Specialised cells

• Sperm cell

  Functions

  • Its role is to deliver genetic material to an egg cell to fertilise it
  • It has half as much genetic material as a normal cell, so that the sperm and egg together will have the normal amount

  Adaptations

  • It has lots of mitochondria to provide the energy for movement
  • It has a flagellum to allow it to swim to reach the egg
  • It is streamlined to make swimming easier 
  • It has digestive enzymes in its head to break through the wall of the egg
• The embryonic stem cells must come from embryos. These are in limited supply, and some people have ethical objections to it, as they think the embryos could have developed into a person.

  The cells could be rejected by the person's immune system as it would identify them as foreign.
• Factors that affect the rate of diffusion

  Concentration gradient 

  Temperature 

  Surface area
• Why does a higher temperature increase the rate of diffusion?

  Higher temperature means particles have more (kinetic) energy

  So they move around faster 

  And can diffuse more quickly
• Explain how increasing the temperature can cause an enzyme to denature.

  High temperatures start to break the bonds holding the enzyme together 

  This causes the enzyme and it's active site to change shape

  This means the enzymes active site will no longer be complementary to the substrate 
• Main uses of glucose in a plant

  Cellular respiration - break down the glucose to release energy 

  Make cellulose - which is used to make strong cell walls

  Make starch - which is used to store glucose for a later time

  Make amino acids - which are used to make proteins 

  Make lipids - these store the energy as fats or oils for later use
• Describe and explain how the rate of photosynthesis varies with temperature. 

  Rate initially increases with temperature...

  ...because particles have more energy and move faster, so react more frequently

  Highest rate is at optimum temperature for enzyme

  At higher temperatures the rate decreases as bonds holding the enzyme together begin to break, and so the enzyme changes shape

  Rate falls to zero as enzymes denature