2. Cell Structure

• Main features of animals

  • Multicellular
  • Cells contain a nucleus with a distinct membrane
  • Cells do not have cellulose cell walls
  • Cells do not contain chloroplasts (so they are unable to carry out photosynthesis)
  • Feed on organic substances made by other living things
  • Often store carbohydrates as glycogen
  • Usually have nervous coordination
  • Able to move from place to place
• Main features of plants

  • Multicellular
  • Cells contain a nucleus with a distinct membrane
  • Cells have cell walls made out of cellulose
  • Cells contain chloroplasts (so they can carry out photosynthesis)
  • Feed by photosynthesis
  • Store carbohydrates as starch or sucrose
  • Do not have nervous coordination
• Biological characteristics of bacteria

  • Microscopic single-celled organisms
  • Possess a cell wall (made of peptidoglycan, not cellulose), cell membrane, cytoplasm and ribosomes
  • Lack a nucleus but contain a circular chromosome of DNA that floats in the cytoplasm
  • Plasmids are sometimes present - these are small rings of DNA (also floating in the cytoplasm) that contain extra genes to those found in the chromosomal DNA
  • Lack mitochondria, chloroplasts and other membrane-bound organelles found in animal and plant cells
  • Some have a flagellum (singular) or several flagella (plural) that allow them to move
• Bacteria

  • Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk)
  • Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia)
• Organelles visible in the cytoplasm of most cells (except prokaryotes) at higher magnification


  • Mitochondria
  • Ribosomes (free in cytoplasm or attached to Endoplasmic Reticulum)
  • Rough Endoplasmic Reticulum (R.E.R.)
  • Vesicles
• Cell structures in both animal and plant

  
• Cell structure ONLY N PLANTS

  
• Producing New Cells

  • The cells in your body need to be able to divide to help your body grow and repair itself
  • Cells grow and divide over and over again
  • New cells are produced by the division of existing cells
• Specialised cells in animals

  • Specialised cells are those which have developed certain characteristics in order to perform particular functions. These differences are controlled by genes in the nucleus
  • Cells specialise by undergoing differentiation: this is a process by which cells develop the structure and characteristics needed to be able to carry out their functions
• Specialised Cells in animals

  
• Ciliated cell

  
• Nerve cell

  
• Red blood cell

  
• Sperm cell

  
• Egg cell

  
• Specialised cells in plants

  
• Root hair cell

  
• Xylem cell

  
• Palisade mesophyll cell

  
• Levels of Organisation in an Organism

  
• Levels of organism

  
• Organ systems

  
• Magnification


  Calculated using the equation: Magnification = Image size ÷ Actual size
• Calculating magnification

  1. Magnification = image size / actual size

  2. Actual size = image size / magnification

  3. Image size = magnification x actual size
• Using millimetres and micrometres as units

  • What this basically means is that 1mm = 1000µm and 1cm = 10,000µm
  • This usually comes up in questions where you have two different units and you need to ensure that you convert them both into the same unit before proceeding with the calculation
• • Remember 1mm = 1000µm
  • 2000 / 1000 = 2 so the actual thickness of the leaf is 2mm and the drawing thickness is 50mm
  • Magnification = image size / actual size = 50 / 2 = 25
  • So the magnification is x 25 (NO UNITS)
• Conversing