Osmosis is the process of movement of water molecules from its
- (a)higher concentration to its lower concentration through a cell wall.
- (b)lower concentration to its higher concentration through a fully permeable membrane.
- (c)higher concentration to its lower concentration through a fully permeable membrane.
- (d)higher concentration to its lower concentration through a semi-permeable membrane.
Correct — D, higher concentration to its lower concentration through a semi-permeable membrane. Two conditions have to be met at once. The membrane must be semi-permeable, letting water through while holding back the dissolved solute — a fully permeable membrane lets everything pass and gives ordinary diffusion, not osmosis. And the movement of the water must be described from where water is more concentrated to where water is less concentrated, which is what this option says: 'water molecules from its higher concentration to its lower concentration'. That is the same direction as the familiar statement 'from dilute solution to concentrated solution', because a dilute solution is one where water is abundant and solute scarce. Only option (d) gets both the direction of the water and the nature of the membrane right.
- (a)higher concentration to its lower concentration through a cell wall. — Direction right, barrier wrong. The cellulose cell wall is freely permeable and stops almost nothing; the selective barrier in a plant cell is the plasma membrane just inside it.
- (b)lower concentration to its higher concentration through a fully permeable membrane. — Wrong on both counts — it reverses the flow of water and then puts a fully permeable membrane in the way, which would rule out osmosis altogether.
- (c)higher concentration to its lower concentration through a fully permeable membrane. — The direction is right, and this is the option that catches most candidates. A fully permeable membrane lets solute cross as freely as water, so the two mix by diffusion and no osmotic pressure ever develops.
Osmosis is the net movement of solvent — in living systems, water — across a semi-permeable membrane from the side where water is more concentrated to the side where it is less. It is a special case of diffusion, made special by the membrane: the solute cannot follow, so the water keeps moving until the pressure it builds on the concentrated side balances the difference. That balancing pressure is the osmotic pressure.
The four options are a two-by-two grid — direction of water crossed with type of membrane — and the exam is checking whether a candidate holds both variables at once. The wording is the part that trips people. 'Water from its higher concentration to its lower concentration' and 'from dilute solution to concentrated solution' describe the same flow; a candidate who half-remembers the second phrasing may reject the first and hunt for an option saying 'lower to higher'. Fix it by tracking the water and not the solute. Push the pressure the other way and past the osmotic pressure and you get reverse osmosis, which is how a domestic water purifier and a desalination plant work.
- Osmosis needs a semi-permeable membrane — one that passes the solvent and holds back the solute.
- Water moves from where water is more concentrated (the dilute solution) to where it is less concentrated (the concentrated solution).
- Across a fully permeable membrane the solute also moves, so the result is diffusion rather than osmosis.
- A plant's cellulose cell wall is freely permeable; the plasma membrane inside it is the selective barrier.
- Reverse osmosis applies a pressure greater than the osmotic pressure on the concentrated side, pushing water the other way — the principle of RO purifiers and desalination.
The membrane is what turns diffusion into osmosis, so read the second half of each option before choosing.
- Describing the direction in terms of the solute and then reading an option written in terms of the water.
- Accepting 'fully permeable' because the direction in the same option looks right.
- Treating the plant cell wall as the selective barrier — that job belongs to the plasma membrane.
As a definition item where the wrong options change one variable at a time, or as an applied item on what a cell does in salt water or in distilled water.
Consider the following statements : 1. During the process of osmosis, the solvent travels from the concentrated solution to the dilute solution. 2. In the reverse osmosis, external pressure is applied to the dilute solution. Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer(d) Neither 1 nor 2
The same definition set as a two-statement trap, and both statements are false. Its first statement reverses the flow exactly as option (b) does here, and its second puts the pressure of reverse osmosis on the wrong side.
Net movement of water from a dilute to a concentrated solution through a selectively permeable membrane is called
- (a) Diffusion
- (b) Dispersion
- (c) Osmosis
- (d) Absorption
Answer(c) Osmosis
The same definition phrased from the solution's point of view rather than the water's — dilute to concentrated through a selectively permeable membrane. Matching that sentence against this option list is the whole exercise.
- practice — not a real PYQ
Raisins placed in plain water swell up. The process responsible is
- (a)diffusion
- (b)osmosis
- (c)active transport
- (d)evaporation
Answer(b) osmosis — water crosses the raisin's semi-permeable covering into the concentrated sugary interior, and the raisin swells.
- practice — not a real PYQ
In reverse osmosis used for purifying water, the external pressure is applied on
- (a)the dilute solution
- (b)the concentrated solution
- (c)the membrane itself
- (d)neither side
Answer(b) the concentrated solution — a pressure greater than the osmotic pressure is applied on the saline side, forcing water through the membrane the other way.