11.2 Light Dependent reaction

Question 1

What does the light dependent reaction involve

Answer 1

The capture of light

Question 2

What are the two purposes of capturing light

Answer 2

1. TO add an inorganic phosphate molecule to ADP, thereby making ATP
2. To split water into Protons (H+) and OH- ions. The splitting of water is by light so it is called photolysis

Question 3

What is oxidation

Answer 3

When a substance gains oxygen or loses hydrogen

Loss of electrons

Question 4

What is reduction

Answer 4

When a substance loses poxygen or gains hyudrogen

Gain of electrons

Question 5

What happens when a chlorophyll molecule absorbs light energy

Answer 5

It boosts the energy of a pair of electrons, raising them to a higher energy level. These electrons become so energetic they leave the chlorophyll molecule

Question 6

What does the absorption of light do to the chlorophyll molecule

Answer 6

It becomes ionised, the process is called photoionisation

Question 7

What has technically happened to a chlorophyll molecule

Answer 7

Oxidised, the electron carrier than gained the electrons has been reduced

Question 8

What happens to the pair of electrons after photoionisation has occured

Answer 8

An electron carrier accepts them

The electrons are then passed down a number of electron carriers in a series of oxidation-reduction reactions. These electron carriers form a transfer chain

Question 9

Where is the electron transfer chain found

Answer 9

In the membranes of thylakoids

Question 10

What happens when electrons are passed onto the next carrier

Answer 10

Each new carrier is at a slightly lower energy level, therefore at each stage electrons lose energy

Question 11

What happens to the energy lost when electrons pass down the transfer chain

Answer 11

It is used to combine an inorganic phosphate molecule with ADP to produce ATP

Question 12

Describe the chemiosmotic theory

Answer 12

1. Each thylakoid is an enclosed chamber into which protons (H+) are pumped from the stroma using proton pumps. The energy to drive this process comes from electrons released when photolysis of water happens. The photolysis of water also produces protons, which further increases their concentration inside the thylakoids
2. OVerall this creates and maintains a concentration gradient of protons across the thylalkoid membrane with a high concentration inside the thylakoid space, and a low concentration in the stroma
3. The protons can only cross the thylakoid membrane through ATP synthase channel proteins - the rest of the membrane is impermeable to protons. These channels form small granules on the membrane surface, they are called stalked granules
4. As the protons pass through these ATP synthase channels they cause changes to the structure of the enzyme which then catalyses the combination of ADP with Pi to form ATP

Question 13

What is the equation for photolysis of water

Answer 13

2H2O -> 4H+ 4E- + O2

Question 14

What happens to the protons from photolysis of water

Answer 14

They pass out of the thylakoid space through the ATP synthase channels and are taken up by NADP

rNAP is imortant because it is a further potential source of chemical energy to the plant

Question 15

What happens to the oxygen from photolysis of water

Answer 15

The oxygen by-product is either used in respiration or diffuses out of the leaf as a waste product

Question 16

Where does the LDR take place

Answer 16

Thylakoids of chloroplasts

Question 17

What do thylakoids stack up to form

Answer 17

The Grana

Question 18

How are chloroplasts structurally adapted to their function of capturing light and carrying out the LDR

Answer 18

1. The thylakoid membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the LDR
2. A network of proteins in the grana hold the chlorophyll in a very precise manner that allows them to absorb the most light
3. The granal membranes have ATP synthase channels within them, which catalyse ATP production. They are selectively permeable, which helps establish a proton gradient
4. Chloroplasts contain both their own DNA and Ribosomes, therefore they can manufacture some of the protons involved in the LDR