biology paper 1

• Eukaryotic cells


  Cells that contain a true 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, 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
• Flagellum

  Allows bacteria to move around more easily
• Cell specialization

  • Cells are adapted structurally to suit their function
  • Involves changes in shape or presence of subcellular structures
  • Sperm cells have a tail and many mitochondria
  • Nerve cells have a branched shape
  • Muscle cells are packed with mitochondria and ribosomes
• Plant cell specialization

  • Palisade cells in leaves have many chloroplasts
  • Root hair cells have an extended shape and no chloroplasts
  • Xylem and phloem cells in vascular bundles are specialized
• Xylem


  Dead hollow tubes that transport water and mineral ions from roots to leaves
• Phloem


  Living cells that transport sugar from leaves to other parts of the plant
• Conditions that favour transpiration are hot, dry, light, and windy weather
• Stem cells

  Unspecialized or undifferentiated cells that can become specialized cells
• Adult human stem cells

  • Relatively few, limited in what they can become
  • Bone marrow stem cells can become blood cells but not neurons
• Embryonic stem cells


  • Can differentiate into many specialized cell types
  • Useful for treating conditions like paralysis and diabetes
  • Ethical issues around using embryos
• Plant meristems

  • Contain stem cells that can become any type of plant cell
  • Allows easy cloning of plants from cuttings
• Resolution


  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
• Calculating magnification


  Size of image / Size of actual object
• 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
• Mitosis


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


  • Occurs after interphase where cell grows and DNA replicates
  • Chromosomes are pulled to opposite ends of the cell
  • 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 the other way
• Diffusion in plants


  • Carbon dioxide diffuses through leaf spongy mesophyll
• Adaptations for faster diffusion

  • Folded structures like alveoli and villi 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
• Osmosis


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