Photosynthesis

Question 1

Where do all the reactions in photosynthesis take place?

Answer 1

chloroplast

Question 2

What are the products of the light dependent reaction?

Answer 2

O2
ATP
NADPH

Question 3

What are the products of the light independent reactions?

Answer 3

Glucose
ADP + Pi
NADP (oxidised)

Question 4

What can glucose be used for?

Answer 4

• respiratory substrate
• stored as starch
• converted (e.g. to beta glucose to form cellulose)

Question 5

What is the endosymbiotic theory of the chloroplast?

Answer 5

• That the chloroplast used to be its own free-living bateria until being taken in by a cell and having its photosynthetic ability harnessed for the cells use.
• evidence for this = double membrane, DNA, 70s ribosomes

Question 6

What is the fluid within the chloroplast called?

Answer 6

stroma

Question 7

What is a stack of thylakoids called?

Answer 7

granum

Question 8

What are the ‘branches’ between granum called?

Answer 8

intergranal lammelae

Question 9

Where do the light dependent reactions take place?

Answer 9

thylakoids

Question 10

Where do the light independent reactions take place?

Answer 10

stroma

Question 11

What are some of the structural adaptations of the chloroplast?

Answer 11

• high surface area of thylakoids + densely packed w/ photosystems
• stroma surrounds thylakoids - short diffusion distance

Question 12

What is a photosystem?

Answer 12

The protein within the membrane that carries out the absorption of light

• has multiple different photosynthetic pigments
• increases area over which photons can be harvested

Question 13

What is the difference between the reaction centre pigment and the accessory pigments?

Answer 13

the reaction centre pigment is always chlorophyll A, accessory pigments may not be chlorA (e.g. ChlorB, xanthophyll, carotene, phaeophythn)

Question 14

what is the purpose of accessory pigments?

Answer 14

to catch a greater range of wavelengths of light

Question 15

What is the purpose of Thin Layer Chromatography? (TLC)

Answer 15

To measure the Rf values of different pigments

Question 16

What is the purpose of the Stationary Phase (silica gel) in TLC?

Answer 16

acts as a constraint on the components in the mixture to make them move slower than the mobile phase

Question 17

What is non-cyclic photophosphorylation (NCPP)

Answer 17

photophosphorylation that involves both photosystems 2 and 1, as well as 2 electron acceptors + 2 ETC’s

Question 18

What is the first step in NCPP?

Answer 18

light hits PSII and this causes excitement of 2 electrons, which get accepted by an electron carrier after leaving PSII

Question 19

What is the second step in NCPP?

Answer 19

• electrons are passed down an ETC from the electron carrier, which releases energy to allow ADP + Pi to form ATP
• light also hits PSI, which causes 2 electrons to leave it to be accepted by an electron carrier. However, they are soon replaced by the 2 electrons which originally left PSII

Question 20

What is the third step in NCPP?

Answer 20

like step 1, electrons are passed down another electron transport chain, except this time they are receieved by NADP, the final electron acceptor, which is reduced to form NADPH.

Question 21

What is Cyclic Photophosphorylation?

Answer 21

photophosphorylation that only involves PSI, as well as only 1 ETC and 1 electron acceptor.

Question 22

What are the steps of CPP?

Answer 22

• Electrons from PSI passed to electron acceptor
• Electrons go down ETC, photophosphorylating ADP to form ATP
• Electrons passed back to electron deficient PSI
• cycle continues as long as light is present

Question 23

What is photolysis?

Answer 23

the splitting of water molecules via light energy

- occurs in thylakoid lumen

Question 24

What is H2O split into?

Answer 24

2H+
2e-
1/2 O2

Question 25

compare cyclic and non-cyclic photophosphorylation

Answer 25

NCPP - uses PSII and PSI, has ATP and NADPH as products - involves photolysis - fate of electrons is to go into NADP reductase to form NADPH CPP - uses PSI, has ATP as product - doesn't involve photolysis - fate of electrons is to continue in cycle going from PSI, electron acceptor, to ETC, back to PSI

Question 26

What are the steps of the Calvin Cycle?

Answer 26

1. 6CO2 + 6RuBP -> 6C intermediate (catalysed by RuBisCO) 2. 6C molecule breaks down into 12 G3P molecules (3C) 3. 12 G3P -> 12 TP - turns 12 ATP -> 12 ADP - turns 12 NADPH -> 12 NADP 4. 2 TP (out of 12) moves from Calvin cycle to form glucose etc. the rest stays within the cycle 5. 10 TP converted to 6 RuBP - 6ATP -> 6ADP

Question 27

What is photorespiration?

Answer 27

When RuBisCO adds O2 into the calvin cycle instead of CO2 | - BAD for the plant

Question 28

What happens to Calvin Cycle in low CO2 environment?

Answer 28

Calvin Cycle stops - RuBP builds up, GP + TP levels decrease massively

Question 29

What happens to Calvin cycle in no light environment?

Answer 29

Calvin Cycle stops - GP levels build up, RuBP + TP levels decrease massively (no light = no NADPH input, therefore cycle stops as GP is made)

Question 30

What is a limiting factor?

Answer 30

Any factor that can slow the rate of reaction when in inadequate supply

Question 31

What are the limting factors for photosynthesis?

Answer 31

- CO2 - light - temperature - NOT water - lack of water would kill plant before having an effect on the rate of photosynthesis

Question 32

How do you measure rate of photosynthesis?

Answer 32

using photosynthetometer, measure the length that the bubble has travelled and then the width of the capillary tube using V=πr2h Volume = amount of oxygen evolved use timer - e.g. amount of oxygen evolved in 1 min etc

Question 33

what is the rate of respiration in plants?

Answer 33

constant = PLANTS ALWAYS RESPIRING

Question 34

What is the light compensation point?

Answer 34

When rate of photosynthesis and rate of oxygen production are equal (no net carbohydrate production)