Economic Importance of Bacteria and Fungi

Bacteria and fungi, while often associated with disease and spoilage, are in fact indispensable to life on Earth and human economies. Their most crucial role lies in the decomposition of dead organic matter. Acting as nature’s primary recyclers, they break down complex substances in dead plants, animals, and waste into simpler minerals. This process of decomposition not only cleanses the environment but also returns vital nutrients like carbon and nitrogen to the soil, making them available for plants to absorb. Without this continuous recycling of essential elements, the soil would quickly become barren and life as we know it would cease to exist. Furthermore, certain bacteria play a fundamental role in the nitrogen cycle by converting atmospheric nitrogen into a usable form for plants through a process called nitrogen fixation, which is vital for soil fertility.

On the beneficial side, humans have harnessed the power of these microorganisms in numerous industries. In agriculture, bacteria like Rhizobium form symbiotic relationships with leguminous plants, enriching the soil with nitrogen and reducing the need for chemical fertilizers. The food industry relies heavily on them; bacteria are used to produce dairy products like yogurt, cheese, and buttermilk through fermentation, while fungi, specifically yeast, are essential for leavening bread and in the brewing of alcohol. They are also pharmaceutical powerhouses, as many antibiotics, such as streptomycin and tetracycline, are derived from bacteria and fungi. Additionally, they are used in the production of vitamins, organic acids like acetic acid (vinegar), and even in the tanning of leather and processing of tobacco.

However, the economic impact of these organisms is not entirely positive. Many bacteria and fungi are pathogens, causing severe diseases in plants, animals, and humans, leading to significant agricultural losses and healthcare burdens. A major economic downside is food spoilage, where these microorganisms decompose stored grains, fruits, vegetables, and other food items, rendering them unfit for consumption and causing massive financial losses annually. Certain bacteria can also cause the spoilage of canned foods, leading to bloating and dangerous toxin production. Therefore, while their benefits are vast and essential, their harmful effects necessitate continuous efforts in preservation, sanitation, and medical treatment to mitigate the damage they can cause.

Exercise 1 (MCQ)

Question 1. 

Bacteria are no more classified as plants primarily because:

1. these are unicellular
2. these are microscopic
3. many of them are parasitic
4. they have no chlorophyll

Question 2. 

A particular species of which one of the following, is the source bacterium of the antibiotic, discovered next to penicillin, for the treatment of tuberculosis?

1. Escherichia 
2. Streptomyces
3. Rhizobium
4. Nitrobacter

Question 3. 

Which bacteria are rod shaped?

1. Coccus
2. Spirillum
3. Bacillus
4. Vibrio

Question 4. 

Which bacteria fixes nitrogen in the soil?

1. Nitrobacter 
2. Nitrosomonas 
3. Rhizobium
4. Clostridium

Exercise 1 (Very short answers)

Question 1. 

Name the three common types of bacteria.

Ans:

Bacteria are universally categorized into three principal types, primarily distinguished by their morphology (shape):

Three Core Bacterial Shapes

1. Cocci (Spheres): These bacteria have a spherical or oval form. Their arrangement after cell division often gives them special names, such as Staphylococci (clumps like grapes) and Streptococci (chains).
2. Bacilli (Rods): Characterized by their rod-like or cylindrical appearance. Bacilli are responsible for many common biological processes and diseases, including the gut bacterium E. coli.
3. Spirilla (Spirals): This category encompasses bacteria that are twisted or coiled, resembling a corkscrew. A variation of this shape is the Vibrio, which has a shorter, comma-like curve.

Question 2. 

Match the items in Column A with those in Column B.

Column A	Column B
(i) Penicillium	(a) Bacteria occurring in chains
(ii) Diplococci	(b) Antibiotic
(iii) Streptococci	(c) Bacteria occurring in pairs

Ans:

Column A	Column B
(i) Penicillium	(b) Antibiotic
(ii) Diplococci	(c) Bacteria occurring in pairs
(iii) Streptococci	(a) Bacteria occurring in chains

Explanation

• (i) Penicillium: This is a genus of mold (fungus) from which the antibiotic penicillin was first discovered and isolated.
• (ii) Diplococci: The prefix “diplo-” means two, and “cocci” means spherical bacteria. Therefore, Diplococci are spherical bacteria arranged in pairs.
• (iii) Streptococci: The prefix “strepto-” means twisted or chain-like. Therefore, Streptococci are spherical bacteria arranged in chains.

Exercise 1 (Short answer type)

Question 1. 

Would you consider the bacteria and yeast as plants? Give a reason.

Ans:

Organism	Biological Kingdom	Key Reason for Non-Plant Classification
Bacteria	Monera (Prokaryotes)	Bacteria are prokaryotic; they lack a membrane-bound nucleus and other complex organelles found in plant cells (which are eukaryotic). Furthermore, they lack chlorophyll for photosynthesis, which is the defining characteristic of most plants.
Yeast	Fungi	Yeast are heterotrophic; they cannot produce their own food. Instead, they obtain nutrients by decomposing or absorbing organic matter, which is the defining mode of nutrition for Fungi. Plants are typically autotrophic (photosynthetic).

Question 2.

In what form bacteria may be present in the air?

Ans:

Bacteria may be present in the air primarily in the form of aerosols or attached to airborne particulate matter .

Forms of Airborne Bacteria

1. Aerosols (Droplets): Bacteria are often suspended in the air within tiny droplets of moisture. These droplets are created when people cough, sneeze, talk, or when water containing bacteria is aerosolized (e.g., from humidifiers or sewage plants).
2. Attached to Particulate Matter: Bacteria frequently attach to airborne dust, pollen, skin flakes, or fibers. This association allows them to remain suspended for longer periods and travel greater distances.
3. Spores: Some types of bacteria (especially Bacillus and Clostridium) can form tough, dormant, and highly resistant structures called endospores. These spores are extremely lightweight, can survive desiccation (drying out) and UV radiation, and are easily carried by air currents. They remain inactive until they land in a favorable environment.

