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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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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…

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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.




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…

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




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…

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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)…

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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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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.

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