23.2 - Biomass transfer through an ecosystem

Question 1

Explain trophic levels

Answer 1

Producer – 1^st trophic level

• Organism that converts light energy to chemical energy by photosynthesis

Consumer – (primary, secondary, tertiary…)

• Organisms that obtain energy by feeding on other organisms
• (Primary consumer feeds on producer)

Decomposers: break down dead organisms by releasing nutrients back into the ecosystem

Question 2

Describe and explain the method for measuring biomass

Answer 2

Biomass at each trophic level is measured by

biomass per organism x no. of organisms in the trophic level.

• In aquatic organisms, a dry mass must be obtained (negating water in the mass calculation)

1. Organisms must be killed to obtain a dry mass
   
   • placed in an 80⁰C over until all water is evaporated
2. Only small samples are taken to minimise organism destruction

UNIT: gm^-2 (**areas of land**); gm^-3 (**areas of water**)

Question 3

What happens to the efficiency of biomass transfer as you pass through trophic levels?

Answer 3

• As you progress through trophic levels, biomass decreases
• Biomass: Cells, tissues, carbs, carbon compounds,
• Useful for energy store in animals
• As animals eat, only a small proportion of food is converted to tissue which can be used as biomass to be eaten in the next trophic level (hence energy reduction for biomass transfer per trophic level)

UNIT: kJm^-2yr^-1

Question 4

Define ecological efficiency and give the formula for it.

Answer 4

Ecological efficiency: Efficiency with which energy or biomass is transferred from one trophic level to another

efficiency = biomass at higherlevel/lower level (as a %)

Question 5

Give reasons for variation in biomass

Answer 5

• Energy lost through respiration (for movements, active transport etc.)
• Energy lost through photosynthetic reactions
• Tissue that cannot be eaten or easily digested (e.g. cellulose, bone)
• Energy help in excreted substances (e.g. urea and carbon dioxide)
• Organisms grow and are not eaten by organisms in the successive trophic level

Question 6

Give reasons for variations in biomass at the producer level.

Answer 6

At the producer level…

Total solar energy that plants convert to organic matter is gross production – some is used in respiration

Remaining energy is converted to biomass – energy available to the next trophic level is net production

net production = gross production - respiratory losses

Question 7

What human activity can manipulate biomass transfer through an ecosystem?

Answer 7

• Biomass flow can be manipulated by growing foods​​​
  
  • Involves diverting energy to food growth and creating artificial ecosystems

1. ​Improving Growth Conditions
2. Improving Efficiency of Energy Conversion to Food
3. Reducing Competitiono

Question 8

How can humans improve growth conditions?

Answer 8

Improving growth conditions

• Greenhouses - crops grow in artifical conditions to enhance growth (extra light, warm temperatures, extra CO₂)
• Irrigation
• Fertilisers
• Crop rotations

Question 9

How can humans improve efficiency of energy conversion to food?

Answer 9

• Use faster-growing crop
• Selective breeding or GM
  
  • Introduce fungus/disease resistance
• Harvest animals as soon as fully grown
• Keep animals in small enclosures, or indoors to reduce energy loss by respiration used to move and keep warm

Question 10

How can humans reduce competition?

Answer 10

• Control pests
• Use selective weedkillers
• Use antibiotics to treat illness