Chapter 4: CELLS


   Bodies of organisms are made of tiny units called Cells. Cell have outer boundary called cell membrane [made up of lipids and proteins], most cells have a nucleus and inside the cell membrane or plasma membrane is present cytoplasm.

Nucleus, cytoplasm and membrane are basic components of cell.

Types of cell components:

  • Endoplasmic Reticulum
  • Golgi body
  • Mitochondria
  • Nucleus
  • Vacuole

Endoplasmic reticulum

    Endoplasmic reticulum is of two types Rough ER – it has ribosome attached to it. Ribosome manufactures proteins. Smooth ER has a role in manufacturing lipids. ER also serves as a transport channel between various regions of cytoplasm or cytoplasm and nucleus.

In vertebrates, SER detoxifies poisons and drugs.  

Golgi body 

 Golgi body helps in formation of lysosomes [contain digestive enzymes which digest wastes, foreign bodies or even damaged cell organelles and the cell itself – hence called suicide bags].

It helps in making complex sugars from simple sugars and stores, packages products in vesicles.


Nucleus contains chromatin material, during division of cell it gets organized into chromosomes. These contain information to be inherited by the next generation in form of DNA.

Functional units of DNA are genes. DNA contains information necessary for organizing and constructing cells.


A single large Vacuole is present in plant cells and multiple small vacuoles in animal cells. Vacuoles store liquids or solid contents.

Centrioles are seen only in animal cells. Plastids are found only in plant cell.

Green plastids called chloroplasts carry chlorophyll. White plastids are called leucoplasts; they store starch, oil and proteins. They have their own DNA and ribosome.


Membranes are porous and allow nutrients and substances to move in or out. Hence it’s selectively permeable. Diffusion plays an important role in exchange of gases. Water is moved by osmosis [Solvent moves from dilute to concentrated solution]. Food is taken in by endocytosis. Cytoplasm and nucleus are called protoplasm.

Plant and Animal Cells:

Plant cells and bacterial cells have cell wall [made of cellulose] outside the membrane. No cell wall in animal cells. Because of cell walls plant cells can withstand much greater variations in surrounding medium than animal cells.


Viruses lack membranes and hence do not show any characteristics of life till they enter a host and use its cell machinery to multiply. They have few biochemical mechanisms on their own; they enter the host and use his processes for their work. They have either DNA or RNA not both. RNA acts genetic material only in viruses.

Facts of Cellular Respiration:

Cellular respiration involves using oxygen [aerobic] to break down food [glucose] into energy; carbon dioxide and water are released.

If this process takes place in absence of oxygen [in yeast] then alcohol, carbon dioxide and energy are formed. This is anaerobic respiration. 

Hence Yeast [single celled organisms] is used in making wine and beer. They convert sugar to alcohol; this process is called fermentation [discovered by Louis Pasteur].

Lactobacillus helps in conversion of milk into curd. Bio fertilizers are organisms that enrich the quality of soil.

Yeast multiplies rapidly and produces carbon dioxide by respiration this causes bubbles of gas that fill the dough and increase its volume. So it’s used in making bread, pastries and cakes. 


  1. Some Antibiotics are made from fungi and bacteria. However antibiotics don’t work against viral infections. Antibiotic like penicillin stops creation of a cell wall in bacteria but as humans don’t create a cell wall it has no effect on humans. Viruses don’t follow these pathways and hence viral infections don’t have antibiotics.
  2. Analgesics relieve pain, antihistamines relieve inflammation.
  3. Sodium benzoate [can be metabolized by body], sodium metabisulphide, salts of propanoic, sorbic acid and edible oils are some common preservatives. Sugar reduces moisture content and so microbes can’t grow.
  4. Aspartame [100x sweeter than sugar; used in cold drinks, cold foods], sucralose [600x], saccharin [550x; used by diabetic patients to sweeten food; is excreted in urine], alitame are artificial sweeteners.
  5. Evolution isn’t progress from lower to higher forms. But evolution seems to have given birth to complex designs even when simpler designs continue to flourish.

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