Chapter 5 Fundamental unit of life class 9 notes

Welcome to Class 9 The Fundamental Unit Of Life notes Notes for Chapter 15.The topics in this page are Discovery of cell ,Cell Theory,Shape, size and number of cells,Differences between Prokaryotic and Eukaryotic cells,Structure of cell, Cell Membrane,Cell Wall,Cell organelles and Nucleus. This is according to CBSE and the NCERT textbook. If you like the study material, feel free to share the link as much as possible.

Table Of Contents

• Introduction
• Discovery of cell
• Cell Theory
• Shape, size and number of cells
• Types of cells
• Differences between Prokaryotic and Eukaryotic cells
• Structure of cell
• Cell Membrane
• Cell Wall
• Cytoplasm
• Cell organelles
• Nucleus

Introduction

• The body of all organisms is made up of tiny microscopic units called cell.
• The cell is a fundamental, structural and functional unit of living organisms and basic unit of life.
• All living organisms are made up of cells. Cells make tissues, tissues together make organ, organs make organ system and organ systems make body of organisms. So cell is called structural unit of life.
• All the basic functions of the body like respiration, excretion etc. are carried out by cell through  its cell organelles, so cell is called functional unit of life.
• Cell biology is the study of cells in all aspects of structure and functions.

Discovery of cell:

• Cell was first discovered by Robert Hook in 1665. He observed the cell in a cork slice with the help of a primitive microscope.
• Anton Von Leeuwenhoek (1674) was the first to observe free cells, like bacteria, protozoa, red blood cells and sperms in his home made microscope.

Cell theory:

• The cell theory, that all the plants and animals are composed of cells and that the cell is basic unit of life, was presented by two biologists, M. Schleiden (1838) and T. Schwann (1839).
• The cell theory was further expanded by a german physiologist, Rudolf Virchow (1855). He gave the phrase Omnis cellula-e-cellula, i.e., all cells arises from pre-existing cells.
• Modified cell theory is termed as cell principle or modern cell theory which postulates that:
  • All living organisms are composed of cells or cell products.
    
  • All living cells arise from pre-existing cells.
    
  • All cells are basically alike in chemical composition and metabolic processes.
    

Shape, size and number of cells:

Cell shape:

• The shape of cells is related to the specific function they perform.
  
• Some cells like Amoeba and WBCs have changing shapes.
  
• In some cases the cell shape could be more or less fixed and peculiar for a particular type of cell; for example, nerve cells have a typical shape.
  

Cell size:

• The size of the cell also varies considerably in different animals and plants.
  
• The average cell size varies from 0.5 to 20µ (µ = micrometer).
  
• In human body, the smallest cell is RBC and the longest one is the nerve cells.
  

Cell number:

• The number of cells in living beings differs from the one in unicellular organisms to many in multicellular forms.
  
• The number of cells in not definite in multicellular organisms, and may increase along with the growth and volume of organism.
  

Types of Cells:

Differences between Prokaryotic and Eukaryotic cells:

Structure of cell:

1. Plasma membrane or cell membrane
2. Cytoplasm and its contents
3. Nucleus

Plasma membrane (cell membrane):

• Plasma membrane is the outermost covering of the cell that separates the contents of the cell from its external environment.
• Plasma membrane is living, thin, delicate, elastic, selectively permeable membrane.
• The plasma membrane is flexible and made up of organic molecules called lipids and proteins.

• Plasma membrane permits the entry and exit of some materials in the cells. It also prevents movement of some other material. Therefore, the plasma membrane is called a selectively permeable membrane.
  
• Substances can pass across a membrane by two processes- diffusion and osmosis.
  Diffusion: Some substances like carbon dioxide or oxygen can move across the cell membrane by a process called diffusion.
  “Diffusion is the spontaneous movement of molecules from a region of its higher concentration to a region of its lower concentration.”
  Example: movement of carbon dioxide and oxygen during respirationin organisms.
  Osmosis:
  The movement of water molecules through a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration is called osmosis.
  

1. Let us see what will happen if you put an animal cell or plant cells into solution of sugar or salt prepared in water?
   

1. If the medium surrounding the cell has a higher water concentration than the cell, i.e., if solution is a very diluted solution, the cell will gain water by osmosis. Such a dilute solution is called hypotonic solution.

