Home Page Textbooks Prentice Hall Biology (California) Section 3.2: Energy Flow

Prentice Hall Biology (California)

1st Edition

Kenneth R. Miller, Levine

ISBN: 9780132013529

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Section 3.2: Energy Flow

Exercise 1

Result

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The two forms of energy that powers living systems are the sunlight and inorganic chemical compounds. Through the help of sun’s energy, photosynthesis is possible. Autotrophs needs energy from the sun to produce glucose and oxygen during photosynthesis. On the other hand, there are organisms which are living in places, such as undersea vents or deep-ocean floor, where the sunlight can’t reach them. Instead of relying on light, these organisms rely on inorganic chemicals through a process called chemosynthesis. Since chemosynthesis does not need energy from the sun, it involves the energy from inorganic chemicals. It uses hydrogen gas, hydrogen sulfide and methane as sources of energy to produce carbohydrates.

Exercise 2

Solution 1

Solution 2

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Energy flows from the sun or inorganic compounds to autotrophs and then to various heterotrophs.

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Energy always flows in one direction in an ecosystem. For example, energy from sunlight goes to a carrot. Energy from the carrot goes to a rabbit after the carrot is eaten. Energy from the rabbit goes to a wolf after a wolf eats the rabbit. Energy from a wolf goes to decomposers after the wolf dies and gets decomposed by worms and other annelids. In this chain energy never flows backwards. For example, energy from the rabbit never goes back to the plant directly.

In an ecosystem there is always a food web that consists of many food chains. The energy from the food chain never cycles unlike matter.

Exercise 3

Solution 1

Solution 2

Step 1

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Usually only ten percent of energy is transferred from one level of a food chain to the next. This is because a large proportion of the energy is expended to power the organism’s life activities.

Step 1

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When an organism obtains energy from a source such as sunlight or food, it uses most of that energy for many of its activities that are essential to life such as maintaining homeostasis.

Step 2

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However, an organism stores some of its obtained energy in the body. This energy is available and may be transferred to another organism at a higher trophic level such as a predator.

Step 3

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In general, only around **10 percent** of the energy obtained by an organism is available for the next trophic level. The remaining 90 percent of the energy is used by the organism itself.

Result

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Around 10 percent

Exercise 4

Solution 1

Solution 2

Step 1

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Energy starts out in the autotroph. The autotroph may get eaten by a herbivore or omnivore have its energy transferred to them. The energy from the herbivore may also transfer to the omnivore when it gets eaten by the omnivore.

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Autotrophs are organisms that can produce their own food. They can be consumed by herbivores and omnivores, which transfers the energy from the autotrophs to these organisms.

Step 2

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Additionally, a herbivore may also be consumed by an omnivore since omnivores can eat both plants and animals. In this case, the energy of herbivores is transferred to the omnivores.

Step 3

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As we can see, these categories of organisms are related to one another in terms of a food chain. Autotrophs such as plants and algae are usually placed at the start of a food chain.

Exercise 5

Solution 1

Solution 2

Step 1

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Energy is transferred between organisms from the producers to the consumers in the trophic levels. This energy is used by them to carry out different life processes.

Step 2

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There are only about 10 % of the energy is transferred from one trophic level to another. The remainder energy is utilized by the organism for life processes and it is eventually released into the environment as heat.

Step 3

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Hence, the pyramid should have 100% energy available at the bottom level, and 10% on the second level, followed by 1% at the third level, and 0.1% at the fourth level, and lastly, 0.01% at the fifth and top-level.

Result

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Level 5 0.01%
Level 4 0.1%
Level 3 1%
Level 2 10%
Level 1 100%
This pyramid Goes up from level 1 to 5.^
Each level will lose 10% of energy.
So from 100% to 10%
10% to 1%
1% to 0.1%
0.1% to 0.01%

And it goes on.

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Section 3.2: Energy Flow

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