ibbiology HL 1.1

• The cell wall is made up of polysaccharides, mainly cellulose.
• Principles of the Cell Theory:

  • All living things are composed of cells (or cell products)
  • The cell is the smallest unit of life
  • Cells only arise from pre-existing cells
• Atypical examples challenging the cell theory:

  • Striated muscle fibres:
  • Muscle cells fuse to form fibres that may be very long (>300mm)
  • Have multiple nuclei despite being surrounded by a single, continuous plasma membrane
  • Challenges the idea that cells always function as autonomous units
  • Aseptate fungal hyphae:
  • Some fungi have a continuous cytoplasm along the length of the hyphae
  • Challenges the idea that living structures are composed of discrete cells
  • Giant Algae:
• • Certain species of unicellular algae may grow to very large sizes (e.g. Acetabularia may exceed 7 cm in length)
  • Challenges the idea that larger organisms are always made of many microscopic cells
• Basic functions integral to survival of living things:

  • Metabolism
  • Reproduction
  • Sensitivity
  • Homeostasis
  • Excretion
  • Nutrition
  • Growth
• Functions of life in Paramecium:

  • Surrounded by cilia for movement (responsiveness)
  • Engulf food via a specialized feeding groove called a cytostome (nutrition)
  • Digest food particles in vacuoles with enzymes (metabolism)
  • Remove solid wastes via an anal pore and liquid wastes via contractile vacuoles (excretion)
  • Exchange gases via diffusion (homeostasis)
  • Divide asexually through fission (reproduction)
• Functions of life in Scenedesmus:

  • Exchange gases and essential materials via diffusion (nutrition / excretion)
  • Produce organic molecules via photosynthesis with chlorophyll pigments (metabolism)
  • Form daughter cells as non-motile autospores through asexual division (reproduction)
  • Exist as unicells or form colonies for protection (responsiveness)
• Factors affecting cell survival:

  • Rate of metabolism is a function of cell mass / volume
  • Rate of material exchange is a function of surface area
  • Cells tend to divide and remain small to maintain a high surface area to volume ratio for survival
• Specialization for material exchange:

  • Cells and tissues increase surface area to optimize material transfer
  • Intestinal tissue may form villi to increase surface area
  • Alveoli in the lungs have microvilli to increase membrane surface
• Stem cells:

  • Self-renewal and potency are key qualities
  • Types include totipotent, pluripotent, multipotent, and unipotent stem cells
• Differentiation and specialization:

  • Differentiated cells have specific regions of DNA packaged as euchromatin and heterochromatin
  • Stem cells can continuously divide and replicate, and have the capacity to differentiate into specialized cell types
• Types of stem cells:

  • Totipotent
  • Pluripotent
  • Multipotent
  • Unipotent
• Exocrine products are released into a duct, which connects to an epithelial surface
• These ducts may arise from a convergence of smaller ductules (each connected to an acinus) in order to enhance secretion
• Examples of digestive glands

  • Salivary glands secrete saliva which contains amylase (breaks down starch)
  • Gastric glands secretes gastric juices which includes hydrochloric acid and proteases (breaks down protein)
  • Pancreatic glands secretes pancreatic juices which include lipase, protease and amylase
  • Intestinal glands secretes intestinal juices via crypts of Lieberkuhn in the intestinal wall
• Click on the image to show false colour representation
• Exocrine glands are composed of a cluster of secretory cells which collectively form an acinus, surrounded by a basement membrane and held together by tight junctions between secretory cells
• Structure of a Typical Exocrine Gland
• Exocrine glands


  Produce and secrete substances via a duct onto an epithelial surface
• Click on the image to contrast gland features – acinus (red) and duct (yellow)
• Exocrine glands secrete to the surface of the body or the lumen of the gut
• Exocrine glands produce and secrete substances via a duct onto an epithelial surface
• The secretory cells possess a highly developed ER and golgi network for material secretion and are rich in mitochondria