Section 5 - 11 Photosynthesis

Question 1

In what form does energy enter plants?

Answer 1

• Energy in light is absorbed by chlorophyll
• Then transferred into the chemical energy of the molecules formed during photosynthesis.

Molecules used by the plant to produce ATP during respiration. Non-photosynthetic organisms feed on the molecules produced by plants and then also use them to make ATP during respiration.

Question 2

What is the main photosynthetic structure un eukaryotic plants?

Answer 2

The leaf

Chloroplasts are the cellular organelles within the leaf where photosynthesis takes place.

Question 3

Where does photosynthesis occur?

Answer 3

Chloroplasts inside the leaves.

Question 4

What are the raw materials of photosynthesis?

Answer 4

water

carbon dioxide

light

Question 5

What are the products of photosynthesis?

Answer 5

oxygen and glucose

Question 6

List adaptations leaves have made for photosynthesis

Answer 6

Question 7

What is the overall equation for photosynthesis?

Answer 7

Question 8

What are the three main stages of photosythesis?

Answer 8

1. Capturing of light energy
2. The light-dependent reaction
3. the light-independent reaction

Question 9

Explain the first stage of photosynthesis

Answer 9

Capturing of light energy

By chloroplast pigments such as chlorophyll

Question 10

Explain the second stage of photosynthesis

Answer 10

Light-dependent reaction

• Some of the light energy absorbed is conserved in chemical bonds.
• During the process an electron flow is created by the effect of light on chlorophyll causing water to split into protons, electorns and oxygen.
• The products are reduced NADP ATP and oxygen

Question 11

During light-dependent photosynthesis what does water break down into

Answer 11

protons

electrons

oxygen

Question 12

What is photolysis?

Answer 12

In light-dependent reaction of photosythesis

water splitting into protons, electrons and oxygen

Question 13

What are the products of light-dependent reactions?

Answer 13

Reduced NADP

ATP

oxygen

Question 14

What is the third stage of photosythesis?

Answer 14

Light-independent reaction

Protons - hydrogen ions used to prodcue sugars and other organic molecules

Question 15

What are the products of light-independent reaction?

Answer 15

Sugars and other organic molecules

Question 16

What are the two distinct regions inside the chloroplast membranes?

Answer 16

• The grana
• The stroma

Question 17

What is grana?

Answer 17

Stacks of up to 100 disc-like structures of thylakoids.

Question 18

What is thylakoids?

Answer 18

Where the light-dependent stage of photosynthesis occurs.

Contains the photosynthetic pigment chlorophyll.

Question 19

What is intergranal lamellae?

Answer 19

Thylakoids that have tubular extentions that join up with thylakoids in adjacent grana.

Question 20

What is the stroma?

Answer 20

A fluid-filled matrix where the light-independent stage of photosynthesis takes place.

Within the stroma are a number of other structures such as starch grains.

Question 21

Where do light-dependent reactions of photosynthesis occur?

Answer 21

Thylakoids in the grana.

Question 22

Where does the light-independent stage of photosynthesis occur?

Answer 22

The stroma

Question 23

For what purposes is energy captured in the light-dependent reaction of photosynthesis?

Answer 23

• To add an inorganic phosphate molecule to ADP, thereby making ATP
• Split water into H+ ions (protons) and OH- ions, As the splitting is caused by the light it is known as photolysis.

Question 24

What is oxidation?

Answer 24

When a substance gains oxygen or loses hydrogen.

Question 25

What is the reduction?

Answer 25

The process when substance loses oxygen or gain hydrogen.

Question 26

What is the result of oxidation?

Answer 26

Results in energy being given out

Question 27

What is the result of reduction?

Answer 27

Energy being taken away.

Question 28

How happens when chlorophyll absorbs light energy?

Answer 28

* boosts the energy of a pair of electrons within the chlorophyll * This raises them to a higher energy level * These electrons are in an excited state * They become more energetic and leave the chlorophyll molecule * The chlorophyll mole becomes ionised

Question 29

What is the process of photoionisation?

Answer 29

* Light energy boosts the energy of a pair of electrons within the chlorophyll * This raises them to a higher energy level * These electrons are in an excited state * They become more energetic and leave the chlorophyll molecule * The chlorophyll mole becomes ionised

Question 30

What happens to the electrons that leave the chlorophyll in photoionisation?

Answer 30

Taken up by an electron carrier. The chlorophyll molecule is oxides and electron carrier is reduced.

Question 31

Why do electrons in the membranes of the thylakoid lose energy?

