biology

• Cytoplasm


  Watery solution where chemical reactions take place
• Ribosomes


  Sites of protein synthesis
• Algae are very simple forms of plant life and also have a cellulose cell wall
• Key structures in a plant cell

  • Chloroplasts
  • Cellulose cell wall
  • Permanent vacuole
• Xylem cells


  • Have very thick walls containing lignin to provide support
  • Have broken down end walls to form long tubes for water and dissolved minerals to flow
• Xylem cells


  Have no nucleus, cytoplasm, vacuole or chloroplasts
• Phloem cells

  • Consist of two types: phloem vessel cells and companion cells
  • Phloem vessel cells have no nucleus and limited cytoplasm, with (sieve plates) to allow flow of dissolved sugars
  • Companion cells provide energy to the phloem vessel cells
• Xylem cells and phloem cells are specialized to carry water, minerals and dissolved sugars up and down the plant
• Optical microscope


  • Has a stage to place the microscope slide
  • Has a light source (lamp or mirror) to illuminate the slide
  • Has objective lenses with different magnifications (4x, 10x, 40x)
  • Has an eyepiece lens with 10x magnification
  • Has coarse and fine focusing dials
• Using an optical microscope to view a prepared slide

  1. Place slide on stage and secure with clips

  2. Select lowest power (4x) objective lens

  3. Slowly turn coarse focus dial to lower lens until it almost touches slide

  4. Look through eyepiece and turn coarse focus dial to bring cells into focus

  5. Use fine focus dial to sharpen focus

  6. Calculate total magnification by multiplying eyepiece (10x) and objective (4x, 10x, 40x) lens magnifications
• Drawing of cells should include a magnification scale, measured by placing a ruler on the stage
• Light microscope limitations


  • Limited magnification
  • Limited resolution - blurred images even with increased magnification
• Electron microscope


  • Much greater magnification and resolution than light microscope
  • Allows seeing fine detail in cell structures like the nucleus
• Mitosis definition 


  The process of cell division that produces two genetically identical daughter cells
• Gametes have unpaired chromosomes
• Chromosomes


  Carry a large number of genes that determine many of our features
• Mitosis copies one cell into two identical cells
• Functions of mitosis


  • Essential for growth and development of multicellular organisms
  • Repairs damaged tissues
  • Occurs during asexual reproduction
• Molecules that move in and out of cells by diffusion

  • Oxygen
  • Carbon dioxide
  • Urea
• Respiration produces carbon dioxide

  Carbon dioxide moves out of the cell by diffusion
• Urea is a waste product produced inside cells


  Urea diffuses out of the cells into the blood plasma
• Factors affecting the rate of diffusion

  • Difference in concentrations (concentration gradient)
  • Temperature
  • Surface area of the membrane
• Greater concentration gradient


  Faster diffusion
• Larger surface area of the cell membrane


  Greater rate of diffusion
• Surface area to volume ratio

  Ratio of the surface area to the volume of an organism
• As organisms get larger, the surface area to volume ratio falls sharply
• Problem for multicellular organisms

  • Surface area is not large enough for their volume
  • Cells in the center cannot get enough oxygen by diffusion
• How animals solve the problem

  • Special structures for gas exchange with high surface area (e.g. lungs)
  • Transport system to carry gases around the body
• Plant cell in water

  Water moves into the cell by osmosis, causing the cell to become turgid (swollen)
• Plant cell in concentrated solution

  Water moves out of the cell by osmosis, causing the cell to become flaccid (shrunken)
• The cell wall prevents the plant cell from bursting when water moves in by osmosis
• Effect of osmosis on plant tissue

  1. Place plant cell in water

  2. Water moves into cell by osmosis, cell expands

  3. Place plant cell in concentrated solution

  4. Water moves out of cell by osmosis, cell shrinks
• Potato


  • Commonly used plant tissue to investigate osmosis
  • Can also use other vegetables like beetroot or parsnip
• Investigating effect of osmosis on plant tissue

  1. Peel potato

  2. Use cork board to produce potato cylinders of same diameter

  3. Trim cylinders to same length (around 3cm)

  4. Measure length and mass of each cylinder

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

  6. Leave overnight to allow osmosis

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

  8. Measure length and mass of cylinders again
• Cells lining the human small intestine

  • Have many mitochondria to provide the energy for active transport
• Stages of mitosis


  1. Interphase

  2. Prophase

  3. Metaphase

  4. Anaphase

  5. Telophase

  6. Cytokinesis
• Interphase


  Cell copies its DNA and makes more organelles like mitochondria and ribosomes
• Prophase


  Nucleus begins to break down, spindle fibers appear
• Metaphase


  Chromosomes line up in the middle of the cell
• Anaphase


  Spindle fibers pull the chromatids away to each end of the cell