Chapter 18 - Organisms and their environment Flashcards
what is ecology?
the study of organisms in their environment
what is a habitat?
the place where an organism lives
what is a community?
all of the population of all the different species in an ecosystem
what is an ecosystem?
a unit containing all of the organisms in a community and their environment, interacting together
what is niche?
the role of an organism in its natural environment; the way in which is interacts with other organisms and with non-living parts of the environment
what is a food chain?
a way of showing the flow of energy between organisms starting with a producer
what is a food web?
a network of interconnected food chains
what is a producer?
an organism that makes its own food, generally using energy from sunlight through photosynthesis
what is a consumer?
an organism that gets its energy by feeding on other organisms
what is meant by the term herbivore?
animals that get their energy by only eating plants
what is meant by the term carnivore?
organisms that mainly eat other animals
what is a pyramid of numbers?
shows the number of organisms at each trophic level
what are decomposers?
organisms that gets their energy from dead or waste organic material
what is a trophic level?
the position that an organism holds in a food chain, food web, pyramid of biomass or numbers
what is a pyramid of biomass?
a pyramid that shows the total dry mass of organisms at each trophic level
what is a pyramid of energy?
a graph showing the relative quantity of energy at each trophic level
what is nitrogen fixation?
converting inert nitrogen gas into a more reactive form such as nitrate ions or ammonia
what is meant by the term nitrification?
converting ammonium ions to nitrate ions
what is meant by the term denitrification?
converting nitrate ions to nitrogen gas
what is meant by the term lag phase?
the stage at the start of a population growth curve where the population remains small and grows only very slowly
what is meant by the term log phase or exponential phase?
the stage in a population growth curve where the population grows at its maximum rate; birth rate exceeds death rate
what is meant by the term stationary phase?
the stage in a population growth curve where the population remains roughly constant; birth rate equal to death rate
what is meant by death phase?
the final stage in a population growth curve where the population falls; death rate exceeds birth rate
what is a sigmoid growth curve?
an S-shaped curve showing the change in the size of population through all the phases in population growth
what is meant by limiting factors?
a factor that is in short supply, which stops an activity happening at a faster rate
what is meant by age pyramid?
a diagram showing the relative numbers of individuals of different ages in a population
what is the main source of energy in biological systems?
the sun
describe the flow of energy in biological systems
*light energy from the sun is trapped by photosynthetic organisms
*energy is stored as chemical energy in organisms
*energy is eventually lost to the environment
how is energy transferred between organisms in a food chain?
by ingestion (organism eating other organisms)
why are biomass transfers not 100 percent efficient?
*egestion (removal of faeces)
*excretion (removal of waste products)
*respiration
*the production of inedible bones and shells
why do food chains usually have fewer than 5 trophic levels?
biomass transfers are not 100 percent efficient and so there is often not enough energy to support 5 trophic levels
why is it most efficient to supply plants as food for humans?
*using the plants as food for livestock wastes energy as the biomass transfers are not 100 percent efficient
*eating plants transfers can maximise the amount of energy gained as there is only one transfer
what is a primary consumer?
an organism that feeds on producers
what is a secondary consumer?
an organism that feeds in primary consumers
what is a tertiary consumer?
an organism that feeds on secondary consumers
explain the impact humans have on food chains and webs by over harvesting certain species
many organisms rely on other organisms for food, over harvesting can reduce the amount of food available for other animals
explain the impact humans have on food chains and webs by introducing other species into a habitat
introducing new organisms increases competition and can interfere with the food chain, causing organisms who cannot compete to die
why are some pyramids of numbers not pyramid shaped?
pyramids of numbers don’t take size and mass of organisms into account
why is a pyramid of biomass a better way of representing a food chain than a pyramid of numbers?
pyramids of biomass take into account the size of the organism and are less easily misinterpreted
describe the carbon cycle
*plants fix carbon dioxide into organic molecules during photosynthesis
*the organic carbon-containing molecules are passed onto organisms that eat the plant
*carbon dioxide is released back into the atmosphere by respiration from animals and plants
*burning fossil fuels also releases carbon dioxide into the atmosphere
state the effect of burning fossil fuels on the carbon dioxide concentration in the environment
burning fossil fuels releases more carbon dioxide into the atmosphere increasing the concentration of co2
state the effect of deforestation on carbon dioxide concentration in the environment
*trees take in carbon dioxide during photosynthesis (decreasing the atmospheric carbon dioxide concentration)
*cutting down trees prevents this and so the atmospheric carbon dioxide concentration doesn’t decrease
describe the water cycle
*water from lakes and oceans evaporates
*the evaporated water condenses into clouds and returns to earth as precipitation
*the water from precipitation is useful for life on land
*the water then returns ti delivers and oceans through surface runoff
why is the water cycle important?
living organisms require water - the water cycle provides organisms in land with a continuous supply of water
briefly describe how nitrogen is cycled through an ecosystem
*nitrogen is fixed by lightening and bacteria
*decomposers break dead matter down into ammonium ions
*nitrifying bacteria convert ammonia into nitrites and nitrates
*plants absorb nitrate ions
*denitrifying bacteria release nitrogen back to the atmosphere
