Wendy's Case Study

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1. Cells structure and Organisation

1.1 Plant Cells and Animal Cells:

Fig.1.0 Basic structures of an animal cell and a plant cell. 1. • • • Cell wall: Porous. Permeable. Non-living structure made of cellulose.

2. Cell membrane/Plasma membrane • Semi-permeable/Partially permeable(Only certain parts can pass through it and some aren't able). 3. • • • Cytoplasm Contains cell organelles. Food substances. Mostly H2O.

4. Vacuole/Sap vacuole/Large central vacuole • Mostly H2O. 5. Nucleus • Controls all activities of a cell. 6. Chloroplasts • Contains green pigment called Chlorophyll which is important for doing Photosynthesis. 7. • • • Differences between plant cells and animal cells Only plant cells have cell wall. Only plant cells have chloroplasts. Plant cells have a large central vacuole while some animal cells have small vacuoles and some doesn't have any. • Plant cells have a regular shape while animal cells have irregular shape.

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1.2 Specialized/Modified cells: 1. Root Hair Cell: • To absorb water and minerals. • Finger-like projection:  Increases surface area for absorption.  Has a larger vacuole to store more H2O.

Fig.1.2 Root hair cell.
2. • • • • Red blood cell: To carry/transport oxygen. Packed with haemoglobin (red pigment). No nucleus. Biconcave shape.

Fig.1.3 Red blood cells. 3. Xylem vessels: • To transport H2O and minerals. • Supporting plant body.

Fig.1.4(a)Whole plant, (b) plant stem and (c)xylem vessel

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2. Diffusion and Osmosis
Monday, October 20, 2008 8:15 PM

2.1 Diffusion 1. Diffusion: • The movement of particles form an area of higher concentration to another area of lower concentration down a concentration gradient.

Fig. 2.1 Representation of diffusion. 2.2 Osmosis
2. Osmosis: • The movement of water molecules from an area of high concentration to an area of lower concentration through a semi-permeable membrane.

Fig. 2.2 (a)The sugar solution in the bag is more concentrated than the water outside the bag. (b)The water in the bag is more dilute than the sugar solution outside the bag. (c)The sugar solution in the bag is of the same concentration as that of the solution outside the bag.

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2.3 Cells and Osmosis:

Fig. 2.3 The behaviour of cells in solutions of different concentrations. 2.4 Active Transport: 3. Active Transport: • The movement of particle from an area of lower concentration to an area of higher concentration by using energy. 4. Active transport is involved in a number of processes occurring within an organism. This includes the absorption of: • Dissolved mineral salts by the root hairs, • Glucose and amino acids by cells in the small intestine of humans.

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Fig. 2.4 Active transport-molecules diffuse against the concentration gradient from B to A. Concentration gradient: • The difference in concentration between a region of a solution or gas that has a high density of particles and a region that has a relatively lower density of particles.

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3. Enzymes
Monday, October 20, 2008 8:18 PM

3.1 What are enzymes? 1. Enzymes: • They are biological catalysts made of protein. They alter the rate of chemical reactions without themselves being chemically changed at the end of the reaction. Catalysts are substances that can change the speed of a chemical reaction. 3.2 Characteristics of enzymes & Factors affecting enzyme activity. 1. • • • • • • • Characteristics of enzymes: They alter or speed up the rates of chemical reactions that occur in a cell. They remain unchanged after a chemical reaction. They are specific.→"Lock & Key" hypothesis (One enzyme act on one substrate) They are affected by temperature. They are affected by pH. They may need other enzymes to work (Coenzymes). They catalyse reversible reactions.

2. Factors affecting enzyme activity:

1) Temperature.

Fig. 3.1 Effect of temperature. A) The enzyme activity is increasing from its inactive...
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