B1: Cell biology

• Cells


  The basic building blocks of life that can replicate independently
• Multicellular organisms contain many cells that divide to grow or replace dead cells, not to create new organisms
• An adult human contains over 40 trillion cells
• Subcellular structures (organelles) common to animal and plant cells

  • Cell membrane
  • Nucleus
  • Cytoplasm
  • Mitochondria
  • Ribosomes
• Plant cells


  • Have a rigid cell wall made of cellulose
  • Contain a permanent vacuole with cell sap
  • Contain chloroplasts for photosynthesis
• Prokaryotic cells (bacteria)


  • Consist of a single cell without a nucleus, mitochondria or chloroplasts
  • Have a circular strand of DNA (chromosome or nucleoid) and may have additional plasmids
  • Some have flagella to propel movement
• Bacteria do not have mitochondria or chloroplasts
• Bacteria have a single circular strand of DNA (chromosome or nucleoid) that is free to float in the cytoplasm
• Some bacteria have additional small rings of DNA called plasmids
• Some bacteria have flagella to propel movement
• Cells


  The basic unit of life that we can see with a normal light microscope, but subcellular structures are only visible with an electron microscope
• Electron microscope


  • Has better resolving power and higher resolution than a normal light microscope
• Calculating cell size


  1. Measure image size

  2. Divide by magnification
• Cell types


  • Eukaryotic cells (have a nucleus)
  • Prokaryotic cells (no nucleus)
• Eukaryotic cells


  • DNA is found in the nucleus
  • Examples: plant and animal cells
• Prokaryotic cells


  • DNA is found in a ring called a plasmid
  • No nucleus
• Subcellular structures


  • Cell membrane
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Chloroplasts (in plant cells)
  • Vacuole (in plant cells)
• Cell membrane


  Keeps everything inside the cell, semi-permeable
• Cell wall


  Extra structure in plant cells and most bacteria, made of cellulose, provides rigidity
• Cytoplasm


  Liquid that makes up the cell, where most chemical reactions take place
• Mitochondria


  Where respiration takes place, releasing energy for the cell
• Ribosomes


  Where proteins are assembled or synthesized
• Chloroplasts


  Where photosynthesis takes place in plant cells
• Vacuole


  Permanent structure in plant cells that stores sap
• Eukaryotic cell nucleus


  Contains DNA stored in 23 pairs of chromosomes (diploid cells)
• Gamete cells


  Have half the number of chromosomes (haploid cells)
• Cell division by mitosis

  1. Genetic material is duplicated

  2. Nucleus breaks down

  3. Chromosomes pulled to opposite sides

  4. New nuclei form, resulting in two identical cells
• Cell specialization


  • Cells specialize to fulfill different functions, e.g. nerve, muscle, root, stem cells
• Stem cells


  Unspecialized cells that can differentiate into various cell types, found in embryos and adult tissues
• Cloning can be used to produce stem cells, but raises ethical concerns
• Diffusion


  Passive movement of molecules or particles from high to low concentration, down the concentration gradient
• Osmosis


  Diffusion of water across a semi-permeable membrane
• Practical on osmosis


  1. Cut equal-sized vegetable cylinders

  2. Weigh and place in varying sugar solutions

  3. Reweigh after a day

  4. Calculate percentage change in mass

  5. Plot against sugar concentration to find no-change point
• Active transport


  Movement of substances through a membrane against a concentration gradient, using energy