Selina Concise Solutions for ICSE Class 9 Biology Chapter 9 Economic Importance Of Bacteria And Fungi

Exercise 1

Question A:
Answer: 1. (d) they have no chlorophyll
2. (b) Streptomyces
3. (c) Bacillus
4. (c) Rhizobium
These characteristics define how bacteria interact with their environment and are utilized by humans. For example, because they lack chlorophyll, they must find other sources of energy to survive.
Teacher's Tip: Remember: No Chlorophyll = No Photosynthesis.
Exam Tip: Always write both the option letter and the full scientific name for full marks in MCQs.

Question B.1:
Answer: The three common types of bacteria are:
1. Cocci (spherical bacteria)
2. Bacilli (rod-shaped bacteria)
3. Spirilla (spiral bacteria)
Bacteria are classified by their physical shapes, which can be seen under a microscope. Each shape helps them survive in different environments or move in specific ways.
Teacher's Tip: Think of "Cocci" as "Circles" and "Bacilli" as "Bars" to remember their shapes.
Exam Tip: Draw simple sketches of a circle, a rod, and a spiral next to these names to show extra understanding.

Question B.2:
Answer: (i) Penicillium - (b) Antibiotic
(ii) Diplococci - (c) Bacteria occurring in pairs
(iii) Streptococci - (a) Bacteria occurring in chains
This matching exercise shows how bacteria can group together or be used to create medicine. Knowing these prefixes helps you identify bacterial arrangements instantly.
Teacher's Tip: "Di-" means two, so Diplococci are pairs; "Strepto-" sounds like "String," which means they form chains.
Exam Tip: For matching questions, rewrite the pairs side-by-side in a clear list.

Question C.1:
Answer: No, bacteria and yeast are not considered as plants because they do not have chlorophyll and their mode of nutrition is not autotrophic, which are characteristic features of plants.
Unlike green plants, these organisms cannot make their own food using sunlight. They must absorb nutrients from other organic sources to live and grow.
Teacher's Tip: If it's not green and making food from sun, it's not a plant in the traditional sense.
Exam Tip: Mention the term "autotrophic" to describe how plants make food compared to bacteria.

Question C.2:
Answer: Bacteria may be present in the form of spores in the air.
Spores act as a protective shield that lets bacteria survive in harsh conditions like dry air. Once they land on a moist surface with food, they "wake up" and begin to grow again.
Teacher's Tip: Think of a spore like a tiny, tough biological space-suit for the bacterium.
Exam Tip: Mention "spores" when discussing how bacteria travel through the atmosphere.

Question C.3:
Answer: Spore formation in bacteria is not considered as a form of reproduction because bacteria reproduce only asexually by means of fission or cell division. Spore formation is just a method of escaping unfavourable conditions.
When a bacterium forms a spore, one cell creates one spore; no new individuals are actually made. It is a survival strategy rather than a way to increase their population.
Teacher's Tip: Spores = Survival; Fission = More bacteria.
Exam Tip: Use the phrase "method of escaping unfavourable conditions" to explain the purpose of spores.

Question C.4:
Answer: Bacteria are unicellular organisms that lack membrane bound cell organelles like chloroplast, mitochondria, etc. and even a well-defined nucleus is absent which states that they have a simpler cellular organization.
Because they lack a nucleus, they are called prokaryotes. Their simple design allows them to replicate very quickly compared to complex plant or animal cells.
Teacher's Tip: Remember: Bacteria are "Pro" (Prokaryotes) - they are the "original" simple cells.
Exam Tip: Mention the absence of "mitochondria" and "nucleus" to define a simple cellular organization.

