Cell Biology

• Eukaryotes

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

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

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Components of bacterial cells

  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA and plasmids
• Orders of magnitude

  A way to understand how much bigger or smaller one object is compared to another
• Structures in animal and plant cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional structures in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Structures in bacterial cells

  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Single circular strand of DNA
  • Plasmids
• Cell specialisation

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

  • Sperm cells
  • Nerve cells
  • Muscle cells
• Specialised plant cells

  • Root hair cells
  • Xylem cells
  • Phloem 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, but some stem cells retain this ability
• In plants, many cell types retain ability to differentiate throughout life
• Magnification calculation

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

  Size of image / magnification = size of object
• Culturing microorganisms

  Growing many microorganisms in the lab using nutrients
• If it were incubated at a higher temperature, nearer 37 degrees (human body temperature), it would be more likely that bacteria that could be harmful to humans would be able to grow
• There are 23 pairs of chromosomes in each cell of the body, resulting in 46 chromosomes in total
• Sex cells (gametes) have half the number of chromosomes, resulting in 23 chromosomes in total
• Cell cycle and mitosis

  1. Interphase: cell grows, organelles increase, DNA replicates

  2. Mitosis: chromosomes line up at equator, cell fibres pull chromosomes to either side

  3. Cytokinesis: two identical daughter cells form
• Mitosis

  • Important for growth, development, replacing damaged cells, and asexual reproduction
• Stem cells

  Undifferentiated cells that can undergo division to produce many more similar cells, some of which will differentiate to have different functions
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
  • Meristems in plants
• Therapeutic cloning

  Producing an embryo with the same genes as the patient, to obtain embryonic stem cells that could be grown into needed cells/tissues
• Benefits of stem cell research

  • Can be used to replace damaged or diseased body parts
  • Unwanted embryos from fertility clinics could be used
• Problems of stem cell research

  • We do not completely understand the process of differentiation
  • Removal of stem cells results in destruction of the embryo
  • People may have religious or ethical objections
  • If growing stem cells are contaminated, an infection can be transferred
• Diffusion

  The spreading out of particles in a solution or gas, resulting in net movement from higher to lower concentration
• Diffusion is passive as no energy is required
• Substances that can move across cell membranes by diffusion

  • Oxygen
  • Glucose
  • Amino acids
  • Water
• Examples of diffusion in the body

  • Oxygen and carbon dioxide in gas exchange
  • Urea from liver to blood to kidneys for excretion
• Factors affecting rate of diffusion

  • Concentration gradient
  • Temperature
  • Surface area
  • Thickness of membrane
• Light microscope

  • Microscope slide
  • Cover slip
  • Onion
  • Forceps
  • Iodine solution
  • White tile
  • Scalpel
  • Any other prepared plant and animal cell slides
• Microscopy

  1. Peel off an epidermal layer on the onion using forceps

  2. Mount onto the microscope slide with a drop of water using a pipette, making sure the tissue lies flat

  3. Add 2 drops of iodine solution to stain the cells

  4. Place the cover slip on by first placing one edge down on the slide and slowly lowering the other side of the cover slip using forceps. Make sure no air bubbles are trapped

  5. Remove any excess stain by soaking it with paper towels

  6. Place the slide on the stage of the microscope

  7. Turn the nosepiece to select a low power objective

  8. Set up the microscope - don't look into the eyepiece yet. Instead, use the coarse adjustment knob to raise the stage until the cover slip just touches the objective

  9. Now look into the eyepiece and turn the coarse adjustment knob to move the stage away until the image comes into focus (doing this helps avoid you breaking the slide)

  10. Turn the nosepiece to select a high power objective

  11. Repeat the same process as above and then look into the eyepiece and turn the fine adjustment knob until the image comes into focus

  12. Make a labelled drawing of a few of the cells you can see, including any features eg. cell wall, nucleus. Write down the magnification

  13. Repeat these steps using a prepared slide
• Prokaryotic

  Cells that do not contain a nucleus
• Eukaryotic

  Cells that contain a nucleus
• Features of plant cells not present in bacterial cells

  • Nucleus
  • Mitochondria
  • Chloroplasts
• Mitochondria

  Where respiration takes place, producing energy for the cell to use
• Cells are the basic unit of all living organisms
• Many different types of cells can be found within one organism, all with specific subcellular structures that enable them to perform their individual roles