Energy And Feeding Relationships

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Transfer of Energy

The Sun is the principal source of energy input to biological systems.
Energy flows through living organisms as light energy and chemical energy.
Energy is transferred from the Sun through food chains and eventually lost to the environment as heat.

Energy is transferred from the sun and through the food chain

Food Chains & Food Webs

A food chain shows the transfer of energy from one organism to the next, starting with a producer.
Arrows in a food chain represent the transfer of energy from one trophic level to the next.
Energy is transferred between organisms by ingestion (eating).
A food web is a network of interconnected food chains, showing more realistic feeding relationships.
Food webs illustrate interdependence – a change in one population affects others.
Most population changes result from human impact (e.g., overharvesting, introducing foreign species).

A food web shows the interdependence of organisms

Trophic Levels (Extended)

A trophic level is the position of an organism in a food chain or web.
Producers form the first trophic level.
Primary consumers (herbivores) are the second trophic level.
Secondary consumers are the third, tertiary consumers the fourth, and quaternary consumers the fifth.
Food chains rarely exceed 5 trophic levels due to energy loss.

Trophic levels describe the position of organisms in a food chain

Efficiency of Energy Transfer (Extended)

Energy transfer between trophic levels is not efficient; much energy is lost to the environment.
Energy is lost through movement, respiration (heat), and excretion (e.g., urea).
Energy in inedible parts (bones, fur, roots) or undigested waste (faeces) does not pass to the next level.
Energy loss explains why food chains are rarely more than 5 organisms long.
It is more energy efficient for humans to eat plants directly than to eat herbivores.

Energy loss at each trophic level

The Carbon Cycle

Carbon is taken from the atmosphere as CO₂ by plants during photosynthesis.
Carbon is passed to animals and decomposers through feeding.
Carbon is returned to the atmosphere as CO₂ by respiration of plants, animals, and microorganisms.
Dead organisms can form fossil fuels over millions of years if decomposers are absent.
Combustion of fossil fuels releases CO₂ back into the atmosphere.
Human activities (burning fossil fuels, deforestation) increase atmospheric CO₂ levels.

The Carbon Cycle

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Practice questions

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1.Define the term herbivore.
Easy
2.State the principal source of energy for food chains.
Easy
3.Complete the sentence about energy flow.
Easy
The arrows in a food chain show the transfer of ____ from one trophic level to the next.
4.Which of the following is a producer in the food chain: grass → rabbit → fox?
Easy
- Agrass
- Brabbit
- Cfox
- Dsun
5.A food web is a network of interconnected food chains.
Easy
True or false?
6.Name the trophic level of topi in the African grassland food web, given that topi eat star grass and are eaten by cheetahs.
Easy
7.State what the arrows in a food chain represent.
Easy
8.Match each process in the carbon cycle with its description.
Medium
- Photosynthesis
- Respiration
- Combustion
- Takes in carbon dioxide
- Releases carbon dioxide
- Burning of fossil fuels releases carbon dioxide

