Module 3: Understanding Energy Transfer

Question 1

Trophic level

Answer 1

The level at which an organism feeds in a food chain.

Question 2

Food chain arrows

Answer 2

show the direction of energy transfer
e.g
producer —-> primary consumer —-> secondary consumer

Question 3

Food web

Answer 3

shows the interactions between different food chains organisms can often feed at different trophic levels in different food chains.
Food webs help to show how energy flows through the whole ecosystem.

Question 4

How is energy lost going up the food chain?

Answer 4

• At each trophic level organisms need energy to carry out life processes. Respiration releases energy from organic molecules like glucose, some of this energy is eventually converted to heat.
• Energy remains stored in dead organisms and waste material, which is then only available to decomposers such as fungi and bacteria. This waste material includes parts of animals and plants that can not be digested by consumers.

Question 5

Why are there fewer organisms at the top of the food chain?

Answer 5

Energy is lost going up the food chain through respiration( some energy lost as heat) and death or waste material, meaning that the energy is then only available to decomposers- preventing the energy from rising further up the food chain.

therefore there is less energy to sustain living tissue at higher levels of the food chain, and so less living tissue can be kept alive. When the organisms in a food chain are about the same size, this means that there will be fewer consumers at the higher levels.

Question 6

Pyramid of numbers

Answer 6

The area of each bar of the pyramid is proportional to the number of individuals in that population or tertiary level: can be drawn for food webs or chains.

Shows pictorially how there are generally fewer organisms at the top of a food chain compared to the bottom, providing that they are all relatively the same size.

Question 7

How could efficiency of energy transfer be measured?

(pyramids of biomass)- how does it work, method and problems

Answer 7

Pyramids of biomass: provides an accurate picture of how much living tissue exist at each level, where the area of the bars is proportional to the dry mass of all the organisms at that tropic level.

Method: collect all organisms in a trophic/population level, put them in an oven at 80 degrees until all water is evaporated. Very destructive to ecosystem so often only wet mass is weighed and dry mass is calculated from previously published data.

Problems: different species may release different amounts of energy per unit mass

Question 8

How could efficiency of energy transfer be measured?

(pyramid of energy)- how does it work, method and problems

Answer 8

Pyramid of energy: calculates the amount of energy in each trophic/population level

Method: burning all organisms in a level in a calorimeter to find how much heat energy is released per gram.

Problems:

• Very destructive and time consuming- often resort back to pyramids of biomass.
• Only take a snapshot of an ecosystem at one moment in time - population sizes fluctuate over time so could provide a distorted idea of the efficiency of energy transfer.

Question 9

How could efficiency of energy transfer be measured?

(pyramid of productivity)- how does it work, method

Answer 9

Productivity- rate at which energy passes through each trophic level drawing a pyramid of energy flow.

• productivity