Biology Paper 1

• Microscopy


  The study of small objects using a microscope
• Light microscope


  • First developed in the mid 17th century
  • Uses light to form an image
  • Can be used to view live specimens
  • Relatively cheap and easy to use
  • Can magnify up to 2,000 times
• Resolution


  The ability to see two things as separate objects
• Light microscope


  • Has a low resolution with a resolving power of around 200 nanometers
• Electron microscope


  • Developed by scientists in the 1930s
  • Uses electrons to form an image
  • Specimens must be dead first
  • Very expensive and has many conditions
  • Can magnify up to 2 million times
  • Has a high resolution of 0.2 nanometers
• The electron microscope is much better than the light microscope in terms of magnification and resolution
• The high magnification and resolution of the electron microscope allows scientists to see and understand lots more about the subcellular structures of cells
• Animal cell


  Contains the following organelles: nucleus, cell membrane, cytoplasm, mitochondria, ribosomes
• Nucleus


  Controls the cell's activities and contains genetic material (DNA)
• Cell membrane


  Responsible for controlling the passage of substances in and out of the cell
• Cytoplasm


  Liquid gel that fills the entire cell and is where chemical reactions occur
• Mitochondria


  Where aerobic respiration occurs, releasing energy for the cell
• Ribosomes


  Site of protein synthesis
• Plant cell


  • Contains the following organelles in addition to those in animal cells: chloroplasts, permanent vacuole, cell wall
• Chloroplasts


  Contain chlorophyll and are the site of photosynthesis
• Permanent vacuole


  Filled with cell sap, helps keep the cell rigid
• Cell wall


  Made of cellulose, strengthens and supports the plant cell
• Animal and plant cells are both eukaryotic cells
• Eukaryotic cells


  Have a cell membrane, cytoplasm, and genetic material enclosed in a nucleus
• Prokaryotic cells


  Lack a true nucleus, have a single loop of DNA in the cytoplasm, may have plasmids and a cell wall, but lack organelles like mitochondria and chloroplasts
• Sperm cell


  • Has a tail to help it swim, many mitochondria in the mid-piece to provide energy, an acrosome containing enzymes to break down the egg, and a large nucleus to contain DNA
• Muscle cell


  • Has many mitochondria to release energy for contraction, special proteins that cause contraction by sliding across each other, and can store glycogen for respiration
• Nerve cell


  • Has a long axon to carry electrical impulses, dendrites to connect to other nerve cells, and nerve endings that release chemical messengers
• Root hair cell


  • Has a large surface area for absorption, a large permanent vacuole to speed up osmosis, and many mitochondria for active transport of mineral ions
• Xylem cell


  • Forms long hollow tubes to allow easy movement of water and mineral ions, has spiral lignin to strengthen the cell walls and support the plant
• Phloem cell


  • Has sieve plates with holes to allow easy movement of dissolved food, and companion cells with many mitochondria to provide energy for the transport
• Diffusion


  The spreading out of particles in a solution or gas from an area of higher concentration to an area of lower concentration
• Osmosis


  The diffusion of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane
• Difference in water concentration between cell interior and exterior

  Determines the rate of osmosis
• Right side of the membrane

  Has less water molecules and more sucrose or solute molecules, therefore it is the concentrated side
• Osmosis


  1. Occurs down a concentration gradient or from a dilute solution to a more concentrated solution

  2. Net movement of water is from the left side to the right side

  3. Water concentration will eventually be equal on both sides

  4. Water molecules will continue to move back and forth across the partially permeable membrane but there's no further net movement of water, the water is balanced on both sides
• Importance of osmosis in animal cells

  • Ensures solutes like glucose and salts are at the right concentration inside the cell
  • The internal environment needs to be kept just right for the cell to work
  • The difference in concentration between the cell's internal environment and the external solution determines how much osmosis occurs
• What happens when a red blood cell is put into a hypotonic solution

  Water moves into the cell, stretching it, and the cell may even burst if a lot of water moves in, killing the cell
• What happens when a red blood cell is put into an isotonic solution


  Nothing happens, as the two solutions are the same, there is no net movement of water, no osmosis occurs
• What happens when a red blood cell is put into a hypertonic solution

  Water moves out of the red blood cell and into the beaker, as the red blood cell solution is more diluted, the cell will shrink and not function properly
• Required practical A: Investigating the effect of concentration of salt or sugar on the mass of plant tissue
• Active transport


  Moves substances from a more dilute solution to a more concentrated solution, against a concentration gradient, requires energy from respiration
• Examples of active transport

  • Mineral ions moving from the dilute solution in the soil into the more concentrated solution in the root hair cells
  • Glucose moving from the dilute solution in the small intestines to the more concentrated solution in the blood vessels
• Mitosis and the cell cycle

  1. Stage 1: Cell grows, increases subcellular structures, DNA replicates

  2. Stage 2: Mitosis - one set of chromosomes pulled to each end of the cell, nucleus divides

  3. Stage 3: Cytoplasm and cell membrane divide to form two identical cells
• Importance of mitosis and the cell cycle

  • Development - from single cell to full organism
  • Growth - new cells needed during childhood and puberty
  • Repair - new cells needed to replace damaged cells