chloroplasts and photosystems

Question 1

What are the adaptations of a leaf for photosynthesis? (5)

Answer 1

1. Thin structure allows rapid light penetration,
2. Waxy cuticle prevents water loss,
3. Upper epidermis is transparent to allow light through,
4. Chloroplasts in the palisade mesophyll can move to optimise light absorption,
5. Spongy mesophyll has air spaces to allow rapid gas exchange

Question 2

What are the two main stages of photosynthesis and where do they take place in the chloroplast? (2)

Answer 2

1. Light-dependent reactions = takes place in the thylakoid membranes,
2. Light-independent reactions (Calvin Cycle) = occur in the stroma

Question 3

How does the shape of the chloroplast contribute to its function? (2)

Answer 3

1. The small, flattened disc shape,
2. Provides a large surface area for light absorption

Question 4

What is the role of the chloroplast envelope? (2)

Answer 4

1. The chloroplast envelope is a double membrane,
2. That controls the substances entering and leaving the chloroplast

Question 5

Why do chloroplasts contain DNA and ribosomes? (2)

Answer 5

1. To quickly manufacture proteins involved in the light-dependent reaction,
2. Such as RuBisCo

Question 6

What is the function of thylakoids in the chloroplast? (4)

Answer 6

1. Thylakoids are fluid-filled sacs stacked to form grana, which are linked by lamellae,
2. The thylakoid membranes provide a large surface area,
3. For the attachment of chlorophyll, electron carriers, and enzymes required for the light-dependent reactions,
4. They are selectively permeable, allowing a concentration gradient to exist

Question 7

What is the role of the stroma in the chloroplast? (3)

Answer 7

1. A fluid-filled matrix containing all the enzymes and organic acids needed for the light-independent reaction,
2. It also contains enzymes required for starch synthesis and breakdown,
3. As carbohydrates produced by photosynthesis and not used immediately are stored as starch grains

Question 8

How does the stroma support the light-dependent reactions? (2)

Answer 8

1. Surrounds the grana,
2. Allowing the products of the light-dependent reactions to diffuse into the stroma easily

Question 9

Where do the light-dependent reactions of photosynthesis occur? (1)

Answer 9

In the thylakoid membranes of the chloroplast

Question 10

Where do the light-independent reactions (Calvin Cycle) of photosynthesis occur? (1)

Answer 10

In the stroma of the chloroplasts

Question 11

What are photosynthetic pigments, and why are they important in photosynthesis? (3)

Answer 11

1. Coloured substances that absorb light energy for photosynthesis,
2. Having more than one pigment allows the plant to absorb a wider range of wavelengths,
3. E.g., chlorophyll a, chlorophyll b, carotene

Question 12

Where are photosynthetic pigments found, and how are they organised? (3)

Answer 12

1. Found in the thylakoid membranes of the chloroplasts,
2. Where they are attached to proteins,
3. Together, the pigment and the protein form a photosystem

Question 13

What are the two types of pigments in photosystems? (4)

Answer 13

1. Primary pigments,
2. Reaction centres where electrons are excited during the light-dependent reactions,
3. Accessory pigments,
4. Make up the light-harvesting system, surrounding reaction centres and transferring light energy to boost electron excitement

Question 14

What are the two types of photosystems used by plants? (4)

Answer 14

1. Photosystem I (PSI):,
2. Absorbs light best at a wavelength of 700nm,
3. Photosystem II (PSII):,
4. Absorbs light best at a wavelength of 680nm