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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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)…

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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:…

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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…

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animals enzymes work slower if temp. is too low ­ 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…

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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…

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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…

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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…

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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 ­…

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2. 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…

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[CO2] affects enzyme activity ­ rubisco
Temperature: - Between 0°C and 25°C rate of psn is approx. doubled for every 10°C increase
­ above this = enzymes denature ­ Extra ­ Above 25°C, rubisco (Ribulose bisphosphate
carboxylase oxygenase) favours the "oxygenase" part of the reaction Rubisco starts to
combine Ribulose…


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