1 - cells

• Cells are the building blocks of life.

  They are the simplest structural and functional units of life
• Many chemical reactions occur continually. For example:

  1. A cell takes in raw materials
  2. It processes these materials to make new molecules
  3. These molecules are either used for the cell itself or transported to other parts of the cell
• A cell has different structures that perform different roles within the cell.

  • such division of labour increases efficiency within the system
  • it ensures that the cell can survive and perform its role within the body
• light microscope:

  • magnification - 1000x
  • micrographs - 2D, coloured images

  electron microscope:

  • magnification - 200000x
  • micrographs - 3D, black and white images (can be artificially colourised)
  • reveals the ultrastructure of the cell
• magnification refers to the number of times the image of an object is larger than its actual size
• prokaryotic and eukaryotic cells both have cytoplasm, plasma membrane, DNA and ribosomes
• prokaryotic cells:

  • lack membrane bound organelles
  • no nucleus - only has presence nucleoid region
  • DNA occurs as a singular loop
  • may have one/more plasmids
  • no mitochondria
  • cell wall is present
  • smaller in size
• eukaryotic cells:

  • has many membrane bound organelles
  • presence of nucleus
  • DNA occurs as numerous linear strands
  • does not have plasmids
  • has mitochondria
  • cell wall is absent in animal cells
  • larger in size
• plasma membrane

  • forms a physical boundary between the cytoplasm of the cell and the external environment
  • separates the contents of the cell from its external environment
  • is selectively permeable
  • regulates the movement of substances according to the needs of the cell
• cell wall

  • only present in plant cells
  • made of cellulose
  • protects the cell from injury and gives the cell a fixed shape
  • fully permeable
• cytoplasm:

  • eukaryotic - the site where most cellular reactions occur
  • is an aqueous medium that contains many dissolved substances and enzymes
  • contains organelles such as: RER, SER, ribosomes, GA, mitochondria and chloroplasts
• nucleus:

  • bound by a double membrane called the nuclear membrane
  • contains genetic information in the form of chromosomes
  • controls cell activities such as cell growth and the repair of worn-out parts
  • essential for cell division
• chromosomes:

  • a long thread like structure found within the nucleus
  • made up of proteins and DNA
  • during cell division, the chromosomes condense and shorten to become thick, rod-shaped structures
• rough endoplasmic reticulum:

  • a network of flattened spaces lined with a membrane
  • appears rough when viewed under the electron microscope (ribosomes)
  • the outer surface is continuous with the nuclear membrane
• ribosomes:

  • small round structures that synthesises proteins in the cell
  • either attached to the membrane of the RER (proteins are transported to the GA)
  • or lies freely in the cytoplasm
• smooth endoplasmic reticulum (SER)

  • no ribosomes attached
  • synthesises substances such as fats and steroids
  • converts harmful substances into harmless substances through detoxification
• golgi apparatus/ body

  • disc-shaped flattened spaces surrounded by membranes
  • vesicles can be seen fusing with one side of the GA, and pinching off the opposite side
  • chemically modifies substances made by the ER
  • stores and packages these substances in vesicles for secretion out of the cell
• how substances made by the ER are moved out of the cell:

  1. vesicles transport substances within the cell. Small vesicles containing substances made by the ER are pinched off from the ER
  2. these vesicles fuse with the GA and release their contents into the GA. Substances made by the ER may be modified in the GA
  3. secretory vesicles containing these modified substances are pinched off from the GA. They the move to the plasma membrane
  4. the secretory vesicles fuse with the cell membrane and their contents are released out of the cell
• mitochondria:

  • small oval-shaped organelles bound by a double membrane
  • aerobic respiration occurs, energy is produced in the form of adenosine triphosphate
• chloroplasts:

  • large double membrane bound organelles
  • oval-structured
  • contains chloropyll
• vacuoles:

  • fluid-filled space surrounded by a single membrane, tonoplast
  • tonoplast is a selectively permeable membrane
  • plant cells: one large central vacuole which contains cell sap
  • cell sap contains dissolved substances such as sugars, mineral salts and animo acids
  • animal cells: many small temporary vacuoles that contain water and food substances
• 1. tissue

  • a group of cells that develop in the same way and have same structures and functions

  1. organ

  • a group of tissues that have combined to form a single structure. The tissues work together to perform a specific overall function

  1. organ system

  • a group of organs within an organism that function collectively to carry out a particular process