Class 12 Biology Chapter 8 Microbes in Human Welfare

Key Concept: Anaerobic Digesters

b) Methane

[Solution Description] In anaerobic digesters, methanogens produce biogas, which is primarily composed of methane (CH_4). This process occurs under anaerobic conditions where organic matter is decomposed by methanogenic archaea.

Key Concept:Process Recognition

b) Fermentation
[Solution Description] The process utilized by Saccharomyces cerevisiae to convert sugars present in fruit juices into ethanol is called fermentation. This biological process is anaerobic, meaning it does not require oxygen.

Key Concept:Environmental Impact

c) Reducing environmental pollution from fertilizer runoff
[Solution Description] Mycorrhiza reduces the reliance on chemical fertilizers by enhancing the plant’s nutrient uptake efficiency. This leads to decreased environmental pollution since fewer chemical fertilizers are required, reducing runoff and contamination of water bodies.

Key Concept: Microbial Gas Production

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] Both the Assertion and Reason are true. When fermenting dough for items like dosa and idli, bacteria such as lactic acid bacteria produce carbon dioxide $(CO_2)$. This gas becomes trapped within the dough structure, causing it to expand and rise. The increase in volume leads to a lighter and fluffier texture, which is essential for these types of food products. Thus, the reason provided correctly explains why $CO_2$ production is significant during the fermentation process.

Key Concept: Microbial Role

b) Coagulates and partially digests milk proteins

[Solution Description] Lactic acid bacteria help coagulate and partially digest milk proteins during curd formation. They convert lactose present in milk into lactic acid, which leads to the thickening of milk, resulting in curd.

Key Concept:Basic Comparison

b) Biocontrol agents promote biodiversity and reduce pollution, while chemical pesticides can harm the environment
[Solution Description] Biocontrol agents have a more positive environmental impact compared to chemical pesticides. They promote balance within ecosystems and reduce pollution, unlike chemical pesticides which can harm non-target species and cause environmental damage.

Key Concept:Methanogens Identification

d) Methanobacterium
[Solution Description] Methanobacterium is one of the common methanogens known to produce methane in anaerobic conditions, such as in biogas production.

Key Concept:Component Identification

b) Settled solids
[Solution Description] Primary sludge is formed from settled solids during the sedimentation process in primary treatment. These solids settle down at the bottom after heavier particles have been separated from the sewage.

Key Concept:Impact on Non-targets

d) All of the above
[Solution Description] Baculoviruses are species-specific and do not harm plants, mammals, birds, fish, or non-target insects.

Key Concept: Basic Concept

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] The assertion states that Lactobacillus bacteria are responsible for converting milk into curd, which is a true statement based on the syllabus. The reason given is that these bacteria produce lactic acid, which then causes the milk proteins to coagulate. This is also a true statement and directly explains how Lactobacillus achieves this conversion.

Key Concept:Basic Function

b) To remove oily stains
[Solution Description] The main function of Lipases in laundry detergents is to break down oily stains, as lipases are enzymes that catalyze the hydrolysis of fats.

Key Concept:BOD Definition

c) Biochemical Oxygen Demand
[Solution Description] In the context of sewage treatment, BOD stands for Biochemical Oxygen Demand, which measures the rate of oxygen uptake by microorganisms in water or effluent.

Key Concept: Simple Processes

c) They decompose waste to form methane.

[Solution Description] Methanogens, such as Methanobacterium, are critical in biogas production as they convert organic material into methane gas during anaerobic digestion, which is a key component of biogas.

Key Concept: Integration

c) They specifically target their host species with minimal non-target effects

[Solution Description] Baculoviruses are highly specific to their host species and have minimal impact on non-target organisms, including beneficial insects. This specificity makes them an excellent choice for integrated pest management systems, where the aim is not only to control the target pest but also to conserve the ecological balance and protect non-target species.

Key Concept:Function Recognition

c) To lower blood cholesterol levels
[Solution Description] According to the syllabus, Statins are used as blood-cholesterol lowering agents.

Key Concept:Biogas Production

a) Methane
[Solution Description] During anaerobic digestion in sludge digesters, methane $(CH_4)$ is the predominant gas produced along with smaller amounts of hydrogen sulfide $(H_2S)$ and carbon dioxide $(CO_2)$.

Key Concept:Microbe-Product Match

d) Fermented bamboo shoots
[Solution Description] Fermented bamboo shoots are a traditional food product where the bamboo shoots undergo fermentation, often involving lactic acid bacteria.

Key Concept:Raw Material Usage

d) Malted cereals
[Solution Description] Malted cereals provide a rich source of carbohydrates that are fermented by Saccharomyces cerevisiae during alcohol production, resulting in the formation of ethanol.

Key Concept:Basic Definition

c) To generate biogas
[Solution Description] Anaerobic digestion breaks down organic material in the absence of oxygen, mainly to produce biogas, which contains methane that can be used as an energy source.

Key Concept:Application Method

b) Sprayed onto plants
[Solution Description] Bacillus thuringiensis (Bt) is available in sachets as dried spores, which are mixed with water and sprayed onto plants. This application method helps evenly distribute the Bt spores over the crop surface to effectively target caterpillar infestations.

Key Concept:Identification

b) Root ecosystems
[Solution Description] Trichoderma species are fungi that are commonly found in root ecosystems where they live freely. Their presence in these habitats allows them to effectively interact with plants and soil microbes.

Key Concept:Microbial Role

b) Methanogens
[Solution Description] Methanogens are a type of bacteria that play a crucial role in the production of methane within biogas plants. They are found in anaerobic environments such as sludge and cattle rumen.

Key Concept:Biocontrol Strategy

d) To reduce pesticide use
[Solution Description] Ladybird beetles are used in pest management due to their diet, which primarily consists of aphids and other small insects that harm plants. By releasing ladybird beetles into agricultural areas or gardens, farmers and gardeners can reduce aphid populations naturally, without the need for chemical pesticides. This strategy significantly decreases reliance on synthetic chemicals, promoting a more sustainable and environmentally friendly form of pest control.

Key Concept:Product Recognition

b) Carbon dioxide
[Solution Description] During the fermentation of bread dough by Saccharomyces cerevisiae, carbon dioxide $(CO_2)$ is produced as a byproduct. This gas creates bubbles in the dough, causing it to expand and rise.

Key Concept: Methanogens Habitat

c) In anaerobic sludge

[Solution Description] Methanobacterium is a type of methanogen that is commonly found in environments where anaerobic digestion takes place. In the context of biogas production, it is often found in anaerobic sludge within biogas plants and in the rumen of cattle. These locations provide the necessary conditions for methanogenesis, particularly the absence of oxygen and presence of decomposing organic matter.

Key Concept:Specific Functionality

a) Anabaena
[Solution Description] Anabaena is known for its ability to form symbiotic relationships with specific plants and can significantly enhance soil fertility by adding organic matter. It plays an important role in recycling nutrients in the soil, especially in rice paddies.

Key Concept: Comparative Analysis

d) None of the above

[Solution Description] Acetobacter aceti is involved in the production of acetic acid, whereas Clostridium butylicum is known for its role in producing butyric acid. The microbe that fits the production of both types of acids does not exist as these are distinctