# High School Biology : Understanding Energy Flow

## Example Questions

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### Example Question #1 : Understanding Energy Flow

A finch eats a caterpillar. Assuming the caterpillar had 100% energy, what percentage of the caterpillar's energy will the finch be able to utilize?

Explanation:

In a standard food pyramid, organisms are divided into trophic levels based on their means of gaining nutrients. As one moves upwards through trophic levels, the number of organisms that can be sustained decreases. This is because energy is lost between each level. Typically, about 90% of the energy in one trophic level is lost during transfer to the next highest level; this leaves on about 10% of the energy to be used by the consumer. Because of this disparity, it is very difficult to maintain large populations at higher trophic levels. This explains why lower level organisms can easily flourish (such as ants), while higher level organisms can easily become endangered (such as tigers).

### Example Question #2 : Understanding Energy Flow

Where does all of the energy in an ecosystem originate?

The water

The animals

The plants

The wind

The sun

The sun

Explanation:

The sun is the source of all energy in an ecosystem. Without the energy from the sun, the plants cannot grow and the animals would not have food to eat. Plants are considered producers, meaning that they are able to convert sunlight into chemical energy. Animals are considered consumers, in that they consume plants or other animals to absorb energy. If you trace back far enough in a food chain, you will always arrive at a producer and, subsequently, the sun.

Living things need water to grow, but it does not directly contribute energy.

### Example Question #3 : Understanding Energy Flow

All of the given answer options represent organisms that could coexist in an ocean ecosystem. In this hypothetical ecosystem, which organism will receive the least amount of energy in the food pyramid?

Seal

Tuna

Anchovy

Green algae

Great white shark

Great white shark

Explanation:

The great white shark is at the top of the food pyramid in its ocean ecosystem. Since it is at the top, it receives the least amount of energy from its food because the amount of energy decreases as one moves up the pyramid.

Green algae contains the pigment chlorophyll, which is responsible for photosynthesis. This makes green algae a producer, and the lowest level of the pyramid. As a result, the green algae will represent the largest amount of energy in the ecosystem. The anchovy eats the algae, the tuna eats the anchovy, the seal eats the tuna, and the shark eats the seal. After each level, approximately 90% of the energy of the pervious level is lost. After four transitions (to get to the level of the shark), only 0.01% of the original producer energy has been transferred to the shark!

### Example Question #4 : Understanding Energy Flow

From where do autotrophs obtain their carbon, nutrients, and minerals?

From human activity and byproducts

From the inorganic environment

From the sun

From other autotrophs

From heterotrophs

From the inorganic environment

Explanation:

Autotrophs are the base part of any food pyramid/web/chain. They take inorganic substances and turn them into organic substances that are later consumed and used by heterotrophs for energy. Most autotrophs absorb carbon dioxide from the atmosphere and minerals/nutrients from the soil in order to feed, reproduce, and grow, drawing their resources from the surrounding inorganic environment.

The sun, while crucial to many autotrophs, provides energy for the processes—however, it does not provide carbon, nutrients, or minerals. Human activity may contribute to the autotrophs' activity, but it is not the main source of the necessary resources.

### Example Question #5 : Understanding Energy Flow

Which type of organism produces its own food/energy?

Heterotroph

Homotroph

Herbotroph

Omnitroph

Autotroph

Autotroph

Explanation:

Autotrophs make their own food, then using cellular metabolism, this food is converted to energy. Examples are plants converting sunlight, carbon dioxide and water into glucose and oxygen (photosynthesis). Then, the plants breakdown glucose, converting this food molecule into the energy molecule ATP via glycolysis, Krebs cycle and electron transport under aerobic conditions, and via fermentation under anaerobic conditions. Heterotrophs, like humans, must ingest organic material (food) in order to meet their energy demands.

### Example Question #6 : Understanding Energy Flow

What happens to energy as it moves up the food pyramid, from producers up to tertiary consumers?

It decreases

It increases

Food pyramids do not involve energy

It varies depending on the food pyramid

It stays the same

It decreases

Explanation:

The energy in a food pyramid decreases as it is tranferred up the pyramid. The bottom of the pyramid, the producers, start with the most energy. When they are eaten by primary consumers, only about ten percent of the energy is transferred to the next level; the rest is lost. The next level of secondary consumers also only keeps about ten percent of the energy from the level below that—only one percent of the original producer-level energy. This loss of energy continues up to the highest level of the pyramid. The lost energy is released as heat into the atmosphere.

### Example Question #7 : Understanding Energy Flow

What is the main source of energy in an ecosystem?

Water

Food

Minerals

The sun

The sun

Explanation:

The sun is the main source of energy in all ecosystems. Plants harvest all their energy through photosynthesis, then other organisms eat the plants (and other producers) to gain energy. Without the sun this process would never happen.

### Example Question #8 : Understanding Energy Flow

What is the main way energy is lost in a food chain?

Nitrogenous waste

None of these

Decomposers

Respiratory heat

Respiratory heat

Explanation:

The majority of energy in a food chain is lost as respiratory heat. Whenever an organism takes food, breaks it down, and converts it to energy, heat is a byproduct that contains the energy lost. About 66% of the energy in a food chain is lost due to respiratory heat. No energy is lost to decomposers, rather, it is transferred to them. The decomposers respire, and create heat as well.

### Example Question #9 : Understanding Energy Flow

Organisms tend to select foods that will give them as much energy as possible, while requiring minimal energy. What is this process called?

Ineffective foraging

Efficient foraging

Preferential treatment

Selective treatment

Efficient foraging

Explanation:

Efficient foraging, also known as economical foraging, is the process by which organisms attempt to maximize their energy return for energy expended. In other words, if a lion was hunting she would want to find food that would give her more energy from eating it than she would spend hunting it.

### Example Question #10 : Understanding Energy Flow

A heterotroph is best defined as which of the following?

Uses sunlight to make food

Uses chemicals to synthesize energy-rich molecules

Must consume other organisms for energy

Combines carbon dioxide with water to produce sugar molecules