Biology Paper 2 - 6.5 Ecosystems

An organism that synthesises organic molecules from simple inorganic ones such as carbon dioxide and water. Most producers are photosynthetic and form the first trophic level in a food chain.

An organism that obtains energy by ‘eating’ other organisms.

A primary consumer feeds on producers.
A secondary consumer feeds primary consumers.
A tertiary consumer feeds secondary consumers.
A quaternary consumer feeds on tertiary consumers.

The position of an organism in a food chain.

1-3% from sun to producers.
5-10% from producers to primary consumers.
15-20% from consumer to consumer.

Sunlight is converted to chemical energy in photosynthesis.

Wrong wavelength.
Reflected (over 90%).
Pass straight through the leaf.
Hits non-photosynthesising parts of the plant e.g. bark.

Some of the organism is not eaten / cannot be digested.
Energy used to maintain body temperature.
Some of the energy is lost in excretion and egestion.
Some energy is used in respiration.

Excretion is the removal of waste products from a living organism.
Egestion is the removal of undigested waste from the body (faeces).

Insufficient energy is available to support a large enough breeding population at trophic levels higher than five.

The mass of living material (without water).

It shows how much of the energy transferred ends up in the next organism.
Biomass indicates how much energy an organism contains.

Total energy captured or assimilated by an organism.
In plants = total sunlight energy used in photosynthesis.
In animals = Energy in food eaten – energy in faeces.

Net productivity (energy used for growth)= gross productivity – respiratory losses.

Energy transfer efficiency = (energy available after transfer / energy available before transfer) X 100

1. Calculate the amount of biomass in a sample of the organisms.

2. Sample x total population size = total amount of energy in the organisms at that trophic level.

3. The difference in energy between the trophic levels is the amount of energy transferred.

An ecosystem = all living organisms (biotic) + all non-living conditions (abiotic).

Rock pool: Biotic - seaweed (producer), limpet (consumer), competition for food will limit number of organisms present. Abiotic - pH, salinity, temperature, low tide results in extreme abiotic conditions – special adaptations needed.
Playing field: Biotic - grass, daisies, clover, dandelion (producers), caterpillars, bees, rabbits (consumers). Abiotic - rainfall & sunlight will affect growth. This in turn will affect the number of consumers the ecosystem can support.
Large tree: Biotic - Leaves are food source for caterpillars & other insects. If too many are eaten this will affect tree growth. Abiotic - drought conditions will impact growth.

Herbicides - reduces competition from weeds.
Fungicides - Crops use more energy for growth & less for fighting infection.
Insecticides and/or introduce natural predators to eat pest species – less biomass lost from the crop.
Fertilisers – growth is not limited due to mineral deficiency.
All of the above means that crops grow faster & become larger, increasing productivity.

Intensive farming methods increase the efficiency of energy conversion so more biomass is produced & productivity is increased: Animals kept in warm, indoor pens & restrict movement. Less energy is wasted keeping warm & moving around. Animals given high energy feed, so more energy available for growth.

Can digest cellulose. Secrete enzymes outside of their bodies & absorb the products of digestion = saprotrophic nutrition. Absorbed substances used for respiration.

Cannot break down cellulose. Break down dead matter into smaller pieces. Create a larger surface area for enzymes to work on.

Photosynthesis.

Saprotrophs release enzymes.
Extracellular digestion.
They then absorb the products of digestion.
They respire, producing carbon dioxide.
Carbon dioxide is taken into the plant in photosynthesis.
Through the stomata.

Methane and carbon dioxide.

Limestone is biological sedimentary rock formed from shells of dead marine organisms that collected on the seabed over millions of years ago.
When limestone is weathered the carbon is released back into the atmosphere as carbon dioxide.

Photosynthesis by plants. Dissolving in the oceans.

Respiration by plants, animals and microbes.
Combustion ie burning wood and fossil fuels such as coal, oil and gas.
Weathering of limestone & chalk.
Thermal decomposition of limestone, for example, in the manufacture of iron, steel and cement

Chlorophyll - magnesium ions.
Phospholipids - phosphate ions.
Proteins - nitrate ions.
Nucleic acids - nitrate ions.

Ammonium (NH4+) or nitrate (NO3-).

1. Saprotrophic digestion = decomposers digest proteins → amino acids.

2. Ammonification = amino acids → form ammonium compounds (NH4+).

3. Nitrification = conversion of ammonium compounds (NH4+) → nitrates (NO3-).

Decomposers and saprotrophic micro-organisms break down the ammonium (NH3) containing molecules into ammonium ions (NH4+) by ammonification.
The ammonium ions (NH4+) are converted to nitrite ions (NO2-), then nitrate ions (NO3-) in nitrification.
The nitrate ions (NO3-) are converted into nitrogen gas in denitrification.

