Food chains, energy transfer + productivity

Question 1

What are saprobionts?

Answer 1

A group of organisms that break down material of dead organisms (they are decomposers)

Question 2

Why do saprobionts act as fertilisers?

Answer 2

They release nutrients when they decompose things

Question 3

What is biomass?

Answer 3

The total mass of living material in a specific area at a given time

Question 4

How can biomass be measured (three ways)?

Answer 4

1. Fresh mass - living mass/weight of plant/animal
2. Dry mass - mass/weight of organism without water
3. Calorimetry

Question 5

Compare measuring biomass using fresh mass vs. dry mass

Answer 5

Fresh mass - easy to access but diff. plants/animals have varying amounts of water
Dry mass - more reliable but organisms have to be killed (time consuming + sometimes not representative)
Issues with both - samples may not be representative

Question 6

What are producers?

Answer 6

Photosynthetic organisms that manufacture organic substances using light energy, water, CO2 + mineral ions

Question 7

What are consumers?

Answer 7

Organisms that obtain their energy by feeding on other organisms rather than using sun’s energy directly

Question 8

What is the difference between a food chain and a food web?

Answer 8

• Food chains that are linked together to form a food web

- Food webs are complex as most animals do not rely on one food source

Question 9

How can chemical energy store in dry mass be estimated (energy at each trophic level)?

Answer 9

Calorimetry:
1. Weigh sample
2. Burn in pure O2 in a sealed chamber (called a bomb)
3. Measure the temp. increase in a fixed volume of water
(shows energy released)

Question 10

Why is energy lost from the sun to the producer?

Answer 10

• Over 90% of the sun’s energy is reflected back into space
• Not all wavelengths of light can be absorbed
• Light may not fall on a chlorophyll molecule

Question 11

Why is energy lost from producer to primary consumer?

Answer 11

• Much of plant material cannot be accessed e.g roots

- Some material cannot be digested

Question 12

What are the 4 reasons for energy losses between consumers?

Answer 12

• Excretory losses
• Respiration
• Indigestible material (bones)
• Death + decay

Question 13

What is GPP?

Answer 13

Gross Primary Production - the total amount of chemical energy created from light energy by plants (producers), in a given area

Question 14

What is NPP?

Answer 14

Net Primary Production - energy available for new biological molecules (growth + reproduction)

Question 15

What is the equation for calculating NPP for producers?

Answer 15

NPP = GPP - R

R - respiratory losses

Question 16

What is the equation for calculating NPP for consumers?

Answer 16

NPP = I-(F+R)
(I - ingested)
(F - faeces)
(R - respiratory losses)

Question 17

What is it called when production is expressed as a rate?

Answer 17

Productivity

Question 18

What is the equation you would use to work out efficiency?

Answer 18

Efficiency = (Energy available after transfer/energy available before transfer) x 100

Question 19

Explain why most food chains rarely have more than 4 trophic levels

Answer 19

The proportion of energy transferred at each trophic level in small (less than 20%)
After 4 trophic levels there is insufficient to support a large enough breeding population

Question 20

What is a food chain?

Answer 20

• It describes a feeding relationship in which the producers are eaten by primary consumers (and these are eaten by secondary consumers etc.)
• Arrows show the direction of energy flow

Question 21

What are trophic levels?

Answer 21

Each stages of the food chain

Question 22

What is productivity?

Answer 22

The rate at which producers convert light energy into chemical energy in photosynthesis