Question C.5:
Answer: (a) Decay and Putrefaction
Decay
1. It is the complete breakdown of organic matter by bacteria.
2. Does not emit a foul smell
Putrefaction
1. It is the incomplete breakdown of organic matter by bacteria.
2. Emits a foul smell
(b) Pasteurization and Sterilization
Pasteurization
1. Temperature - 60°C
2. Does not kill spores
3. Partial sterilization
E.g. Pasteurization of milk
Sterilization
1. Temperature - 110° C
2. Kills even spores
3. Complete sterilization
E.g. Sterilization of canned food
These processes are essential for managing waste and keeping our food supply safe. While decay helps recycle nutrients naturally, sterilization ensures that packaged food is totally free of harmful germs.
Teacher's Tip: Think of "P" in Pasteurization for "Partial" and "S" in Sterilization for "Strong/Super" cleaning.
Exam Tip: When distinguishing between these, always include the specific temperature (60°C vs 110°C).

Question C.6:
Answer: Direct sunlight contains ultraviolet radiations of the sun, which help in killing of mould spores present in air.
Ultraviolet rays damage the DNA of spores, preventing them from growing or reproducing. This is a natural way to keep surfaces clean and reduce the spread of fungi.
Teacher's Tip: Sunlight is like a natural disinfectant provided by nature.
Exam Tip: Mention "ultraviolet radiations" as the specific part of sunlight that kills spores.

Question D.1:
Answer: Bacteria reproduce asexually by means of fission (binary fission), while yeast reproduces asexually by budding producing chains.
Binary fission involves one cell splitting into two identical halves. Budding in yeast looks like a small "bubble" growing out of the parent cell, which eventually detaches.
Teacher's Tip: Fission = Division; Budding = Growing a branch.
Exam Tip: Use the term "asexual" for both to show you know no partner is needed for reproduction.

Question D.2:
Answer: Role of micro-organisms in industrial production:
1. Bacteria are used in the production of vinegar and in the processing of coffee, tobacco, etc.
2. Different flavours of tea, coffee, etc. are produced by certain bacteria.
3. Tanning of leather is basically brought about by sunlight, but there are a few micro-organisms which are involved in this process.
4. Fibres used for making rope, linen, etc. are obtained by loosening the fibres of hemp and flax by retting, which involves the use of bacteria.
5. Bacteria are used for the large-scale production of antibiotics, enzymes, hormones, serum, vaccines and toxoids.
Micro-organisms act as tiny biological factories that create products we use every day. Their ability to ferment or break down substances makes them invaluable in the food and medical industries.
Teacher's Tip: Think of bacteria as "tiny chemical workers" that make your vinegar and tea taste good.
Exam Tip: "Retting" is a key term to remember for how bacteria help make rope and linen.

Question D.3:
Answer: Modes of nutrition in bacteria:
1. Autotrophic bacteria: Able to synthesize their own food
a. Photoautotrophs: Contain chlorophyll and use light energy for the synthesis of food
b. Chemoautotrophs: Obtain energy by oxidizing inorganic compounds
2. Heterotrophic bacteria: Require organic compounds as their main source
a. Saprophytes: Grow on dead and decaying organic matter
b. Parasites: Obtain their food from living host on which they grow
Bacteria have developed many clever ways to get energy, from using the sun to feeding on chemicals. This versatility allows them to survive in almost every environment on Earth.
Teacher's Tip: Saprophytes are "Scavengers" that eat dead stuff; Parasites "Pick" on living hosts.
Exam Tip: Distinguish between "Photoautotrophs" (light) and "Chemoautotrophs" (chemicals) clearly.

Question D.4:
Answer: Uses of bacteria in industry:
1. Tea curing: Certain bacteria are used to produce different flavours of tea.
2. Tanning of leather: Tanning of leather is basically brought about by sunlight, but there are a few bacteria which are involved in this process.
The curing process uses bacteria to change the chemical composition of tea leaves to improve taste and aroma. In leather tanning, bacteria help remove unwanted materials from animal skins to make them soft and durable.
Teacher's Tip: Think of "Curing" as "Flavoring" and "Tanning" as "Softening."
Exam Tip: Be specific about the industry (Tea or Leather) to show how bacteria are applied.

