called classification.
Classification helps scientists learn about how animals live. Classification also helps scientists compare similar animals.

A tiger shark is a fish. It lives underwater. It has fins, not limbs.
Tiger sharks are nocturnal. This means that they are active mostly at night.
A leaf-tailed gecko is a reptile. It has scaly, waterproof skin.
Many geckos have special pads on their toes. The pads help them climb up plants and rocks.
A dwarf crocodile is a reptile. It has scaly, waterproof skin.
Crocodiles hunt their prey in or near water.
A Hermann's tortoise is a reptile. It has scaly, waterproof skin.
A tortoise's shell protects it from predators. When a tortoise feels threatened, it can pull its head and legs inside its shell.

natural science


Question: Select the chemical formula for this molecule.

Choices:
A. B2F3
B. BFe3
C. HB3F
D. BF3

Every substance around you is made up of atoms. Atoms can link together to form molecules. The links between atoms in a molecule are called chemical bonds. Different molecules are made up of different chemical elements, or types of atoms, bonded together.
Scientists use both ball-and-stick models and chemical formulas to represent molecules.
A ball-and-stick model of a molecule is shown below.
The balls represent atoms. The sticks represent the chemical bonds between the atoms.
Notice how each ball is labeled with a symbol made of one or more letters. The symbol is an abbreviation for a chemical element. The ball represents one atom of that element.
Every chemical element is represented by its own symbol. For some elements, that symbol is one capital letter. For other elements, it is one capital letter followed by one lowercase letter. For example, the symbol for the element boron is B and the symbol for the element chlorine is Cl.
The molecule shown above has one boron atom and three chlorine atoms. A chemical bond links each chlorine atom to the boron atom.
The chemical formula for a molecule contains the symbol for each chemical element in the molecule. Many chemical formulas use subscripts. A subscript is text that is smaller and placed lower than the normal line of text.
In chemical formulas, the subscripts are numbers. The subscript is always written after the symbol for an element. The subscript tells you how many atoms that symbol represents. If the symbol represents just one atom, then no subscript is included.
The symbols in the chemical formula for a molecule match the symbols in the ball-and-stick model for that molecule. The ball-and-stick model shown before and the chemical formula shown above represent the same substance.

B is the symbol for boron. F is the symbol for fluorine. This ball-and-stick model shows a molecule with one boron atom and three fluorine atoms.
The chemical formula will contain the symbols B and F. There is one boron atom, so B will not have a subscript. There are three fluorine atoms, so F will have a subscript of 3.
The correct formula is BF3.
The diagram below shows how each part of the chemical formula matches with each part of the model above.

natural science


Question: Select the invertebrate.

Choices:
A. leaf-curling spider
B. whiptail lizard
C. albatross
D. rockfish

Hint: Insects, spiders, and worms are invertebrates.

Vertebrates and invertebrates are both groups of animals.
A vertebrate has a backbone. The backbone is made of many bones in an animal's back. A vertebrate's backbone helps connect the different parts of its body. In the drawings below, each vertebrate's backbone is colored orange.
An invertebrate does not have a backbone. In fact, invertebrates do not have any bones! Some invertebrates have an outer cover on their body called an exoskeleton. Other invertebrates have a soft body.

Like other spiders, a leaf-curling spider is an invertebrate. It does not have a backbone. It has an exoskeleton.
A whiptail lizard is a reptile. Like other reptiles, a whiptail lizard is a vertebrate. It has a backbone.
A rockfish is a fish. Like other fish, a rockfish is a vertebrate. It has a backbone.
An albatross is a bird. Like other birds, an albatross is a vertebrate. It has a backbone.

natural science


Question: How long is a basketball court?

Choices:
A. 23 kilometers
B. 23 centimeters
C. 23 meters
D. 23 millimeters

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using metric units, length can be written with units of millimeters, centimeters, meters, or kilometers. One meter contains 100 centimeters or 1,000 millimeters. So, 1 meter is larger than 1 centimeter, and 1 centimeter is larger than 1 millimeter.
The tip of the pencil shown here is only 1 millimeter wide, but the pencil is about 16 centimeters long.
A red fox is about 1 meter long. The Sydney Harbour Bridge in Australia is about 1,000 meters, or 1 kilometer, in length.

