CDS (II) 2023 General Knowledge · Question 14 of 120

Correct — C, 1 – cell wall; 2 – cell membrane; 3 – endoplasmic reticulum; 4 – nucleus; 5 – vacuole. Work from the outside inwards and the first two labels settle themselves. A plant cell has two boundaries, and the rigid cellulose cell wall is always the outer one, with the plasma membrane lying immediately inside it — so label 1 is the cell wall and label 2 the cell membrane. That single step disposes of option (a), which reverses them. The remaining three labels are read off the drawing itself. The network of membranous tubes and sheets threading through the cytoplasm and running up to the nuclear envelope is the endoplasmic reticulum, label 3. The large rounded body with a distinct double boundary and a dense nucleolus inside it is the nucleus, label 4. The single very large clear space that fills most of a mature plant cell and pushes everything else against the wall is the central vacuole, label 5. Options (b) and (d) keep the boundaries right but swap the nucleus and the vacuole, or the vacuole and the reticulum, around.

• (a)1 – cell membrane; 2 – cell wall; 3 – vacuole; 4 – endoplasmic reticulum; 5 – nucleus — Puts the cell membrane outside the cell wall. In every plant cell the wall is the outermost layer and the membrane lies within it, so this option can be rejected before the rest of the labels are even considered.
• (b)1 – cell wall; 2 – cell membrane; 3 – endoplasmic reticulum; 4 – vacuole; 5 – nucleus — Correct on the two boundaries and on the reticulum, then swaps the last pair — it calls the nucleus a vacuole and the vacuole a nucleus.
• (d)1 – cell wall; 2 – cell membrane; 3 – vacuole; 4 – endoplasmic reticulum; 5 – nucleus — Again right at the boundaries, but it moves the vacuole up to position 3 and pushes the reticulum and the nucleus down a place each, so all three inner labels end up wrong.

A plant cell differs from an animal cell in four visible ways: it has a cellulose cell wall outside the plasma membrane, a single large central vacuole instead of several small ones, plastids including chloroplasts, and no centrioles. The organelles inside are otherwise the familiar set — nucleus, endoplasmic reticulum both rough and smooth, Golgi apparatus, mitochondria, ribosomes and lysosomes. Each has a job: the wall gives shape and resists bursting, the membrane controls what enters and leaves, the reticulum transports material and makes protein and lipid, the nucleus holds the genetic material, and the vacuole stores cell sap and maintains turgor.

Labelling items look intimidating and are usually generous, because the options are almost never independent — they share most of their labels and differ in one or two places, so finding a single certainty collapses the field. Here the certainty is the outside-in order of the two boundaries, and it removes one option outright. The rest has to come from the picture, and there is no way round that: the drawing carries the positions, and this card can teach only what each structure looks like when it is drawn. Recognise the reticulum by its branching tubular network reaching the nuclear envelope, the nucleus by its dark internal nucleolus, and the vacuole by being the single largest empty region on the page. A useful check is that in a mature plant cell the vacuole may occupy well over half the volume — if one space dominates the drawing, that is what it is.

• The plant cell wall is made mainly of cellulose and lies outside the plasma membrane, which is the true living boundary of the cell.
• A mature plant cell has one large central vacuole filled with cell sap; it can take up most of the cell's volume and maintains turgor pressure.
• The endoplasmic reticulum is a network of membranous tubules continuous with the nuclear envelope; the rough form bears ribosomes and handles protein, the smooth form makes lipid.
• The nucleus is bounded by a double membrane pierced by pores and contains the chromatin and one or more nucleoli.
• Cell wall, large central vacuole and plastids are present in plant cells and absent from animal cells; centrioles are the reverse.

• Putting the cell membrane outside the cell wall; the wall is always the outer layer.
• Mistaking the large central vacuole for the nucleus because both are drawn as big rounded spaces — the nucleus carries a nucleolus inside it.
• Assuming a labelled organelle must be unique to plants; the nucleus, reticulum and membrane are shared with animal cells.

As a labelled drawing to match, or as a which-organelle-does-what pairing between structures and their functions.

• practice — not a real PYQ

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

  • (a)Endoplasmic reticulum
  • (b)Cell wall
  • (c)Mitochondrion
  • (d)Golgi apparatus

  Answer(b) Cell wall — along with plastids and a large central vacuole. The other three organelles listed are found in both kinds of cell.

• practice — not a real PYQ

  The large central vacuole of a mature plant cell is mainly responsible for

  • (a)protein synthesis
  • (b)maintaining turgidity and storing cell sap
  • (c)packaging and secretion of materials
  • (d)generating ATP by respiration

  Answer(b) maintaining turgidity and storing cell sap — the pressure of the sap-filled vacuole against the wall is what keeps a non-woody plant upright, and a plant wilts when it is lost.