Biomass Transfer Through An Ecosystem

Question 1

What do food chains and webs tell us

Answer 1

The transfer of biomass, and therefore energy, through the organisms of an ecosystem. Each stage in the chain is known as a trophic level

Question 2

What are the trophic levels

Answer 2

First is always producer, an organism that converts light energy into chemical energy by photosynthesis

Then there is primary consumer - animal that eats producer

Secondary consumer - animal that eats primary consumer

Tertiary consumer - animal that eats secondary consumer

Quaternary consumer - animal that eats tertiary

Food chains don’t normally go further than this as there is not sufficient biomass and stored energy to support any further organisms

Question 3

What do decomposers do?

Answer 3

Break down dead organisms releasing nutrients back into the ecosystem.

Question 4

How can pyramids be used to represent food chains

Answer 4

Food chains can be represented diagrammatically as a pyramid of numbers, with each level representing the number the of organisms at each trophic level or biomass. Producers are at the bottom, going up

Question 5

What is biomass?

Answer 5

The mass of living material present in a particular place or in particular organisms

Question 6

How to calculate biomass at each trophic level?

Answer 6

Multiply the biomass present in each organism by the total number of organisms in that trophic level. This can be presented diagrammatically as a pyramid of biomass

Question 7

What is the easiest way to measure biomass?

Answer 7

Measure the mass of the fresh material present - excluding any water content. Scientists normally calculate ‘dry mass’. Organisms get killed and placed in an oven at 80°C until all water is evaporated. To minimise the destruction of organisms, only a small sample is taken, however it may not be representative of the population as a whole

Question 8

What is biomass measured in?

Answer 8

Grams per square metre for land (g m^-2) and grams per cubic metre for water (g m^-3)

Question 9

Why is biomass at each trophic level always less than the trophic level below

Answer 9

This is because biomass consists of all the cells and tissue of the organisms present, including carbohydrates and other carbon compounds an organism contains. As carbon compounds are a store of energy, biomass can be equated to energy content. When animals eat, only a small portion gets converted into new tissue, this is the only part that is available for the next trophic level to eat

Question 10

What is energy in each trophic level measured in?

Answer 10

Kilojoules per metre squared per year (kJm^-2 yr^-1)

Question 11

What is ecological efficiency?

Answer 11

The efficiency with which biomass or energy is transferred from one trophic level to the next

Question 12

How much sunlight do producers convert to chemical energy and therefore biomass?

Answer 12

1-3% because:

• not all light is available to be used for photosynthesis. 90% reflected, some transmitted, and some of unusable wavelength
• other factors may limit photosynthesis, such as water availability
• a proportion of the energy is ‘lost’ as it is used for photosynthetic reactions

Question 13

What is gross production in plants

Answer 13

The total solar energy that plants convert to organic matter, however 20-50% of this energy is used for respiration. The rest is converted to biomass. This is the energy available to the next trophic level and is known as net production

Question 14

How can energy available to the next trophic level be calculated

Answer 14

Net production = gross production - respiration

Question 15

What is generation of biomass within a producer and consumer called?

Answer 15

Primary production and secondary production

Question 16

How much energy do consumers at each trophic level convert?

Answer 16

10% in their food to their own organic tissue

Question 17

Why do organisms only convert 10% to their own organic tissue?

Answer 17

• not all biomass of an organism is eaten, e.g. plant roots or animal bones may not be consumed
• some energy is transferred to environment as metabolic heat due to respiration and mvmnt.
• some parts of organism are eaten but indigestible (and their energy content) are egested as faeces
• some energy is lost from animal excretory materials like urine

Question 18

How to calculate efficiency of biomass transfer?

Answer 18

Energy or biomass available after the transfer / energy or biomass available before the transfer

X 100

Question 19

How can humans manipulate biomass through ecosystems

Answer 19

Humans need agriculture, this involves manipulating the environment to favour plant species we can eat and to rear animals for food or their produce. Plants and animals get provided with the abiotic factors they need to thrive such as adequate warmth and food. Competition is removed as well as threat of predators such as putting up fences.

Question 20

How do humans reduce biomass loss?

Answer 20

Agriculture- it creates very simple food chains. For animals only three trophic levels are present: producers (animal feed), primary consumers (livestock) and secondary consumers (humans)

And with plants there are only 2: producers (crops) and primary consumers (humans)

Minimum energy is lost due to fewer trophic levels than the natural ecosystem where we would be tertiary or quaternary consumers. Much of the energy possible is transferred into biomass that can be eaten by humans