13.1 - 13.5 Energy and ecosystems

Question 1

What are the sugars produced during photosynthesis used for?

Answer 1

• Respiration
• Starch
• Cellulose
• Lipids
• Proteins (sugars combine with nitrates to form amino acids)

Question 2

Why is not all sunlight used in photosynthesis?

Answer 2

• Most light is reflected back into atmosphere by clouds
• Not all wavelengths of light are used for photosynthesis
• Light may not fall on chlorophyll molecule
• Another factor is limiting the rate of photosynthesis (e.g CO2 conc)

Question 3

Define biomass

Answer 3

Total mass of living material in a specific area at a given time

Question 4

Give the 2 ways in which biomass can be measured

Answer 4

Dry mass:
- Mass of an organism or tissue after all the water in it has been removed

Mass of carbon:
- Generally 50% of the dry mass

Question 5

How do you obtain the dry mass of a sample?

Answer 5

• Place sample in oven
• Heat at 100*c to evaporate water but not burn sample
• Remove and weigh sample at regular intervals
• Once the mass is constant this means all water has been removed

Be careful not to burn sample as this will mean mass is lost in the carbon

Question 6

Define gross primary production

Answer 6

Total quantity of the chemical store in a plant biomass, in a given area or volume in a given time

Question 7

Explain why such a low % of energy is transferred between trophic levels

Answer 7

• Some of the organism is not eaten
• Some parts are not digested and therefore lost in faeces
• Some of the energy is lost in excretory materials (e.g urea in urine)
• Some energy losses occur as heat from respiration

Question 8

Give the equation for calculating the net primary production of consumers

Answer 8

N = I - (F+R)

N = Net production
I = Chemical energy store of ingested food
F = Energy lost in faeces and urine
R = Energy lost in respiration

Question 9

% energy transfer calculation

Answer 9

Energy transfer = (Energy after/Energy before) x 100

Question 10

Define producer/autotroph

Answer 10

An organism that synthesises organic molecules from simple inorganic ones such as carbon dioxide and water

Question 11

Define consumer/heterotrophs

Answer 11

Any organism that gains energy by feeding on another organism

Question 12

Define trophic level

Answer 12

Each stage in a food chain

Question 13

Define herbivore

Answer 13

An animal that eats plants and is therefore a primary consumer

Question 14

Define carnivore

Answer 14

An animal that eats animals and may therefore be a secondary or tertiary consumer

Question 15

Define saprobiont

Answer 15

An organism that obtains its food from the dead or decaying remains of other organisms

Question 16

Give the 2 methods by which farmers can increase the efficiency of energy transfer

Answer 16

1. Simplifying food webs
2. Reducing respiratory losses

Question 17

Describe how farmers may use to simplify food chains

Answer 17

• Insecticides/pesticides
• Herbicides

Biological agents:
- Introducing parasites that kill pests such as lady birds that aphids

Question 18

Describe how greenhouse conditions may be optimised

Answer 18

• Control temp
• Light lamps
• Hydroponics
• Increase CO2 (burners)

Question 19

Describe how respiratory losses are reduced during factory farming

Answer 19

• Movement is restricted (less energy used in muscle contraction)
• Environment kept warm (reduce heat loss from the body)
• Feeding can be controlled (animals receive optimum amount and type of food for growth without wastage)
• Predators excluded
• Given antibiotics

Question 20

Give the 3 ways in which nitrogen gas is converted into nitrogen-containing compounds

Answer 20

1. Nitrogen fixing bacteria (free and in root nodules)
2. Lightning (N2 and 02 react to form nitrogen oxide which then dissolves in rain water)
3. Haber process (Nitrogen and hydrogen used to make ammonia which is then converted to ammonium nitrate for use in fertiliser)

Question 21

Define ammonification

Answer 21

Production of ammonia from organic nitrogen-containing compounds

Saprobionts feed on dead organisms and waste and release ammonium into the soil

Question 22

Define nitrification

Answer 22

The oxidation of ammonium ions into nitrate ions
(NH4+) –> (NO2-) –> (NO3-)

Question 23

Define denitrification

Answer 23

Denitrifying bacteria convert soil nitrates into gaseous nitrogen. This requires anaerobic conditions such as waterlogged soils.

Question 24

How can farmers increase the productivity using the nitrogen cycle?

Answer 24

Ploughing - for aeration

Drainage - to prevent anaerobic conditions

Question 25

What is the name of the nitrogen fixing bacteria in plant root nodules?

Answer 25

Rhizobium

Question 26

What do plant and animals need phosphorus for?

Answer 26

To make biological molecules:
- Phospholipids
- DNA
- ATP

Question 27

Describe the role of mycorrhizae in nutrient cycles?

Answer 27

Mycorrhizae are associations between certain types of fungi and the roots of the vast majority of plants

• The act as an extension of the plant’s root system to increase the total surface area
• They also act as a sponge and allow pants to hold water and minerals around the roots

Question 28

Why are fertilisers needed in agriculture?

Answer 28

Crops are harvested so the mineral ions they contain are removed from the environment, as they are not returned to the soil by decomposers

Question 29

Define leeching

Answer 29

Nutrients are removed from the soil by rainwater and washed into watercourses

Question 30

Must also learn

Answer 30

• Nitrogen cycle
• Phosphorus cycle
• Eutrification

Question 31

Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer of energy through the ecosystem

Answer 31

1.Some light energy fails to strike / is reflected / not of appropriate wavelength
2.Efficiency of photosynthesis in plants is low
3.Respiratory loss / excretion / faeces / not eaten
4.Loss as heat
5.Efficiency of transfer to consumers greater than transfer to producers
6.Efficiency lower in older animals / herbivores / primary consumers / warm blooded animals