Microorganisms - Our Friends and Foes

 Microorganisms

You have seen several kinds of plants and animals. However, there are other living organisms around us which we cannot see with eyes alone. These are called microorganisms or microbes. For example, you might have observed that during rainy season moist bread gets spoilt and its surface gets covered with greyish white patches.

Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae. Some of these common microorganisms are shown in Figure.

Viruses are also microscopic. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal. Some of the viruses are shown in Figure.

Common ailments like cold, influenza (flu) and most coughs are caused by viruses. Serious diseases like polio and chicken pox are also caused by viruses. Diseases like dysentery and malaria are caused by protozoans whereas typhoid and tuberculosis (TB) are bacterial diseases. 

Where do Microorganisms live?

Microorganisms live & survive in varied environmental conditions ranging from ice cold climate to hot springs & deserts to marshy lands. But the most conductive environment for them to grow & multiply is the humid & moist environment. Some microorganisms grow on other organisms while others exist freely. Large numbers of microorganism are found on & inside human body.

Friendly Microorganisms

It is difficult to imagine our lives without the friendly microorganisms. Some of the uses of these microorganisms from our daily life are

1. Preparation of curd, bread & cakes
2. Commercial production of alcohol, wine & vinegar
3. Preparation of medicines
4. Used in agriculture to increase soil fertility
5. In cleaning up of the environment

Commercial Uses

Microorganisms are used in Industries for manufacturing various substances. For example

1. Curd
2. Breads and Cakes
3. Alcohol and Wine
4. Acetic Acid (Vinegar)

Curd is prepared by adding a small amount of curd to milk. This process is called Curding. Curd contains bacteria called Lactobacillus, which helps promotes curding of milk & thus turn milk into curd
                Breads and Cakes are made by adding a small amount of Baker’s Yeast to the dough. The yeast (a fungi) reproduces rapidly in moist and warm conditions and releases carbon dioxide (CO₂) into the dough thus making the bread porous & puffy.
                 The process of conversion of sugar into alcohol is known as Fermentation. This is done in the presence of Yeast. Fermentation was discovered by Louis Pasteur in 1857.
Vinegar is made by fermentation/oxidation of ethanol by acetic acid bacteria.

Medicinal Uses

Microorganisms are used in the field of medicine for preparing various types of medicines. For examples

1. Antibiotics
2. Vaccines

Antibiotics are the medicines that kill or stop the growth of disease causing microorganisms. These medicines are manufactured by growing specific types of bacteria and fungi which have the capability to prevent the growth of other microorganisms. Antibiotics are effective against bacteria but are not very effective against viruses.
Antibiotics are also used in crop production and animal husbandry to control microbial infection in plants and animals respectively
Antibiotics should only be taken on the advice of a doctor and in prescribed doses only. They should be continued for the prescribed duration to ensure that microbes do not get immune to these antibiotic medicines; otherwise they will not be effective when you need it next time.
Penicillin – the first antibiotic was discovered by Alexander Fleming in 1929.
Vaccines are a type of medicines, which help prevent the occurrence of a disease, rather than curing them when they occur. They prevent us from diseases like

• Tetanus
• Polio
• Chicken Pox

How do vaccines work?
Human body has a natural defence system. When a microbe enters the body, the body produces antibodies to fight the intruder. As part of vaccination, weakened or dead cells of infection causing microbes are introduced in the body in a controlled manner. The body fights & kills these microbes by producing suitable antibodies. Even after the infection is cured, these antibodies remain in the body and hence the body remembers how to fight such microbes during future infections.

Vaccine for small pox was discovered by Edward Jenner in 1798.

Agricultural Uses

Some microorganisms can convert nitrogen present in air into Ammonia (NH₃), Nitrites (NO₂) or Nitrates (NO₃) which can be absorbed by the soil. This process is called nitrogen fixing. It increases the fertility of the soil and leads to increased agricultural yield
Examples of such microorganisms are

1. Rhizobium bacteria
2. Blue green algae (They were traditionally considered algae but are now considered as bacteria)

Environmental Uses

Microorganisms decompose the organic waste like vegetable peels, wastes from plants & animals & convert them into manure. It is also important to remember that plastics are not bio-degradable and do not get decomposed. They are harmful to the environment, so we should discourage the use of plastics.

Harmful Microorganisms

Harmful microorganisms affect us in many ways. Some harmful microorganisms cause diseases while others spoil food, clothes & leather etc.

Disease causing Microorganisms

Disease causing microorganisms are called Pathogens. They enter our body through air, water & the food that we eat. They also get transmitted by direct contact with the infected person or can be carried through mosquitoes, flies and animals.
The microbial diseases that spread from an infected person to the healthy person through air, water, food or direct contact are called Communicable Diseases. For example

• Cholera
• Chicken Pox
• TB

Diseases which get transmitted through air are called airborne diseases. Similarly, the diseases transmitted through water are called waterborne diseases.

