b1

• Steps in microscopy practical

  1. Peel off a thin sample of tissue (onion epidermis)

  2. Lay flat on a glass microscope slide and add a drop of suitable stain (iodine)

  3. Lower on a cover slip at an angle

  4. Place the sample on the microscope stage with light on using clips to hold it in place

  5. Use the objective lens with the lowest magnification to focus on the sample (4x)

  6. Slowly turn the coarse focusing dial whilst looking through the eyepiece lens. To make the focus clearer, use fine focusing dial

  7. Draw what is visible

  8. Use a plastic ruler to measure the diameter of the field of view and place this on the drawing to scale alongside the magnification
• Thin sample

  Light can shine through when transparent
• Adding stain

  Cell features have contrast and are more visible
• Lowering cover slip at an angle


  Prevent air bubbles and secure specimen
• Advantages of using your own stem cells rather than embryonic


  cells will not be rejected

  adults can give consent

  no risk of damage to the embryo (potential human life)
• 4 differences between bacteria cell and eukaryotic cell

  • Bacteria has no nucleus, Eukaryotic does
  • Bacteria is smaller
  • Bacteria has plasmids, Eukaryotic does not
  • Bacteria do not have mitochondria, Eukaryotic does
• Describe what happens at each stage:

  a-no change because limited cell division

  b-rapid increase as cells divide rapidly (binary fission) in the plentiful supply of nutrients

  c-no change as cell death rate = cell division rate

  d-begin to decrease as cells die (nutrients run out and toxin build up)

  
• mitosis

  • chromosomes are replicated
  • these chromosomes are pulled apart
  • cytoplasm divides into two by a new cell membrane
  • the set of chromosomes in each new daughter cell are identical
• Why do larger organisms need a respiratory system?


  Smaller SA:V ratio

  Diffusion distance is too large and would take too long to fulfil demands of cells/ organisms
• Adaptations of villi and alveoli

  • both have a large surface area

  o to maximise diffusion

  • both have thin walls or have walls that are one cell thick

  o to reduce diffusion distance

  • both are in close proximity to blood supply

  o to reduce diffusion distance

  • both have a good blood supply

  o to maintain concentration gradient

  • villi have micro villi

  o to (further) increase surface area

  • cells of villi contain many mitochondria

  o for active transport
• Conditions needed for 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.
• Bacteria can be grown in a nutrient broth solution or as colonies on an agar gel plate.
• Aseptic technique


  Procedure to prevent contamination of cultures by microorganisms
• Aseptic technique steps


  1. Spray area with antiseptic spray

  2. Use sterilised Petri dishes and culture media

  3. Create sterile field using Bunsen burner

  4. Sterilise inoculating loop

  5. Sterilise neck of bottle

  6. Dip sterilised loop into bacterial culture

  7. Lift Petri dish lid slightly

  8. Make zig-zag streaks on agar

  9. Secure Petri dish lid with tape and store upside down

  10. Incubate at max 25°C to prevent harmful bacteria growth
• Sterile field

  • Created by updraft of Bunsen burner flame, minimises time cultures/media are open to environment
• Inoculating loop


  • Sterilised by placing in Bunsen burner flame until red hot, then allowed to cool in sterile field
• Bottle neck


  • Placed in Bunsen burner flame to move air out and prevent unknown microorganisms entering
• Petri dish


  • Lid lifted slightly to prevent unwanted microorganisms, secured with tape and stored upside down
• Incubator temperature

  • Maximum 25°C to prevent growth of harmful bacteria
• Why is the Petri dish lid only partially lifted?

  To prevent the entry of microorganisms from the air
• conditions are needed for bacteria to multiply?

  Suitable temperature

  Moisture

  Nutrient presence
• Which two things must a bacterial cell do before it can divide?

  Grow 

  Replicate genetic material
• BINARY FISSION

  1. Bacterial cell grows and replicates genetic material
  2. The two circular strands of DNA move to opposite sides of the cell

  3. A new cell wall from down the middle of the cell

  4. The two halves pull apart to form two cells
• Sperm specialised?

  • 1/2 genetic material
  • streamlined
  • mitochondria
  • flagellum (to swim to egg)
  • digestive enzymes (break a hole into egg)
• An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail.
• Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics.
• The nucleus of a cell contains chromosomes made of DNA molecules. Each chromosome carries a large number of genes. In body cells the chromosomes are normally found in pairs
• grow and increase the number of sub-cellular structures such as ribosomes and mitochondria.

  The DNA replicates to form two copies of each chromosome.

  one set of chromosomes is pulled to each end of the cell and the nucleus divides

  cytoplasm and cell membranes divide to form two identical cells.
• Stem cells from adult bone marrow can form many types of cells including blood cells.
• Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant.
• Treatment with stem cells may be able to help conditions such as diabetes and paralysis.
• Stem cells from meristems used to produce clones of plants quickly + economically.

  • Rare species cloned to protect from extinction.

  • Crop plants with special features eg disease resistance can be cloned -> produce large numbers of identical plants for farmers.
• What is the problem in type 1 diabetes?

  The pancreas is damaged and no longer produces insulin
• What are the 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 embryonic stem cell treatment?

  • rejection risk by the person's immune system as it would identify them as foreign due to different genome
  • limited supply
  • ethical issues
• Risks of using stem cells in medicine

  1. Stem cells could be infected with a virus whilst in the laboratory -> infect the patient.
  2. Stem cells divide quickly - a chance they could divide uncontrollably once they've been transplanted - develop into a tumour. 
• how is exchange surfaces increased?

  having a large surface area

  • a membrane that is thin, to provide a short diffusion path

  • (in animals) having an efficient blood supply

  • (in animals, for gaseous exchange) being ventilated.
• what does HYPERTONIC mean?

  More concentrated solution than the cell
• Hypotonic means

  turgid
• hypertonic means

  flaccid / plasmolysed