CDS (II) 2023 General Knowledge · Question 44 of 120

Correct — A, Mitochondria – Respiration; Chloroplast – Photosynthesis; Ribosome – Protein Synthesis; Rough endoplasmic reticulum – Transport of proteins. Each of the four pairings holds. Mitochondria are described as the powerhouses of the cell, where food is broken down to release energy in the process called cellular respiration and the energy is stored as ATP. Chloroplasts carry chlorophyll, the green pigment that absorbs sunlight, and are where the plant prepares its food by photosynthesis. Ribosomes are the protein factories of the cell — protein synthesis is what they do, and nothing else. The rough endoplasmic reticulum is rough precisely because ribosomes are attached to its surface; the endoplasmic reticulum plays a key role in the synthesis and transport of proteins, fats and some hormones, so once a protein has been made on a ribosome studding its membrane, the rough endoplasmic reticulum is the channel through which it is moved on and sent out of the cell. The other three options each rearrange this set, and every one of them breaks at least two pairings.

• (b)Mitochondria – Respiration; Chloroplast – Photosynthesis; Ribosome – Transport of proteins; Rough endoplasmic reticulum – Protein synthesis — Swaps the last two. Ribosomes are the site where protein is actually assembled, not a transport channel, and the rough endoplasmic reticulum owes its whole identity to carrying those ribosomes and moving what they make. The tempting part is that the rough endoplasmic reticulum genuinely is involved in protein synthesis — but only because ribosomes sit on it, which is why the ribosome must take the synthesis label.
• (c)Mitochondria – Respiration; Chloroplast – Protein synthesis; Ribosome – Photosynthesis; Rough endoplasmic reticulum – Transport of proteins — Hands photosynthesis to the ribosome and protein synthesis to the chloroplast. Only the chloroplast contains chlorophyll, and a ribosome has no pigment and no way to trap light.
• (d)Mitochondria – Photosynthesis; Chloroplast – Respiration; Ribosome – Protein synthesis; Rough endoplasmic reticulum – Transport of proteins — Interchanges the two energy organelles. Mitochondria release energy by breaking food down; chloroplasts capture light energy to build food up. The two run in opposite directions, and only plants have both.

A eukaryotic cell divides its work among membrane-bound organelles. Mitochondria release energy from food by cellular respiration and store it as ATP. Plastids, of which chloroplasts are the green kind, carry out photosynthesis. Ribosomes, which may float free in the cytoplasm or sit on the endoplasmic reticulum, assemble proteins from amino acids. The endoplasmic reticulum is a network of membranes running through the cell; the rough kind carries ribosomes and handles proteins made on them, while the smooth kind lacks ribosomes and deals mainly with fats. The Golgi apparatus then modifies, packages and dispatches what the endoplasmic reticulum sends it.

A four-part matching item is best attacked by finding the pairing you are surest of and eliminating every option that breaks it. Chloroplast with photosynthesis is that anchor for most candidates, and it removes options (c) and (d) at once. What remains is the choice between giving protein synthesis to the ribosome or to the rough endoplasmic reticulum, and the honest way to hold that distinction is to think of them as two steps of one job rather than as rivals: the ribosome is where the chain is built, and the membrane it sits on is what channels the finished protein onward and out. The paper's own wording — synthesis for the ribosome, transport for the rough endoplasmic reticulum — reflects that division of labour. It is worth noting that current NCERT describes the endoplasmic reticulum as playing a key role in both synthesis and transport, so the distinction is one of emphasis, not a claim that the rough endoplasmic reticulum has nothing to do with making proteins.

• NCERT: mitochondria are 'often called the powerhouses of the cell', where food is 'broken down to release energy during a process called cellular respiration' and the energy is stored 'in the form of a molecule called Adenosine Triphosphate (ATP)'.
• NCERT: 'plants prepare their food by the process of photosynthesis … A green pigment called chlorophyll, which is present in the chloroplast absorbs sunlight.'
• NCERT heads its section on ribosomes 'Ribosomes — The protein factories'.
• NCERT on the rough endoplasmic reticulum: 'it has ribosomes attached to its surface, and is mainly involved in protein synthesis and protein secretion'.
• NCERT on the endoplasmic reticulum generally: 'The ER plays a key role in the synthesis and transport of proteins, fats (lipids), and some hormones.'

• Giving protein synthesis to the rough endoplasmic reticulum. The synthesis happens on the ribosomes attached to it, and the membrane's distinctive contribution is channelling and secretion.
• Swapping mitochondria and chloroplast because both are energy organelles; one releases energy from food, the other captures light to make food.
• Forgetting that animal cells have mitochondria but no chloroplasts, so photosynthesis cannot be a general cell function.

As a four-way organelle-to-function match, as a labelled cell picture, or as a single-line question on which organelle performs a named job.

• practice — not a real PYQ

  The rough endoplasmic reticulum appears rough because of the presence of which one of the following on its surface?

  • (a)Lysosomes
  • (b)Ribosomes
  • (c)Mitochondria
  • (d)Golgi bodies

  Answer(b) Ribosomes — they stud the membrane and assemble proteins, which the rough endoplasmic reticulum then channels onward; the smooth kind has no ribosomes and handles fats.

• practice — not a real PYQ

  Which one of the following organelles is present in a plant cell but absent in an animal cell?

  • (a)Mitochondrion
  • (b)Ribosome
  • (c)Chloroplast
  • (d)Endoplasmic reticulum

  Answer(c) Chloroplast — only plant cells carry plastids with chlorophyll and so only they photosynthesise; the other three occur in both kinds of cell.