13.2: Energy transfer and Productivity

Question 1

What is the sun the main source of

Answer 1

The sun is the main source of energy for ecosystems

Question 2

How much energy can be captured by green plants and made available

Answer 2

1-3%

Question 3

Reason for the majority of sunlight not been converted to organic matter

Answer 3

1. Over 90% is reflected back into space by clouds and dust
2. Not all wavelengths of light can be converted into energy
3. Light may not fall on a chlorophyll molecule
4. Carbon Dioxide may be an inhibiting factor

Question 4

What is the Gross Primary Production

Answer 4

The total quantity of the chemical energy store in plant biomass

Question 5

What is Net Primary Production

Answer 5

Gross Primary Production - Respiratory losses

Respiratory losses = 20-50%+

Question 6

What does the figure for Net Primary production mean

Answer 6

It is the amount of energy available for plant growth and reproduction

Question 7

How much of the NPP can be used by primary consumers for growth

Answer 7

Less than 10%

Secondary & Tertiary are more efficient (20%)

Question 8

Why is the percentage of energy available for each level so low

Answer 8

1. Some of the organism isn’t consumed
2. Some part of the organism cannot be digested when consumed, therefore it is excreted as faeces
3. Some energy is lost in excretory products (urine)
4. Some energy losses from respiration - Heat Energy

Question 9

What does the inefficiency of energy transfers explain

Answer 9

1. Why most food chains only have 4-5 trophic levels
2. Why the total mass of organisms is less at higher levels
3. Why the total amount of energy available is less at each level as one moves up the food chain