Biology- unit 1

• When making slides of cells, a drop of stain is often used on the specimen to make parts of the cell more visible and prevent cells from drying out
• Living organisms are made up of cells
• Stains

  • Iodine
  • Methylene blue
• Parts of a microscope

  • Eyepiece lens
  • Objective lens
  • Stage
  • Focus knob
  • Coarse focus
  • Fine focus
  • Lamp/minner
• Magnification is a measure of how much the microscope makes the specimen appear
• If you increase the magnification too much on a microscope, you may lose detail
• Using a microscope

  1. You always start with the lowest magnification:

  2. Easier to find the specimen

  3. Easier to focus a sharp image

  4. Less chance of damaging the lens or slide
• The very best light microscopes can magnify objects to meet submicron levels and can resolve details which are about 0.2 µm apart
• The units commonly used to measure length in biology are millimetres or micrometres
• Most cells are microscopic, so small they can only be seen using a lens
• How to make a slide of onion skin cells

  1. Place a thin layer of onion epidermis on a slide

  2. Add a drop of iodine or water

  3. Slowly lower a coverslip using a mounted needle to prevent air bubbles
• When making a slide, the specimen must be thin to allow light to pass through it
• Resolution is the ability to distinguish detail, by being able to resolve between individual points
• Plant cells have a cell wall made of cellulose and provide the cell with cell sap
• Electron microscopes can distinguish the structures inside cells and the structure of chloroplasts or mitochondria
• Stem cells can divide and turn into different types of specialized cells
• Disadvantages of electron microscope

  • They are very expensive
  • They require a lot of space
  • The specimens are always dead
  • The preparation of samples is very complex
• Adult stem cells can change into different types of specialized cells and are found in our own bodies
• Bacteria cells have circular DNA found in the cytoplasm and may have extra small rings of DNA called plasmids
• Bacteria cells are microscopic, single-celled organisms
• Chloroplasts in plant cells contain chlorophyll which traps sunlight for photosynthesis
• The vacuole in plant cells is large and helps the cell keep its shape
• Electron microscopes can even see the detail of large protein molecules
• Bacteria cells have a cell membrane surrounding the cytoplasm, do not have a nucleus, and have a cell wall not made of cellulose
• Embryonic stem cells are the most useful type of cell in the body and can be obtained from embryos, umbilical cords, and bone marrow
• Some people have ethical issues about using human stem cells because it destroys and kills the embryo, is against human rights, and conflicts with their religious beliefs
• Most organisms are multi-celled, and the cells differentiate and become specialized to carry out a particular job or function
• Chemotherapy and radiotherapy


  Kill healthy white blood cells in the patient as well as cancerous ones
• Embryonic stem cells

  Cells that can differentiate to produce all the different types of cells needed
• Basic Life processes

  • Movement
  • Respiration
  • Sensitivity
  • Nutrition
  • Excretion
  • Reproduction
  • Growth
• Patients receiving stem cell transplant

  May have their immune system compromised and be at risk of infections until they have their transplant
• Adult stem cells

  Cells that can change into 1 type of cell
• Types of stem cells

  • Adult stem cells
  • Embryonic stem cells
• Treatment for leukemia

  1. First stage involves chemotherapy and radiotherapy

  2. Second stage involves getting a transplant of bone marrow
• In single-celled organisms, all 7 life processes are carried out by that one cell
• Stem cells received by the patient

  May divide in an uncontrolled way and produce tumors or unwanted cell types
• In multi-celled organisms, the cells differentiate and become specialised
• Examples of organ systems in humans

  • Nervous system - Detect & respond to stimuli
  • Reproductive system - Production of young
  • Excretory system - Removing poisonous waste, maintaining water balance
• Red blood cells contain haemoglobin to carry oxygen, have no nucleus, and have a biconcave shape
• Diffusion

  1. Diffusion is the movement of molecules from a high concentration to a lower concentration

  2. Diffusion is a passive process as the cell does not need to supply energy

  3. The rate of diffusion depends on the difference in concentration, temperature, surface area, and diffusion distance