23.2 Biomass Tranfer Through An Ecosystem

Question 1

What is the source of energy for almost all the ecosystems on earth?

Answer 1

The sun

Question 2

How is energy from the sun used?

Answer 2

Photosynthetic organisms like plants convert the sun’s light energy into chemical energy, which is then transferred to other non photosynthetic organisms

Question 3

Trophic level

Answer 3

Each stage in a food chain

Question 4

Producer

Answer 4

Organism that converts light energy into chemical energy by the process of photosynthesis

Question 5

Consumer

Answer 5

Organisms that obtain their energy by feeding on other organisms

Question 6

Why is there a limit on the number of trophic levels in a food chain?

Answer 6

There is not sufficient biomass and stored energy left to support any further organisms

Question 7

Decomposers

Answer 7

Feed on dead and decaying matter to release nutrients back into the ecosystem

Question 8

Biomass

Answer 8

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

Question 9

How is biomass at each trophic level calculated?

Answer 9

Biomass in each organism x total number of organisms in that trophic level

Question 10

Why is dry mass taken for pyramid of biomass?

Answer 10

Water content must be discounted

Different organisms have different amounts of water

Question 11

Why is it difficult to find dry mass of organisms?

Answer 11

Organisms have to be killed in order to be dried

Organisms have to be put in an oven at 80oC until all water is evaporated

Question 12

Units for biomass

Answer 12

g/m2 (areas of land)

g/m3 (areas of water)

Question 13

Why is biomass in each trophic level nearly always less than the trophic level below?

Answer 13

Biomass consists of all the cells and tissues of the organism present, including carbohydrates and carbon compounds
As carbon compounds are a store of energy, biomass can be equated to energy content
Only a small proportion of food eaten by animals can be converted into new tissue (biomass)

Question 14

What is biomass at each trophic level measured in?

Answer 14

Kilojoules per metre squared per year

Allows for changes in photosynthetic production and consumer feeding patterns throughout the year

Question 15

Ecological efficiency

Answer 15

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

Question 16

Why can producers only convert 1-3% of sunlight into chemical energy?

Answer 16

Not all the solar energy available is used for photosynthesis

• 90% is reflected
• some is transmitted through the leaf
• some is unusable wavelength

Other factors may limit photosynthesis, such as water availability
Proportion of energy is lost - used for photosynthetic reactions

Question 17

Gross production

Answer 17

Total solar energy that plants convert to organic matter

Question 18

Formula for energy available to the next trophic level

Answer 18

Net production = gross production - respiratory losses

Question 19

Why do consumers at each trophic level convert only around 10% of biomass in their food into their own organic tissue?

Answer 19

Not all of the biomass of an organism is eaten
Some energy is transferred to the environment as metabolic heat, due to movement and respiration
Some parts are eaten but not digested, egested as faeces
Some energy is lost from animals via excretory products such as urine

Question 20

Ecological efficiency formula

Answer 20

Energy or biomass available after transfer / energy or biomass available before the transfer x 100

Question 21

How do we ensure that maximum energy is transferred into biomass that can be eaten by humans?

Answer 21

Agriculture creates very simple food chains
There are just two trophic levels - producers (crops) and humans (consumers)
Minimum energy is lost - fewer trophic levels