The Light Dependant Reaction

Question 1

What’s photoionisation

Answer 1

When light energy excites electrons in an atom or molecule, giving them more energy and causing them to be released

Question 2

Describe the light depend reaction

Answer 2

1. Light energy is absorbed by PSII, this excites electrons in the chlorophyll
2. The electrons move to a higher energy level, these are then released from the chlorophyll and move down the ETC to PSI
3. These electrons must be replaced so light energy splits water into protons(H+ ions), electrons and oxygen (photolysis) - so the O2 in photosynthesis comes from water and is made in the light dependent reaction
4. Energy from the excited electrons moving down the ETC, is used to transport protons into the thylakoid, this forms a protein gradient
5. Protons then move down their concentration gradient into the stroma via the enzyme ATP synthase, the energy from this movement combines ADP+P -> ATP
6. Light energy is absorbed by PSI, which excites electrons again to an even higher energy level
7. Finally the electrons are transferred to NADP, along with a H+ ion from the stroma, to form reduced NADP (NADPH)

Question 3

How are the chloroplasts structurally adapted to their function of capturing sunlight and carrying out the light dependent reaction

Answer 3

Thylakoid membranes provide a large SA for the attachment of chlorophyll, electron carrier and enzymes

A network of proteins in the grana hold the chlorophyll in a very precise manner that allows maximum absorption of light

The granal membranes have ATP synthase channels within them, which catalyse the production of ATP. They are also selectively permeable which allows establishment of a proton gradient

They contain DNA and ribosomes so can easily manufacture some of the proteins involved in the light dependent reaction