GCSE Biology (B1)

• Cells


  The basic building blocks of life that can replicate independently
• Multicellular organisms like animals and plants contain many cells that divide to grow or replace dead cells, not to create new organisms</b>
• Bacteria are single-celled prokaryotic organisms
• Subcellular structures common to animal and plant cells

  • Cell membrane
  • Nucleus
  • Cytoplasm
  • Mitochondria
  • Ribosomes
• Plant cells


  • Have a rigid cell wall made of cellulose
  • Contain a permanent vacuole with cell sap
  • Contain chloroplasts for photosynthesis
• Bacterial cells

  • Lack mitochondria and chloroplasts
  • Have a single circular strand of DNA instead of a nucleus
  • May have additional plasmids
  • May have flagella for movement
• Bacteria are unicellular organisms, each individual cell is a whole organism
• Photosynthesis occurs in the chloroplasts of plant cells, using chlorophyll to absorb light energy
• Mitochondria in cells break down glucose through aerobic respiration to provide energy
• Key groups of living organisms

  • Animals
  • Plants
  • Fungi
  • Protists
  • Bacteria
  • Viruses
• Animals


  • Multicellular
  • Heterotrophs
  • Reproduce sexually
• Plants


  • Multicellular
  • Autotrophs (get energy from sun via photosynthesis)
• Fungi


  • Some are multicellular, some are unicellular
  • Heterotrophs (get energy from other organisms)
  • Use saprotrophic nutrition (secrete digestive enzymes, absorb nutrients)
  • Some have a mycelium body made of hyphae
  • Some are pathogens that can cause disease
• Protists


  • Mostly unicellular
  • Some are autotrophs (can photosynthesize), some are heterotrophs (consume other organisms)
  • Some are pathogens that can cause disease (e.g. malaria)
• Bacteria

  • Unicellular
  • Some can photosynthesize but don't have chloroplasts
  • Most feed off other living or dead organisms
  • Estimated to have more species than all other kingdoms combined
  • Some are pathogens that can cause disease, but most are harmless or helpful
• Viruses


  • Tiny particles, not cells
  • Have a protein coat surrounding genetic material (DNA or RNA)
  • Can only reproduce by infecting and using other living cells
  • Always act as pathogens, causing harm to host organisms
• Eukaryotes (animals, plants, fungi, protists) have DNA in chromosomes and a nucleus, while prokaryotes (bacteria) have loose DNA and no nucleus
• Viruses are much smaller than prokaryotic cells, around 10-100 times smaller
• Microscopy


  The use of microscopes
• How light microscopes work

  1. Light from the room hits the mirror

  2. Reflected upwards through the object

  3. Passes through the objective lens

  4. Passes through the eyepiece lens

  5. Into the eye
• Object


  The real object or sample that you're looking at
• Image


  The image that we see when we look down the microscope
• Magnification


  How many times larger the image is than the object
• Magnification = image size / object size
• Resolution


  The shortest distance between two points on an object that can still be distinguished as two separate entities
• Higher resolution


  More details can be seen, less blurry the image
• The images have the same magnification (100x) but different resolutions
• Light microscope


  Microscope that uses light, small, easy to use, relatively cheap
• Resolution of light microscope

  Limited to 0.2 micrometers, any details less than 0.2 micrometers apart will appear blurry
• What light microscopes can be used to see

  • Individual cells like onion cells
• Electron microscope


  Really big, very expensive, hard to use, only used by scientists in laboratories
• Resolution of electron microscope

  Maximum resolution of 0.1 nanometers, 2000 times better than light microscopes
• What electron microscopes can be used to study

  • Sub-cellular structures like mitochondria
• Electron microscopes can give images with much higher magnifications without going blurry
• Light microscopes


  Pros: small, easy to use, relatively cheap. Cons: limited resolution
• Electron microscopes


  Pros: very high resolution. Cons: big, expensive, hard to use
• Nanometers


  Smallest unit of length you need to know
• Units of length


  • Nanometers
  • Micrometers
  • Millimeters
  • Meters
  • Kilometers
• Each unit is 1,000 times bigger or smaller than the one next to it
• Converting between units of length

  1. Divide by 1,000 to convert to a larger unit

  2. Multiply by 1,000 to convert to a smaller unit