OCR A-level Biology- ecosystems

Whats an ecosystem

All the living organisms that interact with one another in an area and the physical factors present in that area

Which two factors affect an ecosystem

Biotic and abiotic factors

What are biotic factors

Then interactions between living organisms

What are the 5 abiotic factors

Light, temperature, water availability, oxygen availability and soil factors

What are soil factors known as

Edaphic factors

Describe clay

Fine particles, easily waterlogged and forms clumps when wet

Describe loam

Has different sized particles, retains water but doesn’t become waterlogged

Describe sandy

Coarse well-separated particles allowing free draining, doesn’t retain water and is easily eroded

What are the 3 main soil types

Clay, loam and sandy

Whats intraspecific competition

Competitions between members of the same species

Whats interspecific competition

Competition between members of different species

Whats the first trophic level known as

Producer

What are subsequent trophic levels known as

Consumers

What are producers

Organisms that convert light energy into chemical energy by photosynthesis

What are consumers

Organisms that obtain their energy by feeding on other organisms

Why do food chains rarely have trophic levels beyond quaternary consumer

Because there isn’t sufficient biomass and stored energy left to support further organisms

What are decomposes

Organisms which break down dead organisms releasing nutrients back into the ecosystem

Whats biomass

The mass of living material present in a particular place or organism

How do you calculate the biomass at each trophic level

By multiplying the biomass of each organism by the number of organisms in the trophic level

Whats the easiest way to measure biomass

The mass of fresh material present

What must be removed from fresh material to calculate biomass

Water

What must happen to organisms for their dry mass to be calculated

They must be killed

What are the steps to obtaining the dry mass of an organism

Once killed they’re placed in an oven at 80 degrees until all the water has evaporated (their mass stays constant)

Why can calculations of biomass be inaccurate

Only small samples are used which may not be representative of the wider population

Why does biomass decrease between trophic levels

Because only a small proportion of food ingested is converted into new tissue available for the next trophic level to eat

Whats ecological efficiency

The efficiency with which biomass is transferred from one trophic level to the next

Approximately what percentage of sunlight recieved to producers convert to chemical energy

1-3%

Why is the amount of sunlight converted to chemical energy so low

Not all solar energy available is used for photosynthesis some may be reflected, other factors may limit photosynthesis and a proportion of energy is ‘lost’ as its used for photosynthesis

Whats the equation for calculating the energy available for the next trophic level

Net production = gross production - respiratory losses

Roughly what percentage of biomass ingested do consumers convert into their own organic tissue

10%

Why do consumers convert such a low amount of biomass in their food to their tissue

Not all of the biomass of an organism is eaten, some energy is transferred to the environment, some parts of the organism that are eaten are indigestible and are egested, some energy is lost from excretory material

Whats the equation fort the efficiency of energy transfer between trophic levels

Ecological efficiency = energy/biomass available after transfer divided by energy/biomass available before the transfer x100

Whats decomposition

The chemical process in which a compound is broken down into smaller molecules

What sort of organism are decomposers

Satrotrophs

What are satrotrophs

Organisms which obtain their energy from dead or waste organic material by secreting enzymes to break them down

What are detritivores

Organisms which feed on dead and decaying material

Why is nitrogen required by organisms

Because its essential in the formation of amino acids and nucleic acids

Why must nitrogen be converted into different forms

Because nitrogen in the form of nitrogen gas cannot be absorbed by plants

What do nitrogen fixing bacteria do

Convert nitrogen in the air to ammonia

Whats azobacter

A form of nitrogen fixing bacteria found in the soil

Whats rhizobium

A form of nitrogen fixing bacteria found inside the root nodules of leguminous plants

How can the relationship between rhizobium and leguminous plants be described

Symbiotic because the plant gains amino acids produced by the nitrogen fixing bacteria and the bacteria gain carbohydrates they can use as an energy source

