Which one of the following cell organelles may play a role in expelling excess water and wastes in case of unicellular organisms?
- (a)Lysosome
- (b)Vacuole
- (c)Golgi body
- (d)Endoplasmic reticulum
Correct — B, Vacuole. In many freshwater unicellular organisms, such as Amoeba and Paramecium, a specialised contractile vacuole collects the excess water that constantly enters the cell by osmosis, along with some dissolved wastes, and periodically contracts to pump it back out - a process called osmoregulation. So the vacuole is the organelle that expels excess water and wastes.
- (a)Lysosome — Lysosomes are the cell's digestive bags, full of enzymes that break down worn-out parts and food particles; they do not pump out excess water.
- (c)Golgi body — The Golgi apparatus modifies, packages and dispatches proteins and lipids; it plays no part in expelling water.
- (d)Endoplasmic reticulum — The endoplasmic reticulum transports materials and makes proteins (rough ER) and lipids (smooth ER); it does not bail out excess water.
A vacuole is a membrane-bound sac that stores water, food and wastes. In freshwater unicellular organisms a special contractile vacuole handles osmoregulation - collecting the water that floods in by osmosis and expelling it, together with some wastes, to keep the cell from bursting.
Eliminate the organelles with digestive, packaging or transport roles. The organelle whose job is bailing out excess water is the (contractile) vacuole.
- A contractile vacuole in freshwater protists (Amoeba, Paramecium) expels excess water taken in by osmosis, maintaining water balance.
- Vacuoles also store water, food, wastes and, in plant cells, cell sap that provides turgor.
- Lysosomes digest waste, the Golgi body packages secretions, and the endoplasmic reticulum transports and makes proteins and lipids.
- Plant cells usually have one large central vacuole, whereas animal cells have small or no vacuoles.
Only the vacuole (the contractile vacuole in protists) pumps out excess water and wastes.
- Confusing the vacuole with the lysosome (digestion) or the Golgi body (packaging).
- Forgetting that the water-expelling vacuole is specifically the contractile vacuole of freshwater protists.
- Assuming animal cells have large vacuoles like plant cells.
NDA asks which organelle expels water or performs a listed function - match the contractile vacuole to osmoregulation.
Match List I (Physiological processes: Photosynthesis, Mineral uptake, Respiration, Protein Synthesis) with List II (Cell organelles: Plasma membrane, Chloroplast, Mitochondria, Ribosomes) and select the correct answer.
- (a) I-A, II-B, III-C, IV-D
- (b) I-A, II-B, III-D, IV-C
- (c) I-B, II-A, III-C, IV-D
- (d) I-B, II-A, III-D, IV-C
Answer(c) Photosynthesis-Chloroplast, Mineral uptake-Plasma membrane, Respiration-Mitochondria, Protein synthesis-Ribosomes.
Same 'match the organelle to its function' skill - here you must identify the vacuole as the organelle that expels excess water and wastes.
Which one of the following statements about lysosomes is NOT correct?
- (a) They are waste disposal system of the cell
- (b) They breakdown all inorganic materials
- (c) These are also referred to as "suicidal bags"
- (d) Lysosomes stop entry of foreign materials
Answer(b) They breakdown all inorganic materials
Companion organelle-function item - it contrasts the lysosome (digestion) with the vacuole (water and waste expulsion) tested here.
- practice — not a real PYQ
The contractile vacuole in Amoeba is mainly involved in
- (a)digestion of food
- (b)osmoregulation (removing excess water)
- (c)protein synthesis
- (d)respiration
Answer(b) osmoregulation - it expels the excess water that enters by osmosis.
- practice — not a real PYQ
Which organelle is known as the 'suicidal bag' of the cell?
- (a)Vacuole
- (b)Lysosome
- (c)Golgi body
- (d)Ribosome
Answer(b) Lysosome - its enzymes can digest the cell's own contents.