The Carbon Cycle

Question 1

A greenhouse contains a row of fast‑growing sunflowers. During daylight the sunflowers use photosynthesis, and they also respire continuously, both day and night. Which statement most accurately explains how the sunflowers affect the amount of carbon dioxide in the greenhouse air?

Accepted Answer

The sunflowers absorb carbon dioxide to make sugars during the day; although they give some carbon dioxide back through respiration, the amount stored in new plant tissue is greater, so the overall carbon dioxide level drops.

Answer

Because the sunflowers release oxygen, the carbon dioxide level stays the same.

Answer

The sunflowers only take in carbon dioxide at night, so the air gets cleaner after dark.

Answer

Since the sunflowers respire all the time, they put back exactly the same amount of carbon dioxide they took in, so there is no net change.

Question 2

Which statement best describes how energy flows and how matter cycles in a forest ecosystem?

Accepted Answer

Energy enters the ecosystem from the sun, is captured by producers, passed to consumers, and finally released as heat; matter such as carbon cycles continuously through producers, consumers, and decomposers.

Answer

Energy is recycled when consumers eat producers, and matter is lost as heat when organisms die.

Answer

Both energy and matter are transferred only from producers to consumers; decomposers do not play a role in either cycle.

Answer

Matter flows in a single direction from the sun to producers, while energy is recycled among all organisms.

Question 3

In a meadow ecosystem, grass gets energy from the sun, a rabbit eats the grass, a fox eats the rabbit, and when any organism dies, decomposers break it down and return nutrients to the soil for the grass to use. Which statement best describes how matter moves in this ecosystem?

Accepted Answer

Matter is transferred from the grass to the rabbit when the rabbit eats the grass, then from the rabbit to the fox when the fox eats the rabbit, and finally returned to the soil by decomposers when organisms die.

Answer

Matter disappears from the ecosystem when the fox dies because dead matter is no longer part of the system.

Answer

Matter cycles back to the sun when the fox is eaten by a bird, because the sun receives the matter.

Answer

Matter is transferred from the rabbit to the grass when the rabbit excretes waste, and then from the grass to the fox when the fox eats the grass.

Try three questions

A greenhouse contains a row of fast‑growing sunflowers. During daylight the sunflowers use photosynthesis, and they also respire continuously, both day and night. Which statement most accurately explains how the sunflowers affect the amount of carbon dioxide in the greenhouse air?

Which statement best describes how energy flows and how matter cycles in a forest ecosystem?

In a meadow ecosystem, grass gets energy from the sun, a rabbit eats the grass, a fox eats the rabbit, and when any organism dies, decomposers break it down and return nutrients to the soil for the grass to use. Which statement best describes how matter moves in this ecosystem?

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