B17 - Organising an Ecosystem

Question 1

What is at the start of every food chain and why are they so important

Answer 1

• Producers - usually a green plant
• They are important because are the source of all biomass in the food chain as they make glucose from photosynthesis

Question 2

Describe a predator prey cycle e.g. with foxes and rabbits

Answer 2

1. More food available for rabbits so they can survive and reproduce increasing rabbit population
2. Fox popluation also increases aas there are more rabbits to eat and they can survive + reproduce
3. More rabbits will be killed and eaten so rabbit population decreases
4. Less rabbits means less food for foxes so fox population decreases
5. Less foxes means more rabbits can survive and cycle repeats

THE PREDATOR POPULATION ALWAYS INCREASES AFTER THE PREY POPULATION INCREASES

Question 3

Stages in the water cycle

Answer 3

1. Water evaporates from the surface of bodies of water
2. The water cools and condenses forming clouds
3. The water in clouds then falls to the ground by precipitation (rain,snow and hail)
4. Some water instantly evaporates, some goes into the ground (percolation) forming aquifers and the rest forms rivers and streams which go back into the large bodies of water

Question 4

How do organisms play a part in the water cycle

Answer 4

• Plants take up water and it passes through them in the transpiration stream
• Animals take in water through drinking
• Animals release water in their urine faeces and through exhalation

Question 5

Stages in the carbon cycle

Answer 5

• Producers take in CO₂ form the atmosphere for use in photosynthesis
• Plants are eaten by consumers and carbon compounds move along the food chain
• All these organisms undergo aerobic respiration which release CO₂ back into the atmosphere
• Once the organisms die, they decay which release CO₂ and are broken down by detritivores and decomposers
• The detritivores and decomposers also undergo aerobic respiration
• Some carbon in dead organisms can be converted to fossil fuels over millions of years, these fossil fuels can be burnt through combustion which releases Co₂ back into the atmosphere

Question 6

Role of decomposers

Answer 6

• Return Co₂ to the atmosphere
• Return mineral ions to the soil
• They release these from dead microorganisms and their waste products by secreting enzymes

Question 7

Conditions to consider for decomposition

Answer 7

• Temperature
• Mositure
• Oxygen

Question 8

Optimum conditions for decay/decomposition

Answer 8

• Temperature - warmer temperatures at the optimum of the decomposers’ enzymes but not too hot so the enzymes don’t denature
• Moisture - microorganisms need water to survive and act as a medium for chemical reactions in decomposition. No water means no decay
• Oxygen - most decomposers undergo aerobic respiration and a good supply of oxygen is needed for this

Question 9

How to stop decomposition

Answer 9

• Keeping food cool e.g. fridges and freezers
• Vacuum packing
• Putting food in brine

Question 10

How does composting make use of decomposition

Answer 10

• Composting is the decomposition of domestic or farm waste to produce a natural fertiliser for plants
• The decomposers respire aerboically which is exothermic so heats up the surroundings speeding up the rate of decomposition
• Water is also put onto the compost to keep it moist
• Oxygen is supplied to allow aerobic respiration

Question 11

What does anaerobic decay produce and how can it be used

Answer 11

• The microorganisms produce biogas which includes methane
• This process can be used in biogas generators where food waste or animal manure is decomposed anaerobically
• The methane produced acts as a fuel to generate electricity