StemUp: AQA A level Biology 3.5.3 Energy and ecosystems

How do plants synthesise organic compounds in an ecosystem? (1)

From atmospheric or aquatic carbon dioxide

What happens to most of the sugars synthesised by plants? (1)

Used by the plant as respiratory substrates

What are the remaining sugars used for in plants? (2)

- To make other groups of biological molecules

- This forms the biomass of the plant

What is biomass measured in terms of? (3)

- The mass of carbon or dry mass of tissue

- Per given area

- In a given time

What is the unit for biomass? (2)

- Typical units for biomass could be kg·m⁻²yr⁻¹ or g·m⁻²yr⁻¹

- Depending on the size of the plant (or animal) being investigated

How do we carry out a experiment to measure the the biomass of a plant sample? (2)

1. Heat all the plant material (removed from a known area) at regular intervals at a constant temperature until the mass is constant

2. Divide the dry mass by the area from which the plant material was removed

What method is used to estimate the chemical energy store in dry biomass? (1)

Calorimetry

How can you carry out a calorimetry to estimate the chemical energy store in dry biomass? (3)

1. A known mass of a sample of biomass is completely burnt

2. So that all the energy released is used to heat a known volume of water

3. The increase in the temperature of the water is measured

How is the chemical energy of the biomass calculated from the water temperature increase? (2)

By using the fact that 4.2 joules of energy is required to raise the temperature of 1 cm³ (1g) of water by 1 degree Celsius

What does GPP stand for? (1)

Gross primary production

What is meant by the 'Gross primary production'? (3)

- The chemical energy store in plant biomass

- In a given area or volume

- In a given time

What does NPP stand for? (1)

Net primary production

What is meant by the 'Net primary production'? (2)

- The chemical energy store in plant biomass

- After respiratory losses to the environment ‎‏‏‎have been taken into account

How is NPP represented in tropic level diagrams? (1)

The energy that is available to other trophic ‎levels in the ecosystem

What is the unit for NPP and GPP? (1)

kJ m⁻² yr⁻¹

How do you calculate NPP? (1)

Using the formula: NPP = GPP - R

Where R = respiratory losses to the environment

What does N stand for? (1)

Net production of consumers

What is meant by the 'Net production of consumers'? (1)

The chemical energy that is available for growth and reproduction in a consumer

What is the unit for N? (1)

kJ m⁻² yr⁻¹

How do you calculate N? (1)

N = I - (F + R)

Where:

I = The chemical energy store in the ingested food

F - The chemical energy lost to the environment in faeces and urine

R - The respiratory losses to the environment

What is primary productivity? (3)

- The rate at which energy is converted by photosynthetic organisms into biomass

- In a given area

- Over a given time

What is secondary productivity? (3)

- The rate at which energy is converted into biomass by consumers

- In a given area

- Over a given time

What are the units for primary and secondary productivity? (1)

kJ ha⁻¹ year⁻¹

What are the two ways in which farming practices can increase the efficiency of energy transfer? (2)

- Simplifying food webs to reduce energy losses to non-human food chains

- Reducing respiratory losses within the human food chain

How can farming practises simplifying food webs to reduce energy losses to non-human food chains? (2)

- Removing preys from an environment

- Direct consumption of crops by people

How can farming practises reduce respiratory losses within the human food chain? (4)

- Close off areas

- To prevent movement of animals (so less respiration)

- Providing animals with optimised nutrition with balanced and easily digestible diets

- Ensures more energy is used for growth rather than maintenance

How can efficiency of energy transfer be calculated? (3)

Net productivity is NPP