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Cell: The basic unit of life

Introduction:

  • A great diversity of organisms are present on the earth.
  • The cell is the basic unit of a living organism.
  • Some are composed of a single cell and are called unicellular organisms while others are composed of many cells and are called multicellular organisms.
  • Both prokaryotes and eukaryotes are cellular organisms.
  • The eukaryotes contain the membrane-bound nucleus and the prokaryotes are devoid of the same.
  • The prokaryotes include archaebacteria, eubacteria and cyanobacteria whereas eukaryotes include all the protists, plants, animals, and fungi.
  • The intense study of physiological and behavioral processes occurring inside the living organism can result in the understanding of the physico-chemical approach of the cellular organisms along with the use of cell-free systems to investigate.
  • This Physico-chemical approach to study and understand living organisms is called ‘Reductionist Biology’.
  • This approach enables us to describe the various processes in molecular terms and also depicts the diversity, application, and working of such elements as well as the compounds (biomolecules).

Table of contents-

Cell- Basic unit of life
Cell theory and its modification
An Overview of Cell
Prokaryotic (Bacterial) cell
Eukaryotic cell
Cytoplasm & Cell Membrane
Transport of substances across the membrane
Cell Wall.
Endomembrane System- definition, importance, and constituent organelles (Endoplasmic reticulum, Golgi Apparatus, Lysosome and Vacuole)
Mitochondria
Plastids
Ribosomes
Cytoskeleton
Cilia and Flagella
Centrosome and centriole
Nucleus
Chromosome
Special chromosomes (Polytene and Lampbrush chromosomes)
Microbodies (Spherosome, Peroxisome and Glyoxysome)

QUIZ :

Q1. Which of the following statements regarding mitochondrial membrane is not correct?
(1) The outer membrane resembles a sieve
(2) The outer membrane is permeable to all kinds of molecules.
(3) The enzymes of the electron transfer chain are embedded in the outer membrane.
(4) The inner membrane is highly convoluted forming a series of infoldings.

Q2. Which of the following statements regarding cilia is not correct?
(1) Cilia contain an outer of nine doublet microtubules surrounding two single microtubules.
(2) The organized beating of cilia is controlled by fluxes of Ca2+ across the membrane.
(3) Cilia are hair-like cellular appendages.
(4) Microtubules of cilia are composed of tubulin.

Q3. Which one of the following is not a constituent of cell membrane?
(1) Phospholipids
(2) Cholesterol
(3) Glycolipids
(4) Proline

Q4. Select the wrong statement from the following :
(1) The chloroplasts are generally much larger than mitochondria
(2) Both chloroplasts and mitochondria contain an inner and an outer membrane
(3) Both chloroplast and mitochondria have an internal compartment, the thylakoid space bounded by the thylakoid membrane.
(4) Both chloroplast and mitochondria contain DNA.

Q5. Vacuole in a plant cell:-
(1) Lacks membrane and contains air
(2) Lacks membrane and contains water and excretory substances
(3) Is membrane-bound and contains storage proteins and lipids
(4) is membrane-bound and contains water and excretory substances

Q6. In germinating seeds, fatty acids are degraded exclusively in the:-
(1) Peroxisomes
(2) Mitochondria
(3) Proplastids
(4) Glyoxysomes

Q7. Keeping in view the "fluid mosaic model” for the structure of cell membrane, which one of the following statements is correct with respect to the movement of lipids and proteins from one lipid monolayer to the other (described as flip flop movement)?
(1) While proteins can flip-flop, lipids can not
(2) Neither lipids nor proteins can flip-flop
(3) Both lipids and proteins can flip-flop
(4) While lipids can rarely flip-flop, proteins can not

Q8. Plasmodesmata are :-
(1) Connections between adjacent cells
(2) Lignified cemented layers between cells
(3) Locomotory structures
(4) Membranes connecting the nucleus with plasmalemma

Q9. Middle lamella is composed mainly of:-
(1) Phosphoglycerides
(2) Hemicellulose
(3) Muramic acid
(4) Calcium pectate

Q10. The cytoskeleton is made up of:-
(1) Proteinaceous filaments
(2) Calcium carbonate granules
(3) Callose deposits
(4) Cellulosic microfibrils

Answer key:

1. (3)
2. (2)
3. (4)
4. (3)
5. (4)
6. (4)
7. (4)
8. (1)
9. (4)
10. (1)

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