17.3 Photosynthesis

Question 1

Define an autotroph.

Answer 1

Organisms capable of synthesising their own organic compounds from inorganic ones

Question 2

What do you call organisms that can photosynthesise?

Answer 2

Autotrophic

Question 3

Give examples of autotrophic organisms.

Answer 3

Plants, algae

Question 4

What are heterotrophic organisms?

Answer 4

Animals - Obtain organic molecules by consuming other organisms

Question 5

State the WORD equation for photosynthesis and then state the SYMBOL equation for photosynthesis.

Answer 5

Carbon dioxide + water → glucose + oxygen

6CO2 + 6H20 → C6H12O6 + 6O2

Question 6

What is the function of the network of membranes (thylakoids) inside the chloroplast?

Answer 6

Provide a large SA for maximum light absorption

Question 7

Why are there different colour of pigments?

Answer 7

Each pigment absorbs specific wavelengths of light and reflects others

Question 8

What are the 2 common pigments?

Answer 8

Chlorophyll a, primary pigment

Cholorophyll b, other pigment

Question 9

Why do plants have different shades and colours of leaves?

Answer 9

They have a combination of pigments

Question 10

Where is cholorophyll b and other pigments found?

Answer 10

Thylakoid membranes

Question 11

What is the role of a light harvesting system?

Answer 11

Absorb different wavelengths of light and transfer the energy to the reaction centre, where photosynthetic reactions occur

Question 12

What makes a photosystem?

Answer 12

Light harvesting system + reaction centre

Question 13

What are the 2 stages of photosynthesis? Include a description.

Answer 13

1. Light-dependent stage - energy from sunlight is absorbed and used to form ATP. H from water used to reduce coenzyme NADP into reduced NADP
2. Light-independent stage - H from reduced NADP and CO2 is used to build organic molecules, e.g. glucose, supplied by energy from ATP

Question 14

What are the photosystems involved in non-cyclic photophosphorylation? What wavelengths do they absorb?

Answer 14

PSII = 680 nm
PSI = 700 nm

Question 15

What are the 6 stages of non-cyclic photophosphorylation?

Answer 15

1. Light absorbed excites electrons in reaction centres of photosystems
2. Excited electrons are released from reaction centre of PSII and passed to ETC. ATP produced by chemiosmosis
3. Electrons lost from PSII are replaced by electrons from photolysis
4. Excited electrons are released from PSI, passed into ETC, and ATP is synthesised by chemiosmosis
5. Electrons lost from PSI are replaced by electrons released from PSII
6. Coenzyme NADP accepts electrons released from PSI and a H ion, to form NADPH

Question 16

What is the function of NADPH?

Answer 16

Provides reducing power in production of organic molecules, e.g. in light-independent stage

Question 17

What happens in cyclic photophosphorylation?

Answer 17

Electrons leaving PSI are returned back to PSI instead of used to form NADPH.
So PSI can still lead to production of ATP without electrons needed from PSII.

Question 18

What are the 3 steps of cyclic photophosphorylation Type 1 Diabetic gave us?

Answer 18

1. PSI electrons pass into carrier
2. Electron is cycled back to PSI releasing energy
3. Released energy is used to pump H ions into thylakoid space

Question 19

Where does the Calvin cycle occur?

Answer 19

Stroma

Question 20

What does the Calvin cycle use as raw material?

Answer 20

CO2

Question 21

What are the 4 steps of Calvin cycle?

Answer 21

1. CO2 enters spongy mesophyll through stomata by diffusion
2. Carbon fixation - CO2 enters stroma and combines w/ 5-C RuBP, catalysed by RuBisCO
3. 6-C unstable intermediate is produced, which instantly breaks down into 2 GP
4. Each GP turns into TP, using H from NADPH for reduction

Question 22

What molecules can be formed through the calvin cycle?

Answer 22

Amino acids, lipids, glucose