Cells and organelles

• Cell


  The smallest structure that can perform life's functions
• Cell theory


  All organisms are made of cells, which are the basic unit of life
• Components of a cell


  • Cell membrane
  • Cytoplasm
  • Organelles
  • Cytosol
  • Cytoskeleton
  • Inclusions
• Cell membrane


  • Separates the cell contents from the environment outside the cell and from neighbouring cells
  • Encloses the contents of the cell and controls what is able to enter and leave
  • Very thin
• Cytoplasm


  The jelly-like or watery material inside of the cell that fills all the space between the nucleus and the cell membrane
• Cytosol


  The liquid part of the cytoplasm, 75% to 90% water, with a complex mixture of dissolved substances such as salts, and carbohydrates
• Organelles


  The structures within a cell that are specialised for particular functions
• Nucleus


  • The largest organelle
  • A nuclear membrane separates the nucleus from the cytoplasm
  • Nuclear pores allow large molecules to enter and leave the nucleus
  • DNA is stored within the nucleus
  • The nucleolus plays a part in manufacturing proteins
• Ribosomes


  • Very small, spherical organelles where amino acids join together to make proteins
  • May be free in the cytoplasm or attached to the membranes within the cells such as the endoplasmic reticulum
• Endoplasmic reticulum (ER)


  • A network of membranes forming channels through the cytoplasm, used for storage, support, synthesis, and transport
  • Can be classified as rough ER (ribosomes attached) or smooth ER (no ribosomes)
  • Lots of folds to increase surface area for more chemical reactions
• Golgi body


  • Modifies proteins and packages them for secretion from the cell
  • A series of flattened membranes stacked upon one another, usually positioned near the nucleus
  • Proteins produced at the ribosomes pass through the ER to the Golgi body, where small sacs of liquid containing proteins (vesicles) are formed
• Lysosomes


  • Small spheres, bound by a membrane, that are formed from the Golgi body
  • Contain digestive enzymes that break down large molecules
  • Can join with vesicles containing particles or liquids taken into the cell, and break down the material inside
  • Also digest worn-out organelles
• Mitochondria


  • Creates energy in the cells, the power house of the cell
  • Lots of chemical reactions happen here, including some of the chemical reactions of cellular respiration
  • Has a double membrane, with folding of the inner membrane producing a large surface area
• Cilia and Flagella


  • Cilia: numerous and short projections that resemble tiny hairs

  Flagella: longer projections, only found on sperm cells
• Cytoskeleton


  • The framework of protein fibres that gives the cells its shape and assists cell movement

  Consists of microtubules (hollow rods that keep organelles in place or move them around) and microfilaments (move materials around the cytoplasm or move the whole cell)
• Inclusions


  Chemical substances that aren't a part of the cell structure but are found in the cytoplasm, e.g. haemoglobin, pigments