Unit 4 - Populations and Environment

Condensed revision notes from the Nelson Thornes A2 AQA Biology text book - Chapters 1-8


Chapter 1 - Populations

Chapter 2 - ATP

Chapter 3 - Photosynthesis

Chapter 4 - Respiration

Chapter 5 - Energy and Ecosystems

Chapter 6 - Nutrient Cycles

Chapter 7 - Ecological Succession

Chapter 8 - Inheritance and Selection

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  • Created on: 16-05-14 16:16
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AQA Biology ­ Unit 4 (Populations and Environment)
Chapter 1: Populations
Ecology: Study of the inter-relationships between organisms and their environment
[Environment includes biotic factors (competition and predation) and abiotic factors
(temperature, rainfall, PH of soil) ­ Study of the biosphere (Life supporting layer of land, air
and water)
Ecosystem: - A self contained functional unit made up of all the interacting biotic and abiotic
factors in a specific area Two major process to consider: Flow of energy through the system
& the cycling of elements within the system.
Population: A group of interbreeding organisms of the same species living together in a
Community: All the populations of different organisms living and interacting together in the
same place at the same time.
Habitat: Place where a community of organisms lives (There are many habitats within an
ecosystem). Within each habitat are smaller units each with their own microclimate ­
Ecological Niche: A niche describes how an organism fits into its environment ­ It is
essential an organism's role within a community ­ No two species can occupy the same
niche ­ competition for limited resources.
Competition: Arises when two or more organisms share resources that are in insufficient
supply to support all of their needs fully.
Intraspecific Competition - Arises when organisms of the same species share resources (e.g.
food, water, breeding sites, oxygen) ­ the availability of these resources determines
population size.
Interspecific Competition - Can arise when populations of two different species initially
occupy the same niche ­ One population will have a competitive advantage over the other
one population will increase whilst the other decreases ­ one population will eventually
completely diminish ­ competitive exclusion principle (The population that uses the limited
resources most effectively will eliminate the other population)
To show how a factor influences the size of a population it must be linked to the birth rate
and death rate (More food does not necessarily mean more individuals it may just mean
bigger individuals)
By Ross Hayward

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Predation: (Interspecific relationship) ­ Occurs when an organism is consumed by another
A predator is an organism that feeds on another organism (known as their prey)
Predators and their prey have evolved together to avoid extinction ­ one has to match the
improvements of the other.
Investigating predator-prey populations:
When brought together in the lab, prey is usually exterminated ­ range and variety of
habitat is limited to the confines of the lab.…read more

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Number: More quadrats = more reliable. Greater number of species in sample area = more
samples need to be taken.
Position: Random sampling technique ­ Avoids bias ­ divide study area into a grid &
generate random coordinates
Systematic sampling using transects (Line/belt): Important when some form of
transition in the communities of plants and animals takes place ­ seashore.…read more

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­ enzymes denature if temp. is too high.
Metabolic rate is decreased in either case.
Warm blooded ­ able to maintain a relatively constant internal body temp (homeostasis).
However, the further away from the optimum the more energy needed to maintain their
optimum core temp. less energy available for growth ­ organisms mature slower smaller
population size.
Light intensity: - Ultimate source of energy.…read more

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Natural disasters
MEDC countries - Demographic transition = Change in societies where life expectancy is
short and birth rates are high to those where life expectancy is long and birth rates are low
(transition from high birth + death rates to low birth + death rates) ­ leads to levelling off of
population growth curve ­ forms regular sigmoid curve
Age population pyramids:
Increasing population ­ wide base + narrow top high birth rate, low death rate
Decreasing population ­ most people middle aged…read more

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Chapter 2: ATP ­ Adenosine Triphosphate
Organic molecules (glucose) are broken down to produce ATP ­ Energy currency of
biological processes.
Energy: The ability to do work. ­ Measures in joules (J) ­ can be transferred from one form
to another ­ cannot be created or destroyed ­ variety of different forms ­
Energy needed for ­ Metabolism/movement/active transport/maintenance of body temp.
(Birds + mammals are endothermic) ­ need energy to replace that lost as heat/production
of substances (e.g.…read more

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ATP is the source of energy for: Metabolic processes (building up macromolecules from their
basic units)/movement (muscle contraction)/active transport/secretion (ATP needed to
form lysosomes for secretion of cell products) /activation of molecules
Chapter 3: Photosynthesis ­ 6CO2 + 6H2O C6H12O6 + 6O2 (occurs in
Light energy first converted to electrical energy and then into chemical energy (organic
molecules) which in turn is converted to ATP (respiration).
Leaf = Main photosynthetic structure.…read more

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Oxidation and reduction:
Oxidation = Gain of O2/Loss of e-/Loss of H+
Reduction = Loss of O2/Gain of e-/Gain of H+
Light dependent reaction: - Products = Reduced NADP & ATP (Used to reduce CO2 in
Chlorophyll absorbs photons of light energy ­ boosts energy level of electrons ­ electrons
leave chlorophyll (exit photosystem 2) and are taken up by electron carrier (plastoquinone).
Chlorophyll = oxidised, plastoquinone = reduced.…read more

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CO2 combines with ribulose bisphosphate (5-carbon) ­ Rubisco enzyme used ­
produces unstable 6C molecule ­ rapidly splits into two 3C molecules (Glycerate 3-
3. ATP and NADPH from LDR are used to reduce G3P to triose phosphate ­ NADP+
returns to LDR to be reused.
4. 1/6 of triose phosphate is converted to organic substances ­ glucose, fatty acids, and
amino acids.…read more

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CO2] affects enzyme activity ­ rubisco
Temperature: - Between 0°C and 25°C rate of psn is approx.…read more


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