Pseudomonas bacteria require anaerobic conditions, e.g. waterlogged soil.

There are 2 stages of the oxidation carried out by nitrifying bacteria:

1. Ammonium ions (NH4+) → Nitrosomonas → Nitrite ions (NO2-).

2. Nitrite ions (NO2-) → Nitrobacter → Nitrate Ions (NO3-).

This requires oxygen (aerobic) – occurs in soil with air pockets e.g. aerated, well drained soil.

Can occur industrially (Haber process) or when lightning happens. By bacteria.

Free living bacteria – Azobacter - produce ammonia from nitrogen gas. Make amino acids. Release them when they die.
Mutualistic bacteria – Rhizobium - live in root nodules in peas and beans. Bacteria obtain carbohydrates from plant and plant gets amino acids from bacteria.

Fewer aerobic nitrifying and nitrogen fixing bacteria in waterlogged soil.
More anaerobic denitrifying bacteria in waterlogged soil.
This means there is less nitrogen containing molecules for plants.
Therefore plants will grow slower as less proteins and DNA can be made.

Nitrogen is an important molecule in plant growth as it is used to make proteins and DNA.

Rapid growth of algae blocks light.
Reduced photosynthesis of submerged plants so they die.
Saprotrophic microorganisms break down dead plants.
In doing this they respire aerobically, using up the oxygen.
Less oxygen for fish to respire, so aerobic organisms die (eutrophication)

The first species to colonise an area.

At start of succession there is little soil.
Bare soil temperatures fluctuate.
Little nutrients to help growth.

Rapid reproduction.
Ability to fix nitrogen from the atmosphere.
Tolerance to extreme conditions – xerophytes.

Where there is a balanced equilibrium of species where new species do not come and outcompete others.

The pioneer species first colonise an area and grow. They then die and the dead matter forms humus. Now a less hostile environment so new species are able to live in the area due to the improved conditions, and they are a better competitor so the pioneer species are outcompeted. Change in biodiversity. New species able to live in the area due to the improved conditions and they are a better competitor so the previous species are outcompeted. This step keeps repeating until a climax community is reached.

More food sources. More variety of habitats.

To prevent a climax community from forming everywhere. Increases biodiversity.

Increasing biodiversity. Means new drugs and other chemicals can be developed from different species in the future. Aesthetic reasons. Ethical reasons.

When succession is prevented by human activity – the path of succession is deflected from its natural course. For example – a regularly mown grassy field will not develop woody plants as the growing points of woody plants are cut off – only grasses will survive – this then
forms the unnatural climax community.

Plagioclimax – the community that develops is different to any of the natural stages of the ecosystem.

Point / frame quadrat. Randomly place a quadrat in an area. Record the number of individuals of each species in the quadrat. Repeat multiple times. Percentage cover can be used for frame quadrats when frequency
is hard to measure.
Mark-release-recapture techniques (for more mobile species). A known number of individuals are captured, marked and released. Appropriate method of marking is used so that it doesn’t harm the organism. A second random known number of individuals are captured. The number of marked individuals recaptured is recorded and then they are released. Population size can then be calculated from this data using the formula below.
Counting number of species caught in net sweeps/ traps (for mobile species that cannot be marked). Trap, sweep nets or stun individuals using a chemical. Number of individuals caught counted and classified then recorded.

Line / belt transect. Set up a line between two points. Place a quadrat at regular intervals along the transect and record the abundance of each species.

(Total number of individuals in first sample X total number of individuals in second sample) / number of marked individuals recaptured

Marking not removed.
No immigration/emigration.
Sufficient time for marked individuals to mix with the population.
No births/deaths.
Sampling method is the same.

Random samples – no bias involved. Larger sample size. Larger sample area. Smaller quadrat. Same technique in each habitat. Random number generator generating coordinates for quadrat placement. Control/ note abiotic variables.

Stabilise the environment.
Soil development.
Increase availability of water – hold more water.
Some carry out nitrogen fixation – increase minerals/nutrients available.

Grazing, mowing, burning.

Final stage in succession – community in equilibrium with the environment.

Set sample grid. Use of quadrat of suitable size. Choose systematic method – belt or line transect. Repeat line transects / use quadrats (of appropriate size) at regular intervals – random number generator. Identification of species – using a key/book. Record both presence and absence of species. Count number of plants - calculate % of species frequency. Measure % cover of plants. Analyse data using a kite diagram or plot a graph. Carry out statistical test – Spearmans rank.