Biol4 Revision Booklet

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1. Populations
The number of organisms of one species in a habitat
Populations and Ecosystems
Ecosystem: All the organisms living in a particular area and all the abiotic (non
living/biological) conditions.
Biosphere: The life-supporting layer of land, air and water that surrounds the Earth.
Community: The organisms of all species that live in the same area (*group of
Ecological Niche: Comprises of all the conditions and resources required for an organism to
survive, reproduce and maintain a viable population.
Investigating Populations
Large and Random Sampling,
To reduce roll played by chance
So data is representative of the population
To avoid bias
Making results more valid
To carry out statistical tests
Achieved by (1) creating a grid of survey land, (2) use calculator to generate random number,
(3) use numbers as coordinates, (4) place centre of quadrat on coordinate then (5) count
species or percentage cover or abundance scale inside quadrat.
Systematic sampling along transects e.g. useful for succession, (1) set up transect/ tape
measure across area, (2) place quadrats at regular intervals along the line then (5) count
species or percentage cover or abundance scale inside quadrat.
Abundance: number of individuals of a species within a given space
Mark-release-recapture techniques
*Capture sample, mark with appropriate method that does not harm individual (e.g. paint,
tags) and release back to community. After a period of time, take second sample and count
number of marked organisms.

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This technique relies on the following assumptions:
Mark does is not lost/rubbed off
Population size does not change i.e. due to deaths or births
Population has a definite boundary so no immigration or migration
Capture and mark process did not effect individuals likeliness to be captures, e.g.
more afraid of humans making them avoid capture or vice versa
Released individuals have time to distribute themselves evenly among population
Variation in Population Size
Population growth curves
Population size
Carrying capacity
Abiotic factors e.g.…read more

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Intraspecific competition: when individuals of the same species compete for resources e.g.
food, light, water, breeding sites.
Interspecific competition: when individuals of different species compete for resources e.g.
food, light, water, breeding sites. Occurs when populations of two species occupy the same
niche, can result in competitive exclusion (where one species moves or population
Human Populations
There was a large increase in human population due to development of agriculture,
manufacturing and trade being able to sustain a large population (industrial revolution).…read more

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Adenosine Triphosphate (ATP) ­ three phosphate groups. Bonds between phosphate groups
are unstable, so have a low activation energy. When broken they release energy.…read more

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And stroma (site of light-independent reaction), which is a fluid filled matrix.…read more

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The Light-Dependent Reaction (LDR)
When a chlorophyll molecule absorbs light energy, the electrons will be excited to a higher
energy state. The electrons leave the chlorophyll and are taken up by an electron carrier.
Chlorophyll is oxidised, Electron carrier is reduced (OIL RIG ­ Oxidation is loss, Reduced is gain)
The electrons now pass along an electron transport chain in a series of oxidation-reduction
reactions; each carrier has a lower energy level so the electrons lose energy at each stage.…read more

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The Light-Independent Reaction (LIR) / The Calvin Cycle
CO2 from the atmosphere diffuses into the leaf through the stomata and dissolves in water
around the walls of the mesophyll cells. It then diffuses through the plasma membrane,
cytoplasm and chloroplast membranes into the stroma of the chloroplast.
In the stroma, the CO2 combines with the 5C compound ribulose biphosphate (RuBP) using
an enzyme.
The combination of CO2 and RuBP produces two molecules of the 3C glycerate 3-phosphate
(GP).…read more

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Factors Affecting Photosynthesis
CO2 concentration
CO2 is needed in the LIR to be combined with RuBP to form GP, if there is a low
concentration of carbon dioxide then GP cannot be formed, this causes RuBP to
build up and the reaction then stops.…read more

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The splitting of the 6C glucose molecule into two 3C pyruvate molecules, which is an
anaerobic process that occurs in the cytoplasm of the cell.
1. Activation of glucose by phosphorylation
Glucose is first phosphorylated (2 phosphate molecules are added) ­ Pi
comes from hydrolysis of 2 ATP molecules to ADP and Pi ­ releasing energy.
This energy is used to catalyse the next enzyme-controlled reactions by
activating (lowering the activation energy of) glucose.
2.…read more

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In the process, two ATP molecules are produced as a result of substrate level
phosphorylation (when phosphate groups are transferred from donor
molecules to ADP to make ATP, direct linking)
Net Products ­ 2 ATP, 2 NADH, 2 pyruvate.…read more


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