topic 1

• Eukaryotic cells


  Cells with genetic material (DNA) enclosed in a nucleus. Plant and animal cells.

  
• Prokaryotic cells


  Cells with genetic material (DNA) not enclosed in a nucleus. Bacterial cells. Much smaller in comparison.

  
• Genetic material in prokaryotic cells


  • A single loop of DNA. May also have small rings of DNA called plasmids.

  
• Order of magnitude


  A power to the base 10 used to quantify and compare size. 10 (10^1) times bigger = 1 order of magnitude bigger, 100 times (10^2) bigger = 2 order of magnitudes bigger.
• A prokaryotic cell doesn't have DNA is a common misconception

  
• Example application questions


  • Calculate the difference in orders of magnitude between an amoeba and a human egg cell
  • Calculate how many times larger a liver cell is than a bacterial cell and how many orders of magnitude larger
• Sub-cellular structures in animal and plant cells

  • Cell membrane
  • Cytoplasm
  • Nucleus
  • Mitochondria
  • Ribosomes

  
• Additional sub-cellular structures in plant cells

  • Cell wall
  • Chloroplasts
  • Permanent vacuole
• Cell membrane


  Controls movement of substances in and out of cell
• Cytoplasm


  Gel-like substance where chemical reactions take place
• Nucleus


  Contains genetic material (DNA) and controls activities of cell
• Mitochondria


  Site of aerobic respiration and releases energy from glucose
• Ribosomes


  Site of protein synthesis
• Cell wall


  Made of cellulose and strengthens cell
• Chloroplasts


  Contain chlorophyll and absorb light for photosynthesis to make glucose
• Permanent vacuole


  Filled with cell sap and help keep cell turgid / support plant
• Bacterial cells have no sub-cellular structures surrounded by a membrane, e.g. nucleus, mitochondria, chloroplasts
• The cell wall controls what moves in and out of the cell is a common misconception
• Comparison of red blood cell and plant cell structure

  • Both have cytoplasm and cell membrane
  • RBC has no nucleus, plant cell does
  • RBC has no cell wall, plant cell does
  • RBC does not contain chloroplasts or chlorophyll, plant cell does
  • RBC has no (permanent) vacuole, plant cell does
  • RBC contains haemoglobin, plant cell don't

  
• Preparing a microscope slide

  1. Peel off thin layer of plant tissue and place on water drop on slide

  2. Swab inside cheek with cotton bud and smear onto slide

  3. Add a drop of stain

  4. Lower coverslip at an angle without trapping air bubbles

  
• Using a microscope to view cells

  1. Clip slide onto stage and turn on light

  2. Select lowest power objective lens (usually x4)

  3. Use coarse focusing dial to move stage close to lens, then turn to move away until image comes into focus

  4. Adjust fine focusing dial to get clear image

  5. Swap to higher power objective lens, then refocus

  
• Total magnification of a microscope

  Magnification of eyepiece lens x magnification of objective lens

  
• Estimating cell sizes using a microscope

  1. Measure diameter of field of view

  2. Divide this by number of cells that span field of view

  
• Rules of scientific drawing

  • No sketching or shading - only use clear, continuous lines (with a sharp pencil)
  • Include a magnification scale
  • Label important features
• Why use a stain?
• Why use a thin layer of onion tissue?
• Why lower the cover slip at an angle?
• Why view cells using low power objective lens first?
• Safety measure for taking a saliva swab
• How to observe cell structures in greater detail
• Examples of specialised animal cells

  • Sperm cell
  • Nerve cell
  • Muscle cell
• Sperm cell


  • Long tail / flagellum to allow swimming and movement towards egg
  • Many mitochondria for high rate of respiration to release energy for swimming
• Nerve cell


  • Long to carry electrical impulses / signals over long distances
  • Many branches to connect to many other cells forming a network
  • Insulation to speed up transmission of impulses
• Muscle cell


  • Many mitochondria for high rate of respiration to release energy for contraction
• Examples of specialised plant cells

  • Root hair cell
  • Xylem cell
  • Phloem cell
• Root hair cell


  • Long projection to increase surface area for absorption of water by osmosis
  • Many mitochondria for high rate of respiration to release energy for active transport of mineral ions

  
• Xylem cell


  • Lignin in cell wall for strength to withstand pressure of water moving
  • Hollow tubes / no cytoplasm so water / mineral ions can move easily
  • End walls between cells broken down so cells form a long tube
• Phloem cell


  • No nucleus to maximise space for movement of dissolved sugars
  • Pores in end walls so dissolved sugars can move from cell to cell
• Root hair cells do not contain chloroplasts because they are not exposed to light and do not photosynthesise

  
• Adaptations of a salivary gland cell for producing amylase