GCSE Biology

• What is a tissue?

  A group of cells that act together to perform a specific function.

  
• What is an organ?


  A group of different tissues that work together to perform a certain function.
• What is an organ system?


  A group of organs working together to perform a particular function
• Explain how the 3 tissues of the stomach help in the digestion of food? (Muscular, epithelial and glandular)

  Muscular tissue contracts to churn food.

  Glandular tissue makes enzymes and hydrochloric acid to break down food (also makes protective mucus).

  Epithelial tissue covers the outside of your body and your internal organs.
• Describe the function of the digestive system.

  To break down and deliver nutrients to the bloodstream.
• Explain how the small intestine is adapted to aid the absorption of digested good molecules.

  The surface is covered in villi to provide a large surface area for digested food to be absorbed into the blood. The villi also have a many capillaries to maintain a steep concentration gradient for diffusion and active transport of substances. They have thin membranes so diffusion distances are small and have many mitochondria for active transport.
• Why does your body need carbohydrates? Give some examples of foods that are good sources of carbohydrates.

  Carbohydrates provide us with the fuel that makes all of the other reactions of life possible. It provides glucose for respiration to provide energy to metabolic reactions. Examples of carbohydrate-rich foods are bread, potatoes, rice and pasta.

  
• What is the difference between a simple sugar and a complex carbohydrate?


  Simple sugars contain only 1 sugar unit e.g. glucose

  Complex carbohydrates are made up of long chains of sugar units bonded together e.g. starch. These need to be broken down before they can be absorbed into the bloodstream.
• Why does your body need lipids? Give some examples of foods that are good sources of lipids.

  Lipids are a source of energy and a store of energy. They are important for cell membranes and hormones. Examples of lipid rich foods are oils, butter, margarine, cheese and cream.

  
• Why does your body need proteins? Give some examples of foods that are good sources of proteins.

  Proteins are needed for growth and repair of cells and tissues. They also make enzymes. Examples of protein rich foods are meat, fish, pulses and cheese.

  
• Describe two ways you could test food to see if it contained carbohydrates.

  1) Add 3 drops of iodine to the food solution.

  Iodine is a brown colour at the start, if starch is present it turns blue/black.

  
  

  2) Add Benedict's solution to the food solution and place the test tube in a water bath to heat up (80°C).

  Benedict's solution is blue at the start, if glucose is present it turns red.
• Describe how you would test food to see if it contained protein

  Add Biuret solution to the food solution.

  Biuret solution is a blue colour at the start, if protein is present it turns purple.
• Describe how you would test food to see if it contained lipids

  Add Sudan-3 solution to the food solution and shake.

  If a red oil layer floats on the top of the solution lipids are present.

  OR

  Add ethanol to the food solution and shake

  If a cloudy white layer is produced lipids are present.
• What is a catalyst?


  A substance which increases the speed of a reaction, without being changed or used up in the reaction
• What is an enzyme?

  A biological catalyst. They are long strings of protein molecules.
• What are enzymes made from?

  Long chains of amino acids folded into a specific shape.
• What is the active site of an enzyme?

  Where the substrate fits into the enzyme
• Draw a diagram to show the lock and key mechanism of how an enzyme breaks down a substrate molecule

  
• Define the term metabolism


  The sum of all the reactions in a cell or the body
• Describe the 3 types of metabolic reaction catalysed by enzymes

  1) Building large molecules from smaller ones e.g. building glycogen for storage in humans or producing amino acids in plants.

  
  

  2) Changing one molecule into another e.g. converting glucose into fructose.

  
  

  3) Breaking down larger molecules into smaller ones e.g. breaking down excess amino acids into urea.
• Draw a sketch graph to show the effect of temperature on the rate of enzyme action

  
• Explain why the graph is this shape

  As the temperature rises between 0 and 40°C the rate of reaction increases, this is because the enzymes and substrate molecules are gaining energy and moving faster so they will collide and bind with each other more often.

  The rate of reaction reaches an optimum around 40 °C. The rate of reaction then begins to decrease, this is because the protein structure of the enzyme is affected by high temperatures. The long chain of amino acids begins to unravel and the active site changes shape. The substrate no longer fits into the site and so cannot be broken down. The enzyme has denatured.
• Explain the affect that pH has on enzyme action

  A change in pH affects the forces holding the long chain of amino acid into its specific shape (active site). The shape changes and the substrate no longer fits into the active site. This means the substrate will not be broken down.
• Describe how to carry out a practical to find the effect of pH on the rate of reaction of amylase

  - Place 3 test tubes of starch and 3 of amylase into a water bath at 37◦C.

  - Add a different buffer solution to each test tube of starch to alter the pH e.g. pH 4, 6 and 8

  - Collect a spotting tile and place a drop of iodine into each well.

  - Mix the same volume and concentration of amylase into each test tube and start the clock

  - Take a sample from each tube every 30 seconds using a pipette.

  - Drop the sample onto the spotting tile and record the colour of the iodine.

  - If the iodine turns blue/black continue the investigation.

  - When the iodine remains brown the starch has been broken down and the practical is finished.
• Where is bile produced and stored in the body?

  Bile is produced by the liver and stored in the gall bladder.
• Describe the 2 functions of bile in aiding digestion

  1) Protease enzymes in the stomach work best in acidic conditions so the stomach produces hydrochloric acid to provide the optimum pH. Bile neutralises stomach acid as lipase enzymes and trypsin work best in alkaline conditions.

  
  

  2) Bile emulsifies fats to provide a larger surface area for lipase enzymes to work. The larger surface area helps to breakdown fat quicker. (Fats and water do not mix without an emulsifier).
• Name the substrates and products of Carbohydrase(amylase), Protease and Lipase

  Amylase breaks down starch into sugars. Protease breaks down proteins into amino acids. Lipase breaks down lipids into fatty acids and glycerol.
• Where is carbohydrase(amylase) produced?

  Salivary glands, pancreas, small intestine
• Where is protease produced?

  Stomach, pancreas, small intestine
• Where is lipase produced?

  Pancreas and small intestine
• How do you calculate the magnification of a microscope?

  Objective lens magnification X eyepiece lens magnification
• What are the advantages of using a light microscope?

  Advantages:

  - Relatively cheap

  - Easy to use

  - Portable

  - Can magnify up to x2000

  - Resolving power of 200mm

  - Can magnify live specimens
• What are the disadvantages of using a light microscope?

  Disadvantages:

  - Can't magnify as much as an electron microscope

  - Resolving power is less than an electron microscope

  - Can only produce 2D images
• What are the advantages of using an electron microscope?

  Advantages:

  - Can magnify up to x2,000,000

  - Resolving power of 0.2nm

  - Can produce 2D and 3D images
• What are the disadvantages of using an electron microscope?

  Disadvantages:

  - Very expensive

  - Needs to be kept in specially temperature, pressure and humidity controlled rooms

  - Complicated to use and very large

  - Cannot magnify live specimens
• How do you convert mm into µm?

  1mm = 1000µm
• How do you convert µm into nm?

  1µm = 1000nm
• How can you calculate the size of the real object from a microscope image?

  Size of image/Magnification
• Draw and label the 5 main organelles of an animal cell

  
• What is the function of the nucleus?

  Contains the cell's genetic information and controls the activities of the cell.