Question 3. 

Why is spore formation in bacteria not considered as a form of reproduction?

Ans:

Spore formation (specifically endospore formation) in bacteria is not considered a form of reproduction because it is a survival mechanism, not a mechanism for increasing the number of individuals.

Key Differences from Reproduction

1. No Increase in Number: In reproduction, one organism gives rise to two or more new individuals. During endospore formation, one bacterial cell forms only one spore; therefore, there is no increase in the population size.
2. Purpose: The primary purpose of spore formation is dormancy and survival. Endospores are highly resistant, tough, dehydrated structures formed internally to protect the cell’s genetic material from harsh conditions like extreme heat, desiccation, or radiation.
3. Metabolic State: The spore is a non-metabolic, resting stage. Reproduction (like binary fission) requires active metabolism and cell division.
4. Reversibility: When conditions become favorable, the single spore germinates back into a single, active, vegetative bacterial cell. The original cell is not multiplied; it is simply preserved and reactivated.

Question 4. 

In what respect do you consider bacteria as simple organisms?

Ans:

Bacteria are considered simple organisms primarily due to their cellular structure and organization, which is less complex than that of eukaryotic cells (plants, animals, fungi, and protists).

Respects in which Bacteria are Simple

1. Prokaryotic Cell Structure

The most significant aspect of bacterial simplicity is their classification as prokaryotes. This means they lack the internal compartmentalization seen in all other forms of life (eukaryotes).

• No True Nucleus: They do not have a membrane-bound nucleus. Their genetic material (a single, circular chromosome) is concentrated in a region of the cytoplasm called the nucleoid.
• No Membrane-Bound Organelles: They lack complex organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. All metabolic functions that these organelles perform in eukaryotes must occur directly in the cytoplasm or on the inner surface of the plasma membrane.

2. Unicellularity and Body Organization

Bacteria are typically unicellular organisms that exist as a single, self-sufficient entity. They do not form the complex tissues, organs, and organ systems that characterize multicellular organisms like plants and animals.

3. Simpler Genetic Organization

• Single Chromosome: They usually possess only a single, circular chromosome of DNA.
• Reproduction: They reproduce asexually, primarily through binary fission, a relatively straightforward cell division process compared to the complex mitosis and meiosis seen in eukaryotes.

Question 5. 

1. State the differences between decay and putrefaction.

2. State the differences between pasteurization and sterilization.

Ans:

1. Decay vs. Putrefaction

Feature	Decay	Putrefaction
**Substrate (Material) **	Primarily involves the breakdown of Carbohydrates (like cellulose) and Fats.	Primarily involves the breakdown of Proteins (amino acids).
Conditions	Requires the presence of Oxygen (Aerobic process).	Occurs in the absence of Oxygen (Anaerobic process).
Products	Produces odorless compounds, mainly CO2​ and H2​O, and simple organic acids.	Produces foul-smelling, toxic products like amines, skatoles, and H2​S (Hydrogen Sulfide).
Smell	Generally odorless or has a slightly sour smell.	Characterized by a foul, rotten odor.

2. Pasteurization vs. Sterilization

Feature	Pasteurization	Sterilization
Goal	To reduce the number of pathogens and spoilage microbes (not kill all of them) to extend shelf life and ensure safety.	To kill all forms of microbial life, including spores and viruses.
Temperature & Time	Lower temperatures (e.g., 60∘C to 85∘C) applied for a specific time.	Higher temperatures (typically 100∘C and above, often using pressurized steam in an autoclave).
Effect on Product	Minimal change to the taste, nutritional value, or physical properties of the product.	Can cause significant changes to the taste, color, or nutritional content of foods and liquids.
Result	Product is not sterile; it still contains viable spores and thermoduric (heat-resistant) microbes.	Product is rendered sterile (free of all living microorganisms).
Common Use	Milk, fruit juices, beer, and wine.	Surgical equipment, injectable medicines, and laboratory media.

Question 6. 

Why is it generally advised that every living room in the house should get direct sunlight at least for a short time?

Ans:

It’s generally advised that every living room should get direct sunlight for a short time due to significant benefits related to health, hygiene, and well-being.

Benefits of Direct Sunlight Indoors

1. Natural Disinfection (Hygiene)

Direct sunlight, particularly its Ultraviolet (UV) radiation component, acts as a natural disinfectant.

• Kills Germs: UV light has germicidal properties that can effectively kill or inactivate bacteria and other microbes present in household dust and on surfaces.
• Reduces Mold/Mildew: Sunlight helps keep rooms dry and ventilated, discouraging the growth of moisture-loving organisms like mold and mildew, which can harm respiratory health.

2. Boosts Mental and Physical Health

Exposure to natural light, even when filtered through a window, has significant effects on human biology and mood.

• Regulates Circadian Rhythm: Sunlight helps regulate the body’s internal clock, or circadian rhythm. Morning light exposure signals the brain to be awake and alert, leading to improved sleep quality at night.
• Improves Mood: Sunlight stimulates the production of serotonin, often called the “feel-good hormone,” which helps elevate mood, reduce stress, and may alleviate symptoms of Seasonal Affective Disorder (SAD).

3. Energy Efficiency and Aesthetic

• Natural Lighting: Direct sunlight brightens the room, reducing the need for artificial lighting during the day and saving electricity.
• Warmth: On cold days, sunlight contributes to passive solar heating, raising the room temperature and reducing heating costs.
• Aesthetics: Natural light enhances colors, textures, and makes a space feel larger, more open, and more inviting.

