Biology

• The nucleus is the control centre of the cell, containing genetic material (DNA) that controls all activities within the cell.
• The cytoplasm contains organelles such as mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, cytoskeleton, and chloroplasts.
• Mitochondria are responsible for producing energy through aerobic respiration.
• Ribosomes synthesize proteins using information from DNA.
• Ribosomes synthesize proteins using instructions from DNA.
• Endoplasmic Reticulum transports materials around the cell and helps with protein production.
• Golgi Apparatus modifies and packages proteins produced by the ER.
• Endoplasmic Reticulum (ER): A network of membranes involved in protein production and transport.
• Golgi Apparatus: Modifies and packages proteins produced by ER for export or use inside the cell.
• Golgi Apparatus: Modifies and packages proteins produced by ER.
• Lysosomes contain digestive enzymes to break down waste materials and damaged organelles.
• Golgi Apparatus modifies and packages proteins for transport to other parts of the cell or outside the cell.
• Lysosomes: Contain digestive enzymes to break down waste materials inside cells.
• Genetic material


  • Membrane bound
  • Circular molecule
  • Single
• Organelles


  • Few
  • Not double-membrane bound
• Protein synthesis


  70S ribosomes
• Major differences between prokaryotic and eukaryotic cells

  • Size
  • Nucleus
  • Organelles
  • Ribosomes
  • Cell walls
  • Flagella
  • Respiration
• Prokaryotic cells


  • Average diameter up to 40μm
  • No nucleolus
  • No nucleus, DNA
  • Cell walls contain polysaccharides
  • Flagella are simple, without microtubules and not membrane bounded
  • Respiration is by mesosomes
• Eukaryotic cells


  • Nucleus is membrane bound
  • There is nucleolus and DNA is associated with chromosomes
  • Organelles are double membrane-bound
  • 80S ribosomes
  • Cell walls usually contain polysaccharides and amino acids
  • Flagella are complex with microtubules and membrane bounded
  • Respiration is by mitochondria
• The outermost covering of the cell of plants is the cell wall. It is absent in the animal cells.
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• Fig. 3 Diagram of the cell membrane based on the Dauson-Danielli hypothesis.
• Cytoplasm


  Portion of the cell protoplasm that surrounds the nucleus
• Many cellular enzymes are located in the cytoplasm
• In young plant cells, the cytoplasm occupies most of the volume of the cell
• As the cells mature, the cytoplasm occurs as thin layer lining the wall and with thin strands of cytoplasm penetrating throughout the cell
• Cytoplasmic membrane


  Membrane covering the cytoplasm that is detached from the plasma membrane
• Endoplasmic Reticulum


  Network of canals bounded by membranes that traverse the entire cytoplasm
• The Endoplasmic Reticulum extends from the nuclear membrane to the plasma membrane
• The nuclear membrane is double layered, differentiated into
• Rough endoplasmic reticulum (ER)


  Type of ER found in cells that are protein synthesizing
• Smooth or agranular endoplasmic reticulum

  Responsible for synthesizing materials other than protein
• Golgi Complex


  Organelle found in the cytoplasm, responsible for the secretion of lipids, carbohydrates and proteins
• Protein synthesis and secretion

  1. Ribosomes produce protein

  2. Proteins move down canals of endoplasmic reticulum

  3. Proteins reach Golgi complex where they are stored and released when needed

  4. Canals of Golgi complex are continuous with those of endoplasmic reticulum
• Golgi complex in animal cells


  Plays an active role in the transformation of spermatids into spermatozoa (a maturation process)
• Mitochondrion


  • Organelle found in almost every type of cell in the human body, except red blood cells
  • Shape and quantity varies from cell to cell
  • Bounded by two unit membranes, with the inner membrane thrown into folds (cristae) to provide increased surface area
• Prokaryotic cells


  • Smaller diameter
  • Fewer organelles
  • Organelles not membrane-bound
  • 70S ribosomes
  • DNA molecule is circular
  • No nucleus
• Eukaryotic cells


  • May be up to 40μm in diameter
  • Nucleus with double membrane
  • Nucleolus
  • 80S ribosomes
  • Membrane-bound organelles
  • DNA in chromosomes
• The outermost covering of the cell of plants is the cell wall
• Cell wall


  A non-living structure secreted by the protoplast, a strong porous, rather rigid but somewhat elastic wall that provides strength and support to the entire plant body