Chapter 19: Organisms and their environment Flashcards
(24 cards)
What is the principal source of energy input to biological systems?
The sun
What is the flow of energy through living organisms?
Light energy from the sun is harnessed by plants and turned into chemical energy. Plants are eaten by animals, which are eaten by other animals. Energy is eventually transferred to the environment, e.g. as heat
Define ‘food chain’
A chart showing the transfer of energy from one organism to the next, beginning with a producer
Define ‘food web’
A network of interconnected food chains
Define ‘producer’
An organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis
Define ‘consumer’
An organism that gets its energy by feeding on other organisms
Define ‘herbivore’
An animal that gets its energy by eating plants
Define ‘carnivore’
An animal that gets its energy by eating other animals
Define ‘decomposer’
An organism that gets its energy from dead or waste organic material
How do you draw a pyramid of biomass?
Number of individuals x their individual mass
What are the advantages of using a pyramid of biomass rather than a pyramid of numbers to represent a food chain?
Pyramids of biomass take into account the size of organisms at each trophic level, so they provide a more accurate representation of the living matter within an ecosystem. Energy is stored in biomass, so biomass can be used as an approximate representation of the energy available at each level of a food chain
What are the advantages of using a pyramid of energy rather than pyramids of numbers or biomass to represent a food chain?
They highlight the energy lost at each trophic level. Different organisms may not all store the same amount of energy in their biomass, so pyramids of energy allow for more accurate comparisons
Define ‘trophic level’
The position of an organism in a food chain, food web or ecological pyramid
Why is the transfer of energy from one trophic level to another often not efficient?
Only around 10% of energy is passed on to the next trophic level; the rest of the energy is passed into the environment as heat energy during respiration, or used for life processes
Why do food chains usually have fewer than five trophic levels?
Energy transfer is so inefficient that very little usable energy remains after 4 or 5 trophic levels
Why is it more energy efficient for humans to eat crop plants than to eat livestock that have been fed on crop plants?
When directly consuming plants, there is much more energy available to humans than when eating animals that eat the plants, as energy is lost from the animal, which means there is less energy available to pass on to humans.
Describe the carbon cycle
Carbon is taken from the atmosphere into plants through photosynthesis, and is then passed on to animals and decomposers through feeding. It is then returned to the atmosphere through the respiration of plants and animals. When plants and animals die, decomposers feed on them, which fuels respiration and further releases carbon. If animals and plants die in conditions where decomposers are not present, the carbon in their bodies can be converted into fossil fuels, which can be burned to release carbon dioxide into the atmosphere by combustion
Describe the nitrogen cycle
Nitrogen-fixing bacteria, which can be free-living in the soil or present within the root nodules of some plants, convert nitrogen gas into ammonium ions. Nitrifying bacteria convert ammonium ions into nitrite and then nitrate. Plants can then absorb nitrates through their roots, and use them to build amino acids and proteins, and animals feed on plants and get the nitrogen needed. The amino acids undergo deamination, and waste (urine and faeces) from animals sends nitrogen back into the soil in the form of ammonium compounds, to be converted by nitrifying bacteria. Denitrifying bacteria take nitrates out of the soil and convert them back into nitrogen gas.
What are the roles of microorganisms in the nitrogen cycle?
Decomposition, nitrification, nitrogen fixation and denitrification
Define ‘population’
A group of organisms of one species, living in the same area, at the same time
Define ‘community’
All of the populations of different species in an ecosystem
Define ‘ecosystem’
A unit containing the community of organisms and their environment, interacting together
What are the factors affecting the rate of population growth for a population of an organism?
Food supply, competition, predation and disease
What are the factors that lead to each phase in the sigmoid curve of population growth?
Lag phase: the number of mature, reproducing individuals is low, and they may be widely dispersed
Exponential (Log) phase: exponential growth occurs, the conditions are ideal, and the maximum growth rate is reached. Limiting factors do not limit growth much
Stationary phase: limiting factors slow growth as the population has reached the ‘carrying capacity’ of its environment; when the mortality rate = birth rate, the curve levels off and fluctuates around this maximum population size
Death phase: death rate > birth rate due to lack of food, competition, etc.
