Biology

• Components of both plant and animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
• Nucleus


  • Stores genetic information
  • Controls cellular activities
• Cytoplasm


  • Fluid component of the cell
  • Contains organelles, enzymes and dissolved ions and nutrients
• Function of cytoplasm


  Site of cellular reactions e.g. first stage of respiration
• Cell membrane


  Controls the entry and exit of materials into and out of the cell
• Mitochondria


  Site of later stages of aerobic respiration in which ATP is produced
• Organelles found only in plant cells


  • Cell wall
  • Large, permanent vacuole
  • Chloroplasts
• Cell wall


  • Made of cellulose
  • Provides strength
  • Prevents the cell bursting when water enters by osmosis
• Permanent vacuole


  • Contains cell sap (a solution of salts, sugars and organic acids)
  • Supports the cell, maintaining its turgidity
• Chloroplasts


  Site of photosynthesis
• Light microscope


  Passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed
• Pathway of light through a light microscope

  lamp → condenser → specimen → objective lens → eyepiece lens → eye
• Eyepiece lens


  • Magnifies the image
  • Fixed magnification, usually ×10
• Objective lens


  • Magnifies the image
  • Interchangeable magnifications: ×4, ×10, ×40
• Iris diaphragm


  Adjusts the amount of light that passes through the specimen and enters the objective lens
• Condenser


  Focuses light onto the objective lens
• Manual focusing of a light microscope

  Using the coarse focus control and fine focus control
• Coarse focus control


  Used to focus the image under the low-power objective lens
• Fine focus control


  Used to finely adjust the focus of an image
• Cell differentiation


  Process in which unspecialised cells (stem cells) become specialised to have a specific function
• Importance of cell differentiation

  Enables the formation of specialised cells with specific functions e.g. sperm cells, red blood cells
• Tissue


  A group of similar cells which work together to perform a specific function e.g. muscle tissue, xylem tissue
• Organ


  A group of tissues which work together to perform a specific function e.g. brain, heart, kidney
• Organ system


  A group of organs that work together to perform a particular function e.g. nervous system, digestive system
• Organism


  A living thing that is able to function independently e.g. human, sunflower
• the cell wall provides support to the plant cell
• the cell membrane is selectively permeable
• Enzymes


  Biological catalysts that increase the rate of a chemical reaction without being permanently changed themselves
• Enzymes


  • They enable cellular reactions to take place at lower temperatures
• How DNA controls the production of a specific enzyme (higher)

  1. DNA codes for a specific sequence of amino acids

  2. The order of amino acids determines how the enzyme folds and its structure

  3. The shape of the enzyme determines its function
• Substrate


  The chemical that an enzyme works on
• Active site


  The region of an enzyme to which a substrate molecule binds and the reaction takes place
• Enzymes


  • They have a 'high specificity' for their substrate - only substrates with a specific, complementary shape can fit into an enzyme's active site
• What must happen between an enzyme and its substrate for a reaction to occur

  Enzyme and substrate must collide
• Cell membranes


  Partially permeable, enabling some molecules to pass through
• The 'lock and key' model (higher)

  1. Substrate collides with the active site of an enzyme

  2. Substrate binds, enzyme-substrate complex forms

  3. Substrate converted to products

  4. Products released from the active site which is now free to bind to another substrate
• Methods substances can pass through cell membranes

  • Diffusion
  • Osmosis
  • Active transport
• Diffusion


  The net movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient
• Diffusion


  • It does not require energy
• Factors that affect the rate of an enzyme-controlled reaction

  • Temperature
  • pH