Biology (6.5): Ecosystems

ecosystem

ecosystem

the interrelationship between a community of species and the habitats in which they live

community

all of the interdependent populations of species found in a habitat

species

a group of similar organisms who can produce fertile offspring

habitat

the place in which a species lives

biotic and abiotic factors

living and non-living factors

What do biotic and abiotic factors influence? (2)

1. carrying capacity of a population

2. distribution of populations

carrying capacity

maximum size of a habitat

examples of abiotic factors (7)

1. dissolved oxygen conc

2. soil pH

3. light intensity

4. wind intensity

5. temperature

6. moisture/water availability

7. carbon dioxide conc

examples of biotic factors (5)

1. food availability

2. interspecific comp

3. intraspecific comp

4. predator-prey interactions

5. pathogens

interspecific competition

organisms of different species competing for resources

intraspecific competition

organisms of the same species competing for resources

What makes ecosystems

types of dynamism in ecosystems (3)

Examples of cyclic changes (2)

1. seasonal temp changes

2. predator-prey cycles

Examples of directional changed (2)

1. erosion

2. silt deposition in a lake

Examples of one-off changes

natural disasters

what do food chains show?

energy transfer between organisms

What are

types of organisms in food chain (4)

What are producers?

autotrophic

What are primary, secondary and tertiary consumers?

heterotrophic

autotrophic

make their own food

heterotrophic

eat other organisms for food

Why isn’t biomass transfer 100% efficient? (3)

1. respiration

2. not eaten

3. not digestible

efficiency =

biomass transferred / biomass intake x 100

Digesting plant tissue energy and efficiency (2)

1. higher energy

2. lower efficiency

Why does digesting plant tissue have higher energy?

first transfer

Why does digesting plant tissue have lower efficiency?

harder to digest cellulose

digesting animal tissue energy and efficiency (2)

1. lower energy

2. higher efficiency

Why does digesting animal tissue have lower energy?

more transfers, so more losses

Why does digesting animal tissue have higher efficiency?

easier to digest protein

How can you illustrate the biomass at each trophic level? (2)

1. pyramids of number

2. pyramids of biomass

Pyramids of biomass

mass of dry biomass per unit area (g m^-2) at each trophic level

pyramids of number

population of each trophic level in the ecosystem

advantages and disadvantages of pyramids of biomass

more accurate but harder to calculate

advantages and disadvantages of pyramids of number

simplistic but an easily calculated overview

What is considered in the pyramid of biomass?

dry biomass

Steps to determine the dry mass of organisms (4)

1. weigh

2. gently heat to remove water

3. reweigh

4. calculate difference

Issues with using dry mass of organisms

not always appropriate / ethical as it kills the organism

Gross primary productivity (GPP)

rate of conversion of light energy to chemical energy in producers during photosynthesis

What does GPP stand for?

gross primary productivity

Net primary productivity (NPP)

rate of conversion of light energy to chemical energy in producers during photosynthesis minus chemical energy used in respiration

NPP =

GPP - respiratory losses

What does NPP stand for?

Net primary productivity

Gross secondary productivity

rate of chemical energy transfer to consumers from the previous trophic level

Net secondary productivity

rate of chemical energy transfer to consumers from the previous trophic level, minus chemical energy used in respiration

Intensive farming

strategies to increase productivity and so maximise food production, yields and profits in limited space

How to you increase primary productivity? (9)

1. artificial lights

2. glasshouses

3. heating

4. irrigation

5. selective breeding

6. GM

7. crop rotation

8. fertilisers

9. pesticides/herbicides

How do you increase secondary productivity? (7)

1. consume younger animals

2. selective breeding

3. antibiotics

4. sheltered from predators

5. inside for warmth

6. prevent movement

7. high nutrient diet

nutrient cycling

recycling of finite nutrients between biotic and abiotic parts of an environment so they can support organisms indefinitely

Nitrogen cycle

transfer of nitrogen between organisms and the environment

The 4 main processes in the nitrogen cycle (4)

1. nitrogen fixation

2. nitrification

3. ammonification

4. denitrification

nitrogen fixation

nitrogen gas → organic nitrogen

ammonification (decomposition)

organic nitrogen/urea →ammonium

nitrification

ammonium → nitrite → nitrate

denitrification

nitrate → nitrogen gas

What bacteria are used in denitrification?

denitrifying bacteria

What bacteria are used in nitrification to convert ammonium to nitrites?

nitrosomonas

What bacteria are used in nitrification to convert nitrites to nitrates?

Nitrobacter

What bacteria are used in nitrogen fixation to convert nitrogen gas in air to organic nitrogen in the soil?

free-living bacteria in the soil (e.g. azotobacter)

What bacteria are used in nitrogen fixation to convert nitrogen gas in air to organic nitrogen in leguminous plants?

Rhizobium

leguminous plants

have nodules on their roots that house nitrogen fixing bacteria

disruption to the nitrogen cycle

eutrophication

What do excess nitrates entering the water cause?

agal bloom

What does algal bloom do?

blocks out sunlight preventing photosynthesis in lower plants

What happens when algal bloom blocks out the sunlight?

plants die and aerobic bacteria decompose them, bacteria use up all of the oxygen and all aerobic organisms die

carbon cycle

transfer of carbon between organisms and the environment

3 main processes in the carbon cycle (3)

1. respiration

2. photosynthesis

3. decomposition

respiration

6O₂ + C₆H₁₂O₆ →6CO₂ + 6H₂O

Photosynthesis

6CO₂ + 6H₂O → 6O₂ + C₆H₁₂O₆

What disrupts the carbon cycle?

burning of fossil fuels releasing trapped carbon leading to enhanced greenhouse effect and global warming is accelerated

succession

progressive change in a community of organisms over time

pioneer species

the species that begins the process of succession, after colonising an area as the first living things there

Example of succession in a habitat

sand dunes

climax community

the final stable community achieved resulting from succession

From the pioneer species to the climax community, what does changes in the environment cause increases in? (5)

1. abiotic favourability

2. variety of habitats and niches

3. biodiversity

4. interdependence

5. productivity

What are the characteristics of the pioneer species? (5)

1. simple

2. asecual

3. autotrophic

4. hardy/tolerant extremophiles

5. minimal nutrient requirements

What are the characteristics of the climax community? (4)

1. complex

2. auto and heterotrophic

3. sensitive to environmental change

4. complex nutritional requirements

What are the two types of succession?

primary and secondary

primary succession

succession starting from previously uninhabited environment

secondary succession

succession re-starting from a disrupted ecosystem

Deflected succession

succession to an alternative plagioclimax community as a result of human activities, abiotic and biotic factors

What causes deflected succession?

1. human activities

2. abiotic factors

3. other biotic factors

What human activities cause deflected succession?

agriculture, urbanisation and pollination

What abiotic factors cause deflected succession?

wave action, topography and fires

What other