Cell Structure Last-Minute Sum-up

Quick Grasp:

1) All organisms are made up of cells or aggregates of cells which vary greatly in size, shape and Functions.
2) Cells are broadly of two types:

• Prokaryotic: That do not have any organised nucleus or membrane-bound cell organells.
• Eukaryotic: That have membrane-bound organells, an organised nucleus.

3) Plants also possess an external cell-wall outside the cell membrane.
4) The plasma membrane(cell-membrane) is selectively permeable and facilitates osmosis.
5) The endomembrane system includes the GERL (Golgi Body, Endoplasmic reticulum, Lysosomes and           vacuoles too acc. to some).
6) Centrosome and Centriole form the basal body of cilia and flagella that facilitate locomotion. In animals         cells, centrioles also form the spindle apparatus.
7)Nucleus contain nucleoli and chromatin network. It not only controls the activities of organelles, but also        plays a major role in heredity.
8) Endoplasmic reticulum contains tubules and cisternae. They are of two types:

• rough and 
• smooth.

9) The Golgi Apparatus is a membrane-bound organelle composed of flattened sacs. The secretions of cells      are packed in them and transported from the cell.
10) Lysosomes are single-membrane structures containing enzymes for digestion of all types of                            macromolecules.
11) Ribosomes are involved in protein synthesis. These occur freely in the cytoplasm or are associated with          ER.
12) Mitochondria help in oxidative phosphorylation and generation of ATP. The are double-membrane                 bound; the outer membrane is smooth while the inner one folds inwards to form several cristae.
13) Plastids are pigment containing organelles found in plant cells only.

• Chloroplasts are responsible for trapping solar energy for photosynthesis. The grana in the plastid is the site of light reaction and the stroma of dark reaction. They contain chlorophyll.
• The other coloured plastids are called chromoplasts which contain pigments like carotene, xanthophyll, etc.
• Leucoplasts are however the colourless plastids which are mainly used for storing of fat and other substances.

14) The nucleus is enclosed by the nuclear envelope, a double membrane structure with nuclear pores. The          inner membrane encloses the nucleoplasm and the chromatin material.

15) Thus, cell is the structural and functional unit of life.

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