2. If the medium surrounding the cell is exactly the same water concentration as the cell, there will be no net movement of water across the plasma membrane resulting in no change in the size of the cell. Such a solution is called isotonic solution.
3. If the medium has a lower concentration of water than the cell, i.e., if it is very concentrated solution, the cell will lose water by osmosis. Such a concentrated solution is called hypertonic solution.

Cell wall:

• In plant cells, there occurs a rigid cell wall which lies outside the plasma membrane.
• Cell wall is thick, non-living and permeable covering made up of cellulose. Cellulose is a kind of carbohydrate (polysaccharide) and it provides structural strength to the plant.

1. Cell wall protects cell membrane and the internal structures of the cell.
2. It provides rigidity and determines the shape of the plant cell.
3. It prevents drying of the cell and helps it to bear unfavourable conditions.
4. It provides mechanical strength to the plant cells.

• All cells contain living substance called protoplasm. It is jelly-like, viscous, colourless semi-fluid substance in which various cell organelles and inclusion remains in colloidal form.
• Protoplasm can be distinguished in two forms:
  1. Cytoplasm: it is that part of protoplasm which surrounds the nucleus.
  2. Nucleoplasm: it is that part of protoplasm which is located inside the nucleus.

Cytoplasm

• Cytoplasm consists of an aqueous ground substance, the cytosol, containing a variety of cell organelles and other inclusions such as insoluble waste and storage product (starch, lipid, etc.).
  

• Chemically cytoplasm contains about 90% water,, 7% proteins, 2% carbohydrates and lipids and 1% inorganic minerals, minerals vitamins, etc.

Cell organelles:

• A cell has to perform different functions with the help of its various membrane- bound cell organelles.
  
• Cell organelles are “small organs” of the cell and are found embedded in the cytosol. They form living part of the cell and each of them has a definite shape, structure and function.
  

Nucleus:

• The nucleus is a major, centrally located spherical cellular component. It is the centre from where all cellular activities are controlled. It is the carrier of hereditary material in the cell.
• It is bounded by two membranes, both forming a nuclear envelope. The nuclear envelope contains many pores known as nuclear pores and encloses the liquid ground substance, the nucleoplasm.
• The nucleopores allow transfer of materials between the nucleoplasm and the cytoplasm. Within nucleoplasm are embedded two types of nuclear structures- nucleolus and chromatin material. 

• The nucleolus may be one or more in number ad is not bounded by any membrane.
  
• Nucleolus consists of DNA, RNA and protein.
  
• It is the site of ribosome formation. Nucleolus is known as factory of ribosomes.
  

• The chromatin is a thin, thread-like intermingled mass of chromosome material and composed of the genetic substance DNA (deoxyribonucleic acid) and proteins (i.e., histones).
•  DNA stores all the information necessary for the cell to function (metabolism), to grow and to reproduce further cells of the next generation.
• The chromatin is condensed into two or more thick ribbon-like chromosomes during the division of cell.
• Functional segments of DNA are called genes.
• Genes carry information for protein synthesis, which in turn control the development of characters. Since genes are present on chromosomes and chromosomes pass from one generation to the next through, genes are called hereditary units.

1. The nucleus controls all metabolic activities of the cell. If the nucleus is removed from the cell, the protoplasm ultimately dries up and dies.
2. It regulates the cell cycle.
3. It is the storehouse of genes which are concerned with the development and manifestation of all the body characters.
4. Nucleus helps in the formation of ribosomes and RNA.
5. It helps in the transmission of characters from one generation to the next.

Summary> Here is the The Fundamental Unit Of Life notes for class 9 Summary

• Cell is the fundamental organisational unit of life
• Protein-lipid plasma membranes surround cells.
• The cell membrane controls material flow between the organized cell interior and the outside world.
• The cell wall allows plants, fungus, and bacteria to survive in hypotonic media.
• The nucleus in eukaryotes is separated from the cytoplasm by double-layered membrane and it directs the life processes of the cell.
• The ER functions both as a passageway for intracellular transport and as a manufacturing surface.
• The Golgi apparatus stores, modifies, and packages cell-made chemicals in membrane-bound vesicles.
• Most plant cells have large membranous organelles called plastids, which are of two types – chromoplasts and leucoplasts.
• Chromoplasts that contain chlorophyll are called chloroplasts and they perform photosynthesis.
• The primary function of leucoplasts is storage.
• Most mature plant cells have a large central

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