More questions

9.In a food chain, only 10% of energy is transferred from one trophic level to the next. If producers have 10000 kJ of energy, how much energy (in kJ) is available to secondary consumers?
Medium
- A90
- B120
- C100
- D110
10.Explain why there are usually no more than four trophic levels in a food chain.
Medium
11.Name the type of organism that gains its energy from waste organic material from all trophic levels.
Easy
12.Arrange the following organisms in the correct order of a food chain, starting with the producer.
Easy
- hawk
- blackbird
- caterpillar
- fig tree
13.In a four-level energy pyramid (producer, primary consumer, secondary consumer, tertiary consumer), which trophic level is represented by the top layer?
Easy
- Aproducer
- Bprimary consumer
- Csecondary consumer
- Dtertiary consumer
14.In an energy pyramid with producers, primary consumers and secondary consumers, name the trophic level that contains the most energy.
Easy
15.What is the principal source of energy for all food chains?
Easy
- AThe Sun
- BProducers
- CConsumers
- DDecomposers
16.Which trophic level is occupied by primary consumers?
Easy
- AFirst trophic level
- BSecond trophic level
- CThird trophic level
- DFourth trophic level
17.In a food chain, what do the arrows represent?
Easy
- AThe direction of energy transfer
- BThe direction of movement of organisms
- CThe size of organisms
- DThe number of organisms
18.Which of the following is a reason why only about 10% of energy is transferred from one trophic level to the next?
Medium
- AEnergy is lost as heat from respiration
- BEnergy is stored in bones and fur that are not eaten
- CEnergy is lost in faeces
- DAll of the above
19.Which of the following processes return carbon dioxide to the atmosphere? (Select all that apply)
Medium
- APhotosynthesis
- BRespiration
- CCombustion
- DFeeding
- EDecomposition
20.Decomposers obtain energy from dead organic matter and return carbon to the atmosphere as carbon dioxide.
Easy
True or false?
21.Match each trophic level with the correct description.
Medium
- Producer
- Primary consumer
- Secondary consumer
- Tertiary consumer
- Feeds on primary consumers
- Makes its own food
- Feeds on secondary consumers
- Feeds on producers
22.In an energy pyramid, which trophic level contains the most energy?
Easy
- AProducers
- BPrimary consumers
- CSecondary consumers
- DTertiary consumers
23.Match each process in the carbon cycle with its correct description.
Medium
- Photosynthesis
- Respiration
- Combustion
- Decomposition
- Conversion of carbon dioxide into glucose by plants
- Release of carbon dioxide by organisms breaking down glucose
- Release of carbon dioxide from burning fossil fuels
- Release of carbon dioxide from dead organic matter by microorganisms
24.Which of the following are ways that energy is lost from a food chain? (Select all that apply)
Medium
- AHeat from respiration
- BUndigested food in faeces
- CEnergy stored in body parts not eaten
- DPhotosynthesis
- EMovement
25.In a food web, if the population of a primary consumer decreases significantly, which of the following is most likely to happen?
Hard
- AThe population of producers will decrease.
- BThe population of secondary consumers will increase.
- CThe population of secondary consumers will decrease.
- DThe population of decomposers will increase.
26.Arrange the following processes in the correct order as they occur in the carbon cycle, starting with carbon dioxide in the atmosphere.
Easy
- Photosynthesis
- Feeding
- Respiration
- Combustion
27.In a food chain, only about 10% of the energy from one trophic level is transferred to the next. If the producers in a grassland ecosystem have 50,000 kJ of energy available, how much energy (in kJ) is available to the tertiary consumers?
Medium
- A50 kJ
- B500 kJ
- C5,000 kJ
- D50,000 kJ
28.In an energy pyramid for a food chain in a forest, which trophic level contains the largest amount of energy?
Easy
- AProducers
- BPrimary consumers
- CSecondary consumers
- DTertiary consumers
29.Which of the following are reasons why only about 10% of energy is transferred from one trophic level to the next? (Select all that apply)
Medium
- AEnergy is lost as heat from respiration
- BEnergy is used for movement
- CEnergy is stored in bones and fur that are not eaten
- DEnergy is converted to light by bioluminescence
- EEnergy is lost in faeces and urine
30.In a food web, the arrows represent the transfer of energy from one organism to another.
Easy
True or false?
31.Match each organism with its trophic level.
Easy
- Grass
- Rabbit
- Fox
- Flea
- Producer
- Primary consumer
- Secondary consumer
- Tertiary consumer
32.In a food web, if the population of rabbits (primary consumers) decreases significantly, which of the following is most likely to happen in the short term?
Medium
- AThe population of foxes will increase
- BThe population of grass will increase
- CThe population of hawks will increase
