Photosynthesis Flashcards
Chloroplast
An organelle found in plants and green algae that is the site of photosynthesis.
Describe the structure of chloroplast.
- Double membrane (chloroplast envelope).
- Grana (stacks of flattened disks (thylakoids) that contain photosystem I and II, electron transport chain, ATP synthase.
- Grana connected by intergranal lamellae.
- Stroma (fluid-filled matrix containing enzymes).
Where are chloroplasts located in a leaf?
Mainly found in the palisade layer.
How are chloroplasts adapted for photosynthesis?
- Thylakoids give a large surface area for light-dependent reactions.
- Photosynthetic pigments arranged into photosystems to maximise light absorption.
- Stroma directly surrounds grana (products of photosynthesis diffuse directly into the stroma.
- Contain their own DNA (cpDNA) and ribosomes.
- Inner chloroplast membrane less permeable than outer, enabling control over the movement of substances.
How are angiosperm leaves adapted for photosynthesis?
- Large surface area to maximise light absorption.
- Thin to reduce the diffusion distance for carbon dioxide.
- Upper epidermis transparent allowing light to strike mesophyll layers.
- Palisade cells densely packed and contain many chloroplasts.
- Air spaces reduce diffusion distance for carbon dioxide.
- Vein network transports water and minerals to the leaf and takes sugars away.
- Stomata allow carbon dioxide to diffuse into the leaf.
What is a transducer? Why are chloroplasts described as transducers?
- Something that converts one type of energy into another.
- Chloroplasts transduce light energy into the chemical energy of ATP.
What is a photosynthetic pigment?
A molecule present in chloroplasts (or photosynthetic bacteria) that absorbs light energy for photosynthesis. It absorbs specific wavelengths of light and reflects others.
Give some examples of photosynthetic pigments.
- Chlorophylls a and b
- Beta carotene
- Xanthophylls
What is the purpose of chromatography?
To separate different products from a mixture.
What is photosynthesis?
A complex metabolic pathway that synthesises organic molecules from carbon dioxide and water in the presence of light.
What is a photosystem?
- Protein complex consisting of an antenna complex and reaction centre.
- Involved in the absorption of light and transfer of electrons in photosynthesis.
- Two types: PSI and PSII.
How do PSI and PSII differ?
They absorb different wavelengths of light.
Describe the process of light harvesting in photosynthesis.
- Antenna complex absorbs light energy of varying wavelengths and transfers it quickly and efficiently to the reaction centre.
- Energy absorbed by two chlorophyll a molecules which emit “excited” electrons.
What is an absorption spectrum?
A pattern of bands that occurs when a substance absorbs the different wavelengths of light.
What is an action spectrum?
A graph of the rate of photosynthesis against each wavelength of light absorbed by a pigment.
Describe the light-dependent stage of photosynthesis.
- First stage of photosynthesis.
- Takes place in the thylakoids of the chloroplast.
- Uses light energy to produce ATP, reduced NADP and oxygen.
State the two processes of ATP generation by the light-dependent reactions.
Cyclic and non-cyclic photophosphorylation.
Define cyclic photophosphorylation.
The formation of ATP involving PSI only, where NADP+ is not reduced.
Outline cyclic photophosphorylation.
- Involves PSI only (no electron supplied by PSII).
- Excited electrons enter the ETC to produce ATP and then return to PSI.
- No reduction of NADP and no water required to replace lost electrons.
What is the purpose of cyclic photophosphorylation?
Produces additional ATP to meet surplus energy demands of the cells.
Define non-cyclic photophosphorylation.
The formation of ATP and reduced NADP involving both PSI and PSII.
Outline non-cyclic photophosphorylation.
- Involves PSI and PSII.
- Excited electrons enter the ETC to produce ATP.
- NADP acts as a final acceptor and is reduced.
- Water is photolysed to compensate for electrons lost from PSII.
What is the purpose of non-cyclic photophosphorylation?