Question D.5:
Answer: Antibiotics are chemical substances produced by a living organism that kill or stop the growth of disease-causing micro-organisms such as fungi and bacteria.
Examples of antibiotics:
1. Penicillin
2. Streptomycin
These medicines are our best defense against bacterial infections. By targeting the cell walls or life processes of bacteria, they save millions of lives every year.
Teacher's Tip: "Anti" means against, and "Bio" means life - so antibiotics are against bacterial life.
Exam Tip: Name "Penicillin" as the first and most famous antibiotic to get easy marks.

Question D.6:
Answer: No, tinned and sealed food are not always safe to eat as they may contain harmful bacteria like Clostridium botulinum, which may cause serious food poisoning resulting in Botulism. In extreme cases, this condition may even prove to be fatal for life.
This specific bacterium thrives in environments without oxygen, which is exactly what a sealed can provides. Always check for bulges or leaks in cans as these are signs that bacteria might be growing inside.
Teacher's Tip: Remember: "If the can is puffed, the food is tough (bad)!"
Exam Tip: Use the scientific name Clostridium botulinum to identify the cause of botulism.

Question E.1:
Answer: (a) Soil bacteria such as Rhizobium are present in the root nodules of leguminous plants. These bacteria convert free nitrogen of the soil atmosphere to soluble nitrates.
(b) (i) Nitrosomonas converts ammonium compounds to nitrites.
(ii) Nitrobacter converts nitrites to nitrates.
(c) Denitrifying bacteria in the soil break down nitrates present in the soil to release nitrogen gas which enters the atmosphere.
(d) Nitrifying bacteria present in the soil convert nitrogenous wastes of animals and dead remains of plants and animals to ammonia. Ammonia is then converted to ammonium compounds. In this way, plants and animals help in the formation of ammonium compounds.
This nitrogen cycle is vital for keeping soil fertile so plants can grow. Bacteria act as nature's recyclers, turning waste back into food for the Earth.
Teacher's Tip: Think of Rhizobium as a "Nitrogen-fixer" that repairs the soil.
Exam Tip: Match the bacterium name (Nitrosomonas or Nitrobacter) to the correct conversion step.

Exercise 2

Question A.1:
Answer: 1. (b) Yeast
2. (c) Spore formation
3. (d) They do not have a true nucleus.
4. (a) Ethyl alcohol
Yeast is a fungus that is vital for baking because of its fermentation ability. During this process, it turns sugar into alcohol and carbon dioxide, which makes bread rise.
Teacher's Tip: Yeast + Sugar = Alcohol + Gas (CO₂).
Exam Tip: Remember that "Ethyl alcohol" is the specific byproduct of plant/yeast anaerobic respiration.

Question B.1:
Answer: (b) All toadstools are poisonous. (Correct)
(d) Some mushrooms are edible. (Correct)
This distinction is important for safety when exploring nature. While many mushrooms are a healthy food source, toadstools can contain dangerous toxins that are harmful if eaten.
Teacher's Tip: "Toad" in toadstool sounds like something you shouldn't eat!
Exam Tip: Tick both correct observations if asked to identify true statements about fungi.

Question C.1:
Answer: Rhizopus is the common bread mould. It grows not only on bread, but also on a variety of organic matter such as paper, wood, cloth, animal dung, leather goods and food materials such as fruit, bread, pickles, chapati, etc. particularly in warm and humid climate.
This fungus spreads through tiny spores that float in the air and land on organic surfaces. Its fuzzy appearance is actually a network of tiny threads called mycelium.
Teacher's Tip: Mould loves "Warm and Wet" places - like a wet chapati in a box.
Exam Tip: List "warm and humid climate" as the ideal growing condition for bread mould.

Question C.2:
Answer: Direct sunlight contains ultraviolet radiations of the sun which help in killing of mould spores present in air.
UV light is powerful enough to break down the protective coating of spores. This is why keeping items in the sun helps prevent them from getting mouldy.
Teacher's Tip: Sunlight is the enemy of mould; fresh air and sun keep things clean.
Exam Tip: Mention "ultraviolet radiations" to provide the scientific reason for the result.

