B1

• All living things are made of cells, which are either prokaryotic or eukaryotic.
• Animal and plant cells are eukaryotic.
• Eukaryotic cells contain:

  • A cell membrane
  • Cytoplasm
  • A nucleus containing DNA
• Bacterial cells are prokaryotic and much smaller than animal and plant cells.
• Prokaryotic cells contain:

  • A cell wall
  • A cell membrane
  • Cytoplasm
  • A singular circular strand of DNA and plasmids
• Plasmids are small rings of DNA found in the cytoplasm of prokaryotic cells.
• Organelles are structures in a cell that have different functions within it.
• To reach the prefixes of metre below, you multiply by:

  • Centi - 0.01
  • Milli - 0.001
  • Micro - 0.000,001
  • Nano - 0.000,000,001
• The nucleus:

  • Contains DNA coding for a particular protein needed to build new cells
  • Is enclosed in a nuclear membrane
• The cytoplasm:

  • Is a liquid substance in which chemical reactions occur
  • Contains enzymes
  • Encloses the organelles of the cell
• The cell membrane controls what enters and leaves the cell.
• The mitochondria is where aerobic respiration reactions occur, providing energy for the cell.
• The ribosomes:

  • Are where protein synthesis occurs
  • Are found on a structure called the rough endoplasmic reticulum
• Chloroplasts:

  • Are only found in plant cells
  • Are where photosynthesis takes place, providing food for a plant
  • Contain chlorophyll pigment (turning it green) which harvests the light needed for photosynthesis.
• A permanent vacuole:

  • Is only found in plant cells
  • Contains cell sap
  • Is found within the cytoplasm
  • Improves a cell's rigidity
• A cell wall:

  • Is only in plant cells and algal cells
  • Are made from cellulose
  • Provides strength to the cell
• In bacterial cells, the cell wall is made of peptidoglycan instead of cellulose.
• Bacterial cells contain a single circular strand of DNA in place of a nucleus, and contain plasmids.
• Sperm cells are specialised to carry a male's DNA to the egg cell (ovum) for successful reproduction.
• Sperm cells:

  • Have a streamlined head and long tail to aid swimming
  • Have many mitochondria which supply the energy to allow the cell to move
  • contain digestive enzymes in the acrosome (top of the head) which break down the outer layers of membrane of the egg cell
• Nerve cells are specialised to transmit electrical signals quickly from one place in the body to another.
• Nerve cells:

  • Have a long axon, enabling impulses to be carried long distances
  • Have many extensions from the cell body (dendrites) - allowing branched connections to form between nerve cells
  • Have many mitochondria at the nerve endings, which supply energy to make neurotransmitters (which allow an impulse to be passed from one cell to another)
• Muscle cells are specialised to contract quickly to move bones (striated muscle); or to squeeze (smooth muscle, found in blood vessels so blood pressure can be varied) - therefore causing movement.
• Muscle cells:

  • Have special proteins (myosin and actin) sliding over each other, causing the muscle to contract
  • Have lots of mitochondria to provide energy from respiration for contraction
  • Store a chemical called glycogen that is used in respiration by mitochondria
• Root hair cells are specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots.
• Root hair cells:

  • Have a large surface area due to root hairs, meaning more water can move in
  • Have a large permanent vacuole affecting the speed of movement of water from the soil to the cell
  • Have mitochondria to provide energy from respiration for the active transport of mineral ions into the root hair cell
• Xylem cells are specialised to transport water and mineral ions up the plant from the roots to the shoots.
• Upon formation, a chemical called lignin is deposited in xylem cells which cause them to die. They become hollow and are joined end to end to form a continuous tube so water and mineral ions can move through.
• Lignin is deposited in spirals which helps xylem cells withstand pressure from the movement of water.
• Phloem cells are specialised to carry the products of photosynthesis to all parts of the plants.
• In phloem cells:

  • Cell walls of each cell form structures called sieve plates when they break down, allowing movement of substances from cell to cell
  • Despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria of the companion cells.
• To become specialised, stem cells must undergo differentiation to form specialised cells.
• Differentiation involves some genes being switched on or off to produce different proteins.
• A light microscope:

  • Was first used in 1665
  • Has two lenses (objective and eyepiece)
  • The objective lens produces a magnified image
  • The eyepiece lens magnifies and directed the previous image into the eye
  • Is usually illuminated from underneath
  • Has a maximum magnification of x2000
  • Has a maximum resolving power (resolution) of 200nm
  • Can be used to view tissues, cells and large sub-cellular structures
• Electron microscopes:

  • Were developed in the 1930s
  • Use electrons instead of light to form an image
  • This is possible as electrons have a much smaller wavelength than light
  • Are generally in two types (SEM and TEM)
  • SEM, or scanning electron microscope, creates 3D images (at lower magnification)
  • TEM, or transmission electron microscope, creates 2D images detailing organelles
  • Have a maximum magnification of x2,000,000
  • Have a maximum resolving power (resolution) of 10nm (SEM) - 0.2nm (TEM)
• magnification of a light microscope = magnification of the eyepiece lens x magnification of the objective lens
• Size of an object = size of image / magnification
• The culture medium (in culturing microorganisms) contains carbohydrates for energy, minerals, proteins and vitamins.
• Growing microorganisms in nutrient broth solution:

  1. Involves making a suspension of bacteria to be grown
  2. Mixing it with sterile nutrient broth (the culture medium)
  3. Stoppering the flask with cotton wool to prevent air from contaminating it
  4. Shaking regularly to provide oxygen for the growing bacteria
• Growing microorganisms on an agar gel plate:

  • The agar acts as a culture medium, and bacteria grown on it form colonies on the surface.