Paper 2: Topic 7 Ecology - Trophic levels in an ecosystem

Question 1

Define the term trophic level

Answer 1

The feeding stage of an organism within a food chain

Question 2

Which type of organisms are always found on trophic level one?

Answer 2

Producers i.e. plants and algae

Question 3

Explain why each trophic level can have more than one species in it

Answer 3

Each species within a trophic level carries out a specific role in the food chain

Question 4

What is the first trophic level called and what organisms are found in it?

Answer 4

Level 1: Plants and algae make their own food and are called producers

Question 5

What is the second trophic level called and what organisms are found in it?

Answer 5

Level 2: Herbivores eat plants/algae and are called primary consumers

Question 6

What is the third trophic level called and what organisms are found in it?

Answer 6

Level 3: Carnivores that eat herbivores are called secondary consumers

Question 7

What is the fourth trophic level called and what organisms are found in it?

Answer 7

Level 4: Carnivores that eat other carnivores are called tertiary consumers

Question 8

Define the term ‘apex predator’

Answer 8

Apex predators are carnivores with no predators

Question 9

Which trophic level normally has an apex predator

Answer 9

Fourth / Level 4

Question 10

Explain why food chains rarely have more than 4 trophic levels

Answer 10

• Energy is lost between each trophic level along the food chain
• The energy that reaches level 4 is very small
• So this means there is insufficient energy to support a 5th trophic level

Question 11

State the two types of organisms that are decomposers

Answer 11

• Bacteria
• Fungi

Question 12

Explain how decomposers contribute to the recycling of materials in the ecosystem

Answer 12

• Decomposers break down dead plant and animal matter by secreting enzymes into the environment
• Small soluble food molecules then diffuse into the microorganism

Question 13

Why do scientist draw pyramids of biomass?

Answer 13

Pyramids of biomass can be constructed to represent the relative amount of biomass in each level of a food chain

Question 14

Describe what happens to the amount of energy at each trophic level

Answer 14

It decreases as the energy flow along the food chain

Question 15

Describe what happens to the amount of biomass at each trophic level

Answer 15

It decreases as the biomass flow along the food chain

Question 16

Describe what happens to the number of organisms at each trophic level

Answer 16

It generally decreases when you move up a trophic level

Question 17

Describe a situation when the numbers of organisms in a trophic level may be higher than the previous trophic level

Answer 17

Fleas living on a fox

Question 18

Explain what each bar on a pyramid of number represents

Answer 18

The number of organisms feeding at that stage in the food chain in a given period of time

Question 19

Explain what each bar on a pyramid of biomass represents

Answer 19

The biomass of the organisms feeding at that stage in the food chain in a given period of time

Question 20

Define the term biomass

Answer 20

The relative mass of the living material within an organism

Question 21

Answer 21

Question 22

State 3 pieces of information that can be obtained from a pyramid of biomass

Answer 22

1. The sequence of organisms in the food chain (read the pyramid from the base upwards)
2. The amount of biomass available at each trophic level (the area of the bar)
3. The amount of biomass lost between different trophic levels (calculate the difference between the area of the two bars)

Question 23

State the typical energy transfer that occurs between the sun and producers

Answer 23

~1%

Question 24

State 4 reasons why the energy transfer between the sun and the producers is so low

Answer 24

1. Not all the light rays reach the Earth’s surface
2. Not all the light rays hit plants (some hit roads, building etc)
3. Some of the light rays are reflected from the surface of the leaf
4. Some of the light rays pass straight through the leaf and do not hit a chloroplast

Question 25

State the typical biomass transfer that occurs between producers and primary consumers (herbivores)

Answer 25

~10%

Question 26

State 2 reasons why the biomass transfer that occurs between producers and primary consumers (herbivores) is so low

Answer 26

1. The plant uses some of the biomass to produce biological molecules for its own growth
2. The plant uses some of the biomass in respiration to release energy to produce fruits and seeds
3. Not all of the plant is eaten by the herbivore e.g. roots, thorns

Question 27

State the typical energy transfer that occurs between primary consumers (herbivores) and secondary consumers

Answer 27

~20%

Question 28

State 6 reasons why the biomass transfer that occurs between primary consumers (herbivores) and secondary consumers is so low

Answer 28

1. The plant uses some of the biomass to produce biological molecules for its own growth
2. Some of the biomass is converted to waste products and excreted
3. Some of the biomass is undigested and egested
4. Some of the biomass is respired to release energy for movement
5. Some of the biomass is respired to release energy for reproduction
6. Some of the biomass is respired to maintain body temperature

Question 29

List 3 waste products that are formed as part of an organism’s metabolism

Answer 29

1. Carbon dioxide (from respiration)
2. Water (from respiration)
3. Urea (from deamination of excess amino acids)

Question 30

Describe how to calculate the efficiency of biomass transfer

Answer 30