Energy And Ecosystems Flashcards
Give an example of a food chain
Grass –> caterpillar –> toad –> grass snake –> stoat
Define food chain
Description of a feeding relationship and showing direction of energy transfer
Why is most of the sun’s energy not converted to organic matter by photosynthesis?
Over 90% of the sun’s energy is reflected back into space by clouds and dust or absorbed by the atmosphere
Not all wavelengths of light can be absorbed and used for photosynthesis
Light may not fall on a chlorophyll molecule
A factor such as low carbon dioxide levels may limit the rate of photosynthesis
What is the gross production?
The total quantity of energy that the plants in a community convert to organic matter
What is the net production?
The rate at which the plants store energy
What is the equation for net production?
Net production= gross production - respiratory losses
Why is there a low percentage of energy transferred at each trophic level of a food chain?
Some of the organism is not eaten
Some parts are eaten but cannot be digested and are therefore lost in faeces
Some of the energy is lost in excretory materials such as urine
Some energy losses occur as heat from respiration and directly from the body to the environment (high in mammals)
The inefficiency of the energy transfer between trophic levels explains why…
Most food chains have only four or five trophic levels because insufficient energy is available to support a large enough breeding population at trophic levels higher than these
The total mass of organisms in a particular place (biomass) is less at higher trophic levels
The total amount of energy stored is less at each level as one moves up a food chain.
What is the amount of energy available at a trophic level in a food chain measured in?
kJ m^-2 year^-1
What is the equation for energy transfer between trophic levels?
Energy transfer= energy available after the transfer/ energy available before the transfer x100
What are the drawbacks of using a number pyramid to describe a food chain?
No account is taken of size - one giant tree is treated the same as one tiny aphid. This means that sometimes the pyramid is not a pyramid at all or it is inverted.
The number of individuals can be so great that it is impossible represent them accurately on the same scale as other species in the food chain.
Define biomass
Biomass is the total mass of the plants and/or animals in a particular place
What is biomass measured in?
g m^-3
What are the drawbacks of pyramids or numbers and biomass?
Only the organisms present at a particular time are shown so seasonal differences are not made apparent
Which is the most accurate representation of the energy flow through a food chain?
Pyramid of energy
Why are the results for energy much more reliable than for pyramids of biomass?
Two organisms of the same dry mass may store different amounts of energy.
What is the unit used in energy pyramids?
kJ m^-2 year^-1
Net productivity is important in agricultural ecosystems and is effected by two main factors:
The efficiency of the crop at carrying out photosynthesis. This is improved if all necessary conditions for photosynthesis are supplied.
The area of the ground covered by the leaves of the crop
Define pest
An organism which competes with humans for food space, or is a danger to health
Give two disadvantages of biological control
They do not act as quickly, so there is often some interval of time between introducing the control organism and a significant reduction in the pest population
A control organism may itself become a pest
Give three comparisons between biological control and chemical pesticides
Biological control is very specific whereas chemical pesticides have some effect on non-target species
Once introduced biological control organisms reproduces itself whereas chemical pesticides must be reapplied and they are expensive
The pests do not become resistant to their predators but can become resistant to chemical pesticides so new ones have to be developed
Give a few examples of what integrated control systems do
Choosing pest resistant animal or plant varieties
Hand picking pests out of an environment
Providing suitable habitats for natural predators of pests
Using pesticides and biological agents if necessary
Intensive rearing involves keeping animals in confined places. Why?
Their event is restricted and so less energy is used in muscle contraction
The environment can be kept warm in order to reduce heat loss from the body
Feeding can be controlled so that the animals receive the optimum amount and type of food for maximum growth with no wastage
Predators are excluded so that there is no loss to other organisms in the food web
Name two other means, other than intensive rearing, with increase the energy-conversion rate in domesticated animals.
Selective breeding of animals to produce varieties that are more efficient at converting the food they eat into body mass
Using hormones to increase growth rates
