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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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1.2 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…

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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…

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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…

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3. 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. Graph therefore levels out with only cyclic fluctuations due to
variations in factors such as food supply or the population size of…

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pH: 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
optimum
Water & Humidity: where water is scarce, populations are small &
consistent only of species that…

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family. When food scarce territories have become larger provide enough
food. Therefore fewer territories given area = fewer breeding pairs =
smaller population
Interspecific Competition
Occurs when individuals of different species compete for resources
Where populations 2 species initially occupy same niece, 1 normally have
competitive advantage
Population this species…

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1.5 Predation
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…

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1.6 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…

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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.
Death rate = number of deaths per year…

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