ICSE Class 9 Biology Chapter 09 Economic Importance of Bacteria and Fungi

Economic Importance Of Bacteria And Fungi

Syllabus: Economic importance of Bacteria

Useful role of bacteria - medicine: antibiotics, serums and vaccines; Agriculture: nitrogen cycle (role of nitrogen fixing, nitrifying and denitrifying bacteria). Industry: curing of tea, tanning of leather

Harmful role of Spoilage of food, diseases in plants and animals, bio-weapons.

Economic importance of Fungi.

A brief idea of the useful role of Fungi in breweries, bakeries, cheese processing, mushroom cultivation (Processes of manufacture are not required).

(A) Economic Importance Of Bacteria

Bacteria are primitive organisms consisting of single cells (prokaryotes, without a true nucleus). They have no chlorophyll and their body is not differentiated into parts like root, stem, leaves and flowers.

[According to the recent Five Kingdom classification the bacteria are not plants, the reason being that they have no chlorophyll and the mode of nutrition in them is heterotrophic instead of autotrophic.]

9.1 Bacteria - A General Study

The bacteria are most primitive unicellular organisms. Each bacterial cell contains a single chromosome (nuclear material) which is not enclosed in a nuclear membrane.

Bacteria - so numerous and everywhere.

There are several thousand known species of bacteria which occur in air, water, soil, food-stuffs, on or inside the body of living organisms, and in short, practically everywhere. In our own body there are hundreds and thousands of bacteria in mouth, on skin, inside intestines, in the genital tracts, etc. Some bacteria occurring in our intestine are beneficial, they synthesise certain vitamins, such as vitamin B. Certain bacteria are highly injurious causing diseases, but there are others which are highly beneficial.

[According to one estimate, there are more bacteria normally living on your skin than the total number of humans living on Earth. These bacteria are even useful as they prevent the growth of harmful ones]

Size. Bacteria are the smallest living organisms on earth, with an average size of 2 micrometres long and 0-5 micrometre thick (1 micrometre = one-thousandth of a millimetre).

Shape. Shape-wise, the bacteria are usually of four types:

(1) Cocci (spherical bacteria),

(2) Bacilli (rod-shaped bacteria),

(3) Spirilla (spiral or twisted bacteria),

(4) Vibrio (comma-shaped).

Many bacteria live single but some occur in pairs (diplococci), or in long chains (streptococci) or in clusters (staphylococci) (Fig. 9.1).

Fig. 9.1 Kinds of bacteria

Teacher's Note

Bacteria are everywhere around us - in the air we breathe, on our skin, and in our food. Many are helpful, like those in yogurt, while others cause illness. Understanding bacteria helps us stay healthy and use them wisely in medicine and industry.

Structure

Each individual bacterium is rather a simple cell (Fig. 9.2). It contains the living substance protoplasm/protoplast lying within the cell membrane (cytoplasm + bacterial chromosome) surrounded by a non-living stiff cell wall. The cell wall is made of peptidoglycan and not of cellulose (as in plant cells).

A thin cell membrane lies immediately beneath the cell-wall and surrounds the cytoplasm.

There is no well-defined nucleus but chromatin (DNA) material is present in the central region. This chromatin material is in the form of a single circle and is not enclosed in a nuclear membrane, but is attached to the cell membrane at some point.

The cytoplasm contains vacuoles, granules and, in very few cases, some green pigment as well.

Sometimes a slimy protective layer called capsule is present outside the cell wall.

Fig. 9.2 Bacterial cell (diagrammatic)

Movement

Most bacteria cannot move about by their own effort and they are only passively transported by wind, water or contact. But some bacteria possess one or more whip-like flagella which pierce through the cell-wall and capsule. The lashing movements of the flagella provide active locomotion in a liquid environment.

Nutrition

Most bacteria have no chlorophyll, therefore, they depend on readymade food from different sources (heterotrophic). In this category, the bacteria may be:

- saprotrophic (drawing nourishment from decaying dead organisms), or

- parasitic (drawing nourishment from the body of their living hosts).

The bacteria secrete powerful enzymes from their cells into the surrounding food-containing material.

The enzymes make the food material soluble which is then absorbed as a solution into the bacterial cell.

