Ecosystems

Question 1

food chain

Answer 1

• shows flow of energy in the direction of the consumer
• linear
  eg. plant–> herbivore—>omnivore —>tertiary consumer

Question 2

food web

Answer 2

• shows flow of energy between many different organisms
• shows all organisms that eat another and all that eat that one and so on

Question 3

what is biomass and how is it measured?

Answer 3

• mass of living material in an organism or tissue
• measured by dehydrating an organism to measure the dry mass
• water mass is not living so we don’t want to take it into account
• measures carbon mass ad chemical energy of the organism

Question 4

what happens to the energy transferred between trophic levels?

Answer 4

• used in biological processes eg. respiration
• not all of an organism is consumed when killed eg. bone
• parts of organism may be undigestable and is lost as faeces eg. cellulose
• not all wavelengths of light can be absorbed in photosynthesis eg. green light is reflected
• not all sunlight reaches leaves eg. shady areas

Question 5

equation for percentage efficiency of energy transfer

Answer 5

efficiency = useful energy output/energy input x 100

Question 6

equation for efficiency of energy transfer between trophic levels

Answer 6

efficiency = net productivity of primary consumer/ net productivity of producer x 100

Question 7

productivity - gross and net

Answer 7

• the rate at which plants convert light energy into chemical potential energy
• gross primary productivity - total quantity of energy transferred by plants from sunlight
• net primary productivity - energy left as chemical energy after respiration

Question 8

how do you measure energy transfer between trophic levels?

Answer 8

• measure dry mass and burn it in a calorimeter
• energy in a 1g sample x dry mass of 1 organism x number of organisms = energy content

Question 9

techniques to manipulate biomass transfer in agriculture

Answer 9

• artificial light in greenhouses
• optimising distances between plants
• irrigation
• fertilisers
• selective breeding
• fungicides/pesticides

Question 10

techniques to manipulate biomass transfer in livestock

Answer 10

• antibiotics and vaccines
• control predation by fences
• reduce competition for grazing
  -indoor barns to reduce movement and so heat loss

Question 11

why is nutrient cycling important?

Answer 11

• allows for a constant supply of nutrients for the next trophic level
• fundamental to create proteins and nucleic acids

Question 11

why is nutrient cycling important?

Answer 11

• ensures nutrients are available for the next trophic level

Question 12

nitrogen fixation

Answer 12

• nitrogen needs to be converted into a more useful form such as ammonia or nitrate
• Azotobacter - lives freely in the soil
• rhizobium - lives inside root nodules - mutualistic relationship
• these bacteria contain the enzyme nitrogenase which combines atmospheric nitrogen (N2) with hydrogen (H2) to produce ammonia (NH3) which can be absorbed and used by plants

Question 13

rhizobium

Answer 13

• nitrogen fixing bacteria living inside root nodules - growths on leguminous plants
• mutualistic relationship - plant gains amino acids from ammonia, bacteria gains carbohydrates from photosynthesis from plant, used as energy source

Question 14

how does lightening link to nitrogen fixation?

Answer 14

• high temps of lightening bolts break bonds in atmospheric nitrogen
• this causes free nitrogen atoms in the air to bond with oxygen - nitrogen oxides
• these dissolve in moisture to form nitrates which are carried in the soil by the rainfall to producers

Question 15

ammonification

Answer 15

• organic material broken down by saprophytic bacteria to release ammonium ions into soil
• decomposers break down dead organisms, faeces and urine

Question 16

nitrification

Answer 16

• converting ammonia to nitrites then nitrates
• nitrifying bacteria:
  nitrosomonas - oxidises ammonium into nitrites
  nitrobacter - oxidises nitrites into nitrates
• nitrite ions are soluble so can enter plants this way

Question 17

denitrification

Answer 17

• anaerobic conditions cause denitrifying bacteria in the soil back into nitrogen gas in the atmosphere
  -bacteria use nitrates as source of energy for respiration and nitrogen gas is released

Question 18

assimilation of nitrogen from animals

Answer 18

• animals digest plants and convert their proteins into amino acids
• once absorbed they are built up again into proteins
• excess amino acids are deaminated in the liver to form urea

Question 19

carbon cycle

Answer 19

• animal respiration releases CO2
• plants use CO2 in photosynthesis
• dead organisms and waste products release carbon compounds through decomposition
• carbon released back into atmosphere when decomposers respire
• dead organic matter accumulates where decomposers aren’t present - form fossil fuels
• fossil fuels are burnt and CO2 is released back into the atmosphere - combustion

Question 20

succession

Answer 20

all biotic and abiotic changes in an ecosystem over time

Question 21

primary succession stages

Answer 21

• seeds and spores carried by wind land on newly formed or exposed rock and begin to grow
• these are called pioneer species eg. moss, lichen
• they decompose and the dead organic matter forms a layer of soil called humus
• seeds of small plants carried by wind or bird faeces land on humus and adapt to growing in nutrient-poor soil
• these plants die and decompose, the soil becomes deeper and more nutrient-rich
• larger plants and shrubs begin to grow in the deeper soil (more water and nutrients) - intermediate species
• once soil deep enough, large trees can grow and become the dominant species
• this is now a climax community

Question 22

secondary succession

Answer 22

• after a disturbance to a climax community or intermediate community eg. wildfire
• process of succession restarts but not from beginning as some nutrients still exist in the soil

Question 23

how can human activity disturb succession?

Answer 23

• mowing lawn
• livestock grazing eg. lake district lets sheep graze to prevent larger communities growing
• managed burning eg. Heather Moorland - burn old Heather allowing grouse to live there attracting tourists wishing to shoot them