FORMS IN WHICH LIVING CELLS EXIST
There are four forms in which living cells exist. These are:
(1) As Independent or Single and Free- living Organisms:
Independent and free-living organisms are organisms which possess only one cell and are capable of living freely on their own. Each organism, even though it has only one cell can carry out all the life processes such as feeding, movement, reproduction, sensitivity, excretion, growth, respiration, etc. Examples of independent or free-living organisms are Amoeba, Euglena, Paramecium and Chlamy-domonas.
- Amoeba Structure: Amoeba has irregular shape and changes constantly. The protoplasm is made of nucleus and cytoplasm. Embedded in the cytoplasm are food vacuole and contractile vacuole. Amoeba moves with the aid of pseudopodia.
- Paramecium Structure: Paramecium is often described as having a slipper shape. The cytoplasm is composed of ectoplasm and endoplasm. The nucleus consists of two micronucleus and mega nucleus. The cytoplasm also houses the food vacuole, contractile vacuole and cyto-stome. Paramecium moves with the aid of cilia.
- Euglena Viridis Structure: Euglena viridis is a protist and a typical example of an organism sharing the characteristics of plants and animals. The organisms possess flagellum, gullet, contractile vacuole, eye spot, pellicle myonemes etc which make it an animal and chloroplasts, pyrenoids and paramylum granules which also make the organism a protist. Euglena moves with the aid of flagellum
- Chlamydomonas Structure: Chlamydomonas is a simple microscopic plant. It is a unicellular plant, having flagella for movement, eye spot, chloroplasts, food vacuole and contractile vacuole.
(2) As a Colony:
Some organisms are made of many similar cells which are joined or words, these cells form a loosely arranged association of two or more cells but the cells cannot be differentiated from each from each other. This aggregation of independent cells or protists is called a colony.
Examples of organisms which exist as colonies are Volvox, Pandorina, Eudorina and Sponges.
(3) As a Filament:
Certain cells are organised into filaments in which identical cells are joined end to end to form unbranched filaments. Each cell functions
as an independent living cell. Such organisms are multicellular and therefore exist as filament. Popular examples of filamentous organisms are the Spirogyra, Zygnema, Oscillateria Chladophoral, Ulothrix, Oedogonium, etc.
Differences Between Colonial Organism and Filamentous Organism
|Colonial Organism||Filamentous Organism|
|There is absence of intercellular
|There is presence of
|The identical cells form a mass||The identical cells form
in linear form
|Cells are connected by cytoplasmic materials, i.e., physio logically dependent||All cells are physio-
|Examples of colonial organisms are Volvox, Pandorina||Examples of filamentous
organisms are organisms are Spirogyra Zygnema and Oscilateria.
(4) Cells as part of a Living Organism:
In multicellular organisms, a group of numerous, similar cells arranged together and performing a specific function is called a tissue. A group of similar tissues forming a layer in an organism which performs a specific function is called an organ. A group of organs which work together to perform specific function are called a system.
cells lead to tissues; tissues lead to organs while organs lead to system.
Examples are cheek cell, onion cell, epidermal cell, parenchyma cell.