imported cards

• Cytoplasm


  Where most of the chemical reactions that make up life go on
• Cell membrane


  Controls what enters and leaves the cell
• Nucleus


  Contains DNA, the chemical that controls the cell's activities
• Mitochondria


  Structures that carry out aerobic respiration, supplying cells with energy
• Features found only in plant cells

  • Cell wall made of cellulose
  • Large, permanent central vacuole filled with cell sap
  • Chloroplasts which absorb light for photosynthesis
• Chloroplasts are not found in all plant cells, but they are never found in animal cells
• Microscope


  • Eyepiece lens
  • Objective lenses
  • Stage
  • Iris diaphragm and condenser
  • Lamp
• Microscope focusing


  • Coarse focus to get the image roughly into focus
  • Fine focus to fine tune the image and make it as clear as possible
• Microscope slides hold thin specimens or sections, which may be stained using a variety of dyes so that structures can be seen more clearly
• Specialised cells


  • Features modified to suit their function
• Levels of organisation in the structure of living things

  • Tissue
  • Organ
  • Organ system
  • Organism
• In distinguishing plant and animal cells, the cell wall is the key feature, because some plant cells do not have chloroplasts and some animal cells have (temporary) vacuoles
• Diffusion


  The spreading of particles from an area of higher concentration to an area of lower concentration, as a result of random movement
• Osmosis


  The diffusion of water molecules through a selectively permeable membrane from a solution of low solute concentration to a solution of high solute concentration
• Active transport


  The movement of substances against a concentration gradient, requiring energy
• If an animal cell is put into a solution that is more dilute than its cytoplasm

  Water will go in by osmosis and the cell will burst
• Very concentrated solutions


  Damage both plant and animal cells, causing them to lose water and animal cells to shrivel, and plant cells to undergo plasmolysis
• Enzymes


  Special molecules that control the chemical reactions in the body
• Properties of enzymes


  • They are proteins
  • They have a specific molecular shape
  • They are catalysts that speed up chemical reactions without taking part in them
  • They are specific, only catalysing one reaction or one type of reaction
  • Their rate is affected by temperature, pH, and concentrations of enzyme and substrate
• Lock and key theory


  The enzyme molecule must collide with and "lock together" with its substrate, the active site of the enzyme matching the shape of the substrate
• Increasing temperature


  Speeds up enzyme-controlled reactions by making the particles move faster, but high temperatures can denature the enzyme
• pH values far from the optimum


  Can cause the enzyme to denature
• Enzymes do not take part in the reactions they catalyse