Photosynthesis Flashcards
(27 cards)
What is the chloroplast?
An organelle found in plants and algae that is the site of photosynthesis
They are transducers and convert light energy into chemical energy
Where is the chloroplast found in plants?
Palisade mesophyll
How are chloroplasts adapted for photosynthesis?
Thylakoids give A large surface area for light-independent reactions
Storma directly surrounds grana- products of photosynthesis diffuse directly into storms
Contain their own DNA and ribosomes
What is a photosynthetic pigment? And give some examples
A molecule present in chloroplasts that absorbs certain wavelengths of light
Chlorophylls a and b
Beta carotene
What is chromatography used for?
Used to observe and identity the pigments involved in photosynthesis
How is the Rf value calculated?
Distance travelled by pigment / distance travelled by solvent front
Explain the process of chromatography.
1) mixture of pigments is extracted from the leaves and applied the to origin.
2) chromatogram is placed in solvent and left to run
3) pigments travel different distances according to solubility
4) Rf value is calculated and compared to known data to identify pigments.
What is a photosystem?
Light capturing complexes located in the thylakoid membrane that contains different pigments that absorb different wavelengths.
Describe the structure of a photosystem
- the antennae complex contains chlorophyll a, chlorophyll b and the carotenoids xanthophyll and beta carotene. Light energy is absorbed and passed to the reaction centre
- reaction centre contains 2 molecules of chlorophyll a. Electrons in these molecules are excited and rise to a higher level.
Describe the non-cyclic photophosphorylation light dependent reaction
1) photon of light absorbed by pigment in the antennae complex of PSll. Energy passed to reaction centre, an electron from each of the chlorophyll a molecules is excited. This leaves the oxidised chlorophyll a
2) electrons pass through the ETC. Flow of protons allow ATP synthesis
3) A photon of light hits PSl and the same reaction occurs as stage 1. But electron acceptors pass it to NADP forming reduced NADP
4) photolysis of water. Water splits into hydrogen oxygen and electrons. Electrons replace those lost by chlorophyll a. O2 is a by product of
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 fuel ATP as protons flow through it
Describe photolysis
The splitting of A molecule of water in the presence of light that occurs during the light-dependent stage. Producing protons, electrons and oxygen
H2O > 2H+ + 2e + 1/2O2
What happens to the products of photolysis?
H+ = used in proton pump and to reduce NADP
e- = replaces electrons lost from chlorophyll a in PSll
O2 = by-product, used for respiration or diffuses out of the leaf as waste gas
What is the light independent stage also known as?
The Calvin Cycle
Name the 3 main stages of the Calvin cycle
1) Carbon fixation
2) Reduction
3) Regeneration
What happens during carbon fixation of the Calvin cycle?
- taking place in the stroma the 5C compound ribulose bisphosphate takes up carbon dioxide to form an unstable 6C compound. This reaction is catalysed by the enzyme RUBSICO
- the carbon dioxide can be described as ‘fixed’ as it has been converted from a gas into carbohydrate compound.
- the unstable 6C compound immediately breaks down into 2x 3c compounds called glycerate-3-phosphate
What happens during reduction of the Calvin Cycle?
GP is reduced by reduced NADP and using energy from ATP. The 2x 3C GP are converted into 2 3C carbohydrates called Triose phosphate
What happens during regeneration of the Calvin cycle
1C from the Triose phosphate will be used to synthesise a hexose sugar
- the other 5C form ribulose phosphate which is regenerated to ribulose biphosphate using ATP, and the cycle begins again.
What are the essential minerals in A plant and what is their function?
Magnesium - Chlorophyll production
Nitrogen ( as nitrates or ammonium) - Synthesis of nuclei acids, proteins and chlorophyll
What happens if there is a lack of essential minerals?
Nitrogen- reduce growth of all organs and yellowing of leaves
Magnesium - Yellowing of the leaves
What is a limiting factor ?
A variable that limits the rate of a particular reaction.
What occurs in cyclic phosphorylation
The electron acceptor that received electrons from PSl passes them back down the electron transport chain to PSl.
Plants obtain a good source of ATP for the light independent stage by using light to create the high energy electrons needed to power the ETC to drive ATP synthetase
What does the absorption and action spectra indicate?
- both lines peak in the red and blue regions and dip in the green region. This supports that the red and blue light absorbed and used in photosynthesis whereas light in the green region is reflected by the plant and doesn’t contribute to photosynthesis
- absorption (faded lines) = peak absorbances of different wavelengths of light for different pigment
- action (bright lines)= rate of photosynthesis at different wavelengths of light
What is the difference between cyclic and non-cyclic phosphorylation?
cyclic phosphorylation only involves photosystem 1 and photolysis of water isn’t present. Oxygen and NADP isn’t produced either .
whereas non-cyclic produces all of these and involves both 1 and 2.
