AQA Combined - Biology Paper 1

• Eukaryotic cells

  Cells that contain a nucleus
• Eukaryotic cells


  • Cell membrane wrapped around cytoplasm
  • Contain a nucleus
  • Contain ribosomes
  • Contain mitochondria
  • Plant cells and algae cells have a cell wall made of cellulose
  • Plant cells contain chloroplasts and a permanent vacuole
• Nucleus


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


  Liquid gel 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 to release energy from glucose
• Cell wall

  Made of cellulose, strengthens and gives support to the cell
• Chloroplasts


  Absorb light and are the site of photosynthesis
• Permanent vacuole


  Storage of cell sap, used to keep the cell rigid and support the plant
• Prokaryotic cells


  • Smaller than eukaryotic cells
  • Lack a nucleus, DNA exists as a single circular chromosome
  • May have small circles of DNA called plasmids
  • Lack membrane-bound subcellular structures like mitochondria or chloroplasts
  • Ribosomes are smaller than in eukaryotic cells
  • Cell walls are not made of cellulose
  • Some have a flagellum to allow movement
• Cells can be specialized, meaning they are adapted structurally to suit their function
• Specialized cells


  • Sperm cell with a tail and many mitochondria
  • Nerve cell with a branched shape
  • Muscle cell packed with mitochondria and ribosomes
  • Palisade cells in leaves with many chloroplasts
  • Root hair cells with an extended shape to increase surface area
• Plants retain unspecialized stem cells throughout their lifetime, allowing cloning from small pieces
• Xylem


  • Dead hollow tubes reinforced with lignin
  • Transport water and mineral ions from roots to leaves
• Phloem


  • Made of sieve tube elements and companion cells
  • Transport sugar from leaves to rest of plant
• Good conditions for transpiration


  Hot, dry, light, lots of air movement
• Adult humans have limited stem cells that can only become a few different cell types
• Embryonic stem cells can become almost any cell type, useful for treating conditions like paralysis and diabetes
• Therapeutic cloning uses an embryo with the patient's genes to avoid immune rejection
• Plants have meristems containing stem cells that can become any cell type, allowing easy cloning
• Resolution


  Smallest measurement that can be made
• Magnification


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


  • Existed since 16th century
  • Magnification up to 1500x
  • Resolution up to 0.2 micrometers
  • Can't see ribosomes or other very small structures
• Electron microscopes


  • Magnification up to 500,000x
  • Resolution up to 1 nanometer
  • Can view mitochondria and subcellular ultrastructure
• Calculating magnification

  Size of image / Size of actual object
• Using a light microscope to look at prepared slide

  1. Clip the prepared slide onto the stage

  2. Start with stage as high as possible

  3. Use lowest-powered objective lens

  4. Use the coarse adjustment knob to move the stage up to just below the objective lens

  5. Look down the eyepiece; Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus

  6. Adjust the focus of with the fine adjustment knob, until you get a clear image of what's on the slide

  7. If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus
• Mitosis


  Cell division used by body cells for growth and repair
• Mitosis


  • Occurs during the cell cycle after interphase
  • DNA is replicated
  • Chromosomes are pulled to opposite ends
  • Cell divides once to produce two identical diploid daughter cells
• Diffusion


  Passive movement of particles from high to low concentration
• Diffusion in animals


  • Urea diffuses from cells into blood plasma
  • Oxygen diffuses from lungs into bloodstream
  • Carbon dioxide diffuses from bloodstream into lungs
• Diffusion in plants


  • Carbon dioxide diffuses through leaf spongy mesophyll
• Tissues adapted for faster diffusion

  • Alveoli in lungs and villi in intestines have a folded structure to increase surface area
• Diffusion


  The movement of molecules from a region of higher concentration to a region of lower concentration
• Diffusion is not the same as inhaling and exhaling, which involve physical movement of the diaphragm and ribs
• Diffusion in plants


  Carbon dioxide diffuses through the leaf
• Tissues adapted for diffusion

  • Lungs, small intestines, gills in fish
  • Folded structure to increase surface area
  • Thin membrane for shorter distance
  • Good blood supply or ventilation to maintain concentration gradient
• Surface area to volume ratio

  Increasing surface area by cutting or folding an object speeds up transport or chemical reactions
• Osmosis


  The diffusion or movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Osmosis experiment


  1. Use cork borer or knife to make vegetable pieces

  2. Put in solutions of different solute concentrations

  3. Measure change in mass or length as dependent variable

  4. Control variables include type of vegetable, initial mass/length, time