Question 7. 

Would there be any bacteria in an aquarium?

Ans:

These microbes are typically classified into two major categories based on their function:

1. Beneficial Bacteria (The Silent Workhorses)

These organisms are essential for maintaining water quality and form the basis of the aquarium’s biological filtration system.

• Nitrifying Bacteria: These are the most critical group, responsible for the Nitrogen Cycle, which detoxifies the water:
  • Nitrosomonas species convert highly toxic ammonia (from fish waste, uneaten food, and decaying matter) into nitrite.
  • Nitrobacter and Nitrospira species then convert the toxic nitrite into much less harmful nitrate.
• Heterotrophic Bacteria: These break down organic waste (sludge, decaying plants, uneaten food) into smaller compounds, helping to keep the tank clean and clear.

These beneficial bacteria primarily colonize surfaces that offer a high surface area, such as the filter media, gravel, rocks, and décor, forming thin layers called biofilms.

2. Other Bacteria

In addition to the beneficial types, an aquarium will also contain:

• Harmless Bacteria: General microbes that naturally exist in the environment and water.
• Pathogenic (Harmful) Bacteria: Organisms that can cause disease in fish, such as Flexibacter columnaris (causes Columnaris or “cotton-mouth”) or Aeromonas species (causes fin rot). These typically only cause illness if the fish is stressed or the water quality is poor.

Exercise 1 (Long answer type)

Question 1. 

Both bacteria and yeast reproduce by asexual method, but how does this method differ in them?

Ans:

Feature	Bacteria (Prokaryote)	Yeast (Fungus/Eukaryote)
Asexual Method	Binary Fission (Splitting)	Budding (Outgrowth)
Symmetry of Division	Symmetrical. The parent cell divides into two equal or near-equal daughter cells.	Asymmetrical. A small outgrowth (bud) forms on the larger parent cell.
Parent’s Fate	The parent cell loses its identity as it is consumed entirely in the creation of the two new cells.	The parent cell retains its original identity and size after the bud detaches.
Process	The cell elongates, duplicates its DNA, and then the cytoplasm divides evenly down the middle via the formation of a septum.	A small protuberance forms on the parent cell, the nucleus divides, and one daughter nucleus moves into the bud. The bud grows and eventually detaches.

Question 2. 

Describe the role of micro-organisms in industrial production.

Ans:

Microorganisms (microbes) play a vital and indispensable role in large-scale industrial production by acting as living cell factories.They are used in highly controlled environments called bioreactors to perform specific biochemical transformations, primarily through the process of fermentation, to produce valuable substances.

Key Roles and Industrial Products

Microbes—including bacteria, fungi (yeasts and molds), and algae—are manipulated, often through genetic engineering, to enhance the yield of desired products across various sectors.

1. Pharmaceuticals and Medicine 

• Antibiotics: Microbes are the original source for most antibiotics. For example, the fungus Penicillium notatum produces Penicillin, and the bacterium Streptomyces produces Streptomycin.
• Vaccines: Microbes, or components of microbes, are used to create vaccines.Modern biotechnology uses genetically engineered microbes (E. coli or yeast) to produce non-pathogenic vaccine proteins (recombinant vaccines).
• Hormones and Proteins: Microbes are genetically engineered to produce human proteins, such as Insulin, which is mass-produced by inserting the human insulin gene into E. coli or yeast.

2. Food and Beverage Industry

Fermentation is the backbone of this industry, relying on specific microbial action:

• Alcoholic Beverages: The yeast Saccharomyces cerevisiae (Brewer’s Yeast) ferments sugars into ethanol and CO2 for the production of beer, wine, whiskey, and brandy.
• Dairy Products: Lactic acid bacteria (e.g., Lactobacillus and Streptococcus) ferment lactose into lactic acid to produce yogurt, cheese, and buttermilk.
• Baking: Yeast produces CO2 which makes bread dough rise.

3. Chemical and Organic Acid Production 

Microbes efficiently produce commodity chemicals that would be expensive or complex to synthesize chemically:

• Organic Acids: The mold Aspergillus niger is used to produce Citric Acid (a food preservative and flavoring agent), and bacteria like Acetobacter aceti convert ethanol into Acetic Acid (vinegar).
• Organic Solvents: Bacteria like Clostridium species are used to produce industrial solvents such as Acetone and Butanol.

4. Industrial Enzymes 

Enzymes are natural catalysts widely used in industrial processes.Microbes are an inexpensive and abundant source for mass production:

• Amylases, Proteases, Lipases: Used in detergents (to break down stains), in the food industry (to clarify juices or tenderize meat), and in the textile industry.

5. Environmental Applications (Bioremediation) 

• Wastewater Treatment: Specific bacteria and fungi are used in sewage treatment plants to break down and detoxify organic waste and pollutants in water.Biofuels: Yeasts are used to ferment sugars into Ethanol fuel, and certain bacteria are being developed to produce Biodiesel.

Question 3. 

How do bacteria obtain their nourishment?

Ans:

Bacteria obtain their nourishment through highly diverse and flexible metabolic pathways, classifying them into two major groups: autotrophs and heterotrophs. Their cell structure, which lacks internal membrane-bound organelles, means they must absorb nutrients directly across their cell membrane, often by secreting powerful enzymes outside the cell to break down complex food material before absorption.

