NEB Class 12 • Biology • Plant Physiology • Concept Guide

Diffusion, Osmosis & Plasmolysis: NEB Class 12 Biology Guide

Master Diffusion, Osmosis and Plasmolysis through clear concepts, representations, a reliable answer method and exam-focused practice.

ConceptsWorked reasoningNEB practice

Core concept

What Diffusion, Osmosis and Plasmolysis means physically

Diffusion is net particle movement down a concentration gradient; osmosis is net water movement across a selectively permeable membrane; plasmolysis is membrane withdrawal after plant-cell water loss.

Water potential predicts water movement from higher to lower potential; tonicity describes how an external solution changes cell water balance.

The institutional reference gives the wider physical model; the CDC curriculum determines the NEB boundary.

Worked checkpoint with interpretation

An onion epidermal cell in concentrated salt solution loses water and plasmolyses; returning it to water may produce deplasmolysis if the cell remains viable.

Do not stop at the number. State what the sign, ratio, spacing, frequency or direction means. A common error is Saying water moves toward more water, equating osmosis with solute diffusion, or calling a cell wall selectively permeable.

NEB answer method

Model → evidence → equation → check

First identify the system and what the question asks. Label the diagram, apparatus or reaction with SI quantities, then state the principle before selecting an equation. Solve symbolically where possible and check units, limiting cases and chemical or physical meaning.

Stage	Question	Evidence
Model	What is idealised?	Assumption stated
Representation	Which diagram fits?	Labels or balanced equation
Calculation	Which relation follows?	Symbols then SI values
Evaluation	Does it make sense?	Unit, sign and trend check

Make the idea concrete in Nepal

Connect the model to a school laboratory, household technology, health, environment, energy or local material. The example should clarify the science rather than merely mention a place. Compare a prediction with an observation and record uncertainty.

Review the NEB Class 12 Biology revision roadmap and the complete Biology guide. For online or physical tuition, call 9846662070.

Frequently asked questions

Questions students ask about Diffusion, Osmosis and Plasmolysis

What is the central idea of Diffusion, Osmosis and Plasmolysis?+

Which equation should I remember?+

Water potential predicts water movement from higher to lower potential; tonicity describes how an external solution changes cell water balance.

How should I begin a numerical?+

Draw the situation, list known quantities in SI units, choose the governing relation symbolically, substitute once and finish with a unit and reasonableness check.

What is a common exam mistake?+

Saying water moves toward more water, equating osmosis with solute diffusion, or calling a cell wall selectively permeable.

How can I practise this topic?+

Alternate one concept explanation, one diagram and two numericals. Revisit errors after a day instead of only rereading the solution.

Where can I get tuition support?+

For online or physical KTM Tuition classes, call 9846662070. After Grade 12, the MKS Education panel below gives preparation and pre-counselling contacts.

References and next steps

Scope checked against CDC Nepal; concept support from an institutional reference and OpenStax Science. Continue with the Diffusion, Osmosis and Plasmolysis cluster.

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