Biology Paper 1

• Eukaryotic cells


  Cells that contain a true nucleus
• Eukaryotic cells


  • Contain a 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, their 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 that carry sugars and companion cells that supply energy
  • Transports sugars from leaves to rest of plant
• Good conditions for transpiration


  Hot, dry, light, with 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
• Therapeutic cloning uses an embryo with the patient's genes to harvest stem cells without immune rejection
• Plants have meristems containing stem cells that can become any cell type, allowing easy cloning
• Resolution


  The smallest measurement that can be made
• Magnification


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


  • Existed since 16th century
  • Give basic understanding of cells
  • Maximum magnification around 1500x
  • Resolution around 0.2 micrometers
  • Cannot see ribosomes or other very small structures
• Compound light microscopes


  • Have an eyepiece lens and an objective lens that work together to magnify
• Electron microscopes


  • Use a beam of electrons rather than light
  • Much greater magnification and resolution than light microscopes
  • Magnification up to 500,000x
  • Resolution down to 1 nanometer
  • Can view mitochondria and subcellular ultrastructure
• Using a light microscope

  1. Start with stage as high as possible

  2. Use lowest power objective lens

  3. Focus first with coarse wheel, then fine wheel

  4. Switch to higher power objective and focus with fine wheel only

  5. Use a stain to see transparent structures

  6. Troubleshoot if image is out of focus or too small to see
• Cell division hierarchy: nucleus with 23 chromosome pairs, each containing ~1000 genes
• Mitosis


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


  1. Interphase with DNA replication

  2. Chromosomes pulled to opposite ends of cell

  3. 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 in opposite direction
• Diffusion in plants


  • Carbon dioxide diffuses through leaf spongy mesophyll
• Adaptations to improve diffusion

  • Folded structures like alveoli and villi to increase surface area
• Diffusion


  The movement of molecules from a region of higher concentration to a region of lower concentration
• Diffusion examples


  • Urea diffuses from cells into blood plasma to be removed
  • Oxygen diffuses from lungs into bloodstream
  • Carbon dioxide diffuses from bloodstream into lungs
• 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