photosynthesis Flashcards
(21 cards)
site of photosynthesis
chlorophlasts
how are leaves adapted for photosynthesis?
- large sa to absorb light
- transparent cuticle+epidermis= allows light to pass through
- stomata open and close in response to changes in light intensity
- thin- short diffusion distances for gases
describe the structure of a chlorophlast
- flattened organeeles surrounded by a double membrane.
- made up of thylakoids which stack up to form grana
- grana linked by pieces of thylakoid membrane called lamallae
- thylakoid membranes contain photosynthetic pigments
what are photosynthetic pigments?
coloured substances which absorb light energy for photosynthesis e.g chlorophyll a
what is a photosystem?
protein and a pigment
what is the stroma?
fluid filled matrix which contains enzymes,sugars and organic acids. Carbs which are produced in photosynthesis and not used immediately are stored as starch grains in the stroma
adaptations of chlorophlasts
- thylakoid membranes provide a lare SA for attachment of chlorophyll, electron carriers and enzymes
- network of proteins that hold the chlorophyll in the grana in a precise manner that allows maximum absorption of light.
- chlorophlasts contain DNA and ribosomes so can quickly make proteins involved in the light dependent reaction.
features of light dependent reaction
- involves light energy
- takes place in thylakoid membranes
- light excites electrons in chlorophyll= photoionised
- electron transport chain
- produces ATP, NADP and O2.
features of light independent reaction
- aka calvin cycle
- doesnt use light energy directly but relies on products of previous reaction
- takes place in stroma
- produces simple sugars from CO2.
photophosphorylation
process used to make ATP in the light dependent reaction
PSI PSII
used to capture light, absorb light at different wavelengths
non-cyclic phosphorylation
- light energy absorbed by PSII and excites electrons in chlorophyll, electrons move to a higher energy level and are released from chlorophyll
- electrons move down the electron transport chain to PSI
- The excited electrons from PSII must be replaced, light energy splits water (photolysis) into protons, electrons and oxygen.
- excited electrons lose energy as they move down the ETC. This energy is used to actively transport H+ into the thylakoid so it has a higher conc of protons than the stroma forming an eectrochemical gradient
- Protons move down their conc gradient into the strom via ATP synthase through facilitated diffusion= energy from this movement forms ATP
- light energy absorbed by PSI which excites electrons to a high energy level . electrons released from photosystem and transferred to NADP along with H+ from the stroma to form NADPH
chemiosmosis
process of electrons flowing down the ETC and creating a proton gradient across the membrane for ATP synthesis
cyclic phosphorylation
- only uses PSI
- cyclic as electrons from chlorophyll aren’t passed on to NADP but passed back to PSI via electron carriers
- no NADP /O2 produced only small amounts of ATP produced
where does the calvin cycle take place?
in the stroma of chlorophlasts
features of the calvin cycle
- produces TP (triose phosphate) from CO2 and RUBP
- TP converted to glucose and useful organic substances
- Needs ATP and H+ ions to keep the cycle going
- RUBP is regenerated as the reactions are linked in a cycle.
stages of calvin cycle
`1. carboxylation= CO2 diffuses into stroma and combines with RUBP catalysed by enzyme rubisco which combines to form an unstabLe 6 carbon compound which splits into 2 molecules of GP
- Reduction-ATP from light dependent reaction provides energy to convert GP nto TP. reaction also requires H+ ions which come from NADPH. TP converted into many organic substances
- regeneration- 5 out of every 6 carbons of TP used to regenerate RUBP. Regenerating RUBP takes the rest of the ATP produced by the light dependent reaction
how many times does calvin cycle happen for 1 glucose molecule?
6 times
how do TP and GP make carbs
hexose sugars are made by joing 2 molecules of TP together. larger carbs are made by joining hexose sugars togther in diff ways
how do TP and GP make lipids
made using glycerol which is synthesised from TP and fatty acids which is synthesised from GP ( glycerate-3-phosphate)
how do TP and GP make aa
some aa are made from GP
