chloroplasts cell membrane nucleus nucleus cell wall vacuole cytoplasm Animal cell Plant cell Investigating Cells Summary Booklet page 1

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1 1. General: state that cells are the basic units of living things. Sections of living tissue, when examined under a microscope are seen to be made up of similar units. These units consist of cytoplasm, a nucleus and a membrane. These units are called cells. Living things can be distinguished from non-living things because of their cellular structure. 2. General: Explain the purpose of staining animal and plant cells. Some structures will be visible in unstained cells. Stains are taken up by some cell structures. More structures will be clearly seen in stained cells. 3. General: Describe the structural similarities of and differences between animal and plant cells. Both animal and plant cells contain a nucleus, cytoplasm and a cell membrane. Plant cells possess, in addition, a cell wall, chloroplasts and a cell vacuole. Cells can be identified as plant or animal according to their basic structure. chloroplasts nucleus Animal cell cell membrane cytoplasm nucleus cell wall Plant cell vacuole Investigating Cells Summary Booklet page 1

2 4a. General: State that a substance can diffuse from a high concentration to a low one. Diffusion occurs in gases and liquids. Gases and liquids are made up of molecules. low concentration of These molecules are moving all the glucose inside the time, in a random way. cell The movement of molecules is faster in a gas than in a liquid. glucose Diffusion occurs when there is an glucose unequal distribution of molecules. high concentration of Diffusion is the movement of glucose outside the cell molecules from an area of high concentration to an area of low concentration. Diffusion occurs until the molecules are evenly distributed. 4b. Credit: Explain the importance of diffusion to organisms. Gas exchange in organisms occurs in response to a concentration gradient. Gas exchange takes place through the cell membrane in simple organisms. There are organs for gas exchange in larger organisms. 5a. General: Give examples of substances which enter and leave the cell by diffusion e.g. dissolved food, oxygen, carbon dioxide and water. Glucose, oxygen and carbon dioxide pass through the cell membrane by a process of diffusion. These substances must be dissolved in water. 5b. General: State that the cell membrane controls the passage of substances into and out of the cell. The cell membrane contains tiny pores. Investigating Cells Summary Booklet page 2

3 Substances must be in a soluble form before they can diffuse through the membrane. Insoluble substances cannot diffuse through the membrane. 6a. General: Identify osmosis as a special case of the diffusion of water. Osmosis is the movement of water molecules from an area of high water concentration to an area of low water concentration across a selectively permeable membrane. Osmosis occurs when two solutions of different concentrations are separated by a membrane. 6b. Credit: Explain osmosis in terms of a selectively permeable membrane and of a concentration gradient. A membrane, which allows molecules of all sizes to pass through, is permeable. Membranes in living cells are selectively permeable. They do not allow large molecules such as starch or proteins through. There are two selectively permeable membranes in plant cells the cell membrane and the vacuole membrane. A concentration gradient exists when there is an unequal distribution of molecules. During osmosis, water molecules move down this concentrations gradient, from the area of high water concentration to the area of low water concentration, across a selectively permeable membrane. 7. Credit: Explain observed osmotic effects in plants and in animal cells in terms of the concentration of water in the solutions involved. Water diffuses from an area of high water concentration to an area of low water concentration. When plant cells are placed in water (or a plasmolysed cell weaker solution) they become turgid. When plant cells are placed in a more concentrated solution they become flaccid. Plasmolysis occurs when a cell becomes flaccid. turgid cell Investigating Cells Summary Booklet page 3

4 8a. General: State that cell division is a means of increasing the number of cells in an organism. Cell division (mitosis) occurs in special parts of a plant. Cell division (mitosis) and growth are separate processes. New cells arise from pre-existing cells. 8b. General: State that the nucleus of the cell controls cell activities including division. Chromosomes carry information (genes). It is this information which controls the nature of the organism. All the cells of the body contain the same number of chromosomes. 9a. General: State that each of the two cells produced by cell division has a complete set of chromosomes and the same information. Each of the two daughter cells contain a nucleus with the same number of chromosomes present in the original nucleus. Each of the two daughter cells receive exactly the same information, which is also the same as the information in the original cell. 9b. Credit: Describe the stages of mitosis. The stages of mitosis are as follows: i. Chromosomes become visible in the nucleus. ii. Chromosomes then shorten. Each chromosome is made up of 2 identical chromatids that are joined together at a point called the centromere. iii. Nuclear membrane disappears and the chromosomes line up along the centre (equator) of the cell. iv. Spindle fibres attach to each of the centromere, and the two chromatids that make up each chromosome are pulled to opposite ends (poles) of the cell. v. A nuclear membrane forms around each group of chromatids, thus completing nuclear division. Investigating Cells Summary Booklet page 4

5 vi. The cytoplasm then divides forming two daughter cells, each with the same number of chromosomes and same information as the parent cell. 9c. Credit: Explain why it is important that the chromosome complement of daughter cells in multicellular organisms is maintained. Chromosomes carry genetic information (genes). All processes in the cell are controlled by this information. It is therefore vital that this genetic information does not become lost or altered through faults in cell division. 10. General: Identify the correct sequence of stages of mitosis. The sequence of stages in mitosis is: Stage 1 chromosomes not yet visible in the nucleus Stage 2 chromosomes visible as 2 joined chromatids Stage 3 chromosomes line up at the equator and spindle fibres attach at the centromere Stage 6 cytoplasm splits to form 2 new cells each identical to the original cell Stage 5 chromatids now called chromosomes and nuclear membrane forms around these Stage 4 spindle fibres pull chromatids apart and to opposite poles Investigating Cells Summary Booklet page 5

