A2 OCR Biology Key Terms and Definitions Photosynthesis

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Heterotroph
An organism that requires organic nutrients to supply it with a source of carbon.
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Photosynthesis
The manufacture of carbohydrates from inorganic substances (carbon dioxide and water) using energy from light; the light is transformed to chemical energy.
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Autotroph
An organism that makes its own organic nutrients using inorganic carbon source.
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Respiration
The release of chemical energy from glucose or other substrates by oxidation; most of the energy is used to make ATP; respiration takes place in all living cells.
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ATP
Adenosine triphosphate; a substance that acts as the energy currency of a cell, supplying an instantly available energy source that the cell can use.
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Metabolic Pathway
A series of chemical reactions taking place in an organism, in which each step is usually catalysed by an enzyme.
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Light-Dependent Stage
The stage of photosynthesis in which light energy is absorbed by chlorophyll and used to split water and make ATP and reduced NADP.
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Light-Independent Stage
The stage of photosynthesis in which carbon dioxide reacts with RuBP, and carbohydrates are produced; it requires ATP and reduced NADP from the light-dependent stage.
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Envelope
A pair of membranes surrounding an organelle; mitochondria, chloroplasts and nuclei have envelopes.
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Lamellae
Sheets; in a chloroplast, the lamellae are membranes within it.
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Thylakoids
Membrane-enclosed spaces inside a chloroplast, where the light-dependent stage of photosynthesis takes place.
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Grana
Stacks of thylakoids; singular, granum.
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Stroma
The ‘background material’ in a chloroplast, in which the light-independent stage of photosynthesis takes place.
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Photosynthetic Pigments
A molecule that absorbs some colours of light but not others, and transfers the light energy to chemical energy.
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Chlorophyll
A green, light-absorbing pigment essential for the light-dependent stage of photosynthesis in most plants; it comes in two main forms (a and b), which absorb different wavelengths of light.
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Starch Grain
A structure containing large numbers of starch molecules, inside a chloroplast; it is an energy store.
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Ribosomes
Tiny organelles, sometimes free in the cytoplasm and sometimes attached to rough endoplasmic reticulum, where protein synthesis takes place.
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Absorption Spectrum
A graph showing the wavelengths of light absorbed by a pigment.
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Carotenoids
Accessory pigments found in chloroplasts, generally red, orange or yellow in colour.
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Accessory Pigment
A pigment other than chlorophyll - for example, carotenoids; it helps to absorb more wavelengths of light than would be absorbed by chlorophyll alone, and may also have a protective effect.
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NADP
Nicotinamide adenine dinucleotide phosphate; a coenzyme that picks up hydrogen ions when they are removed from a compound, and passes them to another substance.
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Reduced NADP
NADP that has picked up hydrogen ions.
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RuBP
Ribulose bisphosphate; a substrate found in leaves that combines with carbon dioxide during the Calvin Cycle.
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Triose Phosphate (TP)
A three-carbon phosphorylated sugar, the first carbohydrate to be produced in photosynthesis.
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Calvin Cycle
The cyclic series of reactions that makes up the light-independent stage of photosynthesis; it takes place in the stroma of chloroplasts and produces triose phosphate using carbon dioxide, ATP and reduced NADP.
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Photosystem
A cluster of pigment and protein molecules that harvest light energy and channel it to chlorophyll molecules.
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Reaction Centre
The part of a Photosystem to which light energy is funnelled; it contains two chlorophyll a molecules that emit electrons.
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PSI
Photosystem I, involved in both cyclic and non-cyclic photophosphorylation.
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PSII
Photosystem II, involved in non-cyclic photophosphorylation but not cyclic photophosphorylation.
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Photophosphorylation
The production of ATP using energy from light; it takes place on the thylakoid membranes in a chloroplast.
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Electron Carriers
One of the components of the electron transport chain, that picks up electrons from one substance and passes them on to another.
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Electron Transport Chain
A series of molecules that successively gain and release electrons provided by a reduced coenzyme such as NADP; as the electron is passed along it loses energy, and the energy is used to synthesise ATP.
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Photolysis
The splitting of water molecules using energy from light.
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Z-Scheme
A diagram illustrating the changes in energy levels of electrons during the light-dependent reactions of photosynthesis.
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Rubisco
Ribulose bisphosphate carboxylase; an enzyme that catalyses the reaction of RuBP with carbon dioxide.
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Glycerate 3-phosphate (GP)
A three-carbon substance formed following the reaction between RuBP and carbon dioxide, in the Calvin Cycle.
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Limiting Factor
A factor that is preventing a reaction or other process from going any faster; if the supply of the factor is increased, then the reaction rate will increase; with respect to populations above a certain value.
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Photorespiration
An undesirable reaction between RuBP and oxygen, which takes place at high temperatures and high light intensities in some plants.
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Card 2

Front

The manufacture of carbohydrates from inorganic substances (carbon dioxide and water) using energy from light; the light is transformed to chemical energy.

Back

Photosynthesis

Card 3

Front

An organism that makes its own organic nutrients using inorganic carbon source.

Back

Preview of the back of card 3

Card 4

Front

The release of chemical energy from glucose or other substrates by oxidation; most of the energy is used to make ATP; respiration takes place in all living cells.

Back

Preview of the back of card 4

Card 5

Front

Adenosine triphosphate; a substance that acts as the energy currency of a cell, supplying an instantly available energy source that the cell can use.

Back

Preview of the back of card 5
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