Autotrophic Bacteria 

Autotrophic bacteria are “self-feeders” because they synthesize their own complex organic food from simple inorganic substances like carbon dioxide CO2. This group is further divided based on the energy source they use:

• Photoautotrophs: These bacteria use light energy (like plants) to produce food. Examples include cyanobacteria (blue-green algae) and purple sulfur bacteria, which possess pigments like bacteriochlorophyll to carry out photosynthesis.
• Chemoautotrophs: These unique bacteria do not require light. Instead, they derive energy by oxidizing inorganic chemical compounds (like ammonia, hydrogen sulfide H2S, or ferrous iron). This energy is then used to fix CO2 into organic food. Nitrifying bacteria, which are crucial in the nitrogen cycle, are an example of chemoautotrophs.

Heterotrophic Bacteria 

Heterotrophic bacteria cannot synthesize their own food and must obtain pre-formed organic matter from other sources, which is the mode of nutrition for the vast majority of bacteria. This group is categorized based on the source of the organic matter:

• Saprophytes: These are decomposers that obtain their nourishment from dead and decaying organic matter (such as dead plants, animals, or waste products). They are vital environmental recyclers that break down complex organic compounds into simpler forms, often leading to processes like decay and putrefaction.
• Parasites: These bacteria live in or on a living host organism and derive their food directly from the host, often causing harm or disease (pathogenic bacteria) in the process.
• Symbionts/Mutualists: These bacteria live in a beneficial association with another organism, where both partners gain nutritional benefits. A classic example is Rhizobium, which fixes nitrogen for leguminous plants while obtaining sugars from the plant.

Question 4. 

Describe any two uses of bacteria in the industry.

Ans:

Bacteria are extensively utilized in industrial processes due to their high metabolic versatility and rapid growth rate. They essentially act as tiny, efficient biofactories.

Here are two major uses of bacteria in industry:

1. Food and Dairy Production 

Bacteria are essential for the production of numerous fermented foods, primarily through lactic acid fermentation.

• Process: Specific bacteria, mainly from the Lactobacillus and Streptococcus genera (known as Lactic Acid Bacteria or LAB), are added to milk. They break down the milk sugar (lactose) into lactic acid.
• Products: This acid causes the milk proteins to curdle and coagulate, which is the basis for manufacturing products like curd (yogurt), cheese, buttermilk, and sour cream. This process also naturally preserves the food and improves its flavor and texture.

2. Production of Pharmaceuticals and Chemicals 

Bacteria are widely used, often through genetic engineering, to manufacture vital medicines and industrial chemicals.

• Recombinant Proteins (Biopharma): Bacteria like Escherichia coli (E. coli) can be genetically modified to carry human genes. They are then grown in large bioreactors to mass-produce human proteins that are otherwise difficult or impossible to obtain, such as insulin (for diabetes treatment) and human growth hormone.
• Antibiotics: Certain bacteria, particularly species of Streptomyces, naturally produce potent chemicals that are harvested to create life-saving antibiotics (e.g., Streptomycin).

Question 5. 

What are antibiotics? Give ‘two’ examples

Ans:

Antibiotics are a class of antimicrobial drugs used to treat or prevent bacterial infections. They work by either killing the bacteria (bactericidal) or by inhibiting their growth and multiplication (bacteriostatic).

Originally, the term referred to substances produced naturally by microorganisms (like fungi or other bacteria) to fight competing microbes. However, the term is now broadly applied to any compound, whether natural or synthetic, that targets bacteria. It’s crucial to note that antibiotics are ineffective against viral infections like the common cold or flu.

Examples of Antibiotics

Two common examples of antibiotics belonging to different classes are:

1. Penicillin: This was the first antibiotic discovered (by Alexander Fleming in 1928, isolated from the Penicillium mold). Penicillins primarily work by inhibiting the synthesis of the bacterial cell wall, making them particularly effective against many gram-positive bacteria.
2. Amoxicillin: A derivative of penicillin, this is a broad-spectrum antibiotic widely used to treat various infections, including ear, nose, throat, and urinary tract infections. It also works by interfering with the formation of the bacterial cell wall.

• Another Example: Tetracycline is an example of an antibiotic that works by a different mechanism: it inhibits protein synthesis in bacteria, preventing them from growing and reproducing.

Question 6. 

Is tinned and sealed food always safe to eat? Give reasons in support of your answer.

Ans:

Reasons Tinned Food May Be Unsafe

1. Risk of Botulism

This is the most serious risk associated with improperly processed canned food.

• Survival of Spores: The bacterium Clostridium botulinum produces an extremely potent, life-threatening neurotoxin. Its spores are highly heat-resistant and can survive boiling water temperatures.
• Anaerobic Environment: The sealed, low-oxygen environment of the can provides the perfect conditions for these surviving spores to germinate and produce the deadly toxin. Commercial canning requires high pressure and temperature to ensure these spores are destroyed. If the process is inadequate (especially in home canning of low-acid foods), the toxin can form without visible signs of spoilage.

2. Can Integrity Compromise

Physical damage to the container breaches the sterile environment.

• Breach of Seal: If the can is bulging, leaking, cracked, or severely dented, the hermetic (airtight) seal has likely been compromised. This allows airborne bacteria, yeast, and mold to enter the food, leading to microbial growth and spoilage. A bulging can is a strong indicator of gas production by dangerous bacteria like C. botulinum.
• Corrosion/Chemical Contamination: Over long periods, or if the food is highly acidic, the inner lining of the can may degrade, potentially leading to the leaching of metals or chemicals (like BPA from the liner) into the food.

3. Inadequate Processing

If the food manufacturer or home canner fails to follow required protocols, safety is compromised.

• Insufficient Heat Treatment: Not heating the food to the correct temperature for the required duration (especially for low-acid foods like vegetables and meats) means that heat-resistant spores are not killed and can survive to grow later.

4. Spoilage Microorganisms

While less lethal than C. botulinum, some highly heat-resistant (thermoduric) organisms can survive the canning process and cause non-toxic spoilage, resulting in off-flavors, smells, and textures, making the food inedible.

