Biology Revision - Cell Structure PDF

Biology: Revision Cell Structure: **Prokaryotes and Eukaryotes** -For a cell to be a cell, it has to have the following components: \>Cell membrane -- Holds the cell together, separating the inside from the cell from the outside, controlling what can and cannot enter. \>Cytoplasm -- A jelly-lik...

Biology: Revision Cell Structure: **Prokaryotes and Eukaryotes** -For a cell to be a cell, it has to have the following components: \>Cell membrane -- Holds the cell together, separating the inside from the cell from the outside, controlling what can and cannot enter. \>Cytoplasm -- A jelly-like substances where many chemical reactions inside the cell happen. Surround sub-cellular structures. \>DNA -- The genetic material that controls the the activities of the cell. \>Ribosomes -- The site of protein synthesis in the cell. Eukaryotic Cells:\ Plants cells and animal cella's are eukaryotic cells. A defining feature of eukaryotic cells is that their genetic material is enclosed within a nucleus. Prokaryotic Cells: Bacterial cells are a type of prokaryotic cell. A defining feature of prokaryotic cells is that their genetic material is not enclosed within a nucleus, it is found as a single loop of DNA within the cytoplasm and smaller circular pieces of DNA may also be present. -The cell membranes of all prokaryotic cells are surrounded by a cell wall (usually made from a substance called peptidoglycan) Scale and size of cells: **Animal Cells:** The main sub-cellular structure in animal cells:  **Plant Cells:** In addition to the sub-cellular parts found in animals\' cells, plant cells have: **Photosynthesis** Photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplast by light: Equation: Carbon dioxide + Water ------\> Glucose + Oxygen Carbon Dioxide: Diffuses into the leaf through the stomata. Water: Absorbed into the leaf and transported through the xylem to the leaves. Glucose: Used to make substances needed by the plant and for respiration to release energy. Oxygen: Diffused out of the leaf through the stomata and used for respiration. [Factors that affect the rate of photosynthesis:] [Temperature:] The temperature of the environment affects how much kinetic energy particles have, meaning it affects the rate in which carbon dioxide and water is transported throughout the plant. The lower the temperature the leads kinetic energy the particles have which leads to less collisions happening over a period of time. Increasing temperature means the particles have more kinetic energy which increases the likelihood of more collisions happening between reactants and enzymes resulting in the formation of products. However, the increased temperature can cause the enzymes that control the process of photosynthesis to denature which eventually decrease the rate. [Light Intensity: ] The intensity of the light available to the plant will depend on the amount of energy that it has to carry out photosynthesis: the more intense the light, the faster that rate of photosynthesis. This trend will occur until some other factor prevents the rate from increasing further because it is now short in supply. [Carbon Dioxide: ] Carbon Dioxide is also important for the reaction to occur meaning the more carbon dioxide that is present, the faster the rate of photosynthesis. This trend will occur until some other factor prevents the rate from increasing further because it is now short in supply. [Chloroplast:] Chloroplast are needed for photosynthesis to happen as they contain the pigment that chlorophyll which absorbs the light energy. The more chloroplast there are, the faster the rate of photosynthesis. Factors that could affect the number of chloroplasts: - Disease - Loss of leaves - Lack of nutrients **Uses of glucose in plants:** - Used in respiration. - Used to produce cellulose to strengthen cell walls. - Combined with nitrate ions absorbed from the soil to produce amino acids for protein synthesis. - Used to produce fats and oils for storage. - Converted into insoluble starch for storage in the stems, leaves and roots. A test to prove that a plant is photosynthesizing is to test the leaf for starch in the plant using an iodine solution. Glucose is converted to starch so this test can be used to show the effect of light on photosynthesis. Steps: 1. Place leaf into a beaker of water under a Bunsen burner until boiling. Reason: To break down the cell walls. 2. Place leaf into a tube inside the beaker with ethanol for ten minutes. Bunsen burner should be off. Reason: To remove the chlorophyll from leaf. 3. Place leaf in water to wash it off. Reason: To soften leaf. 4. Place leaf on a white tile and add the iodine solution on it. Reason: To prove the presence of any starch. 5. Observe the color changes. Reason: If the color changes blue/black it means starch is present. **Enzymes** Enzymes are biological catalysts made from protein that speed up chemical reactions. The amino acids in the proteins are bonded together which holds the enzymes shape. Sometimes the bonds break which causes the enzymes to lose its shape and become denatured. The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate. Lock and Key model: One way the describe how enzymes work is through the lock and key model. Enzymes and substrates move randomly in solutions. So, when an enzyme and its complementary substrates randomly collide -- with the substrate fitting into the active site - an enzyme-substrate complex forms, and the reaction occurs. A product(s) forms from the substrate which is/are then released from the active site and the enzyme is unchanged, so it will go on to catalyze further reactions. [The effects of temperature and pH on enzyme activity: ] Temperature: - Enzymes work fastest at their 'optimum temperature'. (In humans its 37 degrees celsius) - Increasing temperature from 0 degrees celsius to the optimum increases the activity of enzymes as the more energy the molecules have the faster, they move and the number of collisions increases, leading to a faster rate of reaction. This means that low temperatures do not denature enzymes, but at lower temperatures with less kinetic energy both enzymes and their substrates collide at a lower rate. - Heating beyond the optimum will start to break the bonds and the enzyme will start to dissolve and lose its shape -- this reduces the effectiveness of substrate binding to active site reducing the activity of enzyme. Eventually the shape of active site is lost becomes denatured. pH: - If the pH is too high or low, the bonds that hold the amino acid chain can be destroyed. This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity. - Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop. **Enzymes and Digestion:** There are 3 main types of digestive enzymes: 1. Carbohydrases -- They break down carbohydrates into simple sugars. Amalyse is a carbohydrase which breaks down starches into maltose. They are made in the pancreas, small intestine, and salivary gland. 2. Proteases -- They break down proteins into amino acids. Protein digestion happens in the duodenum in the small intestine and stomach which are made in the pancreas and small intestine. 3. Lipases -- They break down lipids (fats) into glycerol and fatty acids. They are produced in the pancreas and secreted into the duodenum. [The role of bile:] Bile is produced in the liver and stored in the gallbladder. It has 2 main role: - It is alkaline to neutralize hydrochloride acid from the stomach. The enzyme in the small intestine are more alkaline that those in the stomach. It emulsifies fats (breaks down large drops of fat into smaller ones, increasing surface area). - The alkaline conditions and larger surface area allows lipase to chemically break down lipids into glycerol and fatty acids faster. [Products of digestion:] 1. The products of digestion are used to build new carbohydrates, lipids and proteins required by all cells to function properly and grow. 2. Some glucose released from carbohydrate breakdown is used in respiration. 3. Amino acids are used to build proteins.