3.2 Photosynthesis (Part A)

Question 1

What are Autotrophs?

Answer 1

Organisms that are able to make their own food - using a source of energy to make complex organic molecules from inorganic raw materials.

Question 2

What are the two main autotrophs?

Answer 2

Chemoautotrophs and Photoautotrophs

Question 3

What are Chemoautotrophs?

Answer 3

Able to harness energy from exergonic reactions to synthesise their organic food.

Question 4

An example of a Chemoautotroph?

Answer 4

Bacteria

Question 5

What are Photoautotrophs?

Answer 5

Able to synthesise sugars from carbon dioxide and water, using sunlight as a source of energy

Question 6

Which pigment traps the sunlight in Photoautotrophs?

Answer 6

Chlorophyll.

Question 7

Examples of Photoautotrophs?

Answer 7

Green plants, algae

Question 8

What is the definition of Photosynthesis?

Answer 8

The process by which green plants manufacture their carbohydrates in the chloroplasts from atmospheric carbon dioxide and water, in the presence of sunlight.

Question 9

What is the Photosynthesis equation?

Answer 9

Carbon Dioxide + Water —–> Glucose + Oxygen
(light)

Question 10

Where does Photosynthesis occur?

Answer 10

The ‘green parts’ of the plant that contain chlorophyll.

Question 11

Where is chlorophyll found?

Answer 11

In chloroplasts.

Question 12

Where are chloroplasts found?

Answer 12

In the mesophyll cells and guard cells of green leaves.

Question 13

Which type of energy is trapped by chlorophyll in chloroplasts?

Answer 13

Sunlight energy.

Question 14

What does ‘chloroplasts are transducers’ mean?

Answer 14

They contain chlorophyll, which absorbs light energy, and can convert it to chemical energy. This can then be made available as ATP, and then incorporated into molecules such as glucose.

Question 15

How are leaves adapted for photosynthesis?

Answer 15

• The leaves have a large, flat surface, with chloroplasts located close to the top surface for maximum light absorption
• They allow gas exchange through surface pores called stomata - allow CO2 to diffuse into the leaf
• The leaf have a network of air spaces for gases to reach photosynthetic tissue
• The leaves have a thin structure, since light is only absorbed in the first mm of tissue.

Question 16

How are palisade mesophyll cells adapted for photosynthesis?

Answer 16

• Have lots of chloroplasts - the sites of photosynthesis.
• Thin cellulose cell walls - light is absorbed into cell & absorbed more easily
• Chloroplasts can move around inside - maximum light.
• Elongated shape (in upright position) - allows larger numbers of cells to be packed in a leaf’s given area.

Question 17

Structure of a chloroplast?

Answer 17

• Surrounded by a double membrane
• Inner membrane folds & forms thylakoids
• Thylakoids forms stacks called grana.

Question 18

What is a photosynthetic pigment?

Answer 18

A molecule that absorbs a specific wavelength of light.

Question 19

Why is it useful for different wavelengths of light to be absorbed by different photosynthetic pigments?

Answer 19

It allows for a large range of wavelengths to be absorbed.

Question 20

What are the two main classes of photosynthetic pigments? (In flowering plants)

Answer 20

Chlorophylls & Carotenoids

Question 21

What are the two different types of chlorophylls?

Answer 21

Chlorophyll a & Chlorophyll b

Question 22

What are the two different types of carotenoids?

Answer 22

Beta Carotene & Xanthophylls

Question 23

Which parts of the spectrum do Chlorophyll a & b absorb?

Answer 23

The light in the blue-violet and red parts.

Question 24

Structure of chlorophylls?

Answer 24

• A complex ring structure
• A long hydrocarbon tail
• A magnesium atom at the centre of the ring

Question 25

When do plants start to look yellow?

Answer 25

When there is a lack of magnesium in the soil - they can no longer make green chlorophylls.

Question 26

What is the condition where plants produce insufficient chlorophyll?

Answer 26

Chlorosis - chlorotic leaves can be pale, yellow, or yellow-white

Question 27

Which parts of the spectrum do carotenes and xanthophylls absorb?

Answer 27

The light in the blue-violet part.

Question 28

What is an Absorption Spectrum?

Answer 28

A graph indicating how much light a particular pigment absorbs at each wavelength. (Does not indicate if they are actually used in photosynthesis.)

Question 29

What is an Action Spectrum?

Answer 29

A graph showing the rate of photosynthesis at different wavelengths of light. - Can be produced by measuring the mass of carbohydrates produced at each wavelength.

Question 30

What are the two main stages of Photosynthesis?

Answer 30

1. The light dependent stage
2. The light independent stage.

Question 31

What are the particles in/on a thylakoid membrane called?

Answer 31

Photosystems

Question 32

What do photosystems consist of?

Answer 32

• An antenna complex (a collection of accessory pigments)
• A reaction centre, containing 2 chlorophyll a molecules.

Question 33

How many types of photosystems are there?

Answer 33

2 - Photosystem I and Photosystem II

Question 34

Where does light harvesting take place?

Answer 34

On the thylakoid membranes

Question 35

What does light harvesting involve?

Answer 35

• The absorption of various wavelengths of light by chlorophyll & associated pigments
• The energy transfer to reaction centres

Question 36

What is in an antenna complex?

Answer 36

The pigment molecules in the thylakoid membranes, grouped in clusters of several hundred molecules.

Question 37

What does the antenna complex do?

Answer 37

It harvests light energy & passes the excitation to the reaction centre.