Organisation

• What are organs?


  Organs are a group of similar tissues that work together to perform a specific function.
• What are tissues?


  Tissues are a group of similar cells that work together to perform a specific function.
• What are organ systems?


  Organ systems are a group of different organs that work together to perform a specific function.
• What are cells?


  Cells are the smallest unit of life that can replicate independently.
• State the functions of all the organs in the digestive system.


  The glands, such as the pancreas and salivary glands, produce digestive juices.

  
  

  The stomach and small intestine digest food.

  
  

  The liver produces bile.

  
  

  The small intestine absorbs soluble food molecules.

  
  

  The large intestine absorbs water from undigested food, leaving faeces.
• What are enzymes?


  Enzymes are proteins that speed up chemical reactions without being used up (biological catalysts).
• What are catalysts?


  Catalysts are substances that increase the rate of chemical reactions without being used up or changed.
• What is the active site of an enzyme?

  The active site of an enzyme is the place on the enzyme that the substrate binds to.
• What are the issues with the lock and key method?


  The lock and key method does not illustrate the fact that the active site of the enzyme changes slightly to mold to the substrate. This is known as the induced fit model.
• What factors affect the rate of enzyme action?


  Factors that affect the rate of enzyme action include pH and temperature.
• What is the effect of high temperatures and pH on enzyme action?


  High temperatures and pH can cause enzymes to become denatured.
• What is the effect of low temperatures and pH on enzyme action?

  Low temperatures and pH will decrease the rate of enzyme action.
• What does it mean to denature an enzyme?


  When an enzyme is denatured, the active site of the enzyme changes shape so that it is no longer complementary to the substrate.
• Describe how to carry out the required practical on investigating the effect of pH on enzyme activity.


  1) Put a drop of iodine solution into every well of a spotting file.

  2) Place a Bunsen burner on a heat-proof mat, and a tripod and gauze over the Bunsen burner. Put a beaker of water on top of the tripod and heat the water until it is 35 °C (use a thermometer to measure the temperature). Try to keep the temperature of the water constant throughout the experiment. 3) Use a syringe to add 1 cm^3 of amylase solution and 1 cm^3 of a buffer solution with a pH of 5 to a boiling tube. Using test tube holders, put the tube into the beaker of water and wait for five minutes.

  4) Next, use a different syringe to add 5 cm^3 of a starch solution to the boiling tube.

  5) Immediately mix the contents of the boiling tube and start a stop clock.

  6) Use continuous sampling to record how long it takes for the amylase to break down all of the starch. To do this, use a dropping pipette to take a fresh sample from the boiling tube every 30 seconds and put a drop into a well. When the iodine solution remains browny-orange, starch is no longer present.

  7) Repeat the whole experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down.

  8) Remember to control any variables each time (e.g. concentration and volume of amylase solution) to make it a fair test. You could use a pH meter to accurately measure the pH of your solutions.
• State the variables in this experiment.


  In the practical wherein the effect of pH on enzyme activity is investigated:

  
  

  Independent variable = the pH of the buffer solution.

  
  

  Dependent variable = the time taken for the starch to break down.

  
  

  Control variables = concentration of the amylase solution, volume of the amylase solution, and the temperature of the water.
• In the pH enzyme rate of reaction required practical, how can you calculate the rate of reaction?

  In this practical, the rate = 1000 / time.
• What is a balanced diet?

  A balanced diet is a diet that includes everything needed to keep the body healthy.
• What are biological molecules?

  The biological molecules include carbohydrates, lipids, proteins, vitamins, minerals, dietary fibre and water.
• Why do humans need carbohydrates?

  Humans need carbohydrates to provide energy for chemical reactions.
• Why do humans need lipids?


  Humans need lipids to help with insulation and maintaining body temperature, and to act as a long-term store of energy.
• Why do humans need proteins?

  Humans need proteins to help with growth and the production of new cells, and to help repair damaged cells.
• Why do humans need fibre?


  Humans need fibre to help food move through the intestines, and to stop us from getting diarrhoea and dehydration.
• Why do humans need iron?


  Iron is a major component of haemoglobin, which is inside of red blood cells. The function of red blood cells is to transport oxygen around the body to provide energy for cellular respiration. Therefore, if humans do not have enough iron, they may become tired, or even develop anaemia.
• What is the difference between vitamins and minerals?

  Vitamins are organic molecules, whereas minerals are inorganic molecules.
• How do humans lose water from the body?


  Water can be lost from the body through breathing, sweating, and urinating.
• What are carbohydrates made of?

  Carbohydrates are made from atoms of carbon, hydrogen, oxygen: form monomers such as glucose, which can then form polymers such as starch and glycogen (plants).
• What are amino acids made from?

  Amino acids are made from atoms of carbon, hydrogen, oxygen, and nitrogen.
• What are lipids made of?

  Fatty acids are made from one glycerol molecule and three fatty acid molecules.
• What foods contain carbohydates?


  Pasta, potatoes and rice all contain carbohydrates.
• What enzyme breaks down carbohydrates, and what is the product?


  Carbohydrates are broken by carbohydrases. A specific type of carbohydrate, starch (a polymer of glucose) is broken down by a specific type of carbohydrase enzyme called amylase into maltose, which can then be broken down by maltase into glucose.
• Where is amylase found?


  Amylase is found in the salivary glands, pancreas and small intestine.
• What foods contain proteins?

  Nuts, meat, fish and beans all contain protein.
• What enzyme breaks down proteins, and what is the product?

  Protease breaks down proteins into amino acids.
• Where is protease found?

  Protease is found in the stomach (pepsin), pancreas and small intestine.
• What foods contain lipids?

  Cheeses, oils, avocados and chocolate all contain lipids.
• What enzyme breaks down lipids, and what is the product?

  Lipase breaks down lipids into glycerol and fatty acids.
• Where is lipase found?


  Lipase is found in the pancreas and small intestine.
• State the functions of bile in digestion.


  Bile is produced in the liver, where it is stored in the gall bladder before it is released into the small intestine. It serves two main functions:

  
  

  1) The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is alkaline, so it neutralises the acid and makes conditions alkaline. The enzymes in the small intestine work best in these alkaline conditions.

  2) It emulsifies fats (i.e. it breaks the fat into tiny droplets). This gives a much bigger surface area of fat for the enzyme lipase to work on which makes the digestion of fats faster.
• What is the function of the stomach in digestion?


  The function of the stomach in digestion is to pummel food with its muscular walls, and produces hydrochloric acid for two reasons: to kill bacteria, and to give the right pH for the protease enzyme to work (pH 2 - acidic).
• How should you prepare a food sample when conducting a food test?

  1) Get a piece of food and break it up using a pestle and mortar.

  2) Transfer the ground up food to a beaker and add some distilled water.

  3) Give the mixture a good stir with a glass rod to dissolve some of the food.

  4) Filter the solution using a funnel lined with filter paper to get rid of the solid bits of food.