Exercise 1 (Structured/skill type)

Question 1. 

1. Study the diagram given below and then answer the questions that follow:

Briefly describe how nitrogen of the atmosphere is converted to nitrates by leguminous plants.

2. Study the diagram given below and then answer the questions that follow:

Name the bacterium that converts

(i) ammonium compounds to nitrites

(ii) nitrites to nitrates

 3. Study the diagram given below and then answer the questions that follow:

State how the nitrates in the soil get converted to nitrogen of the atmosphere. 

4. Study the diagram given below and then answer the questions that follow:

Role of plants and animals in the formation of ammonium compounds.

Ans:

The diagram illustrates the basic steps of the Nitrogen Cycle . Here are the answers to the questions based on that cycle:

1. Conversion of Atmospheric Nitrogen to Nitrates by Leguminous Plants

The conversion of nitrogen from the atmosphere into nitrates by leguminous plants is called symbiotic nitrogen fixation, and it happens within specialized structures called root nodules.

• Nitrogen Fixation: Certain bacteria, most commonly Rhizobium, live in a symbiotic relationship inside the root nodules of leguminous plants (like peas and beans). These bacteria possess the enzyme nitrogenase, which allows them to capture atmospheric nitrogen gas N2 and convert it into ammonia NH3.
• Ammonia Assimilation: This ammonia is quickly converted into ammonium compounds NH+4, which the host plant can readily assimilate (use) to synthesize proteins and other nitrogenous organic compounds.
• Release to Soil: When the plant or its root nodules die and decompose, these ammonium compounds are released into the soil. Other soil bacteria then convert the ammonium compounds first to nitrites and then to nitrates (the nitrification process shown in the diagram), which can be taken up by other plants.

2. Bacteria that Convert Nitrogen Compounds

The bacteria responsible for these specific steps in the nitrification process are:

(i) Ammonium compounds to nitrites: Nitrosomonas

(ii) Nitrites to nitrates: Nitrobacter

3. Conversion of Nitrates to Atmospheric Nitrogen

The process by which nitrates in the soil get converted back into nitrogen gas N2 and released into the atmosphere is called denitrification.

• This process is carried out by certain soil bacteria (known as denitrifying bacteria), such as species of Pseudomonas.
• These bacteria use the nitrate NO3 as an electron acceptor instead of oxygen in anaerobic conditions, reducing the nitrates back through several steps to dinitrogen gas N2, thereby completing the cycle and returning nitrogen to the atmosphere.

4. Role of Plants and Animals in Formation of Ammonium Compounds

Both plants and animals contribute to the formation of ammonium compounds (ammonification) through the decomposition of their nitrogenous waste and dead remains.

• Role of Animals: Animals excrete nitrogenous waste products (like urea or uric acid) while alive. When animals die, the proteins and nucleic acids in their bodies begin to decompose.
• Role of Plants: When plants die and their tissues decay, the proteins and nitrogenous compounds stored within them are broken down.
• Ammonification: In both cases, the complex organic nitrogen is converted into ammonium compounds NH+4 by the action of decomposing bacteria and fungi (ammonifying bacteria). This is the initial step that links dead organic matter back to the inorganic part of the nitrogen cycle.

Exercise 2 (MCQ)

Question 1. 

Production of ethanol (C2H5OH) occurs in one of the life processes of: 

1. Bread mould
2. Yeast
3. Mushroom
4. Penicillium

Question 2. 

Which one of the following characteristics is found in all fungi but not in all bacteria?

1. Aerobic respiration
2. Cell wall
3. Spore formation
4. A long circular DNA lying loose in the cytoplasm

Question 3. 

Bacteria are referred to as prokaryotes because

1. They have no chlorophyll.
2. They are unicellular.
3. They are free living.
4. They do not have a true nucleus.

Question 4. 

Yeast is used in the production of

1. Ethyl alcohol
2. Acetic acid
3. Cheese
4. Curd

Exercise 2 (Very short answer)

Question 1. 

Tick (✓) mark the correct statement/statements.

(a) All mushrooms are poisonous.

(b) All toadstools are poisonous.

(c) Some toadstools are poisonous.

(d) Some mushrooms are edible.

Ans:

The correct statements are (c) and (d).

• (c) Some toadstools are poisonous. (✓)
• (d) Some mushrooms are edible. (✓)

Explanation 

• Mushroom is the common name often given to the fleshy, spore-bearing fruiting body of a fungus, especially the edible ones (like the common button mushroom).
  • Therefore, statement (a) All mushrooms are poisonous is False.
  • Statement (d) Some mushrooms are edible is True.
• Toadstool is the common name often given to the fruiting body of a fungus that is specifically considered poisonous or inedible.
  • Therefore, statement (b) All toadstools are poisonous is False. Some edible fungi are loosely called toadstools, and some highly poisonous fungi are called mushrooms. The classification is inexact, making the blanket statement inaccurate.
  • Statement (c) Some toadstools are poisonous is True, as many fungi commonly called toadstools are indeed toxic (e.g., Amanita species).

Exercise 2 (Short answer type)

Question 1. 

Where can you find the mould Rhizopus most easily found?

Ans:

You can find the mold Rhizopus (often called Black Bread Mold) most easily on stale bread , particularly if the bread has been left in a warm, moist, and dark place for a few days.

Why Bread is the Best Place

• Nutrient Source: Bread provides a rich source of starch (carbohydrates) and other organic matter that Rhizopus spores can easily colonize and feed upon.
• Spores are Everywhere: Rhizopus spores are extremely common in the air. When they land on a favorable substrate like bread, they germinate.
• Visible Growth: The mold growth is rapid and highly visible. It initially appears as a white, cottony mass, which quickly develops the characteristic black dots—these are the sporangia (spore-producing structures).