- DThe population of snakes will decrease
33.Which of the following is a producer in the food chain: grass → grasshopper → frog → snake?
Easy
- AGrass
- BGrasshopper
- CFrog
- DSnake
34.In a practical investigation, a student placed a known mass of grass in a sealed container with soil and a known mass of rabbits. After one week, the student measured the mass of the rabbits and the remaining grass. Which of the following best explains why the total mass of the rabbits plus grass decreased over the week?
Hard
- AEnergy was lost as heat during respiration
- BGrass grew faster than rabbits could eat it
- CRabbits produced faeces that were not measured
- DThe container allowed light to enter, increasing photosynthesis
35.A student wants to estimate the energy transfer efficiency from one trophic level to the next in a grassland ecosystem. Which of the following measurements would be necessary for the calculation? (Select all that apply)
Medium
- AThe total energy stored in the producers
- BThe total energy stored in the primary consumers
- CThe rate of photosynthesis of the producers
- DThe number of secondary consumers
- EThe energy lost as heat from the primary consumers
36.In a food chain, the arrows point from the consumer to the producer.
Easy
True or false?
37.Match each organism to its trophic level in the food chain: grass → grasshopper → frog → snake.
Easy
- Grass
- Grasshopper
- Frog
- Snake
- Producer
- Primary consumer
- Secondary consumer
- Tertiary consumer
38.Arrange the following processes in the correct order to show how carbon from the atmosphere becomes part of a tertiary consumer, starting with carbon dioxide in the air.
Medium
- Photosynthesis by producers
- Feeding by primary consumers
- Feeding by secondary consumers
- Feeding by tertiary consumers
39.In a food web, if the population of a top predator decreases significantly, which of the following is most likely to happen in the short term?
Medium
- AThe populations of its prey will increase
- BThe populations of its prey will decrease
- CThe populations of producers will decrease
- DThe populations of decomposers will increase
40.A student set up two sealed jars with identical amounts of grass and water. Jar A contained a rabbit; Jar B contained a snake. Both jars were placed in sunlight for one week. Which jar is likely to have the greater total mass of living organisms at the end of the week?
Hard
- AJar A, because the rabbit is a primary consumer
- BJar B, because the snake is a secondary consumer
- CBoth jars will have the same mass because the grass is the same
- DJar A, because the rabbit has a shorter food chain
41.In a food chain, arrows point from the consumer to the producer.
Easy
True or false?
42.Arrange the following processes in the correct order to show how carbon from the atmosphere becomes part of a secondary consumer, starting with carbon dioxide in the atmosphere.
Medium
- photosynthesis by a producer
- feeding by a primary consumer
- feeding by a secondary consumer
- respiration by all organisms
43.In a food web, if the population of rabbits (primary consumers) decreases significantly, which of the following is most likely to happen in the short term?
Medium
- AThe grass population will increase.
- BThe fox population will increase.
- CThe grass population will decrease.
- DThe rabbit population will stay the same.
44.The principal source of energy for all food chains is the Sun.
Easy
True or false?
45.In a marine food chain, phytoplankton are eaten by zooplankton, which are eaten by small fish, which are eaten by large fish. If the biomass of phytoplankton is 5000 kg, what is the approximate biomass of small fish?
Medium
- A500 kg
- B50 kg
- C5 kg
- D0.5 kg
46.Which of the following are ways that energy is lost from a food chain, making it unavailable to the next trophic level? (Select all that apply)
Medium
- AEnergy used in respiration is released as heat
- BEnergy stored in bones and fur that are not eaten
- CEnergy stored in undigested food that becomes faeces
- DEnergy stored in the producer's photosynthesis
- EEnergy used for movement
47.In a food web, arrows point from the consumer to the producer.
Easy
True or false?
48.Complete the sentence: The arrows in a food chain show the transfer of ___ from one organism to the next.
Easy
The arrows in a food chain show the transfer of ____ from one organism to the next.
49.Name the processes in the carbon cycle:
Medium
The process by which plants take in carbon dioxide is ____. The process by which organisms release carbon dioxide is ____. The burning of fossil fuels is called ____.
50.Define the term 'producer'.
Easy
51.In an energy pyramid, name the trophic level that contains the least amount of energy.
Medium
The trophic level with the least energy is the ____.
52.Describe how the over-harvesting of one species could affect other organisms in a food web.
Hard

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