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Cell - The Unit of Life Class 11 Notes Biology Chapter 8

1. Cytology: (G.k. kyios = cell ; logas = study) is the branch of biology that comprises the study of cell structure and function.
2. Cell is the structural and functional unit of all living beings.
3. There are two types of cells:

  • Plant Cell
  • Animal Cell

Animal and Plant CellAnimal and Plant CellDifference between Plant Cell and Animal Cell:

Cell - The Unit of Life Class 11 Notes Biology Chapter 8

Question for Revision Notes: Cell - The Unit of Life
Try yourself:The animal cell is different from a plant cell in having
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Important Points

  • Jan Swammerdam: First to see red blood cells of frog.
  • Marcello Malpighi: Observed small utricles in slice of plant and animal tissue.
  • N. Grew: Initiated cell concept
  • Lamarck: All living beings are formed of cells.
  • Corti: First to point out living substance filled inside the cell. It was called “Sarcode” by Dujardin.
  • In vivo (in life) study: Study of cells in their natural environment within the intact organism.
  • In vitro (cultural condition) study: Study of isolated life system in laboratory and cultural condition.
  • Max Shultze proposed protoplasm theory.
  • Sachs proposed organismic theory.
  • Crystallo: colloidal theory (Fischer), substances dispersed and dissolved in water forming both true solution as well as colloidal solution

4. Difference between Prokaryotic and Eukaryotic Cells

Cell - The Unit of Life Class 11 Notes Biology Chapter 8

Cell - The Unit of Life Class 11 Notes Biology Chapter 8

Question for Revision Notes: Cell - The Unit of Life
Try yourself:Which of the following structure is present only in prokaryotic cell?
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Question for Revision Notes: Cell - The Unit of Life
Try yourself:The genetic material of a prokaryotic cell is known as
View Solution

5. Difference between Primary Cell Wall and Secondary Cell Wall
Cell - The Unit of Life Class 11 Notes Biology Chapter 8
Cell - The Unit of Life Class 11 Notes Biology Chapter 8

6. Difference between Extrinsic Protein and Intrinsic Protein
Cell - The Unit of Life Class 11 Notes Biology Chapter 8
7. Cell Wall

  • Discovery: It was first discovered by Robert Hooke in 1665.
  • Cell wall is the outer most, rigid, protective, non living and supportive layer found in all the plant cells, bacteria, cyanobacteria and some protists.
    Cell - The Unit of Life Class 11 Notes Biology Chapter 8
  • It is not found in animal cells.

Question for Revision Notes: Cell - The Unit of Life
Try yourself:Robert Hooke discovered the_______ of a cell
View Solution

8. Plasma Membrane

  • Definition: Every living cell is externally covered by a thin transparent electron microscopic, elastic regenerative and selectively permeable membrane called the plasma membrane.
    Cell - The Unit of Life Class 11 Notes Biology Chapter 8
  • It is quasi fluid in nature.
  • According to Singer and Nicolson, it is a “protein iceberg in a sea of lipid”.
  • A cell wall lies external to plasmalemma in plant cells, many monerans, some protists and fungal cells.
  • Membranes also occur inside the cells.
  • They are collectively called biomembranes.
  • The term cell membrane was given by C. Nageli and C. Cramer (1855) for the outer membrane covering of the protoplast.
  • It was replaced by the term plasmalemma or plasma membrane by Plowe (1931).

9. Protoplasm

  • Definition: Protoplasm is a complex, granular, elastic, viscous and colourless substance. It is selectively or differentially permeable.
  • It is considered as a “Polyphasic colloidal system”.
  • Discoveries
    (i) J. Huxley defined it as the “physical basis of life”.
    (ii) Dujardin (1835) discovered it and called them “sarcode”.
    (iii) Purkinje (1837) renamed it “Protoplasm”.
    (iv) Hugo Von Mohl (1844) gave the significance of it.
    (v) Max Schultz (1861) gave the protoplasmic theory for plants.

