5.5: Photosynthesis (new)

Question 1

What are the organelles that make up a chloropast?

Answer 1

• Thylakoids
• Grana
• Lamellae
• Stroma
• Strarch grains
• Ribosomes
• Chloropast DNA

Question 2

What are the main roles of the chloroplast?

Answer 2

• Absorb light energy to drive photosynthesis
• Convert light energy into chemical energy

Question 3

What are thylakoids?

Answer 3

Flattened sacs that contain complexes of pigments like chlorphyll in their membranes to absorb light for the light dependent reaction

Question 4

What are grana?

Answer 4

Stacks of thylakoids

Question 5

What are lamellae?

Answer 5

Membraneous extentions that connect thylakoids

Question 6

What are stroma?

Answer 6

Fluid surrounding the thylakoids where the light dependent reaction occurs

Question 7

What are starch grains?

Answer 7

Store sugars

Question 8

What are chlorplast DNA?

Answer 8

Genes that code for protein involved in photosynthesis

Question 9

List the four main photosynthetic pigments?

Answer 9

• Chlorophyll A
• Chlorophyll B
• Xanthophylls and caretenoids

Question 10

What is chlorophyll a?

Answer 10

The main pigment that absorbs red and blue light and reflects green light

Question 11

What is chlorophyll b?

Answer 11

An accessory pigment mostly found with chlorophyll a

Question 12

What is xanthophyll and carotenoids?

Answer 12

Absorb different wavelengths than chlorophyll, broadening the spectrum of light that can drive photosynthesis.

Question 13

Where are photosystems?

Answer 13

Embedded in the thylakoid membrane

Question 14

What do photosystems contain?

Answer 14

• A light harvesting system - contains pigments
• A reaction centre - contains two chlorophyll a molecules

Question 15

What is the balanced photosynthesis equation?

Answer 15

6CO2 + 6H2O → C6H12O6 + 6O2

Question 16

What is the direction of the light in the photosystem?

Answer 16

Light harvesting system absorbs light energy
This is transferred to the reaction center which emits high energy electrons to drive the light dependent reactions

Question 17

What are photosystems?

Answer 17

A protein/antenna commplex in the membrane that contains pigments

Question 18

What are the adaptations of photosystems?

Answer 18

• Large antenna complex - increases the area over which photons can be harvested
• Accessory pigments - can catch a greater range of wavelengths of light

Question 19

What is a photon?

Answer 19

A particle of light, each contains a quantam of energy

Question 20

What is a compensation point?

Answer 20

When photosynthesis and respiration are equal

Question 21

What is a compensation period?

Answer 21

Time taken to reach compensation point
Different in different species
Shade adpated plants reach theirs later (when light is dim)

Question 22

What is part of the light dependent stage and where does it occur?

Answer 22

Happens in the thylakoid membrane

1. The light harvesting photosystem
2. Photolysis
3. Photophosphorylation (cyclic and non cyclic)
4. Formation of NADPH and oxygen (waste product of photosynthesis)

Question 23

What are the two photosystems and their wavelengths?

Answer 23

• Photosystem I -700nm
• Photosystem II - 680nm

Question 24

What are the steps of non cyclic photophosphorylation?

6 steps

Answer 24

1. Energy from photons is transferred to chla in PSII
2. The energy excites electrons, causing two electrons to leave chla in photosystem II
3. Electrons flow down the e.t.c via acceptors and lose energy as they do. Energy is used to phosphorolyse ADP
4. Electrons flow to PSI chla where they replace electrons that have also been excited by light
5. Electrons leave PSI with more energy than PSII (some is used for photolysis
6. The excited electron pair are passed on to the final electron acceptor molecule NADP. Reduces NADP into NADPH

Question 25

What are the steps of chemiosmosis? | 6 steps

Answer 25

1. The energy lost by electrons along the electron transport chain is used to pump protons across the thylakoid membrane into the thylakoid space 2. This produces a proton gradient, where they are in a higher concentration in the thylakoid space. 3. The protons then diffuse through ATP synthase into the stroma 4. This movement powers ATP synthase to produce ATP from ADP and an inorganic phosphate 5. NADP takes up protons and electrons from PSI in the stroma and is reduced. 6. Reduced NADP is carried into the light-independent reaction

Question 26

What is cyclic phosphorylation? | 4 steps

Answer 26

1. Energy from photons is transerred to chla in PSI 2. Energy excites electrons, causing 2 electrons to leave chla in PSI 3. Electrons flow down e.t.c via accepters and lose energy. Energy is used to phosphorolyse ADP 4. The electrons then return to PSI and begin the cycle again

Question 27

What is photolysis and where is it?

Answer 27

* Energy from photons split water * Only at PSI * Oxygen evolving complex - special enzyme that can split water It is only found in PSII which is why we start there

Question 28

Compare cyclic and non cyclic photophosphorylation: * Photosystem * Products * Photolysis

Answer 28

Cyclic: * PSI * ATP * No Non cyclic * PSII & PSI * ATP and reduced NADP * Yes

Question 29

What is part of the light independent reaction and where does it occur?

Answer 29

* Happens in the stroma of the chloroplast 1. Calvin cycle 2. Formation of carbohydrate

Question 30

What happens in the Calvin cycle? | 5 steps

Answer 30

1. CO2 (1C) reacts with RuBP (5C) which is catalysed by the enzyme Rubisco 2. Forms an unstable 6 carbon compound that then splits into 2GP (3C) 3. GP is then reduced into TP, using the energy from ATP being hydrolysed into ADP + Pi 4. Also using the protons from NADP being reduced 5. In 10 of every 12 TP molecules, the atoms are rrearranged to regenerate 6 molecules of RuBP

Question 31

What is glucose and TP used for?

Answer 31

Glucose: * Converted to sucrose * Starch * Cellulose TP * Synthesise amino acids * Fatty acids * Glycerol