Chloroplast

In the syllabus and the exam

Chloroplast is examined both as a cell organelle in the topic of cell structure and, in more functional detail, as the site of photosynthesis under nutrition in plants, so it is one of the few structures tested from two different angles across the syllabus. Candidates should know that chloroplasts are found mainly in palisade and spongy mesophyll cells of the leaf, that they contain chlorophyll within internal membrane stacks, and that both the light-dependent and light-independent stages of photosynthesis take place within this single organelle. Exam questions sometimes ask candidates to explain why palisade mesophyll cells contain more chloroplasts than epidermal cells, expecting an answer linking chloroplast number to the amount of light received and the cell's role in food production. A frequent error is describing the chloroplast as green in colour rather than describing the chlorophyll inside it as green, since the organelle itself is colourless without its pigment content. Another common mistake is confusing the chloroplast with the mitochondrion, particularly when candidates are asked to compare the organelles responsible for photosynthesis and respiration within the same plant cell. Candidates should also be aware that chloroplasts contain their own small amount of DNA and can divide independently within the cell, a feature that is occasionally referenced when comparing chloroplasts and mitochondria as organelles believed to have originated from free-living organisms. This dual examination across topics is also why revision is more effective when candidates connect the structural facts learned under cell structure with the functional facts learned under nutrition in plants, rather than studying the two chapters as if they were unrelated.

Example

Describing cell structure in a leaf, a candidate writes: 'Palisade mesophyll cells contain many chloroplasts, each with stacked membranes called grana that hold chlorophyll and absorb light for the light-dependent stage of photosynthesis.'

Related terms

ChlorophyllPhotosynthesisPalisade mesophyll

Source:SRC-DSKP-EN