paper 1 biology

• Light microscope


  Developed in the mid 17th century, uses light to form an image, can view live specimens, relatively cheap and easy to use, can magnify up to 2,000 times, has a resolution of around 200 nanometers
• Electron microscope


  Developed in the 1930s, uses electrons to form an image, can only view dead specimens, 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
• Animal cell organelles


  • Nucleus (controls cell activities and contains DNA)
  • Cell membrane (controls passage of substances in and out)
  • Cytoplasm (liquid gel where chemical reactions occur)
  • Mitochondria (where aerobic respiration occurs)
  • Ribosomes (protein synthesis)
• Plant cell organelles


  • Nucleus
  • Ribosomes
  • Mitochondria
  • Cytoplasm
  • Chloroplasts (contain chlorophyll for photosynthesis)
  • Permanent vacuole (filled with cell sap for support)
  • Cell wall (made of cellulose, provides strength and support)
• Animal and plant cells are both eukaryotic cells, while bacterial cells are prokaryotic
• Prokaryotic cells


  • Have a cell membrane and cytoplasm
  • Genetic material is a single loop of DNA, not enclosed in a nucleus
  • May have plasmids and a slime layer
  • May have flagella for movement
  • Do not have chloroplasts or mitochondria
• As an organism develops, its cells differentiate and become specialized to carry out particular functions
• Sperm cell


  Has a tail to swim, mid-piece with many mitochondria for energy, acrosome with enzymes to penetrate egg, large nucleus to contain DNA
• Muscle cell


  Has many mitochondria to release energy for contraction, special proteins that cause contraction, can store glycogen
• Nerve cell


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


  Has a large surface area projection, large permanent vacuole for osmosis, many mitochondria for active transport of ions
• Xylem cell


  Forms long hollow tubes with lignin spirals to allow easy movement of water and minerals
• Phloem cell


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


  The spreading out of particles in a solution or gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
• 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 more concentrated solution through a partially permeable membrane
• Osmosis occurs


  From a dilute solution to a more concentrated solution
• Osmosis is important in animal cells to maintain the right internal solute concentrations
• 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 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 will determine 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 dilute, 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


  Substances move from a low concentration to a high concentration, against the concentration gradient
• Active transport


  • Requires energy from respiration
  • Takes place across a partially permeable membrane, just like osmosis
• Active transport in plant roots


  Mineral ions move from the dilute solution in the soil into the more concentrated solution in the root hair cells, against the concentration gradient, requiring energy from respiration
• Active transport in the small intestines


  Glucose is moved from the dilute solution outside the blood vessels to the more concentrated solution inside the blood vessels, against the concentration gradient, using active transport
• Nucleus


  Contains chromosomes made up of DNA, which codes for genes
• Cell cycle


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

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

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


  Development, growth, and repair
• Stem cell


  Undifferentiated cell that can differentiate into specialized cells and regenerate new stem cells
• Embryonic stem cells


  • Found in the embryo, can differentiate into many cell types, can be cloned
• Adult stem cells


  • Found in some adult tissues, more limited in the cell types they can differentiate into
• Plant stem cells


  • Found in meristem tissue, can differentiate into all plant cell types even in adulthood, can be used to clone plants
• Issues with stem cells include risk of viruses, rejection, and ethical concerns
• Binary fission


  Type of simple cell division in bacteria, where the genetic material replicates, the two copies move apart, and the cell splits into two