Photosynthesis

Question 1

Light-dependent reaction

Answer 1

-light energy absorbed by PS 2
-Electrons move to a higher energy level and leave chlorophyll
-Elections transfer energy as they move along the electron transport chain
-Light energy splits water into H ions, O2, and electrons as they need to be replaced whilst this is happening (photolysis)
-The energy those electrons release is used to transport protons (h ions) into the thylakoid, so higher conc of protons than in the stroma. forming gradient
-Protons move down the conc gradient into the stroma via the enzyme ATP synthase (Chemiosmosis)
-The energy from this movement makes ATP
-Light absorbed by PS1, exits 2 electrons to a higher energy level.
-Finally, electrons and protons are transferred to NADP+ to form reduced NADP.

Question 2

Light independent reaction

Answer 2

-CO2 enters the leaf through stomata and diffuses into the stroma
-Here it combines with RuBP (5c) using RUBISCO
-This gives an unstable 6c compound, which breaks down into 2 molecules of GP (3c)
-ATP from LDR provides energy to reduce GP into TRIOSE PHOSPHATE (3c)
-Also requires H ions from reduced NADP, which is oxidised back into NADP+ and returns to the LDR
-TRIOSE PHOSPHATE is then converted into useful organic compounds e.g glucose
-5 out of every 6 molecules of TP is used to regenerate RuBP. This requires the rest of the ATP from the LDR.

Question 3

Limiting factors of photosynthesis

Answer 3

-Light intensity
-Co2 concentration
-Water
-Temperature

Question 4

How leaf is adapted for photosynthesis

Answer 4

-Large surface area to absorb light
-Thin, so a short diffusion pathway
-Numerous stomata for gas exchange
-Long, narrow upper mesophyll cells packed with chloroplasts

Question 5

Where photosynthesis takes place

Answer 5

Chloroplasts
LDR- Thylakoids, chlorophyll is in thylakoids
LIR-Stroma