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AQA BIOLOGY Unit 4

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…

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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…

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niche, can result in competitive exclusion (where one species moves or population
diminishes)

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).

Population growth = (births + immigration) ­ (deaths + emigration)…

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ATP is useful as an immediate energy supply because:

Energy release only involves a single reaction (hydrolysis)
Energy released in small manageable quantities

ATP is the source of energy for:

Metabolic processes ­ energy needed to build macromolecules from basic units
Movement ­ energy needed for muscle contraction (sliding filaments)…

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Site of light-dependent reaction (thylakoids)

Thylakoid membranes provide a large surface area for attachment of chlorophyll,
electron carriers and enzymes that carry out the LDR
Networks of proteins in the grana hold the chlorophyll very precisely to optimise light
absorption
Granal membranes have enzymes attached to them to help manufacture…

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reduced NADP and ATP will enter the grana to be used in the light independent stage of
photosynthesis.

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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,…

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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.

Light intensity

Light is needed in…

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Glycolysis

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…

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The conversion of the 3C pyruvate molecule into carbon dioxide and a 2C molecule called
acetylcoenzyme A. Takes place in the mitochondrial matrix. The link reaction occurs twice for
each glucose molecule since 2 pyruvate molecules are formed in glycolysis.

1. Oxidation
Pyruvate is oxidised by removing hydrogen, this hydrogen…

Comments

Hannah

thanks 

JV31

the unit 4 notes are amazing!

Do you have any unit 5 notes?

L.B

Great notes- thank you so much

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