3.2 Photosynthesis Uses Light Energy To Synthesise Organic Molecules

Question 1

Equation for photosynthesis is

Answer 1

6CO2 + 6H2O –> C6H12O6 + 6O2

Question 2

Some leaf adaptations include

Answer 2

• large surface area to capture light
• have stomata so gases can diffuse
• has airspaces between cells so CO2 can diffuse to the photosynthesising cells
• most chlorophyll is found in the palisade mesophyll
• palisade cells are arranged vertically which allows more light to be absorbed

Question 3

Adaptations of the chloroplast for photosynthesis

Answer 3

• large surface area to maximise light absorption
• can move within the palisade cells to maximise light absorption

Question 4

Chloroplasts contain pigments such as

Answer 4

Chlorophylls - a and b
Carotenoids - xanthophylls, B-carotene

Question 5

Which pigments are accessory pigments

Answer 5

Carotenoids

Question 6

Function of a pigment

Answer 6

Absorb light energy

Question 7

Why are several pigments used

Answer 7

Allow the plants to absorb a wider range of wavelengths of light

Question 8

Chloroplasts are transducers which means

Answer 8

They change energy from light energy to chemical energy

Question 9

what did the Engelmann experiment discover

Answer 9

The site of photosynthesis

Question 10

What happened in the Englemann experiment?

Answer 10

• A light was shone through a prism to separate the different wavelengths of light
• this light was exposed to a suspension of algae with evenly distributed, motile, aerobic bacteria
• after time the bacteria had congregated around the algae exposed to the blue and red regions because this algae photosynthesised more and so produced more oxygen with would attract more bacteria

Question 11

What does Rf stand for and what it the equation

Answer 11

• the movement of the pigment/solute relative to the solvent
• must be equal or less than 1
• Rf= distance moved by solute/distance moved by solvent

Question 12

In chromatography what kind of molecules travel further?

Answer 12

Smaller

Question 13

What is the absorption spectrum?

Answer 13

a graph that shows how much light energy is absorbed at different wavelengths.

Question 14

What is the action spectrum

Answer 14

a graph that shows the rate of photosynthesis at different wavelengths.

Question 15

What is an antenna complex

Answer 15

an array of protein and pigment molecules in the thylakoid membranes with chlorophyll a at the reaction centre. It transfers energy from light of a range of wavelengths to chlorophyll a.

Question 16

What does the reaction centre contain

Answer 16

2 chlorophyll a molecules

Question 17

Where does the light dependent stage occur

Answer 17

Thylakoid membrane

Question 18

Describe what happens in the light dependent stage
Non-cyclic photophosphorylation

Answer 18

1. Photons of light energy are absorbed by chlorophyll a in PSII and each has one electron boosted to an excited state
2. Electrons are accepted by an electron carrier in the thylakoid membrane
3. The oxidised chlorophyll removes electrons from water which produces protons and oxygen through photolysis which occurs in the thylakoid space
4. As electrons pass from carrier to carrier the electron energy is lost which pumps protons from the stroma into the thylakoid space. As protons flow back through the stalked particle 2ATP are made
5. Electrons enter PSI where light excites them which boosts them to an even higher energy level
6. Electrons enter a final electron acceptor and the electrons and protons reduce NADP to NADPH which pass to the Calvin cycle with the 2ATP made

Question 19

Describe what happens in the light dependent stage
cyclic photophosphorylation

Answer 19

Excited electrons from PSI can pass from the electron acceptor to the electron carriers and back through the proton pump to PSI
No PSII, oxygen, NADPH
1 ATP is made

Question 20

Where does the light independent stage occur

Answer 20

Stroma

Question 21

Describe what happens in the Calvin cycle

Answer 21

1. CO2 diffuses into the leaf through the stomata and dissolves in the water surrounding the palisade mesophyll cells before diffusing into the cells
2. Carbon fixation - CO2 combines with ribulose biphosphate using the enzyme RuBisCO to form an unstable 6C compound
3. The unstable 6C compound immediately breaks down into 2 molecules of glycerate 3-phosphate
4. using 1 ATP molecule and 1 NADPH from the light dependent stage, GP is reduced to triose phosphate
5. Through a complex series of reaction most of the triose phosphate is converted into ribulose-5-phosphate
6. RuBp is regenerated from ribulose-5-phosphate using ATP as a source of phosphate
7. From TP glucose, lipids, nucleic acids and amino acids can be manufactured

Question 22

How was the sequence in the Calvin cycle discovered

Answer 22

Using Calvin’s lolipop
• used radioactive 14C in hydrogen carbonate
• at regular intervals the sample was removed into hot methanol (kill algae and stop all reactions)
• then chromatography was used to identify the products by exposing it to X-ray film and detect the products containing 14C and the order they were produced

Question 23

How can carbohydrates be synthesised from the Calvin cycle

Answer 23

2 Triose phosphate can from fructose phosphate which can be converted to glucose

Question 24

How can lipids be synthesised from the Calvin cycle

Answer 24

Glycerate 3-phosphate can form fatty acids
Triose phosphate can form glycerol

Question 25

How can proteins be synthesised from the Calvin cycle

Answer 25

Glycerate 3-phosphate can form the amino acids
ALSO will need a nitrogen from nitrate ions

Question 26

Effect of CO2 on photosynthesis

Answer 26

Low - limiting factor
High - plateau (another limiting factor)
Higher - stomata close

Question 27

Effect of light intensity on photosynthesis

Answer 27

Low - limiting factor
High - plateau
Higher - decrease in rate as it bleaches the pigments

Question 28

Effect of temperature on photosynthesis

Answer 28

Low - limiting factor, low kinetic energy
High - up to optimum, no plateau
Higher - low, denatured enzyme

Question 29

What is the compensation point

Answer 29

When CO2 uptake is 0
The plant uses all the CO2 produced in respiration in photosynthesis

Question 30

When does the compensation point happen

Answer 30

Night and dawn

Question 31

Inorganic nutrients plants need

Answer 31

Nitrogen
Magnesium

Question 32

Mineral ions of nitrogen

Answer 32

Nitrates
Ammonium ions

Question 33

Use of nitrogen in plants

Answer 33

Synthesis of proteins, nucleic acids and chlorphyll

Question 34

Effect of a deficiency of nitrogen

Answer 34

Stunted growth
Chlorosis

Question 35

Magnesium mineral ions

Answer 35

Mg2+

Question 36

How is magnesium used by plants

Answer 36

Used as a component of chlorophyll and is an enzyme cofactor

Question 37

Effect of deficiency of magnesium on a planet

Answer 37

Chlorosis