5.3 Energy In Ecosystems

Question 1

What is an ecosystem?

Answer 1

All of the organisms living in a community plus all the non-living (abiotic) conditions of the area in which they live.

Question 2

What is biomass?

Answer 2

The mass of living material of an organism

Question 3

What are the stages of the food chain?

Answer 3

Producers - primary consumers - secondary consumers - tertiary consumers - apex predator

Question 4

What is dry mass?

Answer 4

The mass of an organism when the water is removed

Question 5

Why is dry mass measured rather than wet mass?

Answer 5

The water content between organisms varies so dry mass is used as a measure of biomass instead of wet mass.

Question 6

How do you measure dry mass?

Answer 6

An organism is dried often in an oven at a low temperature.
The organism is weighed at regular intervals until the mass becomes constant meaning all of the water has been removed.
The dry mass of a sample can be used to estimate the total dry mass of a population or given area.

Question 7

In what two ways are organic molecules used in organisms?

Answer 7

• As respiratory substrates (e.g. glucose)
• To make other biological molecules (carbohydrates, proteins and lipids). These biological molecules form new biomass.

Question 8

Around what percentage of the dry mass is the mass of carbon?

Answer 8

50%

Question 9

How can the energy contained within dry biomass be measured using a calorimeter?

Answer 9

• Burn the biomass in a calorimeter
• The energy released is used to heat a known volume of water
• The change in temperature of the water is used to calculate the chemical energy of the biomass

Question 10

What is gross primary production (GPP)?

Answer 10

Total amount of chemical energy converted from light energy by plants in a given area

Question 11

What is net primary production (NPP)?

Answer 11

The remaining chemical energy when respiratory losses are taken away from gross primary production.
NPP=GPP-R

Question 12

What is a trophic level?

Answer 12

A stage in a food chain

Question 13

What is net production?

Answer 13

The energy in consumers that is available to the next trophic level
I=Energy in ingested food
F=Energy in waste (e.g. faeces)
R=Energy lost in respiration
N=I-(F+R)

Question 14

What is the equation for percentage efficiency of energy transfer?

Answer 14

% efficiency = (net production of trophic level / net production of previous trophic level) x100

Question 15

How can farmers reduce energy lost to other organisms (simplify the food web) to increase primary productivity?

Answer 15

• Use pesticides
• Pest control

Question 16

How can farmers reduce respiratory losses?

Answer 16

• Maximising plant exposure to light.
• Using warmer temperatures in greenhouses.
• Irrigation to maximise water supply.
• Fertilisers can be sprayed on fields to maintain nutrient levels in the soil.
• Limit movement of animals
• Antibiotics - prevents energy lost to pathogens