Chloroplast Structure and Function

Question 1

Structure of Chloroplasts

Answer 1

2-10μm in diameter (larger than mitochondria)
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- Double membrane
- Outer membrane permeable to range of [ions and small molecules]
- Inner membrane contains transport proteins [allowing certain molecules to enter and leave cell]
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- Filled with fluid called stroma, containing CO2, sugars, enzymes and other molecules
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- Thylakoids found in stroma
- Membrane system of flattened fluid filled sacs
- Contain pigments, enzymes and electron carriers
- Stack to form grana
- Grana connected by stroma lamellae ensuring stacks of sacs are connected but distanced
- Large surface area
- Lots of pigment molecules, lots of light absorbed
- Pigments arranged into photosystems
- Funnel like structures, where pigment molecules pass energy down to the next in cluster until primary pigment reaction centre is reached
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- Stroma contains 70S ribosomes, Loop of DNA and Starch Grains
- Loop of DNA codes for chloroplast proteins
- 70S ribosomes code for these proteins
- Sugars formed during photosynthesis are stored as starch in starch grains

Question 2

Where do each of the stages of photosynthesis take place?

Answer 2

Light dependent stage - In thylakoid membranes

Light independent stage - In stroma

Question 3

How are chloroplasts adapted to photoysnthesis?

Answer 3

Stroma
- Contains enzymes catalysing light-independent reactions
- Stroma surrounds grana and membranes so transport of products from light dependent stage to stroma is RAPID
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Grana
- Stack to create large surface area
- Lots of photosystems
- Maximum absorption of light
- More membrane space for ELTC and ATP Synthase enzymes
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DNA
- Chloroplast DNA contains genes for coding proteins and enzymes used during photosynthesis
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Ribosomes
- Presence of ribosomes allows for translation of proteins coded for by the DNA loops
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Inner membrane
- Transport proteins allow certain molecules to enter and leave the chloroplast