Osmosis. Aim: To find the molarity of potato tubers cell sap. BIOLOGICAL KNOWLEDGE

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TABLE OF CONTENTS

Biological Knowledge                                ...                                3

Explanation                                                ...                                3

Types of solutions and its effects on plant cell        ...                                4

Factors affecting rates of osmosis                        ...                                6

Outline Method                                        ...                                9

Apparatus                                                ...                                9

Materials                                                ...                                9

Risk Assessments                                        ...                                9

Precautions                                                ...                                9

Apparatus Diagrams                                        ...                                10

Factors to be controlled                                ...                                11

Method                                                ...                                11

Calculations to be used                                ...                                12

Predicted Results                                        ...                                12

Prior Test                                                ...                                13

Obtaining Evidence                                        ...                                16

Apparatus                                                ...                                16

Materials                                                ...                                16

Risk Assessments                                        ...                                16

Precautions                                                ...                                16

Method                                                ...                                17

Results obtained for Mass                                ...                                18

Results obtained for Length                                ...                                19

Analysis                                                ...                                21

Trends in the Bar charts                                ...                                25

Scientific Explanation                                        ...                                25

Determination of molarity                                ...                                28

How far I have reached my predicted results                ...                                30

                

Evaluation                                                ...                                32

Errors                                                        ...                                32

Accuracy and reliability of my results                        ...                                32

Extension work                                        ...                                33

Bibliography                                                ...                                33

                                

INTRODUCTION

Biology Coursework

Aim: To find the molarity of potato tuber’s cell sap.

BIOLOGICAL KNOWLEDGE

Osmosis is the diffusion of fluid through a semi-permeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration of fluid on both sides of the membrane. A semi-permeable membrane is a porous substance that allows unrestricted passage of water, but not solute molecules or ions.

The concentration of a solution expresses the relative amounts of the substance constituting the solution. Solutions may be described as dilute, concentrated or saturated. A solution is dilute when it has little amount of solute dissolved in it. A solution is concentrated when it has solute dissolved in it to a high point. A solution is said to be saturated when no more solute can be dissolved in it.

Explanation

When a substance such as sugar dissolves in water, the sugar molecules attract some of the water molecules and stop them from moving freely. This reduces the concentration of free water molecules. Therefore, as the amount of solute increases, the number of free water molecules decrease.

Osmosis takes place due to the difference in the concentration of free water molecules on either side of the semi-permeable membrane. It continues as long as the concentration in both sides of the membrane is equal.

The sugar molecules on the right have ‘captured’ half the water molecules. There are more free water molecules on the left of the membrane than on the right, so water will diffuse rapidly from left to right across the partially permeable membrane by osmosis.

Types of solutions and its effects on plant cells

The cytoplasm of a plant cell and the cell sap in its vacuole contains salts, sugars and proteins which effectively reduce the concentration of free water molecules inside the cell. The cell wall is freely permeable but the cell membrane of the cytoplasm is only partially permeable. Therefore, the concentration of the solution, the cell is in, plays a major role in the occurrence of osmosis. The types of solutions and its effects are as follows:

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Hypotonic Solution:

Hypotonic solution is less concentrated than the concentrated solution in the cell’s cytoplasm and the cell sap in its vacuole.

If a plant cell is surrounded by water or a solution more dilute than its contents, water will pass into the vacuole by osmosis. This is because there are more free water molecules outside the cell than the inside. The vacuole will expand and press outwards on the cytoplasm and the cell wall. A plant cell with the vacuole pushing out on the cell wall is said to be turgid ...

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This is a well structured and detailed report. 1. The sources of information need to be referenced. 2. There is some repetition of information that should be removed. 3. The analysis sections should be condensed down into one section. 4. The evaluation is good but needs to discuss reliability. ****