Ecosystems

Question 1

What is an ecosystem?

Answer 1

All interacting living organisms and non living factors within an area

Question 2

What are factors that affect an ecosystem?

Answer 2

Abiotic- light, water availability, oxygen availability, temperature, edophic (soil, which includes soil pH, size and water retention) factors

Biotic- competition (interspecific and intraspecific), predation, diseases

Question 3

Describe the food chain

Answer 3

Shows the transfer of biomass and energy through the organisms in an ecosystem
Each stage is known as a trophic level
First trophic level- producer
Subsequent levels- 1 consumer, 2 consumer

Question 4

Define biomass

Answer 4

The mass of living material in an organism/ area, without water

We do not consider water levels as they can fluctuate based on different factors, eg different times of the day- so it is not a true representation of the amount of energy in a living organism

Question 5

How can biomass be measured?

Answer 5

Using a calorimeter
Collect a sample of organisms
Kill them
Put them in an oven at 80c
When there are 2 same mass readings- biomass as all water has evaporated

Question 6

Producer level efficiency

Answer 6

Not all light is used for photosynthesis- some is reflected, transmitted or is unusable wavelength
Factors may limit photosynthesis- eg water availability
Proportion of energy lost when it is used for photosynthesis

Question 7

Consumer level efficiency

Answer 7

Not all of the biomass of an animal is eaten- eg the bones
Some parts of an animal are eaten but are indigestible
Some energy lost in excretion
Some energy lost as heat during respiration

Question 8

What is net and gross production?

Answer 8

The total solar energy that plants convert to organic matter- gross production
Net production- the total energy available to the next trophic level

Net production= gross production- respiratory losses

Question 9

How can ecological efficiency be increased?

Answer 9

Keep animals indoors/ put fences to restrict movement- limited energy lost in respiration, also exclude wild herbivores and predators
Feed them food with high energy content/ food that they can eat every part

Human use- limit the number of trophic levels to minimise the energy lost

Question 10

What are decomposers

Answer 10

An organism that feeds on and breaks down dead plant and animal matter, turning organic compounds into inorganic nutrients, available for photosynthesising organisms in the environment
They digest their food externally by releasing enzymes
The enzymes break down complex organic molecules into simpler molecules which the decomposer can absorb

Question 11

What are detritivores?

Answer 11

Way in which they are different to decomposers- internal digestion, not external
They help to speed up the decay process by feeding on dead and decaying matter, breaking it down into smaller pieces and also increasing the surface area available for decomposers to work on

Question 12

Describe the nitrogen cycle

Answer 12

1) Nitrogen gas in the atmosphere is turned into ammonium ions- nitrogen fixation
Azotobacter- free living in the soil
Rhizobium- root nodules of legumes

2) Ammonium ions– Nitrite (Nitrosomona)
Nitrite– Nitrate (Nitrobacter)
Nitrification and Oxidation reactions

3) Nirate ions and turned back into nitrogen gas
Done in anaerobic conditions- eg. waterlogged soils
Reduction reaction
Denitrifying bacteria (Pseudosomona)

3) Alternatively, nitrate ions go into the plant
When the plant dies, decomposers feed on it and turn nitrate ions back into ammonium ions (Ammonification)

Question 13

Describe the carbon cycle

Answer 13

Carbon dioxide in the atmosphere is taken up by plants in photosynthesis, released by plants and animals during respiration
Animals eat plants
When they die, decomposers release carbon dioxide back into the environment through respiration
If decomposer not present, the dead matter turns into fossil fuel, which is dug up by humans to combust and produce more carbon dioxide

Question 14

Describe the carbon cycle

Answer 14

Carbon dioxide in the atmosphere is taken up by plants in photosynthesis, released by plants and animals during respiration
Animals eat plants
When they die, decomposers release carbon dioxide back into the environment through respiration
If decomposer not present, the dead matter turns into fossil fuel, which is dug up by humans to combust and produce more carbon dioxide

Question 15

Why do carbon dioxide levels fluctuate?

Answer 15

Carbon dioxide levels are higher at night than they are during the day as plants are not photosynthesising
Higher during winter than during summer as the sunlight period is shorter

Question 16

What is succession

Answer 16

The way in which an ecosystem changes over time

Question 17

What is the difference between primary and secondary succession?

Answer 17

Primary- occurs on an area of land that has been newly formed or exposed, with no soil, eg volcanoes erupting
Secondary- an area of land that has soil but does not have any plants or animals, eg a forest fire

Question 18

Describe the first seral stage of succession

Answer 18

Pioneer species- primary colonisers
Mosses/ lichen
They have the ability to photosynthesise and produce their own energy, tolerance to extreme environments and the ability to fix nitrogen from the atmosphere to increase the mineral content of the soil
They can rapidly produce seeds or spores
Very unstable and subject to change, low biodiversity

Question 19

Describe the second seral stage of succession

Answer 19

Intermediate community-secondary/ tertiary colonisers
Small grass
When pioneer species die and decompose small organic products and nutrients are released onto a thin layer of soil- hummus- which can support the growth of secondary colonisers
Outcompete the pioneer species, previous species
Better adapted to new environment

Question 20

Describe the third seral stage of succession

Answer 20

Climax community
Stable state- very little change over time
Normally a few dominant plants and animals- not the most biodiverse as dominant species outcompete the other species, leading to their elimination

Question 21

What is deflected succession?

Answer 21

When human activities halt the natural flow of succession and prevent the ecosystem from reaching a climax community
The final seral stage reached is the plagioclimax