The best estimate for the length of a basketball court is 23 meters.
23 millimeters and 23 centimeters are too short. 23 kilometers is too long.

natural science


Question: How long is an ice skate?

Choices:
A. 11 feet
B. 11 miles
C. 11 inches
D. 11 yards

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using customary units, length may be written with units of inches, feet, yards, or miles.
There are 12 inches in 1 foot, and 3 feet in 1 yard. There are 5,280 feet in 1 mile.
A football is about 1 foot long. A football field is 100 yards long.

The best estimate for the length of an ice skate is 11 inches.
11 feet, 11 yards, and 11 miles are all too long.

natural science


Question: How long is a pen?

Choices:
A. 15 millimeters
B. 15 centimeters
C. 15 kilometers
D. 15 meters

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using metric units, length can be written with units of millimeters, centimeters, meters, or kilometers. One meter contains 100 centimeters or 1,000 millimeters. So, 1 meter is larger than 1 centimeter, and 1 centimeter is larger than 1 millimeter.
The tip of the pencil shown here is only 1 millimeter wide, but the pencil is about 16 centimeters long.
A red fox is about 1 meter long. The Sydney Harbour Bridge in Australia is about 1,000 meters, or 1 kilometer, in length.

The best estimate for the length of a pen is 15 centimeters.
15 millimeters is too short. 15 meters and 15 kilometers are too long.

natural science


Question:
What do these two changes have in common?
rust forming on a metal gate
saliva breaking down a piece of bread

Choices:
A. Both are only physical changes.
B. Both are caused by cooling.
C. Both are chemical changes.
D. Both are caused by heating.

Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.
In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.
In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Rust forming on a metal gate is a chemical change. As the gate rusts, the metal turns into a different type of matter called rust. Rust is reddish-brown and falls apart easily.
Saliva breaking down a piece of bread is a chemical change. Bread is made up mostly of a chemical called starch. Saliva breaks the bonds between atoms in the starch molecules.
The atoms then link together to form smaller, simpler molecules of sugar. The sugar is a different type of matter than the starch.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are chemical changes. They are not physical changes.
Both are chemical changes.
Both changes are chemical changes. The type of matter before and after each change is different.
Both are caused by heating.
Neither change is caused by heating.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: How long is the Great Wall of China?

Choices:
A. 21,000 kilometers
B. 21,000 centimeters
C. 21,000 meters
D. 21,000 millimeters

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using metric units, length can be written with units of millimeters, centimeters, meters, or kilometers. One meter contains 100 centimeters or 1,000 millimeters. So, 1 meter is larger than 1 centimeter, and 1 centimeter is larger than 1 millimeter.
The tip of the pencil shown here is only 1 millimeter wide, but the pencil is about 16 centimeters long.
A red fox is about 1 meter long. The Sydney Harbour Bridge in Australia is about 1,000 meters, or 1 kilometer, in length.

The best estimate for the length of the Great Wall of China is 21,000 kilometers.
21,000 millimeters, 21,000 centimeters, and 21,000 meters are all too short.

natural science


Question:
What do these two changes have in common?
butter melting on a hot day
cooking an egg

Choices:
A. Both are chemical changes.
B. Both are caused by heating.
C. Both are only physical changes.
D. Both are caused by cooling.

Chemical changes and physical changes are two common ways matter can change.
In a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it reacts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.
In a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Butter melting on a hot day is a change of state. So, it is a physical change. The butter changes from solid to liquid, but it is still made of the same type of matter.
Cooking an egg is a chemical change. The heat causes the matter in the egg to change. Cooked egg and raw egg are different types of matter.
Step 2: Look at each answer choice.
Both are only physical changes.
Butter melting on a hot day is a physical change. But cooking an egg is not.
Both are chemical changes.
Cooking an egg is a chemical change. But butter melting on a hot day is not.
Both are caused by heating.
Both changes are caused by heating.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: How long is a ladybug?

