Topic 1 : cell biology

• Eukaryotic cells


  Cells that contain their genetic material enclosed in a nucleus
• Eukaryotic cells


  • Contain a nucleus
  • Contain a cell membrane
  • Contain cytoplasm
• Prokaryotic cells


  Cells where the genetic material is not enclosed in a nucleus
• Prokaryotic cells


  • Do not have a nucleus
  • Have a cell membrane
  • Have a cell wall
  • Contain cytoplasm
  • May have plasmids
• Prokaryotic cells


  Are much smaller than eukaryotic cells
• Meter


  The base unit of measurement in science
• Centi


  One hundredth
• Centimeter (cm)


  One hundredth of a meter
• Milli


  One thousandth
• Millimeter (mm)


  One thousandth of a meter
• Micrometer (μm)


  One millionth of a meter
• Nano


  One billionth
• Size of objects


  • Hemoglobin molecule is around 5 nm in diameter
• Eukaryotes


  Organisms whose genetic material is enclosed in a nucleus
• Nucleus


  Encloses the genetic material
• Cytoplasm


  Watery solution where chemical reactions take place
• Cell membrane


  Controls the molecules that can enter and leave the cell
• Mitochondria


  • Where aerobic respiration takes place
• Ribosomes


  • Sites of protein synthesis
• Ribosomes are too small to be seen using a light microscope, an electron microscope is required
• Proteins carry out many functions, including enzymes
• Light microscope


  Microscope that uses light, small, easy to use, relatively cheap
• Resolution of light microscope

  Limited to 0.2 micrometers, any details less than 0.2 micrometers apart will appear blurry
• What light microscopes can be used to see

  • Individual cells like onion cells
• Electron microscope


  Microscope that uses electrons, really big, very expensive, hard to use, only used by scientists in laboratories
• Resolution of electron microscope

  Maximum resolution of 0.1 nanometers, 2000 times better than light microscopes
• What electron microscopes can be used to study

  • Sub-cellular structures like mitochondria
• Electron microscopes can give images with much higher magnifications without going blurry
• Light microscopes


  Pros: small, easy to use, relatively cheap. Cons: limited resolution
• Electron microscopes


  Pros: much higher resolution. Cons: really big, very expensive, hard to use
• Multicellular eukaryotic organisms require a continuous supply of new cells for growth, development and repair
• The process through which these cells are generated is known as the cell cycle
• Cell cycle


  1. Growth

  2. DNA replication(mitosis)

  3. Mitosis and division (cytokinesis)
• DNA


  Usually spread out in long strings when cell is not dividing, condenses into chromosomes when cell starts to prepare for division
• Chromosomes


  • Packets of DNA, each containing a large number of genes that control development of different characteristics
  • Eukaryotic cells have two copies of each chromosome, one from mother and one from father
• Humans have 23 pairs of chromosomes, 46 in total
• Animals of different species can't reproduce to have fertile offspring due to different numbers of chromosomes
• Chromosome duplication


  1. Duplicate stays attached to original chromosome, forming an X shape

  2. Each chromosome is colored half green to highlight the fact that the right half is a duplicate of the left half
• Chromosome alignment and separation

  1. Chromosomes line up along the center of the cell

  2. Fibers from either side of the cell attach to respective half of each chromosome and pull the arms to opposite sides, breaking the chromosomes in half
• Cell division (cytokinesis)


  1. Cell membrane and cytoplasm pull apart, forming two daughter cells

  2. Each daughter cell has the same DNA as the parent cell