5- photosynthesis Flashcards
label
light dependant stage
First part of photosynthesis which takes place in the thylakoid membranes of chloroplasts.
what does the light dependant stage involve
• Non-cyclic photophosphorylation.
• Cyclic photophosphorylation.
products of light dependant stage
• Light energy is used to produce ATP and NADPH.
• The ATP and NADPH are used in the second part of photosynthesis (light-independent stage), which doesn’t require light, to create glucose from carbon dioxide.
diagram of light dependant stage
thylakoid membranes role
• They house the proteins and pigments (chlorophyll) necessary for capturing light energy.
• They contain two photosystems (I and
II) which absorb light energy to power the ETC.
• The process leads to the production of
ATP through chemiosmosis.
what do cyclic and non-cyclic photophosphorylation have in common
Both are processes that occur in the thylakoid membranes and contribute to the production of ATP, NADPH, and oxygen.
non-cyclic photophosphorylation
• Uses both photosystem I and Il.
• Makes ATP, NADPH, and oxygen.
• Electrons are not recycled.
• Photolysis of water.
• Oxygen is released as a by-product when water is split (photolysis) to replace electrons in photosystem Il.
cyclic photophosphorylation
• Uses only photosystem I.
• Only makes ATP, doesn’t make
NADPH.
• No photolysis of water.
• No oxygen is released.
light independent diagram
stroma’s role in light independent stage
Where the light-independent reactions (Calvin cycle) of photosynthesis occur.
carbon dioxide fixation
• CO2 is fixed into an organic molecule through a process called carbon fixation.
• CO2 combines with a 5C compound called ribulose bisphosphate (RuBP) to form a 6C compound, which quickly splits into two 3C molecules of glycerate 3-phosphate (GP).
• This reaction is catalysed by the enzyme ribulose bisphosphate carboxylase (RUBISCO).
Use of NADPH and ATP from the light-dependent stage
• The ATP and NADPH produced in the light-dependent stage are used in the Calvin cycle.
• ATP provides energy and NADPH
provides reducing power (electrons) to convert GP into glyceraldehyde 3-phosphate (GALP).
• Some of the ATP is also used to regenerate RuBP to continue the cycle.
use of GALP
• GALP serves as a raw material for the synthesis of various biomolecules.
• It can be used to synthesise monosaccharides such as glucose and fructose.
• It can be converted into amino acids and other molecules necessary for the plant.
carbon dioxide affect on photosynthesis
• Ideal concentration is 0.4%.
• Raising it above 0.4% could lead to stomatal closure, restricting gas exchange.
• At CO2 concentrations below optimal levels (e.g., 0.04%), the rate of conversion of RuBP to GP slows down due to less available CO2.
• This results in an increase in RuBP levels (as it continues to be produced) and a decrease in GP and GALP (as they are being consumed to regenerate RuBP).
light intensity affect on photosynthesis
• Higher light intensities provide more energy for photosynthesis but only specific wavelengths are utilised (red and blue light for chlorophyll a, chlorophyll b and carotene).
• Between points A and B on a typical light intensity graph, light intensity is the rate-limiting factor. As intensity increases, so does the rate of photosynthesis.
• Point B is the saturation point. Any further increase in light intensity will not increase the rate of
photosynthesis, as another factor becomes limiting.
• The compensation point is the light intensity at which the amount of CO2 produced in respiration equals the amount used in photosynthesis, and the amount of 02 used in respiration equals the amount released in photosynthesis.
temperature affect on photosynthesis
• The optimal temperature for photosynthesis is around 25°C.
• Photosynthesis relies on enzymes which function best within a certain temperature range.
• At low temperatures, enzyme activity slows due to reduced kinetic energy.
At high temperatures, enzymes begin to denature and other detrimental effects occur:
• Chlorophyll damage: Reduced pigment availability to absorb light energy, slowing the rate of light-dependent reactions.
• Chloroplast damage: Release of Calvin cycle enzymes, decreasing the rate of light-independent reactions.
• Thylakoid membrane damage:
Fewer sites available for electron transfer, decreasing the rate of light-dependent reactions.
• Stomatal closure: To prevent excessive water loss, which also reduces CO2 intake, slowing photosynthesis.
