Chapter 18 - Organisms and their environment

Question 1

what is ecology?

Answer 1

the study of organisms in their environment

Question 2

what is a habitat?

Answer 2

the place where an organism lives

Question 3

what is a community?

Answer 3

all of the population of all the different species in an ecosystem

Question 4

what is an ecosystem?

Answer 4

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

Question 5

what is niche?

Answer 5

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

Question 6

what is a food chain?

Answer 6

a way of showing the flow of energy between organisms starting with a producer

Question 7

what is a food web?

Answer 7

a network of interconnected food chains

Question 8

what is a producer?

Answer 8

an organism that makes its own food, generally using energy from sunlight through photosynthesis

Question 9

what is a consumer?

Answer 9

an organism that gets its energy by feeding on other organisms

Question 10

what is meant by the term herbivore?

Answer 10

animals that get their energy by only eating plants

Question 11

what is meant by the term carnivore?

Answer 11

organisms that mainly eat other animals

Question 12

what is a pyramid of numbers?

Answer 12

shows the number of organisms at each trophic level

Question 12

what are decomposers?

Answer 12

organisms that gets their energy from dead or waste organic material

Question 12

what is a trophic level?

Answer 12

the position that an organism holds in a food chain, food web, pyramid of biomass or numbers

Question 13

what is a pyramid of biomass?

Answer 13

a pyramid that shows the total dry mass of organisms at each trophic level

Question 13

what is a pyramid of energy?

Answer 13

a graph showing the relative quantity of energy at each trophic level

Question 14

what is nitrogen fixation?

Answer 14

converting inert nitrogen gas into a more reactive form such as nitrate ions or ammonia

Question 15

what is meant by the term nitrification?

Answer 15

converting ammonium ions to nitrate ions

Question 16

what is meant by the term denitrification?

Answer 16

converting nitrate ions to nitrogen gas

Question 17

what is meant by the term lag phase?

Answer 17

the stage at the start of a population growth curve where the population remains small and grows only very slowly

Question 18

what is meant by the term log phase or exponential phase?

Answer 18

the stage in a population growth curve where the population grows at its maximum rate; birth rate exceeds death rate

Question 19

what is meant by the term stationary phase?

Answer 19

the stage in a population growth curve where the population remains roughly constant; birth rate equal to death rate

Question 20

what is meant by death phase?

Answer 20

the final stage in a population growth curve where the population falls; death rate exceeds birth rate

Question 21

what is a sigmoid growth curve?

Answer 21

an S-shaped curve showing the change in the size of population through all the phases in population growth

Question 22

what is meant by limiting factors?

Answer 22

a factor that is in short supply, which stops an activity happening at a faster rate

Question 23

what is meant by age pyramid?

Answer 23

a diagram showing the relative numbers of individuals of different ages in a population

Question 24

what is the main source of energy in biological systems?

Answer 24

the sun

Question 25

describe the flow of energy in biological systems

Answer 25

*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

Question 26

how is energy transferred between organisms in a food chain?

Answer 26

by ingestion (organism eating other organisms)

Question 27

why are biomass transfers not 100 percent efficient?

Answer 27

*egestion (removal of faeces)
*excretion (removal of waste products)
*respiration
*the production of inedible bones and shells

Question 28

why do food chains usually have fewer than 5 trophic levels?

Answer 28

biomass transfers are not 100 percent efficient and so there is often not enough energy to support 5 trophic levels

Question 29

why is it most efficient to supply plants as food for humans?

Answer 29

*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

Question 30

what is a primary consumer?

Answer 30

an organism that feeds on producers

Question 31

what is a secondary consumer?

Answer 31

an organism that feeds in primary consumers

Question 32

what is a tertiary consumer?

Answer 32

an organism that feeds on secondary consumers

Question 33

explain the impact humans have on food chains and webs by over harvesting certain species

Answer 33

many organisms rely on other organisms for food, over harvesting can reduce the amount of food available for other animals

Question 34

explain the impact humans have on food chains and webs by introducing other species into a habitat

Answer 34

introducing new organisms increases competition and can interfere with the food chain, causing organisms who cannot compete to die

Question 35

why are some pyramids of numbers not pyramid shaped?

Answer 35

pyramids of numbers don’t take size and mass of organisms into account

Question 36

why is a pyramid of biomass a better way of representing a food chain than a pyramid of numbers?

Answer 36

pyramids of biomass take into account the size of the organism and are less easily misinterpreted

Question 37

describe the carbon cycle

Answer 37

*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

Question 38

state the effect of burning fossil fuels on the carbon dioxide concentration in the environment

Answer 38

burning fossil fuels releases more carbon dioxide into the atmosphere increasing the concentration of co2

Question 39

state the effect of deforestation on carbon dioxide concentration in the environment

Answer 39

*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

Question 40

describe the water cycle

Answer 40

*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

Question 41

why is the water cycle important?

Answer 41

living organisms require water - the water cycle provides organisms in land with a continuous supply of water

Question 42

briefly describe how nitrogen is cycled through an ecosystem

Answer 42

*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