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

ecosystem

Answer 3

• all the living organisms that interact with one another in a defined area

Question 4

what is biomass and how is it measured?

Answer 4

• mass of living material in an organism or tissue
• measured by dehydrating an organism to measure the dry mass - put in an oven at 80 degrees until all water evaporated
• water mass is not living so we don’t want to take it into account
• measures carbon mass and chemical energy of the organism
• organism must be dead

Question 5

why is not all energy transferred at consumer levels?

Answer 5

• used in biological processes, so transferred to environment as heat eg. respiration
• not all of an organism is consumed when killed eg. bone
• parts of organism may be indigestible and are lost as faeces eg. cellulose
• energy lost in urine

Question 6

why is not all energy transferred at producer level?

Answer 6

• only convert 1-3% sunlight they receive into chemical energy because:
• not all solar energy is available for photosynthesis, 90% reflected
• may be other limiting factors for photosynthesis
• energy used up in photosynthetic reactions

Question 7

how do human activities impact biomass transfer?

Answer 7

• agriculture makes food chains simple - producer, primary consumer, secondary consumer
• this means minimum energy is lost as there are fewer trophic levels

Question 8

equation for percentage efficiency of energy transfer

Answer 8

efficiency = useful energy output/energy input x 100

Question 9

equation for efficiency of energy transfer between trophic levels

Answer 9

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

Question 10

productivity - gross and net

Answer 10

• 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 11

how do you measure energy transfer between trophic levels?

Answer 11

• 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 12

techniques to manipulate biomass transfer in agriculture

Answer 12

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

Question 13

techniques to manipulate biomass transfer in livestock

Answer 13

• antibiotics and vaccines - allows them to grow more efficiently
• control predation by fences
• reduce competition for grazing - more energy from producers transferred to primary consumers and herbivores more well-fed
• indoor barns to reduce movement and so heat loss

Question 14

decomposer

Answer 14

• feeds on and breaks down dead plant or animal matter, turning organic compounds into inorganic ones available to photosynthetic producers
• saprotrophs - obtain energy from dead organic material by externally secreting enzymes which break down material into simple soluble molecules to be absorbed by the decomposer

Question 15

why is nutrient cycling of nitrogen important?

Answer 15

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

Question 16

detritivores

Answer 16

• organisms involved in decomposition
• speed up decay process by feeding on dead material
• they break it into smaller pieces of organic material, increasing SA for decomposers to work on
• eg. woodlice break down wood

Question 17

nitrogen fixation

Answer 17

• 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 18

rhizobium

Answer 18

• 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 19

azotobacter

Answer 19

• free-living soil bacterium involved in nitrogen fixation

Question 20

how does lightening link to nitrogen fixation?

Answer 20

• 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 21

ammonification

Answer 21

• decomposers break down dead organisms, faeces and urine into ammonia and then ammonium ions

Question 22

nitrification

Answer 22

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

Question 23

denitrification

Answer 23

• anaerobic conditions cause denitrifying bacteria to convert nitrates 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 24

assimilation of nitrogen from animals

Answer 24

• 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 25

nitrogen cycle steps

Answer 25

1. nitrogen fixation 2. nitrification 3. denitrification 4. ammonification

Question 26

carbon cycle

Answer 26

- 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 27

why are CO2 levels higher at night?

Answer 27

- photosysnthesis only takes place in the light, CO2 only removed from atmosphere in the day - respiration happens throughout the day and the night, releasing CO2 into atmosphere

Question 28

how does human activity affect CO2 levels and what are the effects?

Answer 28

- combustion of fossil fuels - releases CO2 that has been trapped for years underground - deforestation - less CO2 removed from atmosphere - increased CO2 levels trap more thermal energy (greenhouse gas) in the atmosphere - higher temperature of sea - less gas is dissolved, increasing temp of atmosphere further

Question 29

succession

Answer 29

all biotic and abiotic changes in an ecosystem over time

Question 30

primary succession stages

Answer 30

occurs where soil has not formed yet - 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 31

pioneer species adaptations to colonise the environement

Answer 31

- produce large quantities of seeds or spores - seeds germinate rapidly - photosynthesise to produce own energy - tolerance to extreme environments - ability to nitrogen fix from atmosphere, adding to mineral content of soil

Question 32

secondary succession

Answer 32

- 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 33

how can human activity disturb succession?

Answer 33

human activity can cause deflected succession - 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

Question 34

plagioclimax

Answer 34

- name of final stage of succession if it's stopped artificially eg. by agriculture

Question 35

how do you measure distribution of organisms?

Answer 35

- line transect - laying a line along the ground and taking samples at regular intervals - belt transect - 2 parallel lines marked, samples taken of area between them

Question 36

how do you measure abundance of organisms?

Answer 36

- use random sampling and as large a sample size as possible to decrease the influence of chance 1. capture individuals in sample area 2. mark each individual 3. release and allow time to redistribute 4. recapture in original sample area 5. record no. of marked and unmarked present 6. estimated population size = first sample x second sample / no. recaptures marked individuals