☀️GCSE Biology Edexcel IGCSE☀️Higher☀️- Topic 4: Ecology and the Environment Notes☀️
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Course
Science
Institution
GCSE
Complete set of notes for each specification point (4.1 - 4.18) for Topic 4 (Ecology and the Environment) of the GCSE Biology Edexcel IGCSE Exam Board. Suitable for 2024 or 2025 exams. Written by a GCSE Student, using lots of resources to create accurate notes to aid exams. Includes paper 1 and pap...
4. ECOLOGY AND THE ENVIRONMENT
A – The organism in the environment:
4.1 – understand the terms: population, community, habitat and ecosystem
o Habitat – place where an organism lives
o Population – number of organisms of the same species
o Community – all the different species in a habitat
o Ecosystem – all the organisms living in a particular area and all the non-living (abiotic) conditions
4.2 – practical: investigate the population size of an organism in two different areas using quadrats
Method:
Random (1), quadrat (1), count (1), repeat (1)
1. Place quadrat randomly within sampling area
2. Count the number of organisms within the quadrat Control variables:
3. Repeat this within sampling area + find the mean
o Size of quadrat
4. Repeat the process in another area to compare results
o Method of counting
Population ¿ total area sampled × meannumber of organisms
4.3 – understand the term: biodiversity
o Biodiversity – variety of living organisms present in the world/particular habitat
o Makes sure that ecosystems are stable to depend on each other (for things like food + shelter)
4.4 – practical: investigate distribution of organisms in their habitats + measure biodiversity using quadrats
Method:
Abiotic factors influencers: Biotic factors influencers:
1. Place the quadrat randomly
o Light intensity o Competition predator-
2. Count the number of different
o Water + mineral availability prey relationships
species found within that quadrat
o Soil pH o Diseases
3. Repeat this process + find mean
o Temperature o Hunting
4. Repeat these steps for the second o Availability of food
o Toxic chemicals – builds up in food chains
survey area
NOTE: Instead of counting how many single organisms, can also count the populations in each quadrat
4.5 – understand how abiotic and biotic factors affect the population size and distribution of organisms
B – Feeding relationships:
4.6 – understand the names given to different trophic levels, including producers, primary, secondary and
tertiary consumers and decomposers
o Trophic level – stage/level/place in food chain/web/pyramid
o Producers – organisms that makes their own food by photosynethsis
o Primary consumers – herbivore that only eat plants (producers)
o Secondary consumers – carnivores that eat primary consumers
o Tertiary consumers – carnivores that eat secondary consumers no predators
o Decomposers – bacteria and fungi that break down dead animal’s body and waste for energy, using enzymes
o Decompose – broken down/digested (1), bacteria/fungi (1)
, 4. ECOLOGY AND THE ENVIRONMENT
Number of … Number
Different tertiary consumers 1
Trophic levels 4
Food chains 4
Different predators 3
Different consumers 7
4.7 – understand the concepts of food chains, food webs, pyramids of
number, pyramids of biomass and pyramids of energy transfer
Food Webs:
o Collection of different food chains
o Showing interdependence and how population number can affect the entire
ecosystem
o Head of arrow: animal eats animal at bottom of arrow frog eats grasshopper
Pyramid of number:
o One tree feeds 1000 caterpillar feeds 50 bluetits feeds 2 sparrowhawk
o Producer at the bottom, tertiary consumer at the top
Pyramid of biomass:
o One tree has a big (bio)mass 1000 caterpillars has a smaller mass
o Mass of one tree is more than the mass of the combined 1000 caterpillars etc.
Pyramid of energy transfer:
o Energy decreases by 10% each time
4.8 – understand the transfer of substances and energy along a food chain
o Energy enters most ecosystems in the form of sunlight converted into
chemical energy by producers via photosynthesis
4.9 – understand why only about 10% of energy is transferred from one tropic level to the next
o Approx. 10% of the biomass at each tropic level is transferred to the next tropic level
Why not all the energy in a Mass of the organisms decreases as you go up the pyramid. Why? (MS):
producer passes to primary
o Energy loss/ not all transferred o Not all of each organism eaten
consumer (MS):
o Respiration o Some organisms die
o Respiration o Excretion/urine o Movement
o Uneaten/not all eaten o Egestion/ not digested o Heat loss
o Death
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