Biology paper 1

• This video will allow you to do a last-minute cram on the night before your GCSE exams
• Eukaryotic cells


  Cells that contain a true nucleus
• Components of eukaryotic cells

  • Cell membrane
  • Cytoplasm
  • Nucleus
  • Ribosomes
  • Mitochondria
  • Cell wall (plant cells)
  • Chloroplasts (plant cells)
  • Permanent vacuole (plant cells)
• Nucleus

  Contains the DNA or genetic material and controls the actions of the cell
• Cytoplasm


  The liquid jelly where most of the chemical reactions in the cell take place
• Cell membrane


  Responsible for controlling what can go into and out of the cell
• Ribosomes

  Used to synthesize protein
• Mitochondria


  The site for aerobic respiration which is used to release energy
• Cell wall (plant cells)

  Made of cellulose and strengthens and gives the cell support
• Chloroplasts (plant cells)


  Absorb light and are where photosynthesis takes place
• Permanent vacuole (plant cells)

  A storage of cell sap used to keep the cell rigid to support the plant
• Prokaryotes (e.g. bacteria)


  Lack a true nucleus and membrane-bound subcellular structures
• Bacterial DNA


  Exists as a single circular chromosome, and some may also have small circles of DNA called plasmids
• Bacterial ribosomes


  Significantly smaller than eukaryotic ribosomes
• Binary fission

  The process by which bacteria reproduce, a form of mitosis in single-celled organisms
• Bacteria can rapidly increase in numbers with division times often as short as 20 minutes, provided they have sufficient nutrients and a suitable temperature</b>
• Bacteria can be cultured or grown as colonies in a petri dish filled with a mixture of agar jelly and LB nutrient broth, or in a tube of the same broth
• Streak plate method

  Used to culture bacteria, where the petri dish, culture media, and inoculating loop are sterilized, and a small amount of the bacterial sample is spread in a zigzag pattern
• The plate is stored upside down to prevent condensation that forms on the lid from falling onto the bacterial colonies
• In school, bacteria are typically incubated at 25°C to avoid growing human pathogens while still allowing the desired bacteria to grow
• Measuring the radius of a bacterial colony


  Can be used to calculate the area of the colony using the formula pi*r^2
• Zone of inhibition test


  Used to determine the antimicrobial properties of antibiotics, chemical antiseptics, and natural antiseptics like garlic
• Cell specialization involves changes in shape or the presence of more or fewer subcellular structures to suit the cell's function
• Specialized cells

  • Sperm cell (tail and many mitochondria)
  • Nerve cell (branched shape)
  • Muscle cell (many mitochondria and ribosomes)
• Plants retain unspecialized meristem cells throughout their lifetime, allowing them to be easily cloned from small cuttings
• Specialized plant cells

  • Palisade cells in leaves (many chloroplasts)
  • Root hair cells (extended shape, no chloroplasts)
• Xylem


  Transport water and mineral ions from roots to leaves, made of dead cells reinforced with lignin
• Phloem


  Transport sucrose from leaves to other parts of the plant, made of living cells with companion cells
• Conditions that favor transpiration

  Hot, dry, light, and windy weather
• Stem cells

  Unspecialized cells that can differentiate into various specialized cell types
• Adult human stem cells are limited in the cell types they can become, while embryonic stem cells can become almost any cell type
• Therapeutic cloning involves creating an embryo with the same genes as the patient to harvest stem cells without risk of rejection
• Resolution


  The smallest measurement that can be made
• Magnification


  How much bigger the image looks than the actual object
• Light microscopes


  • Magnification up to 1500x, resolution down to 0.2 micrometers
  • Cannot see structures smaller than the wavelength of light
• Electron microscopes

  • Magnification up to 500,000x, resolution down to 1 nanometer
  • Use a beam of electrons instead of light
• Using the I/O/M triangle

  To calculate magnification, size of object, or size of image given the other two
• There is a required practical about using a light microscope to observe cells
• Mitosis is the type of cell division that occurs in body cells for growth and repair, while meiosis occurs in gamete production
• Be very careful with spelling, as there are several pairs of similar biological terms that can cost you marks if confused