biology paper 1

• Eukaryotic cells


  Cells that contain a true nucleus
• Eukaryotic cells


  • Cell membrane wrapped around cytoplasm
  • Nucleus - a little pack of DNA wrapped in a membrane
  • Ribosomes where protein is made
  • Mitochondria
  • Plant cells and algae cells have a cell wall made from cellulose
  • Plant cells contain chloroplasts full of chlorophyll for photosynthesis
  • Plant cells contain a permanent vacuole full of cell sap
• Nucleus


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


  The 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


  The site for aerobic respiration to release energy from glucose
• Cell wall


  Made of cellulose and strengthens and gives support to plant cells
• Chloroplasts


  Absorb light and are where photosynthesis takes place
• Permanent vacuole


  Storage of cell sap used to keep the cell rigid and support the plant
• Prokaryotic cells (bacteria)


  • Smaller than eukaryotic cells
  • No true nucleus, DNA exists as a single circular chromosome
  • May have small circles of DNA called plasmids
  • No membrane-bound subcellular structures like mitochondria or chloroplasts
  • Ribosomes are smaller than in eukaryotic cells
  • Cell walls not made of cellulose
  • Some have a flagellum to move around
• Cells can be specialized, meaning they are adapted structurally to suit their function
• Specialized cells


  • Sperm cell - has a tail and lots of mitochondria
  • Nerve cell - very branched shape
  • Muscle cell - packed with mitochondria and ribosomes
  • Palisade cells in leaves - have lots of chloroplasts
  • Root hair cells - extended shape to increase surface area
• Xylem


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


  Living cells that transport sugar from leaves to rest of plant, made of sieve tube elements and companion cells
• Good conditions for transpiration


  Hot, dry, light, lots of air movement
• Specialized cells are originally derived from unspecialized or undifferentiated stem cells
• Adult human stem cells

  Relatively few, limited in what they can become
• Embryonic stem cells

  Can differentiate into many cell types, useful for treating conditions like paralysis and diabetes
• Therapeutic cloning


  Making an embryo with the same genes as the patient so stem cells won't be rejected
• 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
  • Compound microscopes have two lenses - eyepiece and objective
• Electron microscopes


  • Much greater magnification (up to 500,000x) and resolution (down to 1 nanometer) than light microscopes, use electron beams instead of light
• Using a light microscope

  1. Start with stage as high as possible

  2. Use lowest power objective lens

  3. Focus first with coarse focusing wheel, then fine focusing wheel

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

  5. Use a stain to see transparent cell structures

  6. Troubleshoot if image is out of focus or too small to see
• Chromosomes


  23 pairs in human body cells, contain DNA and genes
• Mitosis


  Cell division used by body cells for growth and repair, produces two identical diploid daughter cells
• Diffusion


  Passive movement of particles from high to low concentration, down the concentration gradient
• Diffusion in animals


  • Urea diffuses from cells into blood plasma
  • Oxygen diffuses from lungs into bloodstream, carbon dioxide diffuses the opposite way
• Diffusion in plants


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

  • Alveoli in lungs and villi in small intestine have folded structure 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
• Surface area to volume ratio example

  • Cube with volume 64 cm^3 and surface area 96 cm^2

  Cutting cube in half in all 3 dimensions gives 8 smaller cubes with same volume but surface area 192 cm^2
• Osmosis


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