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Photosynthesis
Topic 3.8 & 8.…read more

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State that photosynthesis involves the conversion of light energy into chemical energy
During photosynthesis, light energy from the sun is transferred to chemical energy in the form of
organic compounds for plants, algae and some bacteria.
3.8.2 (1)State that light from the Sun is composed of a range of wavelengths (colours)
Light is a form of electromagnetic radiation produced by the sun and light consists of a spectrum ( a
range of wavelengths) from 400nm to 700nm. Each wavelength is a pure colour, e.g.…read more

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Outline the effects of temperature, light intensity and carbon dioxide on the rate of
photosynthesis.
Limiting Factor Effect
Temperature At low temperatures, all of the enzymes
that catalyse the reaction of the Calvin
Cycle work slowly
At high temperatures, RuBP carboxylase
denatures and works less effectively so
rate of reaction reclines quickly beyond
optimum
Light Intensity Low light intensity means small number
of products in light dependent reactions
limiting rate of photosynthesis overall.…read more

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State that photosynthesis consists of light dependent & light independent reactions.
Photosynthesis consists of light dependent reactions, to produce intermediate compounds, which
are used in light independent reactions to produce glucose, amino acids and other organic
compounds.
8.2.3(3) Explain light dependent reactions
8.2.4(3) Explain
photophosphorylation in terms of chemiosis.
Light Dependent Reactions involve light energy being trapped by the photosynthetic pigment
chlorophyll.…read more

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Chlorophyll are grouped together in photosystems, held in the thylakoid membranes of the grana.
Here, several hundred chlorophyll molecules plus accessory pigments are arranged, which funnel
light energy to the reaction centre.
Photosystem 1: has a reaction centre (single chlorophyll molecule) activated by a light of a
wavelength 700nm.
Photosystem 2: has a reaction centre activated by light of wavelength 680nm
1.…read more

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Thus it forms a cycle, known as the Calvin cycle.
3. Carbon dioxide enters the chloroplast via diffusion and is fixed in a carboxylation reaction
with RuBP to form a six carbon compound which immediately splits, resulting in two
glycerate-3-phosphates.
4. This is carried out by the enzyme ribulose biphosphate carboxylase or rubiso.
5. This initial product is reduced to the 3-carbon sugar phosphate, triose phosphate using
NADPH+H+ and ATP.
6.…read more

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Explain the concept of limiting factors in photosynthesis, with reference to light
intensity, temperature & concentration of carbon dioxide.
SEE IN DEPTH STANDARD LEVEL SECTION FOR DETAILED REFERENCES TO LIGHT INTENSITY,
TEMPERATURE AND CONCENTRATION OF CARBON DIOXIDE.
Limiting Factor: A factor which controls the rate of a process.
Carbon Dioxide: No photosynthesis at very low concentrations, positive correlation with rate of
photosynthesis and at high concentrations rate reaches plateau as limited by another factor.…read more

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