Cells

• Eukaryotes


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotes


  Cells that lack a nucleus and membrane-bound organelles
• Components of bacterial cells

  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA and plasmids (provide survival advantage like antibiotic resistance)
• Orders of magnitude


  A way to understand how much bigger or smaller one object is compared to another
• Prefixes to show multiples of units

  • Centi (0.01)
  • Milli (0.001)
  • Micro (0.000,001)
  • Nano (0.000,000,001)
• Structures in animal and plant cells

  • Nucleus (contain genetic information and control activities of the cell)
  • Cytoplasm (jelly like fluid where chemical reactions take place, suspends all organelles)
  • Cell membrane (acts as a barrier and allows substance to move in or out of the cell)
  • Mitochondria (site of aerobic respiration- releases energy in form of ATP)
  • Ribosomes (site of protein synthesis)
• Additional structures in plant cells


  • Chloroplasts (site of photosynthesis)
  • Permanent vacuole (fills with cell sap to maintain rigidity)
  • Cell wall (supports and strengthens the cell- made from cellulose)
• Cell specialisation


  The process where cells gain new sub-cellular structures to be suited to their role
• Specialised animal cells


  • Sperm cells (digestive enzyme in head called acrosome to break down the egg membrane, half no of chromosomes- fuse to form a gamete with 46, tail for swim, mitochondria- energy for movement)
  • Nerve cells (long axons- connections all over body and dendrites form connections and myelin sheath to insulate and speed up transmission)
  • Muscle cells (mitochondria- energy and aerobic respiration for contraction, layers that slide over each other, glycogen which is for storage and converted into glucose for aerobic respiration)
• Specialised plant cells


  • Root hair cells (large SA:V (high diffusion and osmosis), thin membrane -short path, mitochondria- energy for active transport)
  • Xylem cells (dead cells and hollow tube, lignin for strengthening)
  • Phloem cells (companion cells allow transport and living cells)
• Cell differentiation


  The process where stem cells switch on/off genes to produce different proteins and acquire new sub-cellular structures
• In animals, most cells differentiate early and lose ability to differentiate further
• In plants, many cell types retain ability to differentiate throughout life. Meristem tissue.
• Light microscope

  Has two lenses (objective and eyepiece), illuminated from underneath, max magnification x2000, resolving power 200nm

  Total magnification = eyepiece lens * objective lens

  Eyepiece lens has a magnification of x10

  Objective lens has a magnification of x10, x40, x100.
• Electron microscope


  Uses electrons instead of light, can view deep inside sub-cellular structures, max magnification x2,000,000, resolving power 10nm (SEM) and 0.2nm (TEM)
• Magnification calculation


  Magnification of eyepiece lens x magnification of objective lens
• Size calculation


  Size of image / magnification = size of object
• Standard form


  A way to represent very large or small numbers by multiplying a number between 1 and 10 by a power of 10
• Culture medium


  Contains carbohydrates, minerals, proteins and vitamins to grow microorganisms
• Growing microorganisms in nutrient broth

  1. Make suspension of bacteria

  2. Mix with sterile nutrient broth

  3. Stopper flask with cotton wool

  4. Shake regularly
• Growing microorganisms on agar plates

  1. Sterilise petri dish to kill bacteria on it and pour sterile agar into petri dish.

  Sterilise work bench

  2. Allow to set

  3. Inoculating tube through bunsen burner and then drop it into the bacteria and spread bacteria suspension on surface

  Tape it but leave gaps to allow for air in and store upside down to prevent condensation dripping onto the agar

  4. Incubate at 25 degree celsius- prevent growth of harmful pathogens.
• Standard form


  Multiplying a certain number by a power of 10 to make it bigger or smaller, with the 'number' being between 1 and 10
• Standard form examples


  • 1.5 x 10^-5 = 0.000015
  • 3.4 x 10^3 = 3400
• Culturing microorganisms


  Growing many microorganisms in the lab using nutrients. nutrient broth solution or colonies on an agar gel plate.
• Components of culture medium

  • Carbohydrates
  • Minerals
  • Proteins
  • Vitamins
• In animals, most cells differentiate early and lose ability to differentiate, but some like red blood cells are replaced by adult stem cells
• Growing microorganisms in the lab

  1. In nutrient broth solution

  2. On an agar gel plate
• Sterilisation


  Petri dishes and culture media must be sterilised before use, often by autoclave or UV light, to prevent contamination
• Inoculating loops


  Wire loops used to spread microorganisms on agar plates, must be sterilised by passing through a flame
• Sealing Petri dish


  Lid should be sealed but not completely, to prevent airborne contamination while allowing oxygen entry
• Storing Petri dish


  Dish should be stored upside down to prevent condensation disrupting growth
• Incubation temperature


  Plate should be incubated at 25 degrees to prevent growth of potentially harmful bacteria
• Testing antibiotic effectiveness


  Soak paper discs in antibiotics, place on agar plate with bacteria, measure inhibition zone after incubation
• Formula for calculating cross-sectional area
• Chromosomes


  Contain coils of DNA, with each chromosome carrying many genes
• Chromosome number


  23 pairs in body cells, 23 in sex cells
• Cell cycle and mitosis

  1. Interphase: cell growth, organelle increase, DNA replication

  2. Mitosis: chromosome alignment and separation

  3. Cytokinesis: formation of two daughter cells
• Importance of mitosis


  Growth, development, cell replacement, asexual reproduction
• Stem cells


  Undifferentiated cells that can divide to produce more similar cells, some of which can differentiate
• Types of stem cells

  • Embryonic
  • Adult (e.g. in bone marrow)
  • Meristems in plants