cell biology

• eukaryotic cell is...

  animals cell, plant cell - both contain a nucleus
• which cell contains genetic material enclosed in a cell?

  eukaryotic cells
• prokaryotic cells are...

  bacteria cells with free flowing dna
• what cells genetic information is not enclosed in a nucleus

  prokaryotic cells
• describe a prokaryotic cell (5)

  much smaller than eukaryotic cells

  contain single loop of dna

  contain plasmids (loops of genetic information)

  have cell wall and cell membrane

  contain cytoplasm
• Diffusion


  The spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration
• Molecules that move in and out of cells by diffusion

  • Oxygen
  • Carbon dioxide
  • Urea
• Cells need oxygen for respiration


  Oxygen moves into the cell by diffusion
• 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
• Higher temperature


  Greater rate of 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
• Single-celled organisms like amoeba have a huge surface area for their volume
• Single-celled organisms can rely on diffusion to transport molecules in and out of their cell
• Calculating surface area to volume ratio

  1. Surface area = 6 x side length^2

  2. Volume = side length^3

  3. Ratio = surface area / volume
• 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
• How fish get oxygen

  • Oxygen-rich water passes into the mouth
  • Flows over gills where oxygen diffuses into the bloodstream
  • Deoxygenated blood passes into the gill filaments, oxygen diffuses in, oxygenated blood returns to the body
• Adaptations of gill filaments

  • Massive surface area
  • Thin membrane for short diffusion pathway
  • Efficient blood supply to maintain concentration gradient
• These adaptations make diffusion as efficient as possible in the gills
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Dilute solution

  • Contains a high concentration of water
  • Contains a low concentration of solute (e.g. sugar)
• Concentrated solution

  • Contains a low concentration of water
  • Contains a high concentration of solute (e.g. sugar)
• Osmosis


  Water diffuses from the dilute solution to the concentrated solution through a partially permeable membrane
• Animal cell in water

  Water moves into the cell by osmosis, causing the cell to expand and potentially burst
• Animal cell in concentrated solution

  Water moves out of the cell by osmosis, causing the cell to shrink
• 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
• explain active transport

  movement of substances from a more dilute solution to a more concentrated solution (against the concentration gradient)
• in active transport, particles are moved against the concentration gradient by energy from respiration
• active transport requires enerdy from active transport