Question C.3:
Answer: Role of certain fungi in industrial production:
1. Preparation of fermented foods and bakery products
2. Preparation of alcoholic beverages
3. Preparation of organic acids
4. Production of enzymes
5. Production of antibiotics
6. Production of alcohol
7. Production of wine
8. Bread-making
9. Cheese making
10. Mushroom cultivation
Fungi are the "chefs" and "chemists" of the industrial world. They transform simple ingredients into complex foods like cheese and medicines like penicillin.
Teacher's Tip: Without fungi, we wouldn't have fluffy bread or blue cheese!
Exam Tip: List "Bread-making" and "Antibiotics" as the top two industrial uses of fungi.

Question C.4:
Answer: Useful effects of wine:
In mild quantities, wine acts as a stimulant.
It can be used to stimulate hunger, reduce anxiety and improve digestion.
Harmful effects of wine:
In large quantities, wine can trigger asthma attack and increase blood pressure.
It can cause body ailments, particularly liver cirrhosis.
While small amounts may have medical uses, excessive consumption can lead to severe long-term health problems. It is important to understand both sides of how substances made by fermentation affect the body.
Teacher's Tip: "Mild" can be okay, but "Large" leads to "Liver" damage.
Exam Tip: Mention "liver cirrhosis" as a major harmful effect for a scientifically complete answer.

Question C.5:
Answer: (a) Saprophyte and parasite
Saprophyte
Obtains nourishment from dead and decaying organic matter
Parasite
Obtains nourishment from the body of the living host
(b) Aerobic and anaerobic respiration with regard to products
Aerobic respiration
Products - Carbon dioxide (CO₂), water (H₂O) and energy (ATP)
Anaerobic respiration
Products - Ethanol (2C₂H₅OH), carbon dioxide (CO₂) and energy (ATP)
(c) Decay and putrefaction
Decay
Complete breakdown of organic matter by bacteria without the emission of foul smell
Putrefaction
Incomplete breakdown of organic matter by bacteria along with the emission of foul smell
These comparisons clarify the different ways organisms live and breathe. For example, knowing if a process is aerobic or anaerobic tells you if oxygen is present and what chemicals will be produced.
Teacher's Tip: Remember: Saprophyte = "Scavenger" (dead stuff).
Exam Tip: Use the chemical formula CO₂ and H₂O in your comparisons to score better.

Question D.1:
Answer: Antibiotics are chemical substances produced by a living organism that kill or stop the growth of disease-causing micro-organisms such as fungi and bacteria.
Examples of antibiotics:
1. Penicillin
2. Streptomycin
Antibiotics are special because they are "natural weapons" made by one microbe to kill another. We have learned to harvest these chemicals to use as life-saving medicine.
Teacher's Tip: Think of it as a microscopic "battle" where we use the winner's weapons to help us.
Exam Tip: Define them as substances "produced by a living organism" for the best score.

Question D.2:
Answer: No, tinned and sealed food are not always safe to eat as they may contain harmful bacteria like Clostridium botulinum, which may cause serious food poisoning resulting in Botulism. In extreme cases, this condition may even prove to be fatal for life.
If food is not sterilized properly before sealing, these dangerous bacteria can grow in the oxygen-free environment. This is why canned food must be heated to very high temperatures during processing.
Teacher's Tip: Never eat food from a can that looks "bloated" or swollen.
Exam Tip: The name of the disease is "Botulism."

Question D.3:
Answer: Bacteria can be present in an aquarium. Bacteria are present everywhere; in air, soil, water and foodstuffs. They are found in boiling water and also below 0°C. They are present on the bodies of all living and non-living organisms. They live on readymade food. In short, they are omnipresent. Bacteria are heterotrophic and may be decomposers or micro-aerobic in nature. Their mode of reproduction is very fast.
Bacteria are the most successful life forms because they can survive almost anywhere, even in volcanoes or frozen ice. Their simple needs and fast growth let them colonize every corner of our planet.
Teacher's Tip: "Omnipresent" means they are everywhere at the same time!
Exam Tip: List "air, soil, and water" as the three main places where bacteria are found.

