Biology paper 1 higher

• 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,
• 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
• Microscopy


  The use of microscopes
• 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
• How light microscopes work


  1. Light from the room hits the mirror

  2. Light reflected upwards through the object

  3. Light passes through the objective lens

  4. Light passes through the eyepiece lens

  5. Light enters 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
• Light microscopes


  Microscopes that use light, small, easy to use, relatively cheap
• Resolution of light microscopes


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

  • nucleus, cytoplasm and cell membrane
• Electron microscopes


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

  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 and cons compared to electron microscopes
• 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


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

  2. Multiply by 1,000 to convert to a smaller unit
• Atoms range from 0.1 to 0.5 nanometers across
• Glucose molecules are about 1 nanometer across
• Viruses are about 100 nanometers across
• Bacteria cells are about 1 micrometer across
• Animal and plant cells are 10 to 100 micrometers across
• Human hair is about 100 micrometers wide
• The naked eye can see down to about 100 micrometers
• Light microscopes can see down to about 500 nanometers
• Electron microscopes can see down to about 0.1 nanometers
• Centimeters


  10 millimeters, 100 centimeters in a meter
• Converting centimeters


  1. Divide by 100 to get meters

  2. Multiply by 10 to get millimeters
• Enzymes

  Catalysts made by living organisms