Cell Biology

• Explain how a sperm cell is adapted for its role.

  
  

  Function:

  Its role is to deliver genetic material to an egg cell to fertilise it

  
  

  Adaptations:

  It has half as much genetic material as a normal cell, so that the sperm and egg together will have the normal amount

  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
• Bacteria are unicellular. This means that when they divide by binary fission they're also reproducing as each new cell is a separate organism. This is an example of Asexual reproduction
• Binary Fission Process

  The two circular strands of DNA move to opposite sides of the cell

  A new cell wall from down the middle of the cell

  The two halves pull apart to form two cells
• The plasmids are randomly arranged, so there are often more plasmids in one cell that the other. 
• Division time

  The mean (average) time it takes for a bacterial cell to divide
• Factors affecting the speed of bacterial growth:

  1. Temperature - most bacteria grow fastest in warm environments.
  2. Nutrient availability - bacteria need a good supply of nutrients in order to grow rapidly.
  3. Moisture - most bacteria grow fastest in moist conditions.
  4. Oxygen - different types of bacteria either need the presence or absence of oxygen for growth.
• Cleaning surfaces with disinfectant

  • Cleaning the work area before and after use with alcohol
• Washing hands with antiseptic soap and warm water


  • Before handling microorganisms
• Sterilising all instruments, solutions, and mediums

  Heating objects to a temperature at which all contaminating microorganisms are destroyed
• Creating a sterile field using a Bunsen burner

  1. A sterile field is a sterilised area created by the updraft of the flame

  2. Biologists can try to work within the sterile field

  3. Minimise the time that cultures and growth media are open to the environment
• Growing bacteria in incubators

  Set to a maximum of 25°C to prevent the growth of harmful pathogens which prefer body temperature (37°C)
• Inoculating loop sterilisation

  1. Placed in Bunsen burner flame until red hot

  2. Held in sterile field area and allowed to cool
• Preparing bacterial culture bottle

  1. Lid removed

  2. Neck placed in Bunsen burner flame to move air out and prevent contamination

  3. Sterilised inoculating loop dipped into bacterial culture

  4. Neck flamed again and cap replaced
• Inoculating agar plate

  1. Petri dish lid lifted slightly

  2. Zig-zag streaks made gently and carefully across agar with inoculating loop

  3. Petri dish lid quickly replaced

  4. Lid secured to prevent contamination
• Incubating inoculated plate

  1. Petri dish stored upside down in incubator

  2. Maximum incubator temperature 25°C to prevent growth of harmful bacteria
• Cleaning up

  1. Inoculating loop sterilised again

  2. All work surfaces disinfected
• Steps of stem cell treatment

  1. Extract embryonic stem cells from early embryos.
  2. Grow them in a laboratory.
  3. Stimulate them to differentiate into whichever type of specialised cell that we want.
  4. Give them to the patient to replace their faulty cells.
• drawbacks of using embryonic stems cells in stem cell therapy. 

  Stem cells have a limited supply

  The risk of rejection

  Ethical issues associated with stem cells 
• Risks of using stem cells in medicine

  1. The stem cells could be infected with a virus whilst in the laboratory, which could then infect the patient.
  2. As stem cells divide quickly, there is a chance they could divide uncontrollably once they've been transplanted, and then develop into a tumour. 
• factors that affect the rate of diffusion.

  Concentration gradient 

  Temperature 

  Surface area

  Distance to diffuse across (if diffusing across a membrane)
• Osmosis is the net movement of water molecules across a partially permeable membrane, from a region of higher water concentration, to a region of lower water concentration.
• What would happen to red blood cells if they were placed in pure water?

  If placed in pure water, then the water concentration would be higher outside the cell (in the pure water) than inside the cell. This means that water would move down its concentration gradient into the cell, causing it to swell and possibly burst.
• Osmosis

  Diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Plant cells placed in water

  Water moves into the cell by osmosis, causing the cell to expand
• Plant cells placed in concentrated solution

  Water moves out of the plant cell by osmosis, causing the cell to shrink
• Investigating the effect of osmosis on plant tissue

  1. Peel potato

  2. Use cork board to produce cylinders of equal diameter

  3. Trim cylinders to equal length

  4. Measure length and mass of cylinders

  5. Place cylinders in test tubes with different solutions (0.5M sugar, 2.5M sugar, distilled water)

  6. Leave overnight

  7. Remove cylinders, gently roll on paper towel to remove surface moisture

  8. Measure length and mass of cylinders again
• Percentage change

  Calculated as: (Change in value / Original value) x 100
• Calculating percentage change

  • Potato cylinder starting mass 1.56g, increases by 0.25g - Percentage increase = 16.03%
  • Potato cylinder starting mass 1.32g, decreases by 0.19g - Percentage decrease = 14.39%
• Concentration of sugar solution

  Affects percentage change in mass/length of potato cylinder
• In water, potato cylinder gains mass as water moves in by osmosis. In concentrated sugar solution, cylinder loses mass as water moves out by osmosis. Where line crosses x-axis, no change in mass as concentration outside cell is same as inside.
• Active transport is the movement of molecules across a membrane, from a region of lower concentration to a region of higher concentration. This requires energy from respiration. This is an active process
• Active transport can only take place across a membrane
• Why can't plants absorb mineral ions by diffusion?

  Their concentration is higher in the cell than in the soil