id: 3327
lecture: Magnets can pull or push on each other without touching. When magnets attract, they pull together. When magnets repel, they push apart. Whether a magnet attracts or repels other magnets depends on the positions of its poles, or ends. Every magnet has two poles, called north and south. Here are some examples of magnets. The north pole of each magnet is marked N, and the south pole is marked S. If different poles are closest to each other, the magnets attract. The magnets in the pair below attract. If the same poles are closest to each other, the magnets repel. The magnets in both pairs below repel.
question: Will these magnets attract or repel each other?
choice: (A) attract (B) repel
context: Two magnets are placed as shown. Hint: Magnets that attract pull together. Magnets that repel push apart.
answer: B
rationale: Magnets can pull or push on each other without touching. When magnets attract, they pull together. When magnets repel, they push apart. Whether a magnet attracts or repels other magnets depends on the positions of its poles, or ends. Every magnet has two poles, called north and south. Here are some examples of magnets. The north pole of each magnet is marked N, and the south pole is marked S. If different poles are closest to each other, the magnets attract. The magnets in the pair below attract. If the same poles are closest to each other, the magnets repel. The magnets in both pairs below repel. Will these magnets attract or repel? To find out, look at which poles are closest to each other. The north pole of one magnet is closest to the south pole of the other magnet. Poles that are different attract. So, these magnets will attract each other. The answer is A.
generated_skill:
solution: Will these magnets attract or repel? To find out, look at which poles are closest to each other. The north pole of one magnet is closest to the north pole of the other magnet. Poles that are the same repel. So, these magnets will repel each other.
skill: Identify magnets that attract or repel
id: 3505
lecture:
question: Which term matches the picture?
choice: (A) echinoderm (B) cnidarian
context: Read the text. Invertebrates make up the majority of Earth's living things, but there are many different groups, or phyla, of invertebrates. Jellyfish and sea anemone, for example, are both part of the phylum Cnidaria. Cnidaria comes from a Greek word that means "nettle," a stinging type of plant. Cnidarians are known for the tentacles that surround their mouths, which they use to sting and capture prey. All species that belong in the Cnidaria phyla live exclusively in the ocean. Another phylum of invertebrates found only in oceans is the Echinodermata, a term that comes from Greek words meaning "spiny" and "skin." Echinoderms, members of this phylum, have stiff bodies and often have stiff, sharp spines covering their skins. Unlike a cnidarian's wavy tentacles, these spines are used for protection, not to capture prey.
answer: A
rationale: A cnidarian is an animal with stinging cells called nettles. A sea anemone is a type of cnidarian. The answer is B.
generated_skill:
solution: An echinoderm is a type of sea invertebrate that usually has sharp or spiky skin. A sea urchin is a type of echinoderm.
skill: Determine the meaning of domain-specific words with pictures
id: 3530
lecture: Magnets can pull or push on each other without touching. When magnets attract, they pull together. When magnets repel, they push apart. These pulls and pushes between magnets are called magnetic forces. The strength of a force is called its magnitude. The greater the magnitude of the magnetic force between two magnets, the more strongly the magnets attract or repel each other. You can change the magnitude of a magnetic force between two magnets by changing the distance between them. The magnitude of the magnetic force is greater when there is a smaller distance between the magnets.
question: Think about the magnetic force between the magnets in each pair. Which of the following statements is true?
choice: (A) The magnitude of the magnetic force is greater in Pair 1. (B) The magnitude of the magnetic force is greater in Pair 2. (C) The magnitude of the magnetic force is the same in both pairs.
context: The images below show two pairs of magnets. The magnets in different pairs do not affect each other. All the magnets shown are made of the same material, but some of them are different shapes.
answer: A
rationale: Magnets can pull or push on each other without touching. When magnets attract, they pull together. When magnets repel, they push apart. These pulls and pushes between magnets are called magnetic forces. The strength of a force is called its magnitude. The greater the magnitude of the magnetic force between two magnets, the more strongly the magnets attract or repel each other. You can change the magnitude of a magnetic force between two magnets by changing the distance between them. The magnitude of the magnetic force is greater when there is a smaller distance between the magnets. The magnets in Pair 1 attract. The magnets in Pair 2 repel. But whether the magnets attract or repel affects only the direction of the magnetic force. It does not affect the magnitude of the magnetic force. Distance affects the magnitude of the magnetic force. When there is a smaller distance between magnets, the magnitude of the magnetic force between them is greater. There is a smaller distance between the magnets in Pair 2 than in Pair 1. So, the magnitude of the magnetic force is greater in Pair 2 than in Pair 1. The answer is B.
