Biology paper 1

• Preparing a sample


  1. Break up the food using a pestle and mortar

  2. Transfer to a test tube and add distilled water

  3. Mix the food with the water by stirring with a glass rod

  4. Filter the mixture using a funnel and filter paper, collecting the solution
• Benedict's test for sugars


  • Reagent: Benedict's solution
  • Procedure: Add food sample to a test tube with a few drops of Benedict's solution, put the test tube in a water bath at 80°C for 5 minutes, note down any colour changes
• Iodine test for starch


  Procedure: Add food sample to a test tube, add a few drops of iodine, note down any colour changes
• Emulsion test for lipids

  Procedure: Add food sample to a test tube, add a few drops of distilled water and a few drops of ethanol, shake the solution gently and note down what you see
• Biuret test for protein

  • Reagents: Biuret A and Biuret B
  • Procedure: Add food sample to a test tube, add a few drops of Biuret A and Biuret B, shake the solution gently and note down any colour change
• Colour of positive test result

  • Iodine for starch: blue-black
  • Benedict's for sugar: green to brick-red
  • Ethanol for lipid: cloudy emulsion
  • Biuret for protein: lilac-purple
• Colour of negative test result

  • Iodine for starch: orange-brown
  • Benedict's for sugar: light blue
  • Ethanol for lipid: colourless
  • Biuret for protein: blue
• It is important that you carry out the tests methodically, recording your observations carefully
• Important hazards


  • Biuret solution contains copper (II) sulfate which is dangerous, especially to the eyes - wear goggles
  • Iodine is an irritant to the eyes - wear goggles
  • Sodium hydroxide in biuret solution is corrosive - wash hands immediately if it gets on skin
  • Ethanol is highly flammable - keep away from Bunsen burner
  • Bunsen burner is a hazard
• Gas exchange surfaces


  • Large surface area to allow faster diffusion of gases
  • Thin walls to ensure diffusion distances remain short
  • Good ventilation with air so that diffusion gradients can be maintained
  • Good blood supply (dense capillary network) to maintain a high concentration gradient so diffusion occurs faster
• Gas exchange occurs by the process of diffusion
• Breathing keeps the oxygen level in the alveoli high and the carbon dioxide level low
• Double circulatory system


  A system of blood vessels with a pump (the heart) and valves that maintain a one-way flow of blood around the body
• Heart structure


  • The right side of the heart pumps blood to the lungs for gas exchange (pulmonary circuit)
  • The left side of the heart pumps blood under high pressure to the body (systemic circulation)
• Blood is pumped towards the heart in veins and away from the heart in arteries
• Atria


  The chambers at the top of the heart
• Ventricles


  The chambers at the bottom of the heart
• Pathway of blood through the heart

  1. Deoxygenated blood enters the right atrium

  2. Blood flows down through atrioventricular valves into the right ventricle

  3. Blood travels up through the pulmonary artery to the lungs

  4. Oxygenated blood returns to the left atrium

  5. Blood flows down through atrioventricular valves into the left ventricle

  6. Blood travels up through the aorta to the body
• Adaptations of the heart

  • The walls of the ventricles are much thicker than those of the atria as they are responsible for pumping blood out of the heart and so need to generate a higher pressure
  • The wall of the left ventricle is much thicker than that of the right ventricle as it has to pump blood at high pressure around the entire body, whereas the right ventricle is pumping blood at lower pressure to the lungs
• Atrioventricular valves


  Valves that separate the atria from the ventricles
• Semilunar valves


  Valves found in the two blood arteries that come out of the top of the heart
• The septum prevents the mixing of deoxygenated and oxygenated blood inside the heart
• Cardiac muscle tissue


  • It does not fatigue like skeletal muscle
• The coronary arteries supply the tissue of the heart with oxygenated blood
• Pacemaker


  A group of cells located in the right atrium that coordinate the contraction of the heart muscle and regulate the heart rate
• The pacemaker sends out an electrical impulse which spreads to the surrounding muscle cells, causing them to contract
• If the pacemaker stops functioning properly, it can cause an irregular heartbeat
• Artificial pacemaker


  An electrical device used to correct irregularities in the heart rate, implanted just under the skin with a wire that delivers an electrical current to the heart
• Heart rate


  • The natural resting heart rate is controlled by the pacemaker
  • The faster the heart contracts, the more quickly oxygenated blood can be delivered around the body
  • A lower heart rate is maintained at rest, a higher heart rate is necessary during exercise
• Types of blood vessels

  • Arteries
  • Veins
  • Capillaries
• Arteries

  • Transport blood away from the heart (usually at high pressure)
• Veins

  • Transport blood to the heart (usually at low pressure)
• Capillaries

  • Have thin walls which are "leaky", allowing substances to leave the blood to reach the body's tissues
• Arterial wall

  Thicker than walls of veins to withstand higher blood pressure
• Veins

  • Contain one-way valves to prevent the backflow of blood
• Arterial wall

  Thick layer of smooth muscle and elastic fibres
• Venous wall

  Thin layer of smooth muscle and elastic fibres
• Arteries must withstand high pressures

  Arterial wall is relatively thick with layers of collagen, smooth muscle and elastic fibres
• Elastic fibres in arterial wall

  Allow the artery wall to expand around blood surging through at high pressure when the heart contracts, then recoil when the heart relaxes - this alongside a narrow lumen maintains high blood pressure
• Veins receive low pressure blood

  Venous wall is relatively thin with thinner layers of collagen, smooth muscle and elastic fibres