Topic 11 - Photosynthesis Flashcards
What is photosynthesis?
The process by which organisms convert solar energy to chemical energy
Why do plant leaves have xylem and phloem cells?
Xylem - brings water to leaf cells.
Phloem - carries away sugars produced in photosynthesis.
Purpose of the arrangement of leaves on the plant?
Minimises overlapping, avoiding shadowing of one leaf by another.
Purpose of numerous stomata?
Open and close in response to changes in light intensity.
Purpose of a transparent cuticle and epidermis?
Allows light to penetrate and reach the photosynthetic mesophyll cells.
Purpose of a large surface area?
Collects as much solar energy as possible.
Purpose of many air spaces in the lower mesophyll layer?
Allow diffusion of carbon dioxide and oxygen.
Purpose of long narrow upper mesophyll cells?
Packed with chloroplasts that collect sunlight.
Where in the chloroplast in chlorophyll found?
- Granum
- Imbedded in thylakoid membranes.
Where does the light-dependent reaction occur in photosynthesis?
Thylakoid membranes
The solar energy captured from the light-dependent reaction has two purposes. What are they?
1) To combine ADP and an inorganic phosphate to form ATP.
2) To split two water molecules into 4 electrons, 4 protons, and oxygen.
Light dependent reaction: Part 1 - Making ATP (Photophosphorylation)
1) A chlorophyll molecule absorbs light, boosts a pair of electrons to a higher energy level (Photoionisation).
2) These ‘excited’ electrons leave chlorophyll molecule, taken up by electron carrier. (First sequence of oxidation-reduction reactions).
3) Electrons are passed along a series of electron carriers = electron-transport chain.
4) Energy released as electrons pass down this chain is used to actively transport protons into the thylakoid interior space.
5) Diffuse down gradient and out of thylakoid, into stroma through ATP synthase.
Light-dependent reaction: Part 2 - Photolysis of water
1) Light energy splits water molecules into hydrogen, oxygen, and electrons.
2) Electrons produced are used to reduce the chlorophyll molecule - restoring the electrons it had lost.
3) Oxygen produced is a by-product which is used in respiration or leaves the cell and then the leaf through stomata.
4) Protons are taken up by final electron acceptor - NADP.
5) NADP gains electrons, becomes reduced, becoming reduced NADP, which (along with ATP) is used in the light-independent reaction.
Light-independent reaction: Calvin Cycle
1) CO2 diffuses into leaf through stomata into the stroma of the chloroplast.
2) Using an enzyme (Rubisco), CO2 binds to 5-carbon sugar ribulose bisphosphate.
3) Produces 2 molecules of 3-carbon glycerate 3-phosphate, which are activated.
4) Reduced NADP from light-dependent reaction reduces 2x GP to 2x triose phosphate. Uses ATP from light-dependent reaction.
5) TP goes through reactions to regenerate the ribulose bisphosphate. Reduction of ATP to ADP and Pi provides phosphate needed.
6) 2x TP combine to form one 6C glucose molecule.
7) Glucose molecules combine via condensation to produce larger complex molecules e.g. starch. Used in respiration to produce ATP (plant uses this to produce glucose, and for it to synthesise other organic compounds the plant needs for growth like cellulose, proteins).
Why is ATP required for mitosis?
- Making proteins that make up spindle fibres.
- Splitting the cell into two.
- Moving.