In addition to bread, Rhizopus is also frequently found growing on:

• Fruits and Vegetables: Particularly soft, overripe ones like strawberries, peaches, and tomatoes.
• Damp Organic Material: Any decaying organic matter, but bread offers the most rapid and recognizable growth.

Question 2. 

Why is it generally advised that every living room in the house should get direct sunlight at least for a short time?

Ans:

Advantages of Sunlit Living Spaces

1. Sanitation and Microbial Control

The presence of natural sunlight aids in maintaining a cleaner and healthier indoor environment. The ultraviolet (UV) component of sunlight possesses germicidal properties capable of deactivating or destroying various types of microorganisms, including airborne bacteria and viruses that settle on indoor surfaces. Moreover, sunlight naturally promotes the drying of damp areas, thereby inhibiting the proliferation of mold and mildew, which are common triggers for allergies and respiratory issues.

2. Physical and Psychological Well-being

The human body is positively impacted by exposure to natural light:

• Circadian Rhythm Alignment: Receiving bright light, especially in the morning, is crucial for synchronizing the body’s circadian clock. This promotes wakefulness during the day and contributes to a healthier, more consistent sleep cycle.
• Mood Elevation: Sunlight is a natural stimulus for the release of brain chemicals like serotonin, which are instrumental in regulating mood, combating fatigue, and potentially easing the effects of mood disorders, such as Seasonal Affective Disorder (SAD).

3. Efficiency and Visual Appeal

Integrating sunlight into the living space provides practical and aesthetic benefits.

• Reduced Energy Consumption: Natural light significantly brightens rooms, lessening the reliance on electric lights during daylight hours and resulting in energy savings.
• Passive Heating: Solar energy provides free, passive heat during cooler months, which helps warm the room and lowers the demand on heating systems.
• Enhanced Aesthetics: Sunlight visually transforms an interior, making colors appear more vibrant and creating an atmosphere that feels more spacious and welcoming .

Question 3. 

Describe the role of certain fungi in industrial production.

Ans:

Fungi play a critical and indispensable role in various industrial processes, primarily due to their unique metabolic ability to produce specific enzymes and chemical compounds through fermentation.

Key Roles in Industrial Production

1. Pharmaceuticals (Antibiotics and Drugs):
   • Fungi are a primary source of life-saving drugs. The most famous example is Penicillin, which is mass-produced from the mold Penicillium chrysogenum.
   • They also produce immunosuppressants (like Cyclosporin) and statins (cholesterol-lowering drugs) used in medicine.
2. Food and Beverage Fermentation:
   • Yeast (Saccharomyces cerevisiae) is essential in the baking and brewing industries. It ferments sugars to produce alcohol (for beer and wine) and carbon dioxide CO2 (which causes bread dough to rise).
   • Specific molds (e.g., Penicillium roqueforti) are used to ripen and develop the characteristic flavors and blue veins in cheeses (like Roquefort and Camembert).
3. Enzyme Production:
   • Fungi are highly efficient producers of industrial enzymes like amylases, cellulases, and proteases. These enzymes are used in detergents, paper manufacturing, textile processing (e.g., stone-washing jeans), and biofuel production.
4. Organic Acid Production:
   • Molds like Aspergillus niger are used to produce common food additives and industrial chemicals such as Citric Acid (used in soft drinks and food preservation) and gluconic acid.

Question 4. 

Mention two useful and harmful effects of wine.

Ans:

Wine, like any alcoholic beverage, has effects that depend heavily on the amount and frequency of consumption. What may be seen as a useful effect at a moderate intake often becomes a harmful effect when consumption is excessive or chronic.

Here are two commonly cited useful effects and two common harmful effects of wine:

Useful Effect (Moderate Consumption)

1. Antioxidant Benefits and Cardiovascular Health: Red wine contains polyphenols, particularly resveratrol, which act as antioxidants. These compounds may help protect the lining of blood vessels, reduce inflammation, and help raise HDL (“good”) cholesterol levels. This is why light to moderate red wine consumption has been historically linked to a potentially reduced risk of certain cardiovascular diseases.

Harmful Effects (Excessive or Regular Consumption)

1. Increased Risk of Cancer: Alcohol is classified as a Group 1 carcinogen. Regular consumption, even in moderate amounts, increases the risk for several types of cancer, including breast cancer, esophageal cancer, and colorectal cancer. The risk increases significantly with the amount of alcohol consumed.
2. Liver Damage and Alcohol Dependence: Consistent, heavy consumption overwhelms the liver’s ability to process alcohol. This can lead to a progressive range of liver diseases, starting with fatty liver disease and potentially advancing to alcoholic hepatitis and irreversible cirrhosis (scarring of the liver). Furthermore, regular heavy drinking carries a significant risk of developing alcohol dependence or Alcohol Use Disorder.

Question 5. 

1. Differentiate between: Saprophyte and parasite 

2. Differentiate Between: Aerobic and anaerobic respiration with regard to products 

3. State the differences between decay and putrefaction.

Ans:

1. Saprophyte and Parasite

Feature	Saprophyte	Parasite
Nutrient Source	Feeds on dead, decaying, or non-living organic matter.	Feeds directly on a living host organism.
Relationship to Host	No direct relationship with a living host; it is a decomposer.	Has a direct and intimate relationship with a host, often causing harm or disease.
Location of Digestion	External Digestion: Releases digestive enzymes onto the dead matter and then absorbs the digested soluble nutrients.	Internal Digestion: Usually absorbs nutrients directly from the host’s body tissues or fluids.
Harm to Host	Beneficial to the ecosystem (recycling nutrients).	Harmful to the host (causing sickness, depletion of resources, or death).
Examples	Molds (e.g., Rhizopus), Mushrooms, and most decomposer bacteria.	Tapeworms, Plasmodium (causes malaria), Fleas, and parasitic bacteria.