Produces ATP and reduced NADP for the Calvin cycle.
How does chemiosmosis produce ATP in the light-dependent stage?
- Protons flow down their concentration gradient from the thylakoid space into the stroma via ATP synthase.
- ATP synthase phosphorylates ADP to form ATP as protons flow through it.
Describe photolysis.
The splitting of a molecule of water in the presence of light (energy from the sun) that occurs during the light-dependent stage of photosynthesis. This produces protons, electrons and oxygen.
What happens to the products of photolysis?
- H+ (used in proton pumping and to reduce NADP).
- e- (replaces electrons lost from chlorophyll a in PSII).
- Oxygen (by-product, used for respiration of diffuses out of the leaf as waste gas).
Explain how the ETC results in the production of reduced NADP.
NADP acts as a final electron acceptor, and is subsequently reduced.
Describe the light-independent stage of photosynthesis.
- Second stage of photosynthesis.
- Calvin cycle produces glucose.
- Does not require light energy and takes place in the stroma.
- Uses carbon dioxide and the products of the light-dependent stage to build organic molecules.
What is the light-independent stage also known as?
The Calvin cycle.
Name the three main stages of the Calvin cycle.
- Carbon fixation
- Reduction
- Regeneration
What happens during carbon fixation of the Calvin cycle?
- Reaction between carbon dioxide and ribulose bisphosphate (RuBP) catalysed by enzyme RuBisCo.
- Forms unstable 6C intermediate that breaks down into two molecules of glycerate 3-phosphate (G3P).
What happens during reduction of the Calvin cycle?
- 2xG3P are reduced to 2x triose phosphate (TP).
- Requires 2x reduced NADP and 2x ATP formed during the light-dependent reaction.
- Forms 2x NADP and 2xADP that enters the light-dependent reaction.
What happens during regeneration of the Calvin cycle.
- After 1C leaves the cycle, the 5C compound ribulose monophosphate (RuB) forms.
- Ribulose bisphosphate (RuBP) is regenerated from RuP using 1x ATP
How are nutrients produced as a result of photosynthesis?
- Formation of amino acids from GP (requires nitrates and sulfates).
- TP molecules used to produce sugars e.g. glucose, fructose and sucrose.
What is a limiting factor?
A variable that limits the rate of a particular reaction.
Name the factors that limit the rate of photosynthesis. What stage do they limit?
- Light intensity (light-dependent stage).
- Light wavelength (absorption by chlorophyll).
- Carbon dioxide concentration (light-independent stage).
- Temperature (enzyme-controlled reactions (carbon fixation)).
- pH (enzyme-controlled reactions).
What happens during regeneration of the Calvin cycle.
- After 1C leaves the cycle, the 5C compound ribulose monophosphate (RuB) forms.
- Ribulose bisphosphate (RuBP) is regenerated from RuP using 1x ATP
How are nutrients produced as a result of photosynthesis?
- Formation of amino acids from GP (requires nitrates and sulfates).
- TP molecules used to produce sugars e.g. glucose, fructose and sucrose.
What is a limiting factor?
A variable that limits the rate of a particular reaction.
Name the factors that limit the rate of photosynthesis. What stage do they limit?
- Light intensity (light-dependent stage).
- Light wavelength (absorption by chlorophyll).
- Carbon dioxide concentration (light-independent stage).
- Temperature (enzyme-controlled reactions (carbon fixation)).
- pH (enzyme-controlled reactions).
Describe the role of nitrogen in plant metabolism.
Synthesis of amino acids, nucleotides and chlorophyll.
What does nitrogen deficiency in plants cause?
- Stunted growth.
- Chlorosis (yellowing of the leaves due to insufficient chlorophyll production).
Describe the role of magnesium in plant metabolism.
Central component of chlorophyll.
What does magnesium deficiency in plants cause?
Chlorosis (yellowing of the leaves due to insufficient chlorophyll production).
