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 a nucleus, cell membrane, cytoplasm, mitochondria, and ribosomes
• Plant cell


  Contains a nucleus, cell membrane, cytoplasm, mitochondria, ribosomes, chloroplasts, permanent vacuole, and cell wall
• Animal and plant cells are both eukaryotic cells
• Prokaryotic cell


  Contains a cell membrane, cytoplasm, ribosomes, cell wall, genetic material not enclosed in a nucleus, and may have plasmids and flagella
• Prokaryotic cells, such as bacteria, are different from eukaryotic cells
• Sperm cell


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


  • Has many mitochondria to release energy for contraction
  • Has special proteins that cause contraction by sliding across each other
  • Can store glycogen to be broken down for respiration
• Nerve cell


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


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


  • Forms long hollow tubes to allow easy movement of water and minerals
  • Has spirals of lignin to strengthen the cell walls and support the plant
• Phloem cell


  • Has sieve plates with holes to allow easy movement of dissolved food
  • Has adjacent companion cells with many mitochondria to provide energy for food 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
• Osmosis


  The diffusion of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane
• Osmosis is important in animal cells to maintain the right internal environment
• 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 is 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 burst if a lot of water moves in, killing the cell
• 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

  Water moves out of the red blood cell and into the beaker, 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, requiring 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, which codes for genes
• Cell cycle


  1. Stage 1: Cell growth, increase in subcellular structures, DNA replication

  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 to replace damaged cells
• Stem cell


  Undifferentiated cell capable of differentiating into specialized cells and regenerating new stem cells
• Uses of animal stem cells

  • Embryonic stem cells - can differentiate into many cell types, used for treatment of conditions like paralysis and diabetes
  • Adult stem cells - more limited, found in bone marrow, can differentiate into blood cells
• Uses of plant stem cells


  • Cloning plants quickly and economically
  • Saving rare plants from extinction
  • Cloning crops with desirable features like disease resistance
  • Cloning genetically identical plants for research
• Issues with stem cells include risk of viruses, rejection, and ethical concerns around use of embryos
• Binary fission


  Type of simple cell division in bacteria - genetic material replicates, two copies move to opposite ends, new cell walls form, cytoplasm divides, resulting in two cells
• Binary fission can occur very quickly, e.g. every 20 minutes for Staphylococcus aureus