A LEVEL BIOLOGY- ENERGY AND ECOSYSTEMS: FOOD

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A LEVEL BIOLOGY- ENERGY AND ECOSYSTEMS: FOOD

CHAINS, ENERGY TRANSFER AND PRODUCTIVITY EXAM

QUESTIONS

Actual Qs and Ans Expert-Verified Explanation

This Exam contains:

-Guarantee passing score -32 Questions and Answers -format set of multiple-choice -Expert-Verified Explanation Question 1: How is energy gained and transferred through the trophic levels, starting with the producers?

Answer:

-the primary consumer gains energy from consuming the producer.-this primary producer attains its own energy from sunlight, which is used for photosynthesis.-the secondary consumer attains energy from the primary consumer. The tertiary consumer attains energy by consuming the secondary consumer.Energy is transferred across the food chain, however, energy loss does occur through respiratory and excretory loss.Question 2: What is a representative issue with the methods of measuring biomass?

Answer:

-biomass is measured either by total mass of Carbon or dry mass per tissue in a given area, at a specific time.-however, these methods involve the organisms within the mass being dead, meaning the sample may be small and unrepresentative.

Question 3: What is the formula for net primary production?

Answer:

net primary production= gross primary production-respiratory loss.

NPP= GPP-R

-However, it can refer to Sprobionts, which attain energy mostly from primary producers.Question 4: What is an advantage and disadvantage of measuring the fresh mass of biomass instead of dry mass?

Answer:

-advantage: fresh mass is easy to access.

Disadvantage:

-However, fresh mass can contain varying amounts of water, which adds the total biomass. This means fresh mass can be unreliable or unrepresentative of accurate biomass.Question 5: Why do food chains only have 4 or 5 trophic levels and no greater? (2 marks, markscheme answer)

Answer:

-there is an insufficient energy transfer between trophic levels, due to excretory losses, respiratory losses, etc.-this means an insufficient amount of energy is being transferred to be able to support breeding populations with greater than 4 or 5 trophic levels.Question 6: What are trophic levels? Name the five levels and give examples of each.

Answer:

trophic levels are the feeding relationships between organisms within an ecosystem. The trophic levels

are:

• Producer (grass)

• Primary consumer (mouse)

• secondary consumer(snake)

• tertiary consumer (Hawk)

• Saprobionts (decomposers.)

Question 7: What can energy loss be used to calculate?

Answer:

energy loss can be used to calculate the percentage efficiency of energy transfer across trophic levels in the food chain.

Question 8: What energy sources do organisms use?

Answer:

• photosynthetic organism use energy from the sun.

• energy may also be obtained from consuming other organisms.

Question 9: What is used to measure production in primary and secondary consumers?

Answer:

primary + secondary productivity

Question 10: What is the net primary production?

Answer:

The net primary production is the chemical energy store in plants biomass remaining after respiratory losses have been taken into account.

Question 11: Where is the CO2 is used in photosynthesis derived from?

Answer:

The CO2 used in photosynthesis is aquatic or atmospheric.Question 12: Why is the energy lost bigger between the consumers (primary, secondary, tertiary) than between the producer and consumers?

Answer:

-producers undergo energy loss through excretion of waste products, urine and faeces.-However, producers do not undergo this process, so energy loss is lower between producer and consumer.

Question 13: How is biomass measured?

Answer:

Biomass is measured in two ways:

the total mass of carbon or Dry mass of tissue in a given area.

Question 14: What two factors controls the distribution of species within an ecosystem and give examples of both?

Answer:

-Abiotic factors: non-living factors such as sunlight exposure levels. which is used as a source of energy, and temperature

-Biotic factors: availability of food and predators present in an ecosystem.

Question 15: What are sugars used for in plants?

give examples

Answer:

-most sugars are synthesised by plants and are used as respiratory substrates.-the rest of the sugars are then used to form other biological molecules. e.g, lipids or proteins

Question 16: What are the ways we can measure energy loss?

Answer:

• gross primary production is used to measure energy loss in producers.

• net primary production

• net production, used for consumers higher up in trophic levels.

• primary + secondary production

Question 17: Why is only a low percentage of energy transferred at each trophic stage of the food chain? (3 marks)

Answer:

• respiratory losses occur, in the form of heat loss meaning less energy is transferred between trophic

levels.

• Not all parts of an organism are consumed by a consumer, further contributing to lowered energy

intake and transfer.

• Not all parts of an organism consumed by a consumer can be digested and are therefore excreted

through urine or faeces.Question 18: Why is the number of organisms at once place lower at higher trophic levels?

Answer:

there is an insufficient energy transfer between energy levels to support populations at higher trophic levels.-higher trophic levels have lower energy than lower trophic levels, making the levels insufficient for a