How do we get airborne diseases like common cold?
Common cold is a viral infection of the upper respiratory tract. It can be caused by upto 200 different types of viruses. The virus grows mainly in the nose and produces nasal secretions. When an infected person sneezes, these secretions are blown into the air in the form of tiny droplets. They can straightaway land on another person and cause infection. They can also land on other objects and surfaces in the room where they can survive for upto three hours. If another person touches the contaminated surface, he could also catch cold
There are some insects & animals which can transfer disease causing microbes to human body. They are called Carriers. For example

1. Housefly is a carrier of Cholera
2. Female Anopheles mosquito is a carrier of Malaria
3. Female Aedes mosquito is a carrier of Dengue

They can transfer pathogens either by contaminating our food/water or by biting & transmitting the pathogens to our blood
Microorganisms can cause diseases in plants as well. Almost all the crop yielding plants get affected by diseases caused by microorganisms, thereby affecting the yield of crop. For example

1. Citrus canker affecting citrus fruits is caused by Bacteria
2. Rust of wheat affecting wheat crops is caused by Fungi
3. Yellow veing mosaic of ocra (bhindi) is caused by Virus

This can be controlled by use of chemicals to kill the microbes.
Similarly, Microorganisms can cause disease in animals as well. What affect us most are the diseases affecting cattle, livestock and poultry

1. “Bird flu” affects poultry and is caused by a virus
2. “Foot and Mouth” diseases affects cattle and is caused by bacteria

Microorganisms which spoil our Food, clothes and Leather

The microorganisms that grow on food, produce toxic substances making the food poisonous & unfit for consumption. If this food is consumed it causes illness. This is called ‘Food Poisoning’. In order to prevent ‘Food Poisoning’, we need to preserve our food.

So we can say that Microorganism are our Friends and Foes both.

Cell a Basic Structural and Functional Unit of Life

WHAT IS A CELL?

We know that the body of all living organisms is made up of cells which

carryout certain basic functions. Hence the cells are called “Basic structural and functional units of living organisms”. The classical branch of biology that deals with the study of structure, function and life history of a cell is called

“Cell Biology”

Robert Hooke (1665): He is an English scientist who observed honeycomb like dead cells in a thin slice of cork under microscope. He coined the term ‘cell ‘, which means a small room or compartment

Anton Von Leeuwenhoek (1667): First saw and described living cell

Matthias J Schleiden(1838):a German botanist based on his studies in different plant cells and Theodore Schwann (1839 ), a British zoologist based on his studies on different animal cells formulated ’cell theory’ 

CELL THEORY:

Cell theory was formulated by M J Schleiden (1838) and Theodore Schwann (1839 ). The main principles of cell theory are

• All living organisms are composed of cells and products of cells
• All cells arise from pre existing cells through the process of cell division
• The body of living organisms is made up of one or more cells 

ORGANISMS SHOW VARIETY IN CELL NUMBER, SHAPE AND SIZE

The invention of electron microscope and staining techniques helped scientists to study the detailed structure of cell. The number of cells vary from a single cell to many cells in an

organism. The organisms made up of a single cell are called unicellular organisms. These are capable of independent existence. The single cell carries all the functions like digestion, excretion, respiration, growth and reproduction. So, they are rightly called a cellular organisms

Eg : Amoeba, Euglena, Paramecium etc.

The organisms made up of more than one cell are called multicellular organisms. In multicellular organisms the cells vary in their shape and size depending on their function. The cells are spherical, oval, polyhedral, discoidal, spindle shaped, cylindrical in shape. The shape

of the cells varies with the functions they perform. 

Eg:   Parenchyma cells – Polyhedral cells that perform storage function

         Sclerenchyma cells – Spindle shaped cells that provide mechanical support

         White blood cells – Amoeboid cells that defend the body against pathogens

         Nerve cells – Long and branched that conduct nerve impulses

         Muscle cells – cylindrical or spindle shaped cells concerned with the movement of body

parts 

The size of the cell varies from few micrometers (μm) to few centimeters (cm). The size of bacteria varies from 0.1 to 0.5 μm. The smallest cell PPLO (Pleuro pneumonia like organism) is about 0.1 μ in diameter. The largest cell is an ostrich egg that measures 170 to 180 mm in diameter. Some Sclerenchyma fibres measure up to 60 cm in length. However the average size of the cell ranges from 0.5 to 10 μm in diameter. 

CELL STRUCTURE AND FUNCTION:

A typical cell has an outer non living layer called cell wall. The cell membrane is present below the cell wall. The cell membrane encloses protoplasm. The protoplasm has a semi fluid matrix called cytoplasm and a large membrane bound structure called Nucleus. The cytoplasm has many membrane bound structures like endoplasmic reticulum, golgibodies, mitochondria, plastids, micro bodies, vacuoles; and non membranous structures like Centrosome and ribosomes. These are called cell organelles. The cytoplasm without these cell organelles is called cytosol. The cytoplasm also contains non living inclusions called ergastic substances and cytoskeleton (microfilaments and microtubules)

ANIMAL CELL

PLANT CELL

Comparison of plant and Animal cell
Plant cell		Animal Cell
Cell wall is present		Cell wall is absent
Centrioles are absent		Centrioles are present
Plastids are present		Plastids are absent
Have large vacuole		May have small vacuoles