Choices:
A. 8 millimeters
B. 8 meters
C. 8 centimeters
D. 8 kilometers

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using metric units, length can be written with units of millimeters, centimeters, meters, or kilometers. One meter contains 100 centimeters or 1,000 millimeters. So, 1 meter is larger than 1 centimeter, and 1 centimeter is larger than 1 millimeter.
The tip of the pencil shown here is only 1 millimeter wide, but the pencil is about 16 centimeters long.
A red fox is about 1 meter long. The Sydney Harbour Bridge in Australia is about 1,000 meters, or 1 kilometer, in length.

The best estimate for the length of a ladybug is 8 millimeters.
8 centimeters, 8 meters, and 8 kilometers are all too long.

natural science


Question: How long is a grain of rice?

Choices:
A. 3 meters
B. 3 kilometers
C. 3 centimeters
D. 3 millimeters

Select the best estimate.

Measurements are written with both a number and a unit. The unit comes after the number. The unit shows what the number means.
When you are using metric units, length can be written with units of millimeters, centimeters, meters, or kilometers. One meter contains 100 centimeters or 1,000 millimeters. So, 1 meter is larger than 1 centimeter, and 1 centimeter is larger than 1 millimeter.
The tip of the pencil shown here is only 1 millimeter wide, but the pencil is about 16 centimeters long.
A red fox is about 1 meter long. The Sydney Harbour Bridge in Australia is about 1,000 meters, or 1 kilometer, in length.

The best estimate for the length of a grain of rice is 3 millimeters.
3 centimeters, 3 meters, and 3 kilometers are all too long.

natural science


Question:
What do these two changes have in common?
beating an egg
mixing lettuce and salad dressing

Choices:
A. Both are caused by cooling.
B. Both are chemical changes.
C. Both are caused by heating.
D. Both are only physical changes.

Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.
In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.
In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
Beating an egg is a physical change. Beating an egg mixes together the egg white, egg yolk, and some air. But mixing them together does not form a different type of matter.
Mixing lettuce and salad dressing is a physical change. Together, the salad and dressing make a mixture. But making this mixture does not form a different type of matter.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are physical changes. No new matter is created.
Both are chemical changes.
Both changes are physical changes. They are not chemical changes.
Both are caused by heating.
Neither change is caused by heating.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question:
What do these two changes have in common?
a copper statue turning green
firing a clay pot in a hot kiln

Choices:
A. Both are only physical changes.
B. Both are chemical changes.
C. Both are caused by cooling.
D. Both are caused by heating.

Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.
In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.
In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.

Step 1: Think about each change.
A copper statue turning green is a chemical change. The copper reacts with oxygen in the air. This reaction forms a different type of matter called copper oxide. The copper oxide is green.
Firing a clay pot in a hot kiln is a chemical change. High temperatures cause the clay to slowly harden. After several hours in the kiln, the clay will have changed into a different type of matter.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are chemical changes. They are not physical changes.
Both are chemical changes.
Both changes are chemical changes. The type of matter before and after each change is different.
Both are caused by heating.
Firing clay is caused by heating. But a copper statue turning green is not.
Both are caused by cooling.
Neither change is caused by cooling.

natural science


Question: Select the living thing.

Choices:
A. ferris wheel
B. bracelet
C. rain
D. yak

All living things are made up of cells. Plants, animals, and some fungi have many cells. Other living things are made up of just one cell.
All living things need food and water. Water helps living things break down food and remove waste. Food gives living things energy. They use energy from food to grow and change.
All living things sense changes in their environment. Living things might sense changes by seeing, smelling, hearing, or feeling. Living things can respond to the changes they sense.

A ferris wheel is not a living thing.
A ferris wheel does not have all the traits of a living thing. It moves in a circle, but it does not grow. It does not need food or water.
A yak is a living thing.
Yaks grow and respond to their environment. They need food and water. Yaks are made up of many cells.
A bracelet is not a living thing.
Bracelets do not have all of the traits of living things. They do not grow or respond to their environment. They do not need food or water.
Rain is not a living thing.
Rain is made of water. It helps living things survive. But it does not have all the traits of a living thing. Rain does not grow or need food.

natural science