Complete unit 4 biology AQA revision notes

This is my complete set of unit 4 revision notes for populations and the environment, i hope they come in useful to people

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A2 level Biology notes
Unit 4- Populations and the Environment
1. Populations
1.1 Populations and ecosystems
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Investing populations
1.3 Variation in population size
1.4 Competition
1.5 Predation
1.6 Human populations
2. ATP
2.1 Energy and ATP
3. Photosynthesis
3.1 Overview of Photosynthesis
3.2 The Light- dependent reaction
3.3 The Light Independent Reaction
3.4 Factors Affecting Photosynthesis
4. Respiration
4.1 Glycolysis
4.2 Link reaction and Krebs cycle
4.3 The electron transport chain
4.4 Anaerobic respiration
5. Energy and Ecosystems
5.1 Food chains and Food webs
5.2 Energy Transfer between Trophic Levels
5.3 Ecological Pyramids
5.4 Agricultural Ecosystems
5.…read more

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Ecosystem- It is made up of all the interacting biotic and abiotic features in a
specific area
Population- A group of interbreeding organisms of one species in a habitat.
Community- All the populations of different organisms living and interacting in
a particular place at the same time.
Habitat -The place where a community of organisms lives.
Ecological niche- All the biotic and abiotic conditions required for an organism
to survive, reproduce and maintain a viable population. No 2 species occupy
exactly the same niche.
1.…read more

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Systematic sampling along transects
Sometimes more informative measure abundance & distribution of species in
systematic rather random manner
Particularly important where some form transition in communities plants &
animals take place
Line transect comprise string or tape stretched across ground in straight line,
any organism over which line passes is recorded
Belt transect is strip, usually meter wide, marked putting second line parallel
to first, species occurring w/in belt between lines recorded
Measuring abundance
Random sampling w/ quadrats & transects used obtain measures abundance
Abundance…read more

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Period when population growth declines until its size remains more or less stable.
The decline may be due to food supply limiting numbers or to increase
population.…read more

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H: this affects action enzymes. Each enzyme has optimum pH at which
operates most effectively. Population of organisms is larger where
appropriate pH exists & smaller, or non-existent where pH very different from
Water & Humidity: where water is scarce, populations are small &
consistent only of species that are well adapted living in dry conditions.
Humidity affects transpiration rates in plants & evaporation water from
bodies of animals.…read more

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When food scarce territories have become larger provide enough
food.…read more

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Predation occurs when one organism is consumed by another.
Effect of predator-prey relationship on population size
Predators eat their prey, thereby reducing the population of prey.
With fewer prey available the predators are in greater competition with each
other for the prey that are left.
The predator population is reduced as some individuals are unable to obtain
enough prey for their survival.
With fewer predators left, less prey is eaten.…read more

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Human populations
Human population size and growth rate
Most of our history has been kept in check by food availability, disease, predators
and climate. Two recent events have lead to an explosion in human population:
The development of agriculture
The development of manufacturing and trade that created the industrial
Factors affecting the growth and size of human populations
The basic factors that affect the growth rate of human populations are birth rate
and death rate.…read more

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Natural disasters - the more prone a region is to a drought, famine of disease
the higher its death.
War - deaths during wars produce an immediate drop in population and a
longer term fall as a result of fewer fertile adults.…read more


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