Photosythesis

Question 1

What are the 2 reactions in photosynthesis?

Answer 1

Light-dependent
Light-independent

Question 2

Where does the light dependent reaction take place?

Answer 2

Thylakoid membrane in the chloroplast

Question 3

Where does the light independent reaction take place?

Answer 3

Stroma in the chloroplast

Question 4

Thylakoid membrane

Answer 4

Folded membranes containing photosynthetic proteins
(chlorophyll)
embedded with transmembrane electron carrier proteins
involved in the LDRs

Question 5

What is the advantage of having many pigments from chlorophyll?

Answer 5

Each pigment absorbs a different wavelength of visible light
many pigments maximises spectrum of visible light absorbed
maximum light energy taken in
so more photoionisation and
higher rate of photosynthesis

Question 6

Light dependent reaction

Answer 6

First stage of photosynthesis
occurs in thylakoid membranes
uses light energy and water to create ATP and reduced NADP for LIR
involves photoionisation of chlorophyll, photolysis and chemiosmosis

Question 7

Photolysis

Answer 7

Light energy is absorbed by the chlorophyll and splits water into oxygen, a proton and an electron

Question 8

products of photolysis

Answer 8

protons - combine with coenzyme NADP to produce reduced NADP
electrons - passed along electron transport chain
oxygen - used in respiration or diffuses out leaf via stomata

Question 9

Photoionisation of chlorophyll

Answer 9

Light energy absorbed by chlorophyll excites electrons so they move to a higher energy level and leave chlorophyll

Question 10

Chemiosmosis

Answer 10

Electrons that gained energy move along a series of electron carriers in thylakoid membrane release energy as they go along which pumps proteins across thylakoid membrane
electrochemical gradient made protons pass back across via ATP synthase, producing ATP, down their conc. gradient

Question 11

Light independent reaction

Answer 11

Calvin cycle
uses CO2, reduced NADP and ATP to form hexose sugar
occurs in stroma which contains the enzyme Rubisco
temperature-sensitive

Question 12

calvin cycle

Answer 12

CO2 reacts with ribulose Bisphosphate ( RuBP) and catalysed by rubisco to form 2 molecule of Glycerate-3-Phosphate (GP)
GP is reduced to triose phosphate by the energy from ATP and the proton from reduced NADP
Some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances
The rest of the molecule is used to regenerate RuBP, with the energy released from the hydrolysis of ATP

Question 13

Producing a hexose sugar in LIR

Answer 13

takes 6 cycles
glucose can join to form disaccharides (sucrose) or polysaccharides (cellulose)
can be converted to glycerol to combine with fatty acids to make lipid

Question 14

What is a limiting factor?

Answer 14

A factor which, if increased, the rate of the overall reaction also
increases

Question 15

What are the limiting factors of photosynthesis?

Answer 15

Light intensity
CO2 concentration
temperature

Question 16

How does light intensity limit the rate of photosynthesis?

Answer 16

If reduced, levels of ATP and reduced NADP would fall
LDR limited - less photolysis and photoionisation
GP cannot be reduced to triose phosphate in LIR

Question 17

How does CO2 conc limit the rate of photosynthesis?

Answer 17

If reduced, LIR inhibited
less CO2 to combine with RuBP to form GP
less GP reduced to TP
less TP converted to hexose and RuBP regenerated

Question 18

How does temperature limit the rate of photosynthesis?

Answer 18

LIR inhibited - enzyme controlled (Rubisco)
up to optimum, more collisions and E-S complexes
above optimum, H-bonds in tertiary structure break, active site changes shape - denatured

Question 19

What are some agricultural practices to maximise plant growth?

Answer 19

Growing plants under artificial lighting to maximise light intensity
heating in greenhouse to increase temperature
burning fuel to release CO2

Question 20

What are the benefits of the agricultural practises?

Answer 20

Faster production of glucose = faster respiration
more ATP to provide energy for growth e.g. cell division and
protein synthesis
higher yields so more profit