Topic 1 ~ Key Concepts in Biology

• Organelles in animal and plant cells

  • Nucleus: Contains DNA coding for a particular protein needed to build new cells, enclosed in a nuclear membrane
  • Cytoplasm: Liquid substance in which chemical reactions occur, contains enzymes (biological catalysts, i.e. proteins that speed up the rate of reaction), organelles are found in it
  • Cell membrane: Controls what enters and leaves the cell
  • Mitochondria: Where aerobic respiration reactions occur, providing energy for the cell
  • Ribosomes: Where protein synthesis occurs, found on a structure called the rough endoplasmic reticulum
• Organelles in bacterial cells

  • Cytoplasm: Liquid substance in which chemical reactions occur
  • Cell membrane: Controls what enters and leaves the cell
  • Cell wall: Made of a different compound (peptidoglycan)
  • Chromosomal DNA (circular): Floats in the cytoplasm
  • Plasmids: Small rings of DNA - code for extra genes to those provided by chromosomal DNA
  • Flagella: Long, thin ‘whip-like’ tails attached to bacteria that allow them to move
• Cells specialise by undergoing differentiation


  A process that involves the cell gaining new sub-cellular structures in order for it to be suited to its role
• Bacterial cells are prokaryotic and much smaller
• All living things are made of cells, which can either be prokaryotic or eukaryotic
• Organelles are structures in a cell that have different functions
• In animals, most cells only differentiate once, but in plants many cells retain the ability
• Organelles in plant cells

  • Chloroplasts: Where photosynthesis takes place, providing food for the plant, contains chlorophyll pigment (which makes it green) which harvests the light needed for photosynthesis
  • Permanent vacuole: Contains cell sap, found within the cytoplasm, improves cell’s rigidity
  • Cell wall (also present in algal cells): Made from cellulose, provides strength to the cell
• Contents

  • Eukaryotic and Prokaryotic Cell Functions
  • Specialised Cells and their Functions
  • Microscopy
  • Size, Scale and Estimations
  • Units and Standard Form
  • Core Practical - Investigating Biological Specimens
  • Enzyme Action
  • Enzyme Denaturation
  • Changing Enzyme Activity
  • Core Practical - Effect of pH on Enzyme Activity
  • Rate Calculations
  • Enzymes as Biological Catalysts
  • Higher and Biology Only Core Practical - Investigating Macronutrients
  • Higher and Biology Only Calorimetry
  • Cell Transport
  • Core Practical - Investigate Osmosis in Potatoes
  • Calculating Percentage Gain and Loss
• Animal and plant cells are eukaryotic
• Specialised cells in plants

  • Root hair cells: specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots
  • Xylem cells: specialised to transport water and mineral ions up the plant from the roots to the shoots
  • Phloem cells: specialised to carry the products of photosynthesis (food) to all parts of the plants
• Light microscope

  • Has two lenses
  • Usually illuminated from underneath
  • Maximum magnification of 2000x and a resolving power of 200nm
  • Used to view tissues, cells, and large sub-cellular structures
• Xylem cells

  • Upon formation, a chemical called lignin is deposited which causes the cells to die
  • Lignin is deposited in spirals which helps the cells withstand the pressure from the movement of water
• Specialised cells in animals

  • Sperm cells: specialised to carry the male’s DNA to the egg cell (ovum) for successful reproduction
  • Egg cells: specialised to accept a single sperm cell and develop into an embryo
  • Ciliated epithelial cells: specialised to waft bacteria (trapped by mucus) to the stomach
• Egg cells

  • Surrounded by a special cell membrane which can only accept one sperm cell and becomes impermeable following fertilisation
  • Lots of mitochondria to provide an energy source for the developing embryo
  • Large size and cytoplasm to allow quick, repeated division as the embryo grows
• Electron microscope


  • Uses electrons to form an image
  • Electrons have a much smaller wavelength than light waves
  • Two types: scanning electron microscope
• Microscopy is used to enlarge images of extremely small structures such as cells
• Ciliated epithelial cells

  • Long, hair-like processes called cilia waft bacteria trapped by sticky mucus down to the stomach
  • This is one of the ways our body protects against illness
• Sperm cells

  • Streamlined head and long tail to aid swimming
  • Many mitochondria (where respiration happens) which supply the energy to allow the cell to move
  • The acrosome (top of the head) has digestive enzymes which break down the outer layers of membrane of the egg cell
  • Haploid nucleus - it has 23 chromosomes
• Root hair cells

  • Have a large surface area due to root hairs, meaning more water can move in
  • The large permanent vacuole affects the speed of movement of water from the soil to the cell
  • Mitochondria to provide energy from respiration for the active transport of mineral ions into the root hair cell
• Phloem cells


  • Cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell
  • The energy these cells need to be alive is supplied by the mitochondria of the companion cells
• In the 1930s, the electron microscope was developed, enabling scientists to view deep inside sub-cellular structures such as mitochondria, ribosomes, chloroplasts, and plasmids
• The first cells of a cork were observed by Robert Hooke in 1665 using a light microscope
• Viruses discovered using transmission electron microscopes (TEMs)

  • poliovirus
  • smallpox
  • Ebola
• Common calculations in microscopy

  1. Magnification of a light microscope: magnification of the eyepiece lens x magnification of the objective lens

  2. Size of an object: size of image/magnification = size of object
• Electron microscopes

  • Magnification of up to 2,000,000x
  • Resolving power of 10nm (SEM) and 0.2nm (TEM)
• Electrons


  Used to form an image due to their much smaller wavelength than that of light waves
• Orders of magnitude


  Used to understand the relative size difference between cells and organelles
• Estimations are useful in Biology to estimate quantities when counting is impractical
• Electron microscopes used to examine proteins in much greater detail than light microscopes, leading to important scientific discoveries
• Discovery of the electron microscope has allowed clearer view of organelles, especially very small structures like ribosomes
• Types of electron microscopes

  • Scanning electron microscope (SEM) creates 3D images
  • Transmission electron microscope (TEM) creates 2D images detailing organelles
• Standard form

  Useful for working with very large or small numbers by multiplying a number by a power of 10 to make it bigger or smaller
• Electron microscope was developed, enabling scientists to view deep inside sub-cellular structures such as mitochondria, ribosomes, chloroplasts, and plasmids
• Using microscopes is an important part of investigating biological specimens
• Prefixes before units of measurement

  • Centi - 0.01
  • Milli - 0.001
  • Micro - 0.000,001
  • Nano - 0.000,000,001
• Using a light microscope

  1. Place the slide on the stage and look through the eyepiece lens

  2. Turn the focus wheel to obtain a clear image

  3. Start with the lowest objective lens magnification

  4. Increase the magnification of the objective lens and refocus
• Enzymes require an optimum pH, temperature, and substrate concentration
• Lock and Key Hypothesis

  1. The shape of the substrate is complementary to the shape of the active site, forming an enzyme-substrate complex

  2. Once bound, the reaction takes place and the products are released from the surface of the enzyme
• Total magnification = objective lens magnification x eyepiece lens magnification