C1.3 Photosynthesis

Question 1

What is photosynthesis?

Answer 1

Synthesis of food in a series of reactions using light energy and carbon dioxide.

Question 2

What type of energy conversion occurs during photosynthesis?

Answer 2

Light energy to chemical energy.

Question 3

Where is the chemical energy from photosynthesis stored?

Answer 3

Biomass, within the bonds of the organic compounds.

Question 4

What are the raw materials of photosynthesis?

Answer 4

Carbon dioxide and water.

Question 5

What are the products of photosynthesis?

Answer 5

Glucose and oxygen.

Question 6

What are autotrophs?

Answer 6

Organisms that make their own food.

Question 7

Which type of organisms carry out photosynthesis?

Answer 7

Plants, algae, and cyanobacteria.

Question 8

What is a heterotroph?

Answer 8

An organism that obtains its food from other organisms.

Question 9

Why do chloroplasts contain pigments?

Answer 9

To absorb light energy for photosynthesis.

Question 10

Why do chloroplasts contain multiple photosynthetic pigments?

Answer 10

To absorb a wide range of wavelengths to ensure efficient photosynthesis.

Question 11

How is oxygen produced during photosynthesis?

Answer 11

By the splitting of water.

Question 12

What is the main photosynthetic pigment?

Answer 12

Chlorophyll.

Question 13

What colour of visible light has the shortest wavelength?

Answer 13

Violet (400nm).

Question 14

What colour has the longest wavelength?

Answer 14

Red (700nm).

Question 15

How does light wavelength affect photosynthesis?

Answer 15

Absorption of light varies with wavelength, affecting the rate of photosynthesis.

Question 16

How do pigments absorb visible light?

Answer 16

The pigment molecules absorb photons, causing an electron to become ‘excited’ and jump to a higher energy level.

Question 17

Which wavelengths do not provide enough energy to ‘excite’ an electron?

Answer 17

Green (so it is not absorbed).

Question 18

What are the two main groups of pigments?

Answer 18

Chlorophylls and carotenoids.

Question 19

What do carotenoids do?

Answer 19

Surround chlorophyll and absorb similar & different wavelengths of light, expanding the range of absorbed wavelengths.

Question 20

What is an absorption spectrum?

Answer 20

Shows how much light is absorbed by different pigments at different wavelengths.

Question 21

What is an action spectrum?

Answer 21

A graph that shows the rate of photosynthesis at different wavelengths of light.

Question 22

What are the similarities between an absorbance spectrum and an action spectrum?

Answer 22

Both have two main peaks (at blue-violet and red regions) and a trough in the green-yellow region.

Question 23

What wavelengths does chlorophyll absorb?

Answer 23

Blue-violet and red (green is reflected).

Question 24

What wavelengths do carotenoids absorb?

Answer 24

Mainly blue-violet range.

Question 25

What wavelengths produce the highest rates of photosynthesis?

Answer 25

Blue-violet and red.

Question 26

What are the two types of chromatography?

Answer 26

Paper chromatography and thin-layer chromatography.

Question 27

What are photosystems?

Answer 27

Clusters of chlorophyll and accessory pigments, with a reaction centre that absorbs light and emits an excited electron.

Question 28

Where are photosystems located?

Answer 28

Thylakoid membrane.

Question 29

What processes take place in the thylakoid membrane?

Answer 29

Light-dependent reactions: Photolysis of water, synthesis of ATP by chemiosmosis, reduction of NADP.

Question 30

What is photolysis?

Answer 30

The splitting of water using light energy, producing protons, electrons, and oxygen.

Question 31

Where does photolysis occur exactly?

Answer 31

Photosystem II.

Question 32

What is the chemical equation of photolysis?

Answer 32

2H₂O → O₂ + 4H⁺ + 4e⁻.

Question 33

What are the electrons produced by photolysis used for?

Answer 33

Replacement of electrons lost from the reaction centre in photosystem II and subsequent reactions of the light-independent reaction.

Question 34

What is chemiosmosis?

Answer 34

Movement of protons across a membrane, driving ATP synthesis.

Question 35

What is the role of the proton gradient in the thylakoid membrane?

Answer 35

The proton gradient powers ATP synthase to produce ATP.

Question 36

What is the function of ATP synthase?

Answer 36

It synthesises ATP from ADP and inorganic phosphate, using energy from the proton gradient.

Question 37

Define photophosphorylation.

Answer 37

Light energy being used to phosphorylate ADP to produce ATP.

Question 38

What are the two types of photophosphorylation?

Answer 38

Cyclic (only photosystem I involved) and non-cyclic (both photosystem I and II).

Question 39

What is the main purpose of non-cyclic photophosphorylation?

Answer 39

To produce ATP, NADPH, and O₂, which are needed for the Calvin cycle.

Question 40

What happens to electrons in non-cyclic photophosphorylation?

Answer 40

Electrons are excited in PSII, travel through the electron transport chain to PSI, and reduce NADP⁺ to NADPH.

Question 41

Why does cyclic photophosphorylation occur?

Answer 41

When the plant needs more ATP than NADPH or when the Calvin cycle runs out of NADP+.

Question 42

How does cyclic photophosphorylation differ from non-cyclic photophosphorylation?

Answer 42

Uses only Photosystem I, only ATP is produced, and no water is split.

Question 43

Describe how NADP is reduced during the light-dependent reactions.

Answer 43

NADP+ gains two electrons from photosystem I and one proton from the stroma to become NADPH.

Question 44

What are the useful end-products of the light-independent reactions?

Answer 44

ATP & reduced NADP (NADPH).

Question 45

Is the oxygen produced during the light-independent reactions a useful or waste product?

Answer 45

A waste product.

Question 46

Describe the function of Rubisco.

Answer 46

The enzyme responsible for carbon fixation in the Calvin cycle, attaching CO2 to RuBP.

Question 47

Where do the light-independent reactions/Calvin cycle take place?

Answer 47

Stroma of chloroplasts.

Question 48

What are the three main phases of the Calvin cycle?

Answer 48

1. Carbon fixation - CO2 combining with RuBP using Rubisco. 2. Synthesis of triose phosphate. 3. Regeneration - some triose phosphates leave to form glucose.

Question 49

What are the main products of the Calvin cycle?

Answer 49

Glucose, regenerated RuBP, ADP, and NADP+.

Question 50

Why is the Calvin Cycle a cycle?

Answer 50

Because it starts and ends with the same molecule.

Question 51

Why do light-independent reactions stop when there is no light?

Answer 51

Because they need ATP and NADPH produced by light-dependent reactions.

Question 52

Define carbon fixation.

Answer 52

When CO2 is attached to an organic molecule (RuBP) in photosynthesis.

Question 53

Describe the regeneration of RuBP in the Calvin cycle.

Answer 53

5 triose phosphate molecules are converted to 3 RuBP molecules.

Question 54

How many turns of the Calvin cycle are needed to produce 1 molecule of glucose?

Answer 54

6 turns.

Question 55

What fraction of triose phosphate is used to regenerate RuBP?

Answer 55

5/6 (1/6 used to synthesis organic molecules like glucose).

Question 56

What products, other than glucose, are synthesised from Calvin cycle intermediates?

Answer 56

Carbohydrates, amino acids, and other carbon compounds.

Question 57

Why can't the light-dependent reactions continue without CO₂?

Answer 57

The light-independent reactions rely on CO₂, and a lack of it prevents the Calvin cycle from functioning.