Photosynthesis

Question 1

What is an autotroph?

Answer 1

An organism that synthesises its own nutrients

Question 2

What is a photoautotroph?

Answer 2

An organism that uses light to synthesise nutrients via photosynthesis

Question 3

What is the overall photosynthesis equation?

Answer 3

6CO2 + 6H2O = C6H12O6 + 6O2

remember the devils equation (666)

Question 4

What is a photon?

Answer 4

A particle of light

Question 5

What is carbon fixation?

Answer 5

The process where carbon dioxide is converted to sugars

Question 6

What does Carbon fixation do in terms of the environment?

Answer 6

Helps to regulate CO2 levels in the atmosphere and oceans

Question 7

What is it called when rates of photosynthesis and respiration are equal in a plant?

Answer 7

Compensation point

Question 8

Describe the general structure of a chloroplast

Answer 8

Double membrane with an inter-membrane space

Stroma - a fluid matrix

Grana - Stacks of thylakoid membranes

Inter-granal lamellae - Connect grana together

Question 9

What stage of photosynthesis takes place in the grana?

Answer 9

Light-dependent stage

Question 10

Describe the structure of the thylakoids

Answer 10

A membrane that is folded into a disc-like sac

Question 11

Why are the thylakoids folded?

Answer 11

Provides a large surface area which is important for:

Distribution of photosystems and photosynthetic pigments

Distribution of electron carriers and ATP synthase enzymes

Question 12

Where do the products of the light-dependent stage go?

Answer 12

Diffuse out of thylakoids into stroma

Question 13

What is the stroma made up of?

Answer 13

Enzymes needed to catalyse light independent stage

Starch grains

Oil droplets

Small ribosomes

Question 14

Describe the structure of a Photosystem

Answer 14

A funnel shaped structure in the thylakoid membrane

Contains photosynthetic pigments which absorb specific wavelengths of light

A primary pigments reaction centre at the bottom which is either P700 or P680

Question 15

What are the two types of Chlorophyll a in a photosystem?

Answer 15

P700 and P680

Question 16

Why do photosystems contain a range of pigments?

Answer 16

So the plant can absorb a range of appropriate wavelengths

Question 17

Which photosystem would you find P700 in?

Answer 17

PS1

Question 18

Which photosystem would you find P680 in?

Answer 18

PS2

Question 19

Name 2 accessory pigments?

Answer 19

Carotenoids

Xanthophylls

Question 20

What are the 4 stages of the Light-dependent stage?

Answer 20

Light harvesting in Photosystems
Photolysis of water
Photophosphorylation
Formation of NADPH (reduced NADP)

Question 21

What catalyses Photolysis?

Answer 21

An enzyme in PS2

Question 22

Which Photosystem does photolysis occur in?

Answer 22

PS2

Question 23

Why does photolysis occur?

Answer 23

To provide H+ ions for photophosphorylation

Provide e- to replace lost electrons in photophosphorylation

Question 24

What is photophosphorylation?

Answer 24

Production of ATP from ADP and Pi

Question 25

What are the two types of photophosphorylation?

Answer 25

Non-cyclic | Cyclic

Question 26

Which photosystem (s) does non-cyclic photophosphorylation occur in?

Answer 26

PS1 and PS2

Question 27

Which photosystem (s) does cyclic photophosphorylation occur in?

Answer 27

Only PS1

Question 28

Which type of photophosphorylation produces more ATP?

Answer 28

Non-cyclic

Question 29

Describe the process of Non-cyclic photophosphorylation

Answer 29

In PS2: Photon strikes PS2 and energy is channeled to primary pigment Energy excites a pair of electrons which escape the chlorophyll molecule Electron carrier in thylakoid captures electrons electrons are replaced by those from photolysis Redox reactions pass e- down ETC in thylakoid releasing energy This energy used to pump H+ into the inter-membrane space Protons accumulate in the inter-membrane space forming an electrochemical gradient Protons diffuse via channels associated with ATP synthase stimulating ATP production As H+ passes through channel it is accepted by NADP to form NADPH In PS1: Photon excites an electron that is lost protein-iron-sulphur complex called ferredoxin accepts the electrons and passes them to NADP in the Stroma

Question 30

Describe the process of Cyclic photophosphorylation

Answer 30

Photon excites an electron in PS1 that is lost Pass electron to ETC that then passes it back to PS1 ATP is produced as the electron moves down ETC The cycle continues

Question 31

Where does the light-independent stage occur?

Answer 31

Stroma

Question 32

What are the 2 sources of CO2 for the light independent stage?

Answer 32

From the air, diffuses through the stomata of the leaf From respiration, CO2 produced as a by-product

Question 33

What is the Calvin Cycle?

Answer 33

The series of reactions where CO2 is converted to organic molecules

Question 34

What is the role of RuBP (ribulose bisphosphate)?

Answer 34

A carbon dioxide acceptor

Question 35

What is RuBisCO?

Answer 35

An enzyme that catalyses the reaction between CO2 and RuBP

Question 36

Describe the stages of the Calvin Cycle

Answer 36

CO2 reacts with RuBP to form an unstable 6C compound (catalysed by RuBisCO) 6C compound breaks down into GP, the carbon has now been fixed GP is reduced using H+ from NADPH from the LDR. This makes TP (triose phosphate). This uses ATP from the LDR 10/12 TP molecules are used to reform RuBP, the other 2 are the product.

Question 37

Does the Calvin Cycle run when it is dark?

Answer 37

No, though it doesn't directly use light energy is requires the products of the LDR which does use light energy

Question 38

What are the uses of TP?

Answer 38

Synthesise carbohydrates such as Glucose, Sucrose, Starch and Cellulose Synthesise Amino acids, Fatty acids and Glycerol Reform RuBP

Question 39

What are the main factors affecting photosynthesis?

Answer 39

Light intensity Carbon Dioxide Concentration Temperature Water Stress

Question 40

What is the limiting factor?

Answer 40

It is the factor that is preventing the rate of photosynthesis getting any faster

Question 41

What happens to concentrations of GP, TP and RuBP when light intensity falls?

Answer 41

GP cant be reduced to TP TP levels fall and GP accumulates RuBP falls because there is no TP to regenerate it

Question 42

What happens to concentrations of GP, TP and RuBP when CO2 concentration falls?

Answer 42

RuBP cant accept it No GP formed No TP formed

Question 43

What happens to the rate of photosynthesis at different temperatures?

Answer 43

It is an enzyme catalysed reaction Low temperatures it is slow At optimum (30'C) it is at its fastest Above 45'C enzymes become denatured and reaction slows

Question 44

What happens to rate of photosynthesis when a plant is under water stress?

Answer 44

When plant is under water stress it closes stomata to reduce water loss This also reduces gaseous exchange Makes CO2 less available so photosynthesis greatly decreases