Paper 1 Overview

• 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


  Liquid jelly where most 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


  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)


  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 strand of DNA and some may also have small circles of DNA called plasmids
• Bacterial ribosomes


  Significantly smaller than eukaryotic ribosomes
• Binary fission


  Bacteria reproduce by this special name for 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</b>
• Preparing a streak plate

  1. Sterilize the petri dish, culture media, and inoculating loop

  2. Use the inoculating loop to put a small amount of the bacterial sample onto the agar plate and spread it in a zigzag pattern

  3. Tape down the lid with small pieces of adhesive tape to allow oxygen in

  4. Incubate the plate upside down at 25°C to avoid growing human pathogens
• 10% of the marks on GCSE Biology papers are for maths skills at a GCSE maths level
• Calculating the area of a bacterial colony

  1. Measure the radius of the circular colony

  2. Use the formula pi r^2 to calculate the area
• Zone of inhibition test

  1. Use an agar plate totally covered with a bacterial culture

  2. Introduce antiseptics in the form of paper discs soaked in the chemicals

  3. Measure the area around each paper disc where no bacteria are growing - this is the zone of inhibition
• The bigger the zone of inhibition, the better the antiseptic works
• Cell specialization


  Cells are adapted structurally to suit their function
• Specialized cells


  • Sperm cell (tail and many mitochondria)
  • Nerve cell (branched shape)
  • Muscle cell (many mitochondria and ribosomes)
  • Palisade cells in leaves (many chloroplasts)
  • Root hair cells (extended shape, no chloroplasts)
• Xylem


  Transport water and mineral ions from roots to leaves in a process called transpiration
• Phloem


  Transport sucrose (sugar) from leaves to other parts of the plant in a process called translocation
• The best conditions for transpiration are hot, dry, light, and windy weather
• Stem cells


  Unspecialized cells that can differentiate into many different cell types
• Embryonic stem cells


  Can differentiate into almost any cell type, useful for treating conditions like paralysis and diabetes
• Adult stem cells


  More limited in the cell types they can become, e.g. bone marrow stem cells can only become blood cells
• Plants have meristems containing stem cells that can become any cell type, allowing easy cloning from cuttings
• 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
  • Can't see structures smaller than this like ribosomes
• Electron microscopes


  • Much greater magnification (up to 500,000x) and resolution (down to 1 nanometer)
  • Can view mitochondria and subcellular ultrastructure
• Calculating magnification


  1. Use the formula: Magnification = Size of image / Size of object

  2. Make sure units are the same for both measurements
• Using a light microscope

  1. Start with lowest power objective lens and highest stage

  2. Focus first with coarse adjustment, then fine adjustment

  3. Switch to higher power objective if needed

  4. Use a stain to see transparent cell components
• Mitosis is used by body cells for growth and repair, while meiosis is used to produce gametes
• Be very careful with spelling of similar biological terms, as any ambiguity will cost you marks
• Nucleus


  Part of a eukaryotic cell
• Chromosomes


  23 pairs in a human body cell, each containing about a thousand different genes made of DNA