Biology P1

• The first topic is cell biology and we're starting with microscopy
• Light microscope


  It was first developed in the mid 17th century and it uses light to form an image
• Light microscope


  • Can be used to view live specimens
  • It's pretty cheap and easy to use
  • The best ones can magnify up to 2,000 times
• Resolution


  The ability to see two things as separate objects. A high resolution means you can see lots of detail and everything is clear and separated.
• Light microscope


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


  It was developed by scientists in the 1930s and it uses electrons to form an image
• Electron microscope


  • The specimens must be dead first so it can't be used to view living specimens
  • It's a very expensive microscope and it has a lot of conditions so that needs to be capped on
  • The magnification can be up to two million times
  • It has a really high resolution of just 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 and plant cells are both eukaryotic cells
• Prokaryotic cells are different from eukaryotic cells. All bacteria are prokaryotes.
• Organelles in a prokaryotic cell

  • Cell membrane
  • Cytoplasm
  • Ribosomes
  • Cell wall (not made of cellulose)
  • Single loop of DNA (not enclosed in a nucleus)
  • Plasmids
  • Slime layer
  • Flagellum/Flagella
• Prokaryotic cells don't have chloroplasts or mitochondria as they are too small to fit inside them
• As an organism develops, its cells differentiate and become specialized to carry out particular functions
• Sperm cell


  • Tail to help it swim
  • Mid-piece with many mitochondria to release energy for movement
  • Acrosome with digestive enzymes to penetrate the egg
  • Large nucleus to contain DNA
• Muscle cell


  • Many mitochondria to release energy for contractions
  • Special proteins that cause contractions by sliding across each other
  • Can store glycogen to be broken down for respiration
• Nerve cell


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


  • Protrusion to provide large surface area for absorption
  • Large permanent vacuole to speed up osmosis
  • Many mitochondria for active transport of mineral ions
• Xylem cell


  • Long hollow tubes with removed cell walls to allow easy movement of water and mineral ions
  • Spirals of lignin to strengthen the cells and support the plant
• Phloem cell


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


  The spreading out of particles of any substance in solution, resulting in a net movement from an area of higher concentration to an area of lower concentration
• Diffusion is a passive process as it happens down a concentration gradient and no additional energy is needed
• Factors affecting rate of diffusion

  • Temperature (higher temperature increases rate)
  • Concentration gradient (steeper gradient increases rate)
  • Surface area (larger surface area increases rate)
• Osmosis


  The diffusion of water molecules from a dilute solution to a concentrated solution through a partially permeable membrane
• Osmosis is a passive process like diffusion, as it happens down a concentration gradient
• Difference in water concentration across a cell membrane

  Determines the amount of osmosis that occurs
• Osmosis is important in animal cells to maintain the right internal environment for the cell to function
• Left side of the membrane

  Has more water molecules
• 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

  2. From a dilute solution to a more concentrated solution

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

  4. Water concentration will eventually be equal on both sides

  5. Water molecules will continue to move back and forth across the partially permeable membrane but there is no further net movement of water
• 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

  1. Water moves into the cell, stretching it

  2. If a lot of water moves in, the cell may burst
• What happens when a red blood cell is put into an isotonic solution

  No net movement of water, no osmosis occurs
• What happens when a red blood cell is put into a hypertonic solution

  1. Water moves out of the cell and into the beaker

  2. The cell will shrink and not function properly
• Required practical A by osmosis looks at 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 the 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 intestine into the more concentrated solution in the blood vessels
• Nucleus


  Contains chromosomes made up of DNA
• Cell cycle


  1. Stage 1: Cell growth, DNA replication

  2. Stage 2: Mitosis - chromosomes pulled to each end, nucleus divides

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


  Development, growth, repair