Science and Technology Class 9 Notes Chapter 8 Maharashtra Board

Useful and Harmful Microbes

Introduction to Microbes

What are Microbes? Microbes are tiny living organisms that are too small to see with our eyes and are found everywhere around us.

Characteristics:

• They include bacteria, fungi, viruses, and protozoa.
• Some need oxygen to live (aerobic), while others don’t (anaerobic).
• They can reproduce quickly and affect our daily life in both good and bad ways.

Observation:

• Microbes can be seen using a microscope after staining (e.g., with methylene blue).

Useful Micro-organisms

Lactobacilli

What are They?

• Lactobacilli are rod-shaped, anaerobic bacteria that move and live without oxygen.

How to Observe:

• Smear buttermilk on a slide, stain with methylene blue, and observe under a microscope (10X or 60X) to see blue, moving rods.

Role in Yoghurt Making:

• They ferment lactose (milk sugar) into lactic acid.
• This lowers the pH, causing milk proteins to coagulate, turning milk into yoghurt with a sour taste.
• The low pH also kills harmful microbes in milk.

Uses of Lactobacilli:

1. Make milk products like yoghurt, buttermilk, ghee, cheese, and shrikhand.
2. Used in fermenting cider, cocoa, and vegetable pickles on a large scale.
3. Help treat stomach discomfort when combined with other microbes.
4. Ferment fodder for cattle like cows and buffaloes.
5. Used in wine and bread production.

Health Benefits:

• Doctors recommend yoghurt or buttermilk for indigestion because lactobacilli kill harmful bacteria.
• Probiotic foods with lactobacilli boost immunity by fighting bad microbes in the gut.

Problems:

• Yoghurt can turn bitter or frothy if other bacteria grow due to improper storage.

Rhizobium: Symbiotic Bacteria

What are They?

• Rhizobium are rod-shaped bacteria found in root nodules of leguminous plants (e.g., beans, soyabean).

Observation:

• Stain thin sections of root nodules with safranin and observe pinkish rods under a microscope.

Symbiotic Relationship:

• Rhizobium fix nitrogen from the air into nitrates, nitrites, and amino acids for plants.
• Plants provide carbohydrates to rhizobium in return (mutual benefit).

Importance:

• Enriches soil with nitrogen, making beans and pulses high in protein.
• Reduces the need for chemical fertilizers, lowering costs and pollution for farmers.
• Root remains after harvest add bacteria to the soil.

Rhizobial Inoculation:

• Seeds are coated with rhizobium powder before sowing to boost nitrogen supply, even for non-leguminous crops.

Yeast

What is Yeast?

• Yeast is a unicellular fungus with over 1500 species, having a eukaryotic cell with a nucleus and cell wall.

Reproduction:

• Reproduces asexually by budding, where a small daughter cell grows on the parent cell.

Observation Experiment:

• Mix yeast, sugar, and lukewarm water in a bottle with a balloon.
• After 10 minutes, the balloon inflates due to carbon dioxide; limewater turns milky, confirming CO2.
• Microscope shows oval yeast cells with buds.

Fermentation Process:

• Yeast converts sugar into alcohol and carbon dioxide during fermentation.
• Used in bread-making (CO2 makes dough rise) and alcohol production (e.g., wine, ethanol).

Industrial Uses:

• Ferments molasses (from sugarcane) to make ethanol, a smokeless fuel.
• Used with grains like maize and barley for alcohol production.

Bread-Making:

• Yeast fermentation produces CO2, making dough spongy and easy to digest, unlike plain chapattis.

Bio-remediation:

• Yarrowia lipolytica absorbs toxins from palm oil production.
• Saccharomyces cerevisiae removes arsenic, and Alcanivorax bacteria clean oil spills.

Antibiotics

What are They?

• Antibiotics are carbon compounds from bacteria and fungi that kill or stop harmful microbes.

Discovery:

• Dr. Alexander Fleming discovered penicillin in 1928 from Penicillium fungus, revolutionizing medicine.

Types:

• Broad-Spectrum: Work against many bacteria (e.g., ampicillin, tetracycline) when the germ is unknown.
• Narrow-Spectrum: Target specific bacteria (e.g., penicillin, gentamycin) when the germ is identified.

Uses:

• Penicillin treats infections like pneumonia, ear infections, and scarlet fever caused by bacteria like Streptococci.

Precautions:

• Take only with a doctor’s prescription.
• Complete the full course, even if feeling better.
• Don’t use for colds or share with others.

Research Institute:

• National Institute of Virology (Pune, 1952) studies diseases with WHO support.

Harmful Micro-organisms

Fungi

Harmful Effects:

• Spores grow on leather, gunny bags, and wood in moist conditions (rainy season), weakening them.
• Grow on food like pickles and jams, releasing mycotoxins that make food poisonous.

Prevention:

• Store food with salt or oil to reduce moisture.
• Use preservatives to stop fungal growth.

Clostridium

What are They?

• Clostridium are anaerobic, rod-shaped bacteria that form endospores and spoil cooked food.

Harmful Effects:

• Cause food poisoning during feasts due to toxins.
• Species like Clostridium botulinum and tetani are dangerous.

Prevention:

• Store food properly to avoid anaerobic conditions.

Other Harmful Microbes

Types:

• Viruses (e.g., cause chicken pox), bacteria (e.g., cholera), protozoa, and fungi cause diseases.

Examples of Diseases:

• Pneumonia, diphtheria, and root rot are caused by microbes.