Question E.1:
Answer: (a) Moulds are commonly present in air, water, etc. Hence, they were already present when moist bread was kept covered with the bell-jar.
(b) If bread was not covered with the bell-jar, moulds would have still appeared, but after some time. The warm and humid conditions inside the bell-jar promote rapid production of mould.
(c) Moulds do not grow below freezing point inside a refrigerator.
(d) Mycelia appear first on the bread.
(e) Bread mould obtains its nourishment through extracellular digestion from the substratum on which it grows. This mode of nourishment is called saprophytic nutrition.
This experiment shows that mould is always around us in the form of invisible spores. By creating a warm, trapped space with the bell-jar, we simply give those spores the perfect "home" to grow faster.
Teacher's Tip: Bell-jar = Greenhouse for mould.
Exam Tip: Identify the mode of nourishment as "saprophytic nutrition" for full marks.

Question E.2:
Answer: Major steps in the cultivation of common edible mushrooms:
1. Composting: Composting involves mixing of various components such as wheat or paddy straw, chicken manure and organic and inorganic fertilizers in a fixed proportion. The temperature of compost is maintained at around 50°C. The compost is kept undisturbed for about one week.
2. Spawning: ‘Mushroom seed’ in the form of mycelium of mushroom to be grown is introduced into the heap of compost and left for spreading for around two days.
3. Casing: Casing is the most important step of mushroom cultivation. It involves spreading of a thin layer of soil over the compost. This provides humidity and support to the mushroom. It also serves to prevent the desiccation of the compost heap and helps in temperature regulation at around 20°C-25°C to forbid the growth of pests and diseases. The provision for circulating air around the compost bed should also be made.
4. Cropping and harvesting: Three major growth stages are observed, before mushrooms attain a fully grown form. Firstly, the mycelium, i.e. a network of fibrous mass, spreads out in 2 to 6 weeks, followed by the tiny pin head stage and finally the button stage, which is marked by an increase in the mushroom size, until it acquires marketable size.
5. Preservation: Mushrooms have a very short shelf-life. Processes such as vacuum cooling, bombardment by gamma radiation, followed by storage at 15°C, freeze drying in a solution of citric acid, ascorbic acid and brine, etc. are used for the preservation of mushrooms.
Farming mushrooms is very different from farming vegetables because they grow on decomposing matter instead of soil. Each step, from composting to preservation, is carefully controlled to ensure the mushrooms are safe and delicious to eat.
Teacher's Tip: Spawning is like "planting" and Casing is like "covering" your crop.
Exam Tip: Name "Casing" as the most important step for providing support and humidity.

Question E.3:
Answer: a. Denitrifying bacteria are a boon to farmers because they curb the excess supply of nitrates to plants. Excessive nitrates can even harm the ecosystem as a whole because some wild plants like cultivated crops can thrive on nitrogen. Growth of these plants is favoured in nitrogen-saturated environments which can upset the ecosystem. Denitrifying bacteria are a curse to farmers because they breakdown soil nitrates to release free nitrogen gas into the atmosphere, thereby reducing the levels of nitrogenous compounds in the soil.
Yeast respires anaerobically in the absence of oxygen. It breaks down carbohydrates into simpler products such as ethanol by fermentation. The quality of alcohol produced varies with the kind of yeast employed.
b. During the baking process, yeast added to the dough ferments sugar and produces carbon dioxide. This causes the dough to rise, and when baked, the gas bubbles expand, giving the bread a light and spongy texture. Therefore, yeast is used in bakeries and breweries.
Bacteria and yeast play complex roles in our lives, sometimes helping us and sometimes making things harder. While yeast is a hero in the kitchen for making bread fluffy, soil bacteria are essential for keeping the Earth's atmosphere and soil in balance.
Teacher's Tip: Yeast is the "balloon blower" of the bread dough!
Exam Tip: Explain that CO₂ gas bubbles are what make bread "light and spongy."