6 11a. General: Explain why enzymes are required for the functioning of living cells. Enzymes speed up the chemical reactions in living cells. For example, catalase, which is found in a variety of plant and animal tissues, breaks down hydrogen peroxide with the release of oxygen gas. 11b. General: Explain the meaning of the term catalyst. A catalyst speeds up a chemical reaction. A catalyst remains unchanged during the reaction. A catalyse repeats the reaction over and over again without being changed. Enzymes are catalysts. 11c. Credit: Explain the term specific as applied to enzymes and their substrates. The substance on which an enzyme acts is called its substrate. Each enzyme has a characteristic shape. A substrate molecule fits into the shape of the enzyme molecule at an active site. The reaction takes place while the enzyme and substrate molecules are fitted together. After the reaction has occurred the enzyme is released unchanged. Each enzyme can only react with one type of substrate molecule e.g. amylase only reacts with starch. products active sites + + enzyme substrate Enzyme-substrate complex enzyme Investigating Cells Summary Booklet page 6

7 12a. General: Give an example of an enzyme involved in the chemical breakdown of a substance. The enzyme amylase breaks down starch into maltose. The word equation for this breakdown reaction is: amylase Starch maltose 13a. General: Give an example of an enzyme involved in synthesis. The enzyme phosphorylase is involved in the reaction by which starch is made from glucose. In this reaction the glucose is in a special reactive form called glucose-1-phosphate. The word equation for this synthesis reaction is: Phosphorylase Glucose-1-phosphate small starch large 14a. General: State that enzymes are proteins. Enzymes are made from proteins. 14b. General: Describe the effect of temperature on enzyme activity. The rate of enzyme activity increases with temperature up to a maximum rate. Further increase in temperature results in a rapid decrease in enzyme activity to zero. At high temperatures, proteins, and therefore enzymes are denatured. 14c. General: Describe the effect of a range of ph on the activity of pepsin and catalase. Pepsin breaks down protein. Pepsin has a narrow working ph range of ph2 ph4. Investigating Cells Summary Booklet page 7

8 Catalase has a narrow working ph range of ph6 ph9. An enzyme does not function outside its working ph range. An enzyme has a ph at which it functions best. 14d. Credit: Explain the term optimum as applied to the range of conditions in which enzymes operate. The optimum temperature for an enzyme is the temperature at which it has the greatest activity. The optimum ph for an enzyme is the ph at which it has greatest activity. The optimum ph for pepsin is 2-3. The optimum ph for catalase is ph7. The optimum temperature for enzymes in humans is 37 C. Investigating Cells Summary Booklet page 8

9 15. General: State three reasons why living cells need energy. Living cells need energy for: i. cell division. ii. growth iii. mechanical work and movement iv. uptake of chemicals v. building up molecules (chemical work) 16. Credit: State that fats and oils contain more chemical energy per gram than carbohydrates or protein. Igniting a food sample releases chemical energy as mainly heat energy, with some light and sound energy. This heat energy can be absorbed by water and brings about a temperature rise. The temperature rise depends on the mass of the food, the mass of the water and the nature of the food sample. Only the heat energy is absorbed by the water. Some of the heat energy heats the surrounding air and is not absorbed by the water. Fats and oils contain twice as much energy per gram as carbohydrate and protein, such that the calorific value per 1g burned is: i. fats and oils = 37kJ ii. carbohydrates = 17kJ iii. proteins = 22kJ 17a. General: State that cells need oxygen to release energy from food during aerobic respiration. In order for aerobic respiration to occur oxygen must be readily available to cells, thus in order for energy to be released from cells, through aerobic respiration, oxygen is essential. Investigating Cells Summary Booklet page 9

10 17b. General: Describe aerobic respiration in terms of a word equation. glucose + oxygen raw materials Carbon + water + energy dioxide waste products useful product Aerobic respiration occurs in a series of linked reactions controlled by enzymes. Whole organisms can be used in investigations of aerobic respiration in cells. The volume of oxygen taken in by an organism is equal to the volume of oxygen given out. A simple respirometer can be used to investigate oxygen uptake by an organism. A respirometer contains a chemical to absorb carbon dioxide given out by the organism. A respirometer must be kept at a constant temperature. 18. State that carbon dioxide is given off by cells during tissue respiration and is derived from food. Carbon dioxide: i. turns lime water milky. ii. puts out a burning splint iii. turns bicarbonate indicator solution from red to yellow Certain chemicals can remove carbon dioxide from air. Both plants and animals respire to produce carbon dioxide. The carbon dioxide produced during respiration comes from glucose. Investigating Cells Summary Booklet page 10

11 19a. General: State that heat energy may be released from cells during respiration. Energy released by respiration as heat may raise the organism s temperature above that of the surroundings. Heat will therefore be lost to the surroundings. A differential air thermometer can be used to detect heat being given off by organisms. Both plants and animals release some energy as heat. Energy released as heat is useful energy in some organisms, but waste energy in others. 19b. Explain the importance of energy released from food during respiration to the metabolism of cells. Metabolism describes all the chemical reactions taking place inside a cell or a whole organism. Organisms convert chemical energy to other useful and waste forms. Wasted energy must be got rid of quickly. Heat energy may raise the temperature of the cell and increase the reaction rates of enzyme-controlled reactions. Some reactions release energy as the reaction takes place. Some reactions require constant energy input to take place. Some reactions require a small initial energy input to take place. Energy release in cells must be controlled. A special chemical is continually formed and broken down and acts as an energy store. Investigating Cells Summary Booklet page 11