I have condensed the entire A Level Biology AQA Unit 7 genetics, populations, evolution and ecosystems section into an easy to read, concise booklet for MUCH cheaper than the typical revision guides which are too long and often overwhelming. These notes make all of the hardest A level biology topic...
Genetics, populations,
evolution & ecosystems
Ecosystems
Species - group of organisms that have similar characteristics that can breed to
produce fertile offspring
Population - all the individuals of a particular species in a particular place at a
particular time
What is a community? all the population of different species in a particular place at a
particular time
What is a habitat? the place where an organism lives
What is an ecosystem? a mix of different communities and habitats and how they interact
based on abiotic and biotic factors
What is ecological niche? an organisms role/position in an ecosystem – in terms of how it
interacts with abiotic and biotic factors
Why can 2 different species not occupy the same ecological niche?
interspecific competition over limiting factors / resources (a/b)
Competitive exclusion principle = Better adapted species will outcompete the
other
, 1.9 Population in Ecosystems
How to sample non-mobile / slow moving sessile organisms e.g (barnacles)
plant species over a large area?
1. Grid area
2. Use random number table to generate coordinates
3. Place quadrats at coordinates
4. Count no. organisms in quadrat
5. Repeat with at least 10 quadrats
6. Calculate mean no. organisms per quadrat
7. (area of habitat / area of 1 quadrat) x mean no. organisms per quadrat
How to sample species along a path? Line Transect
- use a transect
- Place a tape along the path and count all plants which touch the tape
How to sample species along a path? Belt Transect
- place a tape along the path and, at regular intervals, place a quadrat and
measure abundance
How to sample animal (mobile) species in an area?
1. Set up trap to capture organisms
2. Mark organisms in a way that will not reduce their risk of survival
3. Count no. organisms in sample
4. Release organisms leaving enough time for them to redistribute into the
population
5. Set up another trap to capture a 2nd sample of organisms
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