Paper 1 bio

• What is a microscope used for


  Magnify things to make them look bigger
• What are electron microscopes used for


  Have a higher resolution

  show more detail images

  higher magnification small things
• 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 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 genetic material as a single loop of DNA in the cytoplasm, may have plasmids and a cell wall, but lack organelles like mitochondria and chloroplasts
• Specialized animal cells


  • Sperm cell: has a tail for movement, acrosome to break down egg, many mitochondria
  • Muscle cell: has many mitochondria for energy, special proteins for contraction, can store glycogen
  • Nerve cell: has a long axon to carry electrical impulses, dendrites to connect to other cells, nerve endings with mitochondria
• Specialized plant cells

  • Root hair cell: has a large surface area, large permanent vacuole, many mitochondria
  • Xylem cell: forms long hollow tubes, has spiral lignin to strengthen and support
  • Phloem cell: has sieve plates to allow movement of dissolved food, companion cells with mitochondria
• Diffusion


  The spreading out of particles in a solution or gas 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 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

  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 - 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 the concentration gradient
  • Requires energy from respiration
• Examples of active transport

  • Mineral ions moving from soil into plant roots
  • Glucose moving from small intestines into bloodstream
• Mitosis and the cell cycle

  1. Stage 1: Cell growth, DNA replication

  2. Stage 2: Chromosomes pulled to opposite ends, nucleus divides

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


  • Development from a single cell
  • Growth during childhood and puberty
  • Repair of damaged tissues