Describe and explain how succession occurs. (6)
Pioneer species
- occurs on bare land
- germinate easily & withstand harsh conditions
Intermediate species
- decomposition of pioneer species helps form soil
- seed can germinate & grow into seedlings
Climax community
- soil contains more nutrients
- increase in biodiversity
Why is it rare to find a natural food chain with more than five trophic levels. (2)
- Energy lost at each trophic level
- insufficient energy remaining to support further trophic levels
Explain the advantage of 2 different earthworm species occupying different ecological niches. (2)
- reduced competition for food
- ensures both species survive
Describe how carbon dioxide reaches palisade mesophyll cells from the atmosphere. (3)
- CO2 enters via a stoma
- by diffusion
- & diffuses through palisade cell’s cell wall and c.s.m
Define: carbon fixation
- removal of CO2 from air
- C atoms from CO2 incorporated into organic material
Explain how ice cores can give clues about the Earth’s atmosphere. (2)
- ice forms from compaction of snow
- so ice contains tiny trapped air bubbles from the era it formed
Give 2 reasons each why CO2 and methane levels are increasing. (4)
CO2
- burning of fossil fuels
- deforestation
Methane
- human activity e.g. coal mining
- from landfill sites
Explain how a peat bog can give clues about the climate over a period of time. (3)
- peat forms in layers
- pollen grains trapped in peat
^ species can be identified to figure out climate conditions at the time
Explain how moss being highly absorbent can help stabilise ecosystems. (2)
- holds water in ground
- prevents flash flooding
Define: species. (2)
- group of organisms with similar physiological features
- that are able to produce fertile offspring
Explain the importance of peer reviewing in the scientific community. (3)
- ensures results are reliable
- assesses validity of experiment
- to identify flaws in results analysis
Explain how a mutation could lead to a change in an organisms characteristic. (2)
- mutation changes DNA base sequence
- resulting in new allele
Explain importance of heritable variation in evolution. (3)
- caused by diff. alleles
- advantageous alleles more likely to pass to offspring so allows natural selection
- non-heritable variation NOT passed onto offspring
Compare and contrast allopatric and sympatric speciation. (4)
Similarities:
- both lead to new species forming over time
- result in changes to allele frequency within population
- populations must be genetically isolated
Differences:
- Allopatric is geographically isolated, sympatric occurs without.
