Ecosystems 6.3.1

Question 1

Ecosystem

Answer 1

The interactions between all the living organisms and the non-living conditions found in an area (biotic and abiotic factors). Dynamic system.

Question 2

Examples of biotic factors

Answer 2

• organisms present
• size of populations
• competition between or within a species

Question 3

Examples of abiotic factors

Answer 3

• light availability
• temperature
• water availability
• oxygen availability

Question 4

Equation for efficiency of biomass transfers between trophic levels

Answer 4

efficiency = biomass transferred / biomass intake x100

ie. energy after transfer / energy before transfer x 100

Question 5

Biomass

Answer 5

the mass of living material present in a particular place of in particular organisms. Can be equated to energy content

Question 6

How do you measure biomass?

Answer 6

Calculate the dry mass of organisms present by heating to 80°C. However this presents problems as organisms have to be killed to be dried

Question 7

Reasons for energy loss between trophic levels

Answer 7

• plants can’t use all the light energy from the sun. Some is wrong wavelength, some passes straight through the leaves, some hits non-photosynthesising parts eg. bark
• some parts of food aren’t eaten by organisms eg. roots, bones so energy isn’t taken in and is passed to decomposers
• some parts of food are indigestible so come out as faeces. also passed to decomposers
• respiratory loss (energy used for movement/heat)

Question 8

Net productivity

Answer 8

the amount of energy stored that becomes biomass (≈ 10%). This energy is available to the next trophic level

Question 9

Equation for net productivity

Answer 9

net productivity = gross productivity - respiratory loss

Question 10

Gross productivity

Answer 10

energy available - energy not taken in

ie. all the energy that an organism takes in. Not all of this is available to the next trophic level, due to respiratory losses

Question 11

How do human activities manipulate the transfer of biomass through ecosystems?

Answer 11

• plants and animals are provided with the abiotic conditions they need to survive for agricultural purposes
• competition is removed
• threat of predators is removed
• use of herbicides/ insecticides
• minimise the no. trophic levels in the food chain to minimise loss of energy/biomass

Question 12

Decomposer

Answer 12

• organism that feeds on/breaks down dead plant or animal matter, converting organic compounds into inorganic nutrients available to photosynthetic producers.
• Mostly microorganisms.
• saprotrophic

Question 13

Detritivores

Answer 13

Speed up the decay process by feeding on detritus (dead and decaying material). Break it into smaller pieces of organic material, increasing the SA for decomposers to work on.
eg. woodlice and earthworms

Question 14

Nitrogen fixation

Answer 14

• combines atmospheric nitrogen with hydrogen to make ammonia which can be used by plants
• N₂ + 3H₂ → 2NH₃
• by nitrogen-fixing bacteria
• -contain enzyme nitrogenase
• -eg. Azotobacter, Rhizobium

Question 15

Azotobacter

Answer 15

Nitrogen-fixing bacteria

Free living soil bacteria

Question 16

Rhizobium

Answer 16

Nitrogen-fixing bacteria
Lives inside root nodules
Have a symbiotic mutualistic relationship with the plant
- plant gains a.as from Rhizobium
- bacteria gains carbs from made plant during photo.

Question 17

Nitrification

Answer 17

• ammonium compounds in soil are converted to nitrogen-containing molecules that can be used by plants (nitrites and nitrates)
• by nitrifying bacteria
• nitrification is an oxidation reactions so only occurs in well aerated soil

1. Nitrosomonas oxidises NH₃ to nitrites NO₂⁻
2. Nitrobacter oxidises nitrites NO₂⁻ to nitrates NO₃⁻

Question 18

Nitrosomonas

Answer 18

oxidises NH₃ to nitrites NO₂⁻

Question 19

Nitrobacter

Answer 19

oxidises nitrites NO₂⁻ to nitrates NO₃⁻

Question 20

Denitrification

Answer 20

In the absence of O₂ eg. waterlogged soils

Denitrifying bacteria convert nitrates NO₃⁻ back to atmospheric N₂

The bacteria use the nitrates as a source of energy for resp.

Question 21

Ammonification

Answer 21

decomposers convert N₂ containing molecules in dead organisms, faeces, and urine into NH₃ compounds

Question 22

What are the names of the processes involved in the carbon cycle?

Answer 22

decomposition, photosynthesis, respiration, combustion, weathering

Question 23

Why is it important to recycle carbon?

Answer 23

Present in all organic molecules eg. fats, carbs, proteins

Question 24

succession

Answer 24

the process by which an ecosystem changes over time,

as a result of changes to the environment, causing the plant and animal species present to change

Question 25

primary succession

Answer 25

area of land that is newly formed or exposed. No soil or organic material present initially

eg. bare rock

Question 26

secondary succession

Answer 26

areas of land where soil is present , but there are no plant or animal species

eg. bare earth after a forest fire

Question 27

examples of situations where primary succession takes place

Answer 27

• volcano erupts and creates a layer of new rock
• sand is blown by the wind or deposited by the sea to create new sand dunes
• silt and mud deposited at river estuaries
• glaciers retreat, depositing rubble and exposing rock

Question 28

what are the stages in succession known as

Answer 28

seral stages

Question 29

name the stages of primary succession

Answer 29

pioneer species
intermediate community
climax community

Question 30

what are the adaptations of pioneer species that make them suitable to colonise inhospitable environments?

Answer 30

• can produce large quantities of seeds or spores which are blown by the wind and deposited onto new land
• seeds germinate rapidly
• can photosynthesise
• can tolerate extreme environments
• can fix nitrogen from the atmosphere (adding to the mineral content of soil)

Question 31

humus

Answer 31

organic component of soil that is formed when organisms from the pioneer species die and decompose

contains minerals eg. nitrates and can retain some water

allows secondary colonisers to be supported

Question 32

what are the 2 components of the new soil formed in the intermediate community?

Answer 32

weathering of bare rock

humus

Question 33

what is the climax community

Answer 33

last seral stage of succession
community is in a stable state
a few dominant species

Question 34

when is the highest biodiversity during succession?

Answer 34

mid-succession, not at the climax community

as later on dominant species outcompete pioneer and intermediate species

Question 35

climatic climax

Answer 35

the climax community for a particular climate

Question 36

plagioclimax

Answer 36

human activity causes deflected succession

the final stage (climax community) is known as a plagioclimax

Question 37

how is succession deflected?

Answer 37

• grazing animals trample vegetation
• removal of vegetation to plant crop
• burning to clear forest

Question 38

how to measure the distribution of organisms

Answer 38

• belt or line transect (systematic sampling)

Question 39

systematic sampling

Answer 39

different areas within a habitat are identified and then sampled separately

allows scientists to see how abiotic factors affect the distribution of organisms

Question 40

how to measure the abundance of a plant species

Answer 40

quadrats placed randomly

Question 41

how to measure the abundance of an animal species

Answer 41

capture-mark-release-recapture

estimated pop. size = no. in 1st sample x no. in 2nd sample / no. recaptured marked individuals