Science Grade 7 Chapter 5 Review Answers

Chapter 5 Review Answer:

1. The “ingredients” of photosynthesis are carbon dioxide, water, and sunlight.

2. Sample answer: kelp → sea urchin → sea otter → shark

3. If dead organisms did not decompose, the bodies would quickly cover Earth and nutrients contained in the bodies would not be recycled for other organisms to use.

4. Decomposers play an important role in the carbon cycle.

5.

Ecosystem Role	Examples
producer herbivore carnivore omnivore scavenger detrivore decomposer	Grass, maple trees Cow, rabbit Lion, polar bear Black bear, human Vulture, hyena Earthworm, beetle Bacterium, mould

6. A producer gets its energy from the Sun. A consumer gets energy from the other organisms it eats.

7.

(a) A food chain includes only one link to and from each organism. A food web can have many links going to or coming from each organism.

(b) A carnivore kills organisms for food. A scavenger eats the remains of organisms that are already dead.

(c) Decomposers break down wastes and dead plant and animal matter into simpler substances, and consume those substances. Detrivores consume larger pieces of wastes and dead plant and animal matter.

(d) A primary consumer eats producers. A secondary consumer eats primary consumers.

8. In this ecosystem the algae would be producers, mosquito larvae would likely be primary consumers, salmon would be secondary consumers, and eagles would be tertiary consumers.

9. The saying “energy flows and matter cycles” is related to the fact that new matter is not created; it is recycled in an ecosystem. Energy cannot be recycled. It can flow only one direction in an ecosystem. New energy must continually enter the ecosystem.

10. An organism stores in its body only about 10 % of the energy from the food it takes in. Only the energy stored in an organism’s body can be passed on to the next organism in the food chain. Such large energy “losses” at each level of the energy pyramid of numbers means that there is relatively little energy left after a few levels to support many organisms.

11. Four ecological roles are producer, scavenger, detrivore, and decomposer. Grass is an example of a producer. A raven is an example of a scavenger. A beetle is an example of a detrivore. Bacteria are examples of decomposers.

12. Every time energy passes from one organism to another, a great deal of energy is “lost,” and only a small amount of energy is available to the next level of the energy pyramid (link in the food chain). Long food chains are less effective in transferring energy because a larger number of organisms is needed at lower levels to support the organisms at the highest levels.

13. Sample answer: The two arrows pointing from the sky to the trees represent plants taking in carbon dioxide during photosynthesis. The arrow pointing from the trees to the air and from the grass to the air represents organisms releasing carbon dioxide into the atmosphere. The arrow pointing from the smokestack into the air represents carbon dioxide being released into the atmosphere through the burning of fossil fuels. The arrow pointing from the trees into the ground represents carbon being stored in the remains of dead organisms. The longest arrow, pointing from the ground up into the air, represents carbon dioxide being released into the atmosphere when organisms decompose. The arrow pointing from the shallow subsurface to the rocks deeper underground represents carbon being stored in fossil fuels, which form when the remains of organisms are buried and compressed.

14.

 (a) It takes more energy to raise animals than to raise plants because you must first raise plants to feed the animals. So, vegetarianism allows for a shorter food chain, which results in less “lost” energy.

(b) Sample answer: I agree that vegetarianism would be a good way to help the environment because less land would be needed for farming, and less energy would be needed to grow and transport food crops.