B1 - Cell biology

• Organisms


  Can be Prokaryotes or Eukaryotes
• Facts about cells

  • All living things are made of cells
  • Cells can be either prokaryotic or eukaryotic
  • Eukaryotic cells are complex and include all animal and plant cells
  • Prokaryotic cells are smaller and simpler, e.g. bacteria
• Eukaryotes


  Organisms made up of eukaryotic cells
• Prokaryote


  A prokaryotic cell, a single-celled organism
• Subcellular structures in animal cells

  • Nucleus
  • Mitochondria
  • Cytoplasm
  • Cell membrane
  • Ribosomes
• Plant cells contain the same subcellular structures as animal cells, but they also have:

  • Cell wall

  • Permanent vacuole

  • Chloroplasts
• Nucleus - Controls activity of the cell and contains it's genetic material
• Mitochondria - Site of aerobic respiration (energy production)
• Cytoplasm - where most of the chemical reactions take place
• Cell membrane - controls what goes in and out of the cell, holds the cell together
• Ribosomes - Where protein synthesis takes place
• Cell wall - made of cellulose and supports the cell and provides strength and rigidity
• Vacuole - contains cell sap and supports the cell
• Chloroplasts - absorb light and do photosynthesis
• In bacterial cells, the roles of the mitochondria and chloroplasts are taken over by the cytoplasm
• Plasmids - small circles of DNA in bacterial cells' cytoplasm. They allow bacterial cells to move genes from one cell to another
• Flagella - a tail-like structure that helps bacteria cells move
• Bacteria cells contain:

  • Plasmid DNA

  • Chromosomal DNA

  • Flagella

  • Cytoplasm

  • Cell wall
• The DNA of bacteria is usually found as one circular chromosome, but some bacteria have plasmids
• Chromosomes


  Structures in the nucleus of a cell made of DNA
• Each chromosome carries hundreds to thousands of genes
• Genes


  Contain the code to make different proteins and control the development of different characteristics
• Different species have different numbers of pairs of chromosomes, e.g. humans have 23 pairs
• Cell cycle

  1. Growth

  2. Division
• Mitosis

  1. One set of chromosomes is pulled to each end of the cell

  2. The nucleus divides

  3. The cytoplasm and cell membranes divide to form two identical cells
• During mitosis, chromosomes line up along the centre of the cell, divide and the copies move to opposite poles
• Each 'daughter' cell, that is a product of mitosis, has the same number of chromosomes, and contains the same genes, as the parent cell
• Cell division by mitosis


  • Makes new cells for growth and development of multicellular organisms
  • Repairing damaged tissues
  • Asexual reproduction
• Stem cells


  Undifferentiated cells that can divide to make different types of cells
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
• Embryonic stem cells


  • Can make all types of cells
• Adult stem cells


  • Can only make certain types of cells
  • Their capacity to divide is limited
• Some people are concerned about using stem cells from cloned embryos because there may be infection risks and they may have ethical or religious objections
• In plants, stem cells are found in meristems
• Plant stem cells


  • Can be used to produce clones of plants quickly
• Diffusion


  The net movement of particles from an area of higher concentration to an area of lower concentration until they are evenly spread out
• Examples of diffusion in living organisms

  • Oxygen and carbon dioxide diffuse during gas exchange in lungs, gills and plant leaves
  • Urea diffuses from cells into the blood plasma for excretion by the kidney
  • Digested food molecules from the small intestine diffuse into the blood
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Plant cell


  Typical size: 0.1 mm in diameter
• Animal cell


  Typical size: 0.02 mm in diameter