Biology (9-1) - 0970 CIE

Osmosis

Overview

Leave a limp stick of celery in water and it turns crisp again; soak a potato chip in salty water and it goes floppy. Both are caused by osmosis, the movement of water across a partially permeable membrane. It is how plants stand upright, how roots drink, and how every cell keeps its water balance.

In this lesson you will learn the role of water in organisms, what osmosis is, how to investigate it, and how solutions of different strengths change plant and animal cells. At Extended level you will use water potential and the terms turgid, flaccid and plasmolysis to explain what you see.

Objectives

Describe the role of water as a solvent in organisms with reference to digestion, excretion and transport
State that water diffuses through partially permeable membranes by osmosis
State that water moves into and out of cells by osmosis through the cell membrane
Investigate osmosis using materials such as dialysis tubing
Investigate and describe the effects on plant tissues of immersing them in solutions of different concentrations
State that plants are supported by the pressure of water inside the cells pressing outwards on the cell wall
[Supplement] Describe osmosis as the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane
[Supplement] Explain the effects on plant cells of immersing them in solutions of different concentrations by using the terms: turgid, turgor pressure, plasmolysis, flaccid
[Supplement] Explain the importance of water potential and osmosis in the uptake and loss of water by organisms

Lesson Note

Osmosis explains support in plants, water uptake by roots, and why animal cells must be bathed in a fluid of the right concentration. It is one of the most heavily examined practical topics: percentage change in mass calculations and predicting the fate of a cell in a solution come up constantly. Get the direction of water movement right and the marks follow.

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Lesson Evaluation

Congratulations on completing the lesson on Osmosis. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

Osmosis is the movement of: A. any particles down a gradient B. water across a partially permeable membrane C. ions using energy D. sugar into a cell Answer: B
Water moves by osmosis from a region of: A. low to high water potential B. high to low water potential C. equal water potential D. low to low water potential Answer: B
A potato cylinder has initial mass 4.0 g and final mass 3.6 g. The percentage change is: A. +10% B. -10% C. -4% D. +4% Answer: B
A plant cell that has taken in water and is firm is described as: A. flaccid B. plasmolysed C. turgid D. lysed Answer: C
A red blood cell placed in pure water will: A. become turgid B. shrink C. burst D. stay the same Answer: C