2. Aerobic and Anaerobic Respiration (Products)

Feature	Aerobic Respiration	Anaerobic Respiration (in plants/yeast)
Oxygen	Requires Oxygen (O2​).	Occurs in the absence of O2​.
Completeness of Breakdown	Complete oxidation of glucose.	Incomplete oxidation of glucose.
Final Products	Carbon Dioxide (CO2​) and Water (H2​O).	Ethanol (C2​H5​OH) and Carbon Dioxide (CO2​).
Energy Yield	High yield (36–38 ATP).	Very low yield (2 ATP).

3. Decay and Putrefaction

Feature	Decay	Putrefaction
Process Type	Aerobic process (requires O2​).	Anaerobic process (occurs without O2​).
Substrate (Material)	Primarily involves the breakdown of Carbohydrates (like cellulose) and Fats.	Primarily involves the breakdown of Proteins (amino acids).
Products	Produces simple, generally odorless compounds, mainly CO2​ and H2​O.	Produces foul-smelling, often toxic products like amines, skatoles, and Hydrogen Sulfide (H2​S).
Smell	Generally odorless or may have a mild, earthy odor.	Characterized by a foul, rotten smell.

Exercise 2 (Long answer type)

Question 1. 

What are antibiotics? Give ‘two’ examples

Ans:

Definition

An antibiotic is a type of antimicrobial substance that either kills bacteria (bactericidal) or slows or stops their growth (bacteriostatic). They are typically derived from or inspired by natural compounds produced by other microorganisms (like fungi or bacteria) to gain a competitive advantage.

Two Examples

1. Penicillin: The first widely used antibiotic, originally discovered from the Penicillium mold. It primarily works by interfering with the synthesis of the bacterial cell wall, making it bactericidal.
2. Streptomycin: An antibiotic produced by the bacterium Streptomyces griseus. It works by binding to the bacterial ribosome, thereby inhibiting the bacteria’s ability to synthesize proteins (a bacteriostatic mechanism). It is historically significant for treating tuberculosis.

Question 2. 

Is tinned and sealed food always safe to eat? Give reasons in support of your answer.

Ans:

The preservation method of canning aims to kill harmful microorganisms and then seal the product to prevent recontamination, but this process can fail for several reasons:

Reasons Canned Food May Not Be Safe

1. Inadequate Sterilization

If the food was not heated sufficiently during the canning process, or if the process time was too short, highly resistant bacterial spores may survive.

• The most significant risk is the survival of Clostridium botulinum spores. If these spores germinate in the low-oxygen (anaerobic) environment of the sealed can, they produce the deadly botulinum toxin, which causes botulism, a severe form of food poisoning.

2. Physical Damage or Compromised Seal

Even if initially sterile, the food can become contaminated later if the seal is broken.

• Dents and Swelling (Bulging): A severely dented can, especially around seams, can compromise the seal. Swelling or bulging is a dangerous sign, usually indicating the production of gas by active bacteria (often C. botulinum$) inside the can.
• Rust or Punctures: Any rust or minute hole can allow bacteria and air to leak in, leading to spoilage and potential pathogen growth.

3. Chemical Contamination

Over time, especially if stored improperly (e.g., in high heat), the acidity of the food can react with the metal of the can.

• While modern cans are lined, a breach in the lining can lead to the leaching of metals (like tin or lead) into the food, although this is less common with modern production standards.

Question 3. 

Would there be any bacteria in an aquarium?

Ans:

Role of Bacteria in an Aquarium

The most vital role of bacteria in an aquarium is performing biological filtration through the Nitrogen Cycle:

1. Ammonia NH3 Production: Fish waste, uneaten food, and decaying plant matter break down to produce highly toxic ammonia.
2. Ammonia to Nitrite: Nitrosomonas bacteria colonize surfaces (gravel, décor, and especially filter media) and convert this toxic ammonia into another toxic compound: nitrite.
3. Nitrite to Nitrate: Nitrobacter and Nitrospira bacteria then convert the toxic nitrite into much less harmful nitrate.

Without these bacteria, ammonia and nitrite levels would quickly build up and kill the aquatic life.

Where They Live

These beneficial bacteria primarily reside in the biofilm that covers all surfaces in the tank, especially the filter media and the substrate (gravel or sand), as these areas provide the most surface area and constant water flow.

Exercise 2 (Structured/Kill type)

Question 1. 

1. If you leave a piece of moist bread covered under a small bell jar at a warm place, mould grows on it in a few days. Answer the following with reference to this observation: How did the mold get inside the bell-jar? 

2. If you leave a piece of moist bread covered under a small bell jar at a warm place, mould grows on it in a few days. Answer the following with reference to this observation: What would happen if the bread was not covered by the bell-jar?

3.If you leave a piece of moist bread covered under a small bell jar at a warm place, mould grows on it in a few days. Answer the following with reference to this observation: What would happen if moist bread was placed in a refrigerator? 

4. If you leave a piece of moist bread covered under a small bell jar at a warm place, mould grows on it in a few days. Answer the following with reference to this observation: What appears first on the bread-the mycelia or the spores? 

5. If you leave a piece of moist bread covered under a small bell jar at a warm place, mould grows on it in a few days. Answer the following with reference to this observation:How does bread mould obtain nourishment? What type of nourishment is it- epiphytic, autotrophic, parasitic symbiotic, or saprophytic?

