Which one of the following organelles is not found in animal cells?

Correct — C, Cell wall. Animal cells are bounded only by the plasma membrane, a flexible lipid bilayer, which is why animal tissue can take on so many shapes and why animals developed skeletons and muscles for support. A rigid cellulose wall outside the membrane is found in plants, and walls of other materials in fungi (chitin) and bacteria (peptidoglycan) — never in an animal cell.

• (a)Cell membrane — The cell membrane is present in every cell that exists, animal cells included; it is the outermost layer of an animal cell rather than an absent one.
• (b)Endoplasmic reticulum — Endoplasmic reticulum runs through animal cells in both rough and smooth forms, handling protein processing and lipid synthesis respectively.
• (d)Lysosome — Lysosomes are, if anything, more characteristic of animal cells than plant cells — the membrane-bound bags of digestive enzymes often called the cell's suicide bags.

The plasma membrane is universal; the cell wall is not. Plant cells lay a cellulose wall outside the membrane, which gives shape, resists bursting when water enters by osmosis, and lets plants stand upright without a skeleton. Animal cells trade that rigidity for flexibility and mobility. Two other plant features follow the same pattern — plastids including chloroplasts, and a single large central vacuole.

Only one option in the list is a structure and not an organelle in the strict sense, and it is the answer — the wall is an extracellular product, which is exactly why animals can do without it. Candidates lose this one by reading past the option and picking lysosome, on a half-memory that lysosomes are somehow special. They are special, but in the opposite direction.

• Animal cells have a plasma membrane but no cell wall.
• Plant cell walls are made of cellulose; fungal walls of chitin; bacterial walls of peptidoglycan.
• Plastids, including chloroplasts, and one large central vacuole are further plant-cell features absent from animal cells.
• Lysosomes contain hydrolytic enzymes and are prominent in animal cells.
• The rough endoplasmic reticulum carries ribosomes and handles protein transport; the smooth form makes lipids.

• Picking lysosome on a vague memory that it is unusual.
• Confusing the cell wall with the cell membrane, which every cell has.
• Assuming fungi have cellulose walls like plants — theirs are chitin.

The most frequently repeated cell-biology item across CAPF, CDS and NDA, usually phrased as 'not found in animal cells' or as a plant-versus-animal comparison.

• practice — not a real PYQ

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

  • (a)Ribosome
  • (b)Chloroplast
  • (c)Mitochondrion
  • (d)Golgi apparatus

  Answer(b) Chloroplast — plastids are confined to plant cells; the other three are common to both.

• practice — not a real PYQ

  The cell wall of a fungus is made mainly of

  • (a)cellulose
  • (b)chitin
  • (c)peptidoglycan
  • (d)lignin

  Answer(b) chitin — cellulose is the plant wall material and peptidoglycan the bacterial one.