Whats do nitrifying bacteria do

Convert ammonium compounds in the soil into nitrites and nitrates

What does nitrosomonas do

Converts ammonium compounds in the soil into nitrites

What does nitrobacter do

Converts nitrites into nitrates

Whats the formula for a nitrite

NO2-

Whats the formula of a nitrate

NO3-

What conditions does nitrification need to occur

Well aerated soil

What do denitrifying bacteria do

Convert nitrates in the soil back to nitrogen gas

In which conditions does denitrification occur

Anaerobic conditions e.g. waterlogged soil

Whats ammonification

When decomposers convert nitrogen compounds in dead organisms into ammonium compounds

How else can nitrogen fixation occur without bacteria present

Through lightning

By what process is carbo returned from carbon containing comopounds in decomposers to carbon dioxide

Decomposition

By what process does carbon dioxide turn into carbon containing compounds in producers

photosynthesis

By what process do carbon containing compounds in consumers and producers turn into carbon dioxide

Respiration

Why are carbon dioxide levels higher at night

Because photosynthesis can’t occur and so carbon dioxide isn’t removed from their air

Why are carbon dioxide levels higher on a summers day than a winters day

Because photosynthesis rates are higher on a summers day

When during the day are carbon dioxide levels highest

At night

Over the past 200 years why have global atmospheric CO2 levels increased

The combustion of fossil fuels and deforestation

Why does combusting fossil fuels increase CO2 levels

It releases carbon previously trapped beneath the earths surface and converts it to CO2

Why does deforestation increase CO2 levels

It removes photosynthesising organisms reducing carbon dioxide absorption and if burnt releases more carbon dioxide

What’d the greenhouse effect

Carbon dioxide traps thermal energy in the atmosphere worsening global warming

Why has global warming reduced the carbon bank in the oceans

Because as water is heated less gas can be dissolved in it so more carbon dioxide is released

How can we study how the atmosphere has changed over time

By looking at ice bubbles within Antarctica glaciers and analysing the composition if the bubbles

Whats primary succession

Succession which occurs on an area of land that’s newly formed or on bare rock

Whats secondary succession

Succession that occurs on areas of land where soil is present but no animal or plant species are present

What are examples of primary succession

After volcanic eruptions, newly formed sand dunes, silt and mud deposits, glacial retreat

What are the stages of succession known as

Serial stages

What are the main seral stages

Pioneer community, intermediate community, climax community

What are pioneer species

Species arriving as spores or seeds which begin colonising an inhospitable environment

What are some adaptations of pioneer species

The ability to produce a large quantity of spores/seeds, quickly germinating seeds, the ability to photosynthesise, tolerance to extreme conditions, nitrogen fixing abilities

Why are intermediate communities able to form

Pioneer species die and decompose releasing organic products into the soil allowing it to support new growth

What are examples of secondary colonisers

Mosses

What are examples of tertiary colonisers

Ferns

What are common adaptations of tertiary colonisers

Wavy cuticles which protect them from water loss

Whats the climax community

The final seral stage where the community is in a stable state/shows very little change

Why does biodiversity decrease during the intermediate/climax community

Because dominant species out-compete other species eliminating them

Whats deflected succession

When succession is stopped artificially

Whats the final stage of deflected succession

Plagioclimax

Whats one of the main reasons for deflected succession

Agriculture

What are examples of systematic sampling

Belt and line transects

Whats line sampling

Laying down a line and taking samples at regular intervals along the line

What’s a belt transect

Sampling between two parallel lines

What factors increase the number of organisms

Immigration and births

What factors decrease the number of organisms in an area

Emigration and death

Whats a population

A group of similar organisms living in a given area at a given time

Whats the equation for estimating population per area

Number of individuals in a sample / area of sample

How can animal population be measured

Capture-mark-release-recapture

Describe the method to measure animal abundance

Capture as manny individuals as possible within a sample area, mark/tag each individual, release the marked animals, leave time for them to redistribute, recapture as many individuals as possible, record the number of marked and unmarked individuals in the sample

Whats the Lincoln index equation

Number of individuals in the first sample x number of individuals in second sample divided by the number of recaptured marked individuals

Why can quadrats not be used for most animal species

Because they move too quickly

What value is used to determine the biodiversity present in a habitat

Simpsons diversity index