Chapter 2 Cell Structure and Cell Organisation






  • Cell is the basic structural and functional unit of all organisms.
  • Robert Hook coined the term "cell" for the box like structures he found in thin sections of plant material in 1965.
  • A cell carries out basic life activities such as respiration, excretion and digestion.
  • The three basic components of a cell are plasma membrane, cytoplasm and nucleus.
  • Plant and animal cells contain various types of organelles, such as nucleus, nucleolus, chromosomes, endoplasmic reticulum, mitochondria ,Golgi apparatus, lysosome, chloroplast, centriole and vacuole.
  • Each organelle carries out its own specific function in a cell.
  • Cells are organised in the formation of tissues, organs and systems in humans, animals and plants.
  • Unicellular organism like the amoeba and the paramecium are aquatic and are able to carry out all the activities necessary for living.
  • The amoeba has no fixed shape, feeds on microscopic organisms, like the diatom and bacteria.
  • Amoeba's mode of feeding is phagocytic.
  • Locomotion in amoeba is by protruding pseudopodium.
  • It reproduces asexually by binary fission and sporulation.
  • The paramecium is shaped like the base of a shoe.
  • Its' surface is covered by cilia (thread like fine structures).
  • The cilium is used in movement.
  • Paramecium feeds on bacteria and reproduces sexually and asexually.
  • Cell organisation in multicellular organism is as follows:
Cell --> Tissue --> Organ --> System of organs --> Multicellular organism.
  • Homeostasis is a process that controls and regulates the physical and chemical factors of the internal environment of a cell so that it is always maintained at optimal level for cell survival.
  • These factors include temperature, pH, osmotic pressure as well as the sugar and salt concentration of the body's internal environment.
  • The homeostatic mechanism is carried out through a negative feedback system in the body.

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