Summary

  • All organisms are made of cells or aggregates of cells.
  • Cells vary in their shape, size and activities/functions.
  • Based on the presence or absence of a membrane bound nucleus and other organelles, cells and hence organisms can be named as eukaryotic or prokaryotic.
  • A typical eukaryotic cell consists of a cell membrane, nucleus and cytoplasm. Plant cells have a cell wall outside the cell membrane.
  • The plasma membrane is selectively permeable and facilitates transport of several molecules.
  • The endomembrane system includes ER, golgi complex, lysosomes and vacuoles.
  • All the cell organelles perform different but specific functions. Centrosome and centriole form the basal body of cilia and flagella that facilitate locomotion.
  • In animal cells, centrioles also form spindle apparatus during cell division.
  • Nucleus contains nucleoli and chromatin network. It not only controls the activities of organelles but also plays a major role in heredity.
  • Endoplasmic reticulum contains tubules or cisternae. They are of two types: rough and smooth.
  • ER helps in the transport of substances, synthesis of proteins, lipoproteins and glycogen. The golgi body is a membranous organelle composed of flattened sacs.
  • The secretions of cells are packed in them and transported from the cell. Lysosomes are single membrane structures containing enzymes for digestion of all types of macromolecules.
  • Ribosomes are involved in protein synthesis. These occur freely in the cytoplasm or are associated with ER.
  • Mitochondria help in oxidative phosphorylation and generation of adenosine triphosphate. They are bound by double membrane; the outer membrane is smooth and inner one folds into several cristae.
  • Plastids are pigment containing organelles found in plant cells only.
  • In plant cells, chloroplasts are responsible for trapping light energy essential for photosynthesis. The grana, in the plastid, is the site of light reactions and the stroma of dark reactions.
  • The green coloured plastids are chloroplasts, which contain chlorophyll, whereas the other coloured plastids are chromoplasts, which may contain pigments like carotene and xanthophyll.
  • The nucleus is enclosed by nuclear envelop, a double membrane structure with nuclear pores. The inner membrane encloses the nucleoplasm and the chromatin material. Thus, cell is the structural and functional unit of life.

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