Respiration. Some bacteria respire by absorbing atmospheric oxygen (aerobic), others need no free oxygen (anaerobic). The anaerobic bacteria are killed if exposed to air.

Reproduction. Reproduction in bacteria is only asexual by means of fission or cell division. The circular DNA duplicates. The cell expands and the two DNA are pulled apart. The cell constricts at the middle separating the two cells (Fig. 9.3). Depending on the type of bacteria the two daughter cells may either remain attached or may separate from each other as independent cells.

Fig. 9.3 Reproduction in bacteria by fission

Bacteria Reproduce Very Fast

Under ideal conditions some bacteria divide at a very fast rate, once in every half hour. At this rate of growth and division starting with a single bacterium, at the end of 24 hours there would be 281,514,871,750,656 bacteria!

Highly primitive type of sexual reproduction has been found in very few bacteria and is extremely simple. In this method two bacteria of different strains (but of the same species) come together (conjugation). The plasmid of the donor may be transferred into the recipient through a hollow tubelike extension of the donor cell.

Spores to overcome unfavourable conditions. When unfavourable conditions set in, such as the drying up of vegetation, the bacterial cell draws its content into a spherical mass which becomes surrounded by a thick and hard protective wall. This little rounded body is a spore which is contained within the original cell-wall (Fig. 9.4), but later becomes free when the cell-wall ruptures. Such spores are usually the resting stages which can withstand unfavourable conditions.

- These can tolerate extreme dryness,

- Some cannot be killed even at the temperatures of boiling water or frozen ice,

- Some can tolerate poisonous chemicals.

The spores can be carried far and wide by various means such as wind, water or contact. On meeting favourable conditions the spores germinate, their dormant protoplasm becomes active and streams out of the ruptured wall in the form of a new bacterium.

Fig. 9.4 A bacterium forming a spore inside itself.

[Spore-formation in bacteria is not a method of reproduction but simply a method of escaping unfavourable conditions]

Teacher's Note

Bacterial spores are nature's way of creating a pause button. When things get tough - no water, extreme heat, or harsh chemicals - bacteria form spores to survive. This is why certain spores can survive even boiling water and why food preservation is so important.

Progress Check

1. Name the three common shapes of bacteria.

2. Give the technical terms for the following patterns of occurrence of bacteria

(i) In pairs

(ii) In long chains

(iii) In clusters

3. List the kinds of nutrition in bacteria.

4. What is the common method of reproduction in bacteria?

5. Why do bacteria produce spores?

9.2 Useful Role Of Bacteria In Medicine

Bacteria are used in medicine in the production of antibiotics, serum and vaccines.

9.2.1 Antibiotics

An antibiotic is a chemical substance produced by a living organism which can stop the growth of some disease-producing bacteria and fungi.

Today, we know of dozens of antibiotics widely used in the treatment of numerous infections. Examples: streptomycin, chloromycetin, tetracycline, penicillin.

Penicillin - The first produced antibiotic (from a fungus and not bacterium). How it was discovered is described below.

In 1929 Alexander Fleming observed that some bacteria growing in a culture were destroyed by an accidental contamination of a mould Penicillium notatum (Fig. 9.11 p. 99). He discovered that this mould produced a substance which suppressed the growth of many bacteria, and the substance was named penicillin, the first antibiotic for medical use. But remember, penicillin is the product of a mould (fungus) and not of a bacterium.

Next antibiotic streptomycin was discovered by Selman Waksman in a similar way. Its source organism was the bacterium Streptomyces griseus.

Some well-known antibiotics, their sources and the diseases treated are as follows:

Criteria for a good antibiotic

1. It should be able to kill a variety of disease-producing microorganisms ("broad spectrum" antibiotic).

2. It should not produce undesirable side-effects.

3. It should not kill normal bacteria of the host.

Other uses of antibiotics

- As food preservatives, especially for fresh meat and fish.

- For treating animal feed.

- For controlling plant pathogens.

Teacher's Note

Antibiotics are one of humanity's greatest medical discoveries. They work like targeted weapons against harmful bacteria, but we must use them wisely to prevent bacteria from developing resistance to them.

This is a preview of the first 3 pages. To get the complete book, click below.