8 CELL THE UNIT OF LIFE
Cell
A cell is defined as the most basic, structural and functional unit of all living organisms. Essentially, a cell is a structure that contains organelles which provide necessary functions to sustain itself. However, not all cells are the same.
Prokaryotic cells (8 CELL THE UNIT OF LIFE)
- Membrane-bound nucleus is absent.
- Cells are smaller in size.
- Single chromosome is present.
- Membrane-bound organelles are absent.
Eukaryotic cells
- Membrane-bound nucleus is present.
- Cells are larger in size.
- More than one chromosome is present.
- Membrane-bound organelles are present.
Animal cell
- Cell membrane is composed of lipids that are arranged in bilayer. The lipid component is mainly composed of phosphoglycerides. Later it was found that protein is also present in cell membrane. Ratio of protein and lipids varies in different cells. 8 CELL THE UNIT OF LIFE
- Membrane protein may be integral or peripheral. Integral protein remains buried in membrane but peripheral protein lies on the surface.
- Singer and Nicholson (1972) proposed fluid mosaic model. According to this model, the quasi-fluid nature of lipid enables lateral movement of protein within the bilayer of lipids.
Eukaryotic cells:
Eukaryotic cells Possess an organized nucleus with nuclear envelope and have a variety of complex locomotory and cytoskeletal structures.
Active Transport
The transport involves an expenditure of energy by the cells, It occurs against the concentration gradient. It is a rapid process.
Passive Transport
The cells do not spend energy in passive transport, this transport is always along the concentration gradient. It is comparatively slow process.
Endoplasmic Reticulum
Endoplasmic Reticulum are the tubular structure scattered in the cytoplasm. Rough endoplasmic reticulum bears ribosomes on its surface. RER is involved in protein synthesis and secretion. Smooth endoplasmic reticulum does not bear ribosomes on its surface. SER is involved in lipid synthesis and steroidal hormones.
Golgi apparatus
Golgi apparatus was first observed by Camillo Golgi in 1898 near nucleus. They consist of many flat, disc-shaped sacs or cisternae stacked parallel to each other. Golgi apparatus performs the function of packaging of materials and its transportation. A number of protein synthesized by ribosomes are modified in cisternae of Golgi apparatus. Golgi apparatus is the site for synthesis of Glycoproteins and glycolipids.
Lysosomes
Lysosomes are membrane-bound vesicular structures formed by the process of packaging in the Golgi apparatus. They are rich in hydrolytic enzymes- lipase, protease, carbohydrates active at acidic PH. These enzymes are capable of digesting carbohydrates, proteins, lipids, and nucleic acids.
Vacuoles
Vacuoles are membrane-bound space found in cytoplasm containing water, sap and excretory product. They are bound by single membrane. They form contractile vacuole and food vacuole in many organisms.
Mitochondria
Mitochondria is double membrane-bound structure with the outer membrane and inner membrane dividing its lumen in two compartments. The inner membrane forms a number of infoldings called cristae towards the matrix.
Plastids
Plastids are found in plant cells and in Euglenoids.
Plastids are three types:
Chloroplast (Contain chlorophyll and caratenoids).
Chromoplast (Contain carotene and xanthophyll).
Leucoplast (Colorless plastids).
Chloroplast:
Contains chlorophyll pigment and carotenoids and performs photosynthesis
Chromoplast:
Contains carotene and xanthophylls. They impart a specific color to flowers and fruits and help in pollination and dispersal of seeds
Leucoplast:
They are colorless and store various food products, e.g., amyloplasts- store starch, proteinoplasts or aleuroplasts- store proteins, elaioplasts- store fat.
Q. In living organisms detailed description that brings out their knowledge of diversity is about
A) Their form B) Their appearance
C) Both D) None
Q. What brought out the unit of diversity the cellular organisation of all life form:
A) Theory of evolution B) Species theory
C) Cell theory D) Darwinian theory
Q. What is not true about physico-chemical approach:-
A) Established by analysis of living tissue for element and compounds.
B) Explains what type of organic compounds is present in living organism.
C) Explains the abnormal process that occur during any diseased condition.
D) This approach is known as forward biology.