generated_skill:
solution: Distance affects the magnitude of the magnetic force. When there is a smaller distance between magnets, the magnitude of the magnetic force between them is greater. There is a smaller distance between the magnets in Pair 1 than in Pair 2. So, the magnitude of the magnetic force is greater in Pair 1 than in Pair 2.
skill: Compare magnitudes of magnetic forces
id: 3681
lecture: Magnets can pull or push on each other without touching. When magnets attract, they pull together. When magnets repel, they push apart. These pulls and pushes between magnets are called magnetic forces. The stronger the magnetic force between two magnets, the more strongly the magnets attract or repel each other. You can change the strength of a magnetic force between two magnets by changing the distance between them. The magnetic force is stronger when the magnets are closer together.
question: Think about the magnetic force between the magnets in each pair. Which of the following statements is true?
choice: (A) The magnetic force is stronger in Pair 1. (B) The magnetic force is stronger in Pair 2. (C) The strength of the magnetic force is the same in both pairs.
context: The images below show two pairs of magnets. The magnets in different pairs do not affect each other. All the magnets shown are made of the same material.
answer: B
rationale: Magnets can pull or push on each other without touching. When magnets attract, they pull together. When magnets repel, they push apart. These pulls and pushes between magnets are called magnetic forces. The stronger the magnetic force between two magnets, the more strongly the magnets attract or repel each other. You can change the strength of a magnetic force between two magnets by changing the distance between them. The magnetic force is stronger when the magnets are closer together. Distance affects the strength of the magnetic force. When magnets are closer together, the magnetic force between them is stronger. The magnets in Pair 1 are closer together than the magnets in Pair 2. So, the magnetic force is stronger in Pair 1 than in Pair 2. The answer is A.
generated_skill:
solution: Distance affects the strength of the magnetic force. When magnets are closer together, the magnetic force between them is stronger. The magnets in Pair 2 are closer together than the magnets in Pair 1. So, the magnetic force is stronger in Pair 2 than in Pair 1.
skill: Compare strengths of magnetic forces
id: 3823
lecture: A solution is made up of two or more substances that are completely mixed. In a solution, solute particles are mixed into a solvent. The solute cannot be separated from the solvent by a filter. For example, if you stir a spoonful of salt into a cup of water, the salt will mix into the water to make a saltwater solution. In this case, the salt is the solute. The water is the solvent. The concentration of a solute in a solution is a measure of the ratio of solute to solvent. Concentration can be described in terms of particles of solute per volume of solvent. concentration = particles of solute / volume of solvent
question: Which solution has a higher concentration of green particles?
choice: (A) Solution A (B) Solution B (C) neither; their concentrations are the same
context: The diagram below is a model of two solutions. Each green ball represents one particle of solute.
answer: B
rationale: A solution is made up of two or more substances that are completely mixed. In a solution, solute particles are mixed into a solvent. The solute cannot be separated from the solvent by a filter. For example, if you stir a spoonful of salt into a cup of water, the salt will mix into the water to make a saltwater solution. In this case, the salt is the solute. The water is the solvent. The concentration of a solute in a solution is a measure of the ratio of solute to solvent. Concentration can be described in terms of particles of solute per volume of solvent. concentration = particles of solute / volume of solvent In Solution A and Solution B, the green particles represent the solute. To figure out which solution has a higher concentration of green particles, look at both the number of green particles and the volume of the solvent in each container. Use the concentration formula to find the number of green particles per milliliter. Solution A has more green particles per milliliter. So, Solution A has a higher concentration of green particles. The answer is A.
generated_skill:
solution: In Solution A and Solution B, the green particles represent the solute. To figure out which solution has a higher concentration of green particles, look at both the number of green particles and the volume of the solvent in each container. Use the concentration formula to find the number of green particles per milliliter. Solution B has more green particles per milliliter. So, Solution B has a higher concentration of green particles.
skill: Compare concentrations of solutions
id: 4717
lecture:
question: Which rock layer is older?
choice: (A) the limestone layer (B) the sandstone layer
context: The following diagram shows an example of a rock sequence. Use the rock sequence to answer the question below.
answer: B
rationale: A rock sequence is a series of rock layers. Rock layers can be found in many different types of rocks, including sedimentary rocks. Sedimentary rocks form from layers of sediment. The oldest rock in a rock sequence is at the bottom of the sequence. The youngest rock is at the top. The answer is A.
generated_skill:
solution: Look at the diagram of the rock sequence. The double-headed arrow on the left tells you how the rock layers are arranged by age. In this diagram, the older layer is shown below the younger layer. The sandstone layer is older than the limestone layer.
