A2 energy in ecosystems (topic 5)

Question 1

biomass def

Answer 1

mass of carbon OR dry mass of tissue per area

Question 2

consequence of too much fertiliser

Answer 2

leaching => nutrients being removed from the soil, and entering water systems leading to eutrophication

Question 3

eutrophication

Answer 3

nitrates leached from the soil into water is used by surface algae to grow rapidly (algal bloom)
they absorb light for photosynthesis and prevent light reaching below the surface
plants die, dead plant material allows saprobionts to grow as they feed on it
the saprobionts use oxygen to respire, water oxygen levels drop too low to support aerobic organisms so fish die
anaerobic organisms increase as aerobic competitors are gone, they decompose dead material and release toxic products that make the water putrid

Question 4

population def

Answer 4

a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed

Question 5

community def

Answer 5

populations of different species in a particular area

Question 6

ecosystem def

Answer 6

community and non living factors coming together

Question 7

carrying capacity def

Answer 7

population size that an ecosystem can support

Question 8

what can affect carrying capacity

Answer 8

abiotic factors

competition - inter and intra specific

predation - predator prey relationship

Question 9

predator prey relationship

Answer 9

1. When the prey is eaten by the predator the population of the prey falls.
2. This results in the predator population growing, however means that more prey is consumed.
3. Therefore the population of prey reduces and there is increased competition for the the prey
   between the predators.
4. The lack of food for the predators means that the population falls meaning that less prey is
   eaten.
5. This allows the population of the prey to recover and therefore the cycle occurs over in a
   oscillating manner

Question 10

how to estimate size of population

Answer 10

randomly placed quadrats or quadrats along a belt transect for slow/no moving organisms

% cover = suitable when individual numbers are hard to count
frequency = expressed as a decimal or %, no of times an organism appears in the sampling area

mark release recapture =>
1. Known number of species is captured and marked in a way that doesn’t reduce their chance of survival.
2. These marked organisms are then released again into the same area they were caught.
3. After a suitable length of time another known number of organisms are captured, with the
number of these that are marked being recorded.

Question 11

estimated population size equation for motile organisms

Answer 11

total no individuals in first sample x second sample
—————————————————————————
number of marked individuals recaptured

Question 12

pioneer species def and characteristics

Answer 12

species that colonised an inhabitable environment
- usually asexually reproduce (rapidly multiply to increase pop)
- use wind to disperse seeds or spores
- rapid germination of seeds on arrival
- ability to photosynthesise (as there’s light and less food)
- ability to fix nitrogen from atmosphere (as there’s less soil nutrients)
- tolerate extreme conditions

Question 13

succession def

Answer 13

changes to ecosystems over time in relation to the species that occupy a particular area

Question 14

primary succession steps

Answer 14

• area is first colonised by pioneer species eg lichens (adapted to survive in such harsh conditions)
• the organisms die and are decomposed by microorganisms leading to soil formation
• environment now more suitable for more complex organisms
• over time, the soil becomes richer in minerals so larger plants such as shrubs can survive
• eventually a climax community is established which is the final stage of succession, a self-sustaining and stable community of organisms

Question 15

secondary succession

Answer 15

previously colonised area where a community that existed has been cleared by something eg forest fire
a soil layer is already present so succession begins at a later stage

Question 16

reasons for conservation

Answer 16

personal - maintaining planet and therefore our life system

ethical - other species occupied earth long before us, should be allowed to coexist with us and we should have respect for living organisms

economic - living organisms contain a huge gene pool that can make millions of substances, may prove valuable in future

cultural and aesthetic - variety adds interest to everyday lives and inspires poets, writers, artists etc