Cells

• Cells

  The smallest units from which all organisms are made
• Types of organisms

  • Unicellular
  • Multicellular
• Examples of single-celled organisms

  • Bacteria
  • Yeast
• All cells are made from existing cells. New cells are formed when a fully grown cell divides.
• Microscope

  A tool used to see cells clearly
• Light microscope

  • Shines light through the specimen
  • Uses glass lenses to magnify and focus the image
  • Can magnify up to 1500 times
• Photomicrograph

  A photograph taken using a light microscope
• Electron microscope

  • Uses a beam of electrons instead of light
  • Can magnify up to 500,000 times
• Electron micrograph

  A picture taken with an electron microscope
• Cell membrane

  • A very thin layer of protein and fat that surrounds the cell
  • Controls what goes in and out of the cell
  • Partially permeable
• Cell wall

  • A tough layer outside the cell membrane
  • Found in plant, fungal and bacterial cells
  • Made mainly of cellulose
  • Fully permeable
• Cytoplasm

  • The jelly-like material that fills a cell
  • Contains many dissolved substances, especially proteins
  • Where metabolic reactions take place
• Vacuole

  • A fluid-filled space inside a cell, separated from the cytoplasm by a membrane
  • Plant cells have large, permanent vacuoles containing cell sap
  • Animal cells have smaller vacuoles called vesicles
• Nucleus

  • Where the genetic information is stored
  • Contains chromosomes made of DNA
• Chloroplast

  • Found in plant cells
  • Contains chlorophyll
  • Where photosynthesis takes place
  • Can contain starch grains
• Mitochondrion

  • Where aerobic respiration takes place
  • Releases energy from glucose
• Ribosome

  Where the cell makes proteins
• Muscle cells have more mitochondria than other cells because they need more energy.
• Amino acids

  Long chains that are linked together in a particular sequence to form protein molecules
• Mitochondrion

  A small structure in a cell, where aerobic respiration releases energy from glucose
• Aerobic respiration

  Chemical reactions that take place in mitochondria, which use oxygen to break down glucose and other nutrient molecules to release energy for the cell to use
• Ribosomes

  Very small structures in a cell that use information on DNA to make protein molecules
• Cell membrane


  • Separates the inside of the mitochondrion from the rest of the cell
• Mitochondria are the parts of the cell where aerobic respiration happens. This is how energy is released from glucose.
• Bacterial cells are rather different from the cells of animals and plants
• Bacterial cell

  • Has a cell wall made of peptidoglycan, not cellulose
  • Has a partially permeable cell membrane pressed tightly against the inside of the cell wall
  • Has cytoplasm and ribosomes, but no mitochondria or chloroplasts
  • Has a circle of DNA instead of chromosomes inside a nucleus
• Bacterial cells are also known as prokaryotic cells
• Plasmids

  Small, circular molecules of DNA, found in many prokaryotic cells in addition to the main much larger circle of DNA
• Scientists can use the plasmids in the genetic modification of cells and organisms, which you can read about in Chapter 20
• Bacteria reproduce by dividing into two
• Differences between bacterial cells and animal/plant cells

  • Bacterial cells have no nucleus
  • Bacterial cells have a cell wall made of peptidoglycan, not cellulose
  • Bacterial cells have a circular DNA molecule, not chromosomes
• Multicellular organisms, such as humans or plants, may contain many millions of cells
• Not all cells in a multicellular organism are alike - they are specialised to perform particular functions
• Examples of specialised cells

  • Ciliated cells
  • Neurones
  • Red blood cells
  • Sperm cells
  • Egg cells
  • Root hair cells
  • Palisade mesophyll cells
• Tissue

  A group of similar cells that work together to perform a particular function
• The stomach contains different tissues, including a layer of muscle cells and a layer of cells that secrete digestive enzymes
• Plants also have tissues, such as the palisade tissue in leaves
• Organ

  A group of different tissues that carry out a function together
• The stomach is an organ, as are the heart, kidneys, and lungs
• Organ system


  Several organs that work together to perform a particular function