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Which one of the following cellular parts is correctly described?
A
Lysosomes – optimally active at a pH of about 8.5
B
Thylakoids – flattened membranous sacs forming the grana of chloroplasts
C
Centrioles – sites for active RNA synthesis
D
Ribosomes – those on chloroplasts are larger (80S) while those in the cytoplasm are smaller (70S)
Detailed Solution
Thylakoids are flattened membranous sacs present in the stroma of the chloroplast; they are arranged in stacks like piles of coins called grana. This description is correct.
Lysosomes contain hydrolytic enzymes that are optimally active at an acidic pH (about 5), not at pH 8.5.
Centrioles form the basal bodies of cilia and flagella and the spindle apparatus; active ribosomal RNA synthesis takes place in the nucleolus.
Ribosomes of chloroplasts are the smaller 70S type, while the cytoplasmic ribosomes of eukaryotes are the larger 80S type; the statement has them reversed.
Hence the correctly described part is the thylakoids.
Lysosomes contain hydrolytic enzymes that are optimally active at an acidic pH (about 5), not at pH 8.5.
Centrioles form the basal bodies of cilia and flagella and the spindle apparatus; active ribosomal RNA synthesis takes place in the nucleolus.
Ribosomes of chloroplasts are the smaller 70S type, while the cytoplasmic ribosomes of eukaryotes are the larger 80S type; the statement has them reversed.
Hence the correctly described part is the thylakoids.