10. Cytoplasm

  • The substance that occurs around the nucleus and inside the plasma membrane containing various organelles and inclusions is called cytoplasm.
    Cell - The Unit of Life Class 11 Notes Biology Chapter 8

11. Mitochondria

  • Definition: (Gk – Mito = thread; chondroitin = granule) Mitochondria are semi-autonomous having hollow sac-like structures present in all eukaryotes except mature RBCs of mammals and sieve tubes of phloem.
    Cell - The Unit of Life Class 11 Notes Biology Chapter 8
  • These are absent in all prokaryotes like bacteria and cyanobacteria.
  • Mitochondria are also called chondriosome, chondrioplast, plasmosomes, plastosomes and plastochondriane.

Question for Revision Notes: Cell - The Unit of Life
Try yourself:The figure below shows the structure of a mitochondrion with its four parts labelled A, B, C and D. Select the part correctly matched with its function.
Cell - The Unit of Life Class 11 Notes Biology Chapter 8
View Solution

12. Plastids

  • Definition: Plastids are semiautonomous organelles having DNA, RNA, Ribosomes and double-membrane envelope that store or synthesize various types of organic compounds such as ATP and NADPH + H+ etc.
  • These are the largest cell organelles in a plant cell.
  • History: Haeckel (1865) discovered plastid, but the term was first time used by Schimper (1883).

Table: Difference between chlorophyll a and b
Cell - The Unit of Life Class 11 Notes Biology Chapter 8

13. Endoplasmic Reticulum

  • Definition: It is a well-developed electron microscopic network of interconnected cisternae, tubules and vesicles present throughout the cytoplasm, especially in the endoplasm.
  • Discovery: Garnier (1897) was the first to observe the ergastoplasm in a cell. The ER was first noted by Porter, Claude, and Fullman in 1945 as a network. It was named by Porter in 1953.

14. Golgi Complex

  • Definition: Golgi complex is made up of various membranous systems e.g. cisternae, vesicles and vacuoles.
  • These are also called Golgi bodies, golgisomes, lipochondrion, dictyosomes, Dalton complex, idiosomes or Baker’s body.
  • These are also called “traffic police” of the cell.
  • Discovery: First observed by George (1867) but it’s morphological details were given by Camillo Golgi (1898), in nerve cells of barn fowl and cat.

Cell - The Unit of Life Class 11 Notes Biology Chapter 8

Question for Revision Notes: Cell - The Unit of Life
Try yourself:Which of the following is common to both ER and Golgi complex?
View Solution

The document Cell - The Unit of Life Class 11 Notes Biology Chapter 8 is a part of the NEET Course NCERT Exemplar & Revision Notes for NEET.
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FAQs on Cell - The Unit of Life Class 11 Notes Biology Chapter 8

1. What is a cell?
Ans. A cell is the basic structural and functional unit of all living organisms. It is the smallest unit of life, capable of carrying out all the necessary functions for survival.
2. What are the different types of cells?
Ans. There are two main types of cells - prokaryotic and eukaryotic cells. Prokaryotic cells are found in bacteria and lack a nucleus, while eukaryotic cells, found in plants, animals, fungi, and protists, have a well-defined nucleus.
3. What is the function of a cell?
Ans. Cells perform various functions such as obtaining nutrients, converting nutrients into energy, carrying out metabolic activities, reproducing, and maintaining homeostasis. They also play a crucial role in growth, development, and the overall functioning of an organism.
4. How are cells structured?
Ans. Cells have a distinct structure which includes a cell membrane, cytoplasm, and genetic material. The genetic material is housed either in a nucleus (in eukaryotic cells) or in the cytoplasm (in prokaryotic cells). Additionally, cells may have various organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and ribosomes.
5. How do cells communicate with each other?
Ans. Cells communicate with each other through various mechanisms such as direct contact, chemical signals, and electrical signals. This communication is essential for coordinating the activities of different cells within an organism and maintaining proper functioning.
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