- 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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