T7 - trophic levels in an ecosystem

Question 1

What type of organism is present at the first trophic level in a food chain?

Answer 1

The first trophic level contains producers. These are mainly plants that produce their own carbon compounds through photosynthesis.

Question 2

True or False? The second trophic level of a food chain contains secondary consumers.

Answer 2

False. The second trophic level contains primary consumers, which are herbivores that feed on producers. Secondary consumers are found at the third trophic level.

Question 3

What type of organism is present at the third trophic level of a food chain?

Answer 3

The third trophic level contains secondary consumers, which are carnivores or omnivores that feed on primary consumers.

Question 4

Name two predators in the fourth trophic level in this food web.

Answer 4

IMAGE Predators in the third trophic level include: the hawk, the fox.

Question 5

Identify one consumer which occupies the third and the fourth trophic level.

Answer 5

IMAGE The consumer which occupies the third and fourth trophic level is the fox.

Question 6

True or False? Decomposers occupy all trophic levels of an ecosystem.

Answer 6

False. Decomposers occupy all trophic levels apart from the first trophic level which is always occupied by plants and algae.

Question 7

What do food chains show?

Answer 7

Food chains show the transfer of energy from one organism to the next.

Question 8

True or False? The source of all energy in a food chain is the sun.

Answer 8

True. Producers absorb light energy from the sun, converting it into stored chemical energy which passes up the food chain. There are one or two very unusual exceptions to this rule, e.g. food chains that gain energy from chemicals.

Question 9

What do food webs show?

Answer 9

Food webs show networks of interconnected food chains that show the interdependence between organisms in an ecosystem.

Question 10

What effect might an increase in the population of primary consumers have on a food web?

Answer 10

An increase in a population of primary consumers in a food chain might have the following effects: A decrease in the population of any producers eaten by the population, An increase in the population of any secondary consumers that feed on the population, A decrease in the population of any other primary consumer populations within the food web.

Question 11

What do pyramids of biomass show?

Answer 11

Pyramid of biomass show the mass of living material present at each stage of a food chain.

Question 12

True or False? Pyramids of biomass are always pyramid-shaped.

Answer 12

True. Pyramids of biomass are always pyramid-shaped, regardless of what the pyramid of numbers for that food chain looks like.

Question 13

Which trophic level is found at the base of the pyramid of biomass?

Answer 13

The first trophic level (the producers) is always found at the base of the pyramid of biomass.

Question 14

Define ‘biomass’.

Answer 14

Biomass is the dry mass of an organism (excluding water content).

Question 15

How does energy enter food chains?

Answer 15

Energy enters food chains by the process of photosynthesis; light energy from the sun is converted into stored chemical energy in the tissues of producers.

Question 16

How is energy transferred up food chains?

Answer 16

Energy is transferred up food chains when organisms consume the tissues of other organisms and convert it to biomass.

Question 17

True or False? When a primary consumer eats a plant, all of the chemical energy stored in the plant is transferred to the biomass of the primary consumer.

Answer 17

False. While some of the chemical energy stored in the producer is transferred to the biomass of the primary consumer when it is eaten, much of it is transferred elsewhere, e.g. to the environment as heat or in waste products.

Question 18

What happens to the biological molecules, e.g. proteins, in the tissues of a primary consumer when they are eaten by a secondary consumer?

Answer 18

The biological molecules in the tissues of a primary consumer are broken down during digestion, after which some of them may be used to build the biomass of the secondary consumer and some will be lost in waste products.

Question 19

Approximately what percentage of the biomass at each trophic level is passed on to the next?

Answer 19

Approximately 10 % of the biomass at each trophic level is passed on to the next.

Question 20

What are some reasons for biomass loss at each trophic level of a food chain?

Answer 20

Biomass is lost at each trophic level because: Organisms rarely eat every part of the consumed organism, Some tissues cannot be fully digested by the consumer so any undigested material is egested in faeces, Large amounts of glucose are used in respiration, Material is lost in metabolic waste, e.g. urea in urine, water and carbon dioxide in respiration.

Question 21

True or False? Energy is lost from food chains when organisms transfer energy to new biomass.

Answer 21

False. When energy is transferred to new biomass it is stored in the tissues; this stored chemical energy is available to the next trophic level.

Question 22

Why are food chains rarely made up of more than five trophic levels?

Answer 22

Food chains are rarely made up of more than five trophic levels because of the energy losses at each trophic level; the total energy available eventually becomes too small to support another trophic level.

Question 23

True or False? Pyramids of biomass and energy are always pyramid-shaped due to energy losses between trophic levels.

Answer 23

True. Energy losses at each trophic level mean that each subsequent trophic level will contain less stored energy in the form of biomass.