Ans:

1. How did the mold get inside the bell-jar?

The mold entered the bell-jar as spores that were already present in the air surrounding the bread and the bell-jar before it was covered. Mold spores are microscopic, extremely light, and are constantly floating in the atmosphere. They settled onto the moist bread, which provided the ideal conditions for them to germinate and grow into the mold you observe.

2. What would happen if the bread was not covered by the bell-jar?

If the moist bread was not covered by the bell-jar, mold growth would still occur, likely even faster.

• The bread would still be colonized by airborne spores.
• The mold would have access to unlimited fresh oxygen, which supports faster growth for most molds.
• The open environment might also slightly increase the rate of drying, but the primary factor is the constant supply of air and spores.

3. What would happen if moist bread was placed in a refrigerator?

If the moist bread was placed in a refrigerator, mold growth would be severely inhibited or stopped entirely.

• The refrigerator provides a low temperature (around $4^\circ\text{C}$).
• Mold growth requires warmth for optimal enzyme activity. Low temperatures slow down the metabolic rate of the mold spores and hyphae, preventing or greatly delaying the visible growth and spread of the mold. The bread would likely remain mold-free for a longer time.

4. What appears first on the bread—the mycelia or the spores?

The spores are present first, but the mycelia (the visible thread-like growth) appear first as the mold structure.

• The spore lands on the bread.
• The spore germinates, sending out microscopic filaments called hyphae.
• The mycelium is the entire network of these hyphae. It is the white, cottony mass that you see as the first sign of growth on the bread.

Therefore, the mycelia are the first visible sign of growth.

5. How does bread mold obtain nourishment? What type of nourishment is it?

Bread mold obtains nourishment by a process called extracellular digestion.

1. The mold (e.g., Rhizopus) secretes powerful digestive enzymes (like amylase) onto the bread.
2. These enzymes break down the complex organic matter in the bread (like starch and sugars) into simpler, soluble forms.
3. The mold then absorbs these simple, dissolved nutrients through its cell walls.

The type of nourishment is saprophytic.

• Saprophytic organisms (saprophytes) are those that obtain their nutrients from dead or decaying organic matter. Since the bread is non-living, Rhizopus is a saprophyte.

Question 2. 

Write in proper sequence the five major steps in the cultivation of the common edible mushrooms.

Ans:

The cultivation of common edible mushrooms, such as the White Button Mushroom (Agaricus bisporus), is a multi-step process that utilizes the fungus’s natural life cycle. These steps must be followed sequentially for successful commercial production.

Five Major Steps in Mushroom Cultivation

The five major steps in the proper sequence are:

1. Composting (Substrate Preparation):
   • This initial phase involves mixing raw materials (like straw, horse manure, gypsum, and supplements) and allowing them to undergo controlled microbial fermentation. The goal is to create a nutritionally selective medium that the mushroom mycelium can easily colonize, while preventing the growth of competitor fungi and bacteria. This process is often split into Phase I (outdoor mixing and wetting) and Phase II (indoor pasteurization and conditioning to kill pests/ammonia).
2. Spawning (Inoculation):
   • Spawn (the “seed” of the mushroom, which is grain colonized by the mushroom’s mycelium) is introduced and mixed uniformly into the prepared compost. This step is equivalent to planting the crop.
3. Spawn Run (Incubation):
   • The compost is placed in climate-controlled rooms, and the temperature is maintained to allow the mycelium (the white, thread-like vegetative part of the fungus) to grow and colonize the entire composted substrate completely. This takes about 2 to 3 weeks.
4. Casing:
   • A thin layer of moist, non-nutritive material (the casing layer), typically a mixture of peat moss and chalk/limestone, is spread over the colonized compost. The casing layer provides a reservoir of moisture, gives support, and creates the micro-environment needed to trigger the transition from vegetative growth to reproductive growth.
5. Fruiting and Harvesting (Cropping):
   • The temperature is lowered, and the humidity and ventilation are increased. This environmental shock triggers the formation of tiny mushroom buds called pins, which mature into full-sized mushrooms (the fruiting bodies). Mushrooms are harvested in cycles called flushes over several weeks.

Question 3. 

1. Comment on the following:Denitrifying bacteria are a blessing as well as a curse to farmers. 

2. Comment on the following: Yeast is used in bakeries and breweries.

Ans:

1. Denitrifying Bacteria: Blessing and Curse to Farmers

Role	Blessing (Benefit)	Curse (Detriment)
Process	They complete the Nitrogen Cycle by converting excess nitrate (NO3−​) back into atmospheric nitrogen (N2​) gas.	They reduce the available nitrogen compounds (NO3−​) that plants need for growth.
Why it Helps	Prevents nitrate pollution of groundwater and surface water. Excess nitrate can harm ecosystems (e.g., algal blooms) and drinking water quality.	This process essentially undoes the work of fertilizer and nitrogen-fixing bacteria, forcing farmers to spend more money and energy to reapply nitrogen.
Conditions	Their activity helps in balancing the global nitrogen budget.	Their activity is especially high in waterlogged (anaerobic) and acidic soils, leading to significant loss of the crucial nutrient for crops.

2. Yeast is Used in Bakeries and Breweries 

Industry	Role of Yeast	Resulting Product/Process
Bakeries	Gas Production: Yeast consumes sugars in the dough and produces carbon dioxide (CO2​) as a by-product of fermentation.	The CO2​ gas gets trapped in the dough, causing it to rise (leavening). This creates the light, spongy texture of bread.
Breweries	Alcohol Production: Yeast ferments sugars (from malted barley, grapes, etc.) and produces ethyl alcohol (C2​H5​OH) and carbon dioxide.	The ethanol is the intoxicating component of beer and wine. The CO2​ contributes to the carbonation and head of the beverage.