Combined Science - Biology : Paper 1

• Cell


  Basic building block of all living organisms
• Specialised cells


  • Become more efficient at their job but may lose the ability to do other jobs
  • Most animal cells differentiate at an early stage, but many plant cells can differentiate throughout their life
  • Once mature, animal cells divide only for cell division and repair
• Specialised animal cells


  • Sperm
  • Nerve
  • Muscle
• Specialised plant cells


  • Root hair
  • Xylem
  • Phloem
• Sperm cell


  • Tail to propel the sperm
  • Many mitochondria for energy
  • Nucleus contains one set of genetic material
  • Acrosome contains enzymes to penetrate egg
• Motor neurone (nerve cell)

  • Dendrites
  • Cell body
  • Axon
  • Sheath
• Muscle cell


  • Nucleus
  • Mitochondria for energy
  • Protein fibres that contract
• Xylem


  • Cells arranged end to end with end walls broken down
  • Cell walls strengthened by lignin
• Phloem


  • End walls allow sugars through but support the tubes
  • Cells arranged end to end into tubes
  • Companion cells
• Root hair cell


  • Lots of mitochondria for active transport
  • Long projection to increase surface area
• Tissue


  Group of cells with similar structure and function, working together
• Organ


  Group of different tissues working together to perform a specific job
• Organ system


  Groups of organs working together to do a particular job
• Enzyme


  Biological catalyst that speeds up chemical reactions
• Enzymes


  • Large protein molecules
  • Have an active site
  • Each catalyses a specific reaction
  • Have an optimum temperature and pH
• Lock and key theory

  Model to explain how enzymes work - the substrate (key) fits into the enzyme's active site (lock)
• High temperatures cause enzymes to denature, which is an irreversible and permanent change
• Digestive enzymes


  Produced by specialised cells and pass out into the digestive system to catalyse reactions
• Enzymes


  Biological catalysts that speed up chemical reactions in living organisms
• Enzymes


  • They are all large proteins
  • They have a space within the protein molecule called the active site
  • Each enzyme catalyses a specific reaction
  • They work best at a specific temperature and pH called the optimum
• Lock and key theory

  A model used to explain how enzymes work: the chemical that reacts (substrate) fits into the enzyme's active site
• Denaturing


  An irreversible and permanent change to the enzyme's shape caused by high temperatures
• If the active site has temporarily changed shape or is denatured, the enzyme will not work and the substrate will no longer sit into the active site
• Digestive enzymes


  • Protease
  • Lipase
  • Carbohydrase
• Amylase


  A carbohydrase that breaks down starch into maltose
• Protease


  Breaks down proteins into amino acids
• Lipase


  Breaks down lipids (fats) into fatty acids and glycerol
• Bile is a liquid made in the liver and stored in the gall bladder. It is alkaline to neutralise hydrochloric acid from the stomach. It also emulsifies fat to form small droplets, increasing the surface area for enzymes to act on
• Bile does not contain any enzymes, so it does not digest any fat molecules. It just breaks up fat droplets into smaller ones
• Investigating the effect of pH on the rate of reaction of amylase enzyme

  1. Put a test tube containing starch solution and a test tube containing amylase into a water bath at 37*

  2. After 5 minutes, add the amylase solution to the starch

  3. Every 30 seconds, take a drop from the mixture and test it for starch using iodine solution

  4. Record how long it takes for starch to be completely digested

  5. Repeat the experiment at different pH values using different buffer solutions
• Blood


  A tissue made of a liquid called plasma, which has three different components suspended in it: red blood cells, white blood cells and platelets
• Red blood cells


  • They contain haemoglobin, which binds to oxygen to transport it from the lungs to the tissues and cells
  • They do not contain a nucleus, so there is maximum capacity for haemoglobin
  • They are very small, so they can fit through tiny capillaries
  • They are shaped like biconcave discs, providing a large surface area for oxygen to quickly diffuse through
• White blood cells


  • They are essential to protect the body against infection
  • They can change shape, squeezing out of the blood vessels into the tissues or to surround and engulf microorganisms
• Platelets


  Fragments of dead cells, which collect at wounds and trigger blood clotting
• Arteries


  • They transport blood from the heart to your organs
  • They have thick walls made from muscle and elastic fibres
• Veins


  • They transport blood from the organs to your heart
  • They have thinner walls with valves to prevent backflow
• Capillaries


  • They allow substances needed by the cells to pass out of the blood
  • They allow substances produced by the cells to pass into the blood
  • They are narrow, thin-walled blood vessels
• The heart pumps blood around the body in a double circulatory system. Blood passes through the heart twice on each circuit
• There are four chambers in the heart: the left and right atria, which receive blood from veins; the left and right ventricles, which pump the blood out into arteries
• How blood flows through the heart

  1. Blood enters the heart through the atria

  2. The atria contract and force blood into the ventricles

  3. The ventricles then contract and force blood out of the heart

  4. Valves make sure the blood flows in the correct direction