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 resolving power of around 200 nanometers
• Electron microscope


  • Developed by scientists in the 1930s
  • Uses electrons to form an image
  • Specimens must be dead
  • Very expensive and has many conditions
  • Can magnify up to 2 million times
  • Has a resolution of 0.2 nanometers
• The electron microscope is much better than the light microscope in terms of magnification and resolution
• Organelles in animal cells

  • Nucleus
  • Cell membrane
  • Cytoplasm
  • Mitochondria
  • Ribosomes
• Organelles in plant cells

  • Nucleus
  • Cell membrane
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Eukaryotic cells


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotic cells


  Cells that lack a nucleus and membrane-bound organelles, such as bacteria
• Features of prokaryotic cells

  • Cell membrane
  • Cytoplasm
  • Ribosomes
  • Cell wall
  • Single loop of DNA
  • Plasmids
  • Slime layer
  • Flagella
• Prokaryotic cells lack chloroplasts and mitochondria
• Cell differentiation


  The process by which cells become specialized to carry out specific functions
• Specialized animal cells


  • Sperm cell
  • Muscle cell
  • Nerve cell
• Sperm cell


  • Tail for swimming
  • Mitochondria in mid-piece for energy
  • Acrosome with enzymes to penetrate egg
  • Large nucleus to contain DNA
• Muscle cell


  • Mitochondria to release energy for contraction
  • Contractile proteins
  • Ability to store glycogen
• Nerve cell


  • Long axon to carry electrical impulses
  • Dendrites to connect to other nerve cells
  • Nerve endings to release chemical messengers
• Root hair cell

  • Large surface area for absorption
  • Large permanent vacuole for osmosis
  • Many mitochondria for active transport
• Xylem cell


  • Hollow tubes for easy water/mineral movement
  • Spiral lignin for strength and support
• Phloem cell


  • Sieve plates for easy transport of dissolved food
  • Companion cells with mitochondria to provide energy
• Diffusion


  The spreading out of particles in a solution or gas from an area of higher concentration to an area of lower concentration
• Diffusion is a passive process that does not require additional energy
• Factors affecting rate of diffusion

  • Temperature
  • Concentration gradient
  • Surface area
• Osmosis


  The diffusion of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane
• Osmosis is a passive process that occurs down a concentration gradient
• Difference in water concentration across a cell membrane


  Determines the rate of osmosis
• Hypotonic solution


  More dilute than the cell's internal environment
• When a red blood cell is put in a hypotonic solution


  Water moves into the cell, causing it to stretch and potentially burst
• Isotonic solution


  Has the same concentration as the cell's internal environment
• In an isotonic solution, there is no net movement of water (no osmosis)
• Hypertonic solution


  More concentrated than the cell's internal environment
• When a red blood cell is put in a hypertonic solution


  Water moves out of the cell, causing it to shrink
• Active transport


  1. Moves substances from a low concentration to a high concentration (against the concentration gradient)

  2. Requires energy from respiration
• Dilute solution


  Low concentration of solute
• Concentrated solution


  High concentration of solute
• Active transport allows plants to absorb mineral ions from the dilute solution in the soil into the more concentrated solution in the root hair cells
• Active transport in the small intestine allows glucose to be moved from the dilute solution in the intestine into the more concentrated solution in the blood
• Nucleus


  Contains chromosomes made up of DNA
• Cell cycle


  1. Stage 1: Cell growth and DNA replication

  2. Stage 2: Mitosis - Chromosomes separate and nucleus divides

  3. Stage 3: Cytoplasm and cell membrane divide to form two new cells
• Mitosis


  • One set of chromosomes is pulled to each end of the cell
  • Nucleus divides
  • Cytoplasm and cell membrane divide to form two new cells