Answer 31

* They pass through electron carriers in a series of oxidation-reduction reactions. * These form an electron transfer chain. * Each carrier is at a slightly lower energy level than the previous one in the chain * so electrons lose energy at each stage.

Question 32

What theory is used to explain the process of ATP production?

Answer 32

The chemiosmotic theory

Question 33

What is the chemiosmotic theory?

Answer 33

Makes ATP * Each thylakoid is an enclosed chamber where protons are pumped from the stroma using proton pumps. * The energy to drive process comes from electrons released when water molecules are split by light - photolysis * This produces protons increasing conc. inside thylakoid space * creating and maintaining conc. gradient - high in thylakoid space and low in the stroma * Protons cross thylakoid membrane using ATP synthase channel proteins * As travel through the protons change the structure which catalyses the combination of ADP with inorganic phosphate to form ATP *

Question 34

Why is the chlorophyll short of electrons?

Answer 34

They lose electrons when light strikes a chlorophyll molecule.

Question 35

What is the equation for photolysis of water?

Answer 35

Question 36

Explain the process of photolysis of water

Answer 36

* protons are passed through ATP synthase channels and taken up by an electron carrier called NADP * This makes NADP reduced * Reduced NADP is the main product of the light-dependent stage and it enters the light-independent reaction taking electrons from chlorophyll molecules. *

Question 37

Why is reduced NADP important?

Answer 37

It is a further potential source of chemical energy to the plant.

Question 38

What is a by-product of photolysis of water?

Answer 38

oxygen

Question 39

What is the oxygen from photolysis of water used for?

Answer 39

* Either Respiration * Or diffuses out of the leaf as a waste product of photosynthesis.

Question 40

In what ways has chloroplasts been structurally adapted to their function of capturing sunlight and carrying out the light-dependent reaction of photosynthesis?

Answer 40

* Thylakoid membrane - large SA for attachment of chlorophyll, electron carriers and enzymes * Network of proteins hold chlorophyll to enable maximum absorption of light * Granal membranes have ATP synthase channels - catalysing the production of ATP and creating a proton gradient * Chloroplasts contain DNA and ribosomes so can produce proteins involved in IDR

Question 41

What are the products of the light-dependent reaction of photosynthesis?

Answer 41

ATP and reduced NADP

Question 42

What are the products of the light-dependent reaction of photosynthesis used for?

Answer 42

Products - ATP and reduced NADP Used to reduce glycerate 3-phosphate in the second stage of photosynthesis. - this is in the light-independent reaction.

Question 43

Where does the light-independent reaction of photosynthesis take place?

Answer 43

In stroma of the choloplasts.

Question 44

What process explains the light-independent reactions of photosynthesis?

Answer 44

Calvin Cycle Worked out by Melvin Calvin

Question 45

What are the stages of the Calvin Cycle?

Answer 45

1. CO2 from the atmosphere diffuses into leaf - stomata - dissolves in water around walls of mesophyll cells. 2. Then diffuses through cell-surface membrane, cytoplasm and chloroplast membranes into the stroma of the Coloplast 3. In stroma, CO2 reacts with **5-carbon compound ribulose biphosphate (RuBP)** a reaction catalysed by enzyme - **ribulose bisphosphate carboxylase AKA rubisco** 4. Reactions between CO2 and RuBP produces two molecules of **3-carbon glycerate 3-phosphate (GP)** 5. Reduced NADP from light-dependent reaction is used to reduce glycerate 3-phosphate to **triose phosphate** using energy supplied by ATP. 6. NADP is reformed and used again in light-dependent reaction to be reduced again by accepting more protons 7. some triose phosphate molecules are converted to organic substances that the plant requires such as starch, cellulose, lipids, glucose, amino acids and nucleotides. 8. Most triose phosphate molecules are used to regenerate **riboluse bisphophate** using ATP from the light-dependent reaction.

Question 46

What reacts with CO2 in the light-independent reaction of photosynthesis?

Answer 46

**5-carbon compound ribulose biphosphate (RuBP)**

Question 47

What enzyme is present in the light-independent reaction of photosynthesis?

Answer 47

ribulose bisphosphate carboxylase AKA rubisco

Question 48

What is produced in the reaction between CO2 and RuBP?

Answer 48

two molecules of 3-carbon glycerate 3-phosphate (GP)

Question 49

In what ways is the chloroplast adapted to carry out the light-independent reaction of photosynthesis?

Answer 49

* Matrix contains enzymes for IIR - this is membrane bound in chloroplast so the chemical environment is maintained * Stroma fluid surrounds the grana so products of LDR can easily diffuse into the stroma * Containing both DNA and ribosomes so protein manufacturing is effecient.