IGCSE BIO 19. organisms and their environment

food chain

shows transfer of energy from one organism to the next, beginning with a producer

trophic level

position of an organism in a food chain, food web, or ecological pyramid

food web

network of interconnected food chains

producer

organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis

consumer

organism that gets its energy by feeding on other organisms

herbivore

animal that gets its energy by eating plants

carnivore

animal that gets is energy by eating other animals

decomposer

organism that gets its energy from dead or waste organic material

population

group of organisms of one species, living in the same area at the same time

community

all of the populations of different species in an ecosystem

ecosystem

unit containing the community of organisms and their environment, interacting together

what is principal source of energy input to biological system?

sun

ways of energy being lost between tropic levels?

respiration for movement, producing waste materials which are passed to decomposers, as heat energy

ways of energy being usefully used between tropic levels?

reproduction, growth

why is energy transfer between trophic levels inefficient?

because between each tropic levels, some energy is lost by respiration and other life processes such as movement, and producing waste materials, and as heat energy

pyramid of numbers

pyramid that shows the number of organisms at each tropic level in a food chain

advantages of pyramid of numbers

easy to give an overview, easy to compare changes in population numbers over different times

disadvantages of pyramid of numbers

size of organisms are not considered, numbers can be too great to represent accurately

pyramid of biomass

pyramid that shows the total biomass at each tropic level in a food chain

advantages of pyramid of biomass

overcomes the problems of pyramids of numbers

disadvantages of pyramid of biomass

only uses samples from population so it is impossible to measure biomass accurately, organisms must be killed to measure dry mass

pyramid of energy

pyramid that shows movement of energy through the food chain over time

advantages of pyramid of energy

over time, no inverted pyramid, can incorporate solar energy into the system

types of human impacts on food chain or web

overharvesting, introduction of foreign species

processes in carbon cycle

photosynthesis (CO2 in atmosphere → organic compounds in plants), respiration (organic compound → CO2 in atmosphere), feeding (organic compound in plants→ organic compound in animals), decomposition (dead organic compound → CO2 in atmosphere), fossilization (organic compound in plants → carbon in fossil fuels), combustion (carbon in fossil fuels → CO2 in atmosphere)

how can CO2 concentrations in atmosphere can increase?

by combustion of fossil fuels (actively adding CO2), cutting down of forests (less CO2 fixed into organic compounds)

processes in nitrogen cycle

nitrogen fixation (nitrogen gas in atmosphere → ammonium ion, by lightning and bacteria), nitrification (ammonium ion → nitrite ion → nitrate ion, by nitrifying bacteria), denitrification (nitrate ion → nitrogen gas in atmosphere, by bacteria), decomposition (dead protein → ammonium ion), deamination, absorption of nitrate ions by plants, feeding, production of amino acids and proteins

factors affecting the rate of population growth for a population of an organism

food supply, competition, predation, disease

stages in sigmoid population growth curve

lag phase (too less organism to reproduce, time taken to adjust in new environment), exponential phase (rapid reproduction, birth rate > death rate, growth not limited by competition), stationary phase (competition for resources, limiting factor comes into effect, birth rate = death rate), death phase (severely limited resources, death rate > birth rate)

population pyramid

graphical illustration that shows the distribution of various age groups in a population