skill: Interpret evidence from fossils in rock layers
id: 5146
lecture: 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.
question: In this food web, which organism contains matter that eventually moves to the earthworm?
choice: (A) mushroom (B) short-tailed weasel
context: 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.
answer: B
rationale: 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. The only arrow pointing from the short-tailed weasel 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 short-tailed weasel to the earthworm. The only arrow pointing from the mushroom leads to the grizzly bear. The only arrow pointing from the grizzly bear leads to the mushroom. In this food web, matter moves in a loop. It does not move from the mushroom to the earthworm. The answer is A.
generated_skill:
solution: 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.There are three paths matter can take from the bear sedge to the earthworm: bear sedge->brown lemming->Arctic fox->earthworm. bear sedge->brown lemming->snowy owl->earthworm. bear sedge->brown lemming->parasitic jaeger->rough-legged hawk->earthworm. There are four paths matter can take from the bilberry to the earthworm: bilberry->Arctic fox->earthworm. bilberry->brown lemming->Arctic fox->earthworm. bilberry->brown lemming->snowy owl->earthworm. bilberry->brown lemming->parasitic jaeger->rough-legged hawk->earthworm. There is one path matter can take from the short-tailed weasel to the earthworm: short-tailed weasel->snowy owl->earthworm. There is one path matter can take from the snowy owl to the earthworm: snowy owl->earthworm.
skill: Interpret food webs II
id: 5625
lecture:
question: Which term matches the picture?
choice: (A) camouflage (B) mimicry
context: Read the text. The way an animal looks can help to keep it safe from predators. Some animals use camouflage. These animals may blend into their environments so that it is hard for them to be seen. Other animals find safety in being seen. Many venomous animals, for example, have brightly colored skins that warn off predators. Finally, some animals may use mimicry to stay safe. These animals look like, or mimic, venomous animals so that predators will stay away.
answer: A
rationale: A tree bark pattern matches the picture. The answer is B.
generated_skill:
solution: Camouflage is at work when an animal is hard to see because it looks like its environment. For example, some butterflies look like leaves, so they are better hidden from predators.
skill: Determine the meaning of domain-specific words with pictures
id: 6323
lecture: 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 are thicker than 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. The oxygen you breathe is a gas. The helium in a balloon is also a gas.
question: Are the bubbles in soda a solid, a liquid, or a gas?
choice: (A) a gas (B) a solid (C) a liquid
context: N/A
answer: A
rationale: 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 are thicker than 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. The oxygen you breathe is a gas. The helium in a balloon is also a gas. The bubbles in soda are a liquid. A liquid takes the shape of any container it is in. If you pour soda into a different container, the bubbles will take the shape of that container. But the bubbles will still take up the same amount of space. The answer is C.
generated_skill:
solution: The bubbles in soda are filled with carbon dioxide gas. Carbon dioxide gas spreads out to fill a space. Carbon dioxide fills all the space inside the bubbles. If the bubbles pop at the surface of the soda, the carbon dioxide will expand to fill a much larger space.
skill: Identify and sort solids, liquids, and gases
id: 7094
lecture: An object has different properties. A property of an object can tell you how it looks, feels, tastes, or smells. Properties can also tell you how an object will behave when something happens to it. Different objects can have properties in common. You can use these properties to put objects into groups. Grouping objects by their properties is called classification.
question: Which property do these four objects have in common?
choice: (A) sticky (B) translucent (C) sweet
context: Select the best answer.
answer: B
rationale: An object has different properties. A property of an object can tell you how it looks, feels, tastes, or smells. Properties can also tell you how an object will behave when something happens to it. Different objects can have properties in common. You can use these properties to put objects into groups. Grouping objects by their properties is called classification. Look at each object. For each object, decide if it has that property. A sticky object can attach or stick to other things. All four objects are sticky. A translucent object lets light through. But you cannot see clearly through a translucent object. The honey is translucent, but the wet ice cube and the marbles are not. Sugar has a sweet taste. The wet ice cube and the marbles are not sweet. The property that all four objects have in common is sticky. The answer is A.
generated_skill:
solution: Look at each object. For each object, decide if it has that property. A translucent object lets light through. But you cannot see clearly through a translucent object. All four objects are translucent. A sticky object can attach or stick to other things. The honey is sticky, but the marbles are not. Sugar has a sweet taste. The honey is sweet, but the wet ice cube and the marbles are not. The property that all four objects have in common is translucent.
skill: Compare properties of objects