Chapter 2 Photosynthesis

Question 1

How is the leaf adapted for photosynthesis?

Answer 1

• A large SA to capture as much light as possible
• Thin shape allows light to penetrate through the leaf
• Stomatal pores and air spaces in the spongy mesophyll to allow gas exchange required for Calvin cycle
• clear waxy layer on surface to allow light to penetrate through leaf
• upper palisade cells packed with chloroplasts

Question 2

Define photo phosphorylation

Answer 2

An endergonic reaction bonding a phosphate ion to a molecule of ADP using energy from light, making ATP.

Question 3

Describe the structure of chloroplast

Answer 3

Chloroplast

Question 4

How are chloroplast biological transducers?

Answer 4

Converts energy in the photons of light into chemical energy, made available through ATP

Question 5

Where are photosynthetic pigments found in the chloroplast?

Answer 5

Within the thylakoid membrane

Question 6

What are the two types of pigment?

Answer 6

Chlorophyll and carotenoids

Question 7

What are the 2 types of chlorophyll and what colour are they?

Answer 7

Chlorophyll a (yellow-green)
Chlorophyll b (blue-green)

Question 8

What are the two types of carotenoids and what colour are they?

Answer 8

Beta carotene (orange)
Xanthrophylls (yellow)

Question 9

What is an absorption spectrum?

Answer 9

A graph showing how much light is absorbed at different wavelengths.

Question 10

What is an action spectrum?

Answer 10

A graph showing the rate of photosynthesis at different wavelengths.

Question 11

Where are photosystems located?

Answer 11

Thylakoid membrane

Question 12

What does a photosystem contain?

Answer 12

An antenna complex, a reaction centre (photosystem I or II)

Question 13

What is an antenna complex?

Answer 13

An array of protein and pigment molecules in the thylakoid membranes of the grana that transfer energy from light to chlorophyll a at the reaction centre.

Question 14

What are the features of photosystem I?

Answer 14

Arranged around a chlorophyll a molecule with an absorption peak of 700nm. It is also called P700.

Question 15

What are the features of photosystem II?

Answer 15

Arranged around a molecule of chlorophyll a with an absorption peak of 680nm. It is also called P680

Question 16

Why is chlorophyll a the most significant molecule of the reaction centres?

Answer 16

It passes energy to the subsequent reactions of photosynthesis

Question 17

What are the differences between cyclic and non-cyclic photophosphorylation?

Answer 17

In cyclic, Electrons flow from PSI to the electron acceptor and back while electrons in non-cyclic go straight to the stroma from the thylakoid to NADP

Question 18

What is the role of photoloysis of water in the light dependent stage?

Answer 18

When water molecules absorb light, they split into hydrogen, oxygen and electrons. Electrons replace the ones lost in PSI. The hydrogen reduces NADP. Oxygen diffuses out of the stomata of the plant as waste.

Question 19

How is ATP made by cyclic photophosphorylation?

Answer 19

As light hits PSI, it excites the electrons in molecules of chlorophyll a causing them to be emitted. The electrons are carried by electron acceptors, releasing energy that power proton pumps. An electrochemical gradient of hydrogen ions across the thylakoid membrane is made. As the H+ flow down the gradient passing through ATP synthetase, ADP is phosphorylated to ATP

Question 20

How is ATP made by non-cyclic photophosphorylation?

Answer 20

Electrons emitted from PSII is carried by electron acceptors, releasing energy that power proton pumps. An electrochemical gradient of hydrogen ions across the thylakoid membrane is made. As the H+ flow down the gradient passing through ATP synthetase, ADP is phosphorylated to ATP. The electrons then enter PSI. The electrons from PSI and the photolysis of water reduce NADP.

Question 21

Where does the light independent reaction take place?

Answer 21

Stroma

Question 22

What are the products of the light independent reactions?

Answer 22

Glucose

Question 23

Outline the Calvin cycle

Answer 23

Ribulose biphosphate combines with CO2 catalysed by RuBisCo forming a 6-C compund. The compund is unstable and breaks down into 2 molecules of glycerate-3-phosphate (GP). GP is is reduced to triose phosphate by reduced NADP, using energy from the light dependent stage. NADP is reformed. Most of the triose phospate is converted to glucose phosphate and then starch by condensation. Some triose phosphate goes through several reactions and regenerates the ribulose biphosphate, so the cycle can continue