food chains and energy transfer

producers

photosynthetic organisms that produce organic substances using light energy and water

consumers

- primary consumers: organisms that consume producers to obtain their energy
- secondary consumers: consume primary consumers
- tertiary consumers: feed on secondary consumers
- quaternary consumers: feed on tertiary consumers

annivor vs carnivor

anniovor: eats both plants and meat

carnivor: an animal that eats other animals and may therefore be a secondary or tertiary consumer

food web

many food chains linked together, of organisms within a single habitat

food chain: describes a feeding relationship between organisms

trophic level: position occupied by a group of organisms in a food chain; each stage in a food chain

biomass

the mass of living material (or chemical energy stored)

ecosystem

all the living organisms in an area including the abiotic (non-living) conditions (e.g. temp, pH)

what does a motorised stirrer do?

distributes heat evenly

what is the role of an insulated container?

reduces heat loss to environment

pyramid of numbers

the number of organisms at each trophic level (doesn’t take size or biomass into account)

pyramid of biomass

the biomass of an organism is the dry mass (some organisms have a relatively low biomass, but can reproduce rapidly to sustain larger consumers)

pyramid of energy

the rate at which energy is transferred; energy is lost at each transfer; energy consumed by each organism is used for different things (e.g. respiration and excretion), so energy transfer decreases

what are the sugars produced in photosynthesis used for?

respiration and making biological molecules (e.g. cellulose), which forms the plants biomass

how is energy transferred through the living organisms of an ecosystem?

along a food chain

dry mass

- mass with water removed
- dry mass is used because the water content varies between species

how can you determine the dry mass of a plant?

- heat at 100 degrees to evaporate water
- weigh and reheat until no further change in mass

what can you find out from burning biomass in a colorimeter?

an estimate of the amount of chemical energy stored

how is a colorimeter used to find an estimate of the amount of chemical energy stored?

a sample of dry biomass is burnt, and the energy is released to heat a known volume of water

how do you find the amount of energy released from sample per gram (J)?

(mass of water (g) x temp rise (degrees Celsius) x 4.2) / mass of food sample (g)

what do the arrows in food chains represent?

the transfer of energy

decomposers

break down dead or undigested material, allowing nutrients to be recycled

detritivors

organisms that feed on detritus creating a larger surface area for microorganisms

detritus

dead or decaying material

saprobiontic bacteria

microorganisms that release enzymes, digesting the food externally and then absorbing the products (organic molecules are broken down into inorganic ions that can be used by producers)

gross primary product (GPP)

the chemical energy store in plant biomass, in a given area or volume

net primary product (NPP)

gross primary production - respiratory losses

(NPP = GPP - R)

primary productivity

the rate of primary production

how do you measure primary productivity?

measured as biomass in a given area in a given time, e.g. kJ ha-1 year-1

what percentage of solar energy reaching earth’s surface (per unit area and time) ends up as net primary productivity?

about 1%

how do you work out net production?

chemical energy store of ingested food - (energy lost in faeces/urine + energy lost in respiration)
N = I - (F + R)

how do you work out percentage efficiency?

(energy available after the transfer / energy available before the transfer) x 100

how do you increase yield?

increase the efficiency of energy transfer via intensive rearing of livestock (more energy from respiration is used for growth)

respiratory losses reduced

- movement restricted - less muscle contraction
- warm environment - reduces heat loss from the body

food webs simplified

- competitors excluded → (e.g. other mammals such as rabbits that compete with cows for grass)
- predators excluded → no loss to other organisms in the food web

explain why an increase in shoot biomass can be taken as a measurement of net primary productivity

1. represents dry mass
2. represents gross production minus respiratory losses

Freshwater marshes have one of the highest rates of GPP and NPP of all ecosystems. Carbon use efficiency (CUE) is the ratio of NPP:GPP. Freshwater marshes have a high CUE. explain why freshwater marshes have a high CUE and the advantage of this.

1. low respiration
2. more growth

Suggest one way in which an increase in the uptake of phosphate could increase plant growth.

used to produce ATP

Arbuscular mycorrhiza fungi (AMF) are fungi which grow on, and into, the roots of plants. AMF can increase the uptake of inorganic ions such as phosphate.

Suggest one way in which AMF may benefit from their association with plants.

Example of a carbon-containing biological compound e.g. carbohydrate / amino acid / vitamin;

The ecologists dried the samples in an oven at 103 °C for 24 hours. Describe how the ecologists could have determined whether or not this drying removed all the water from a sample of wood.

(After 24 hours)
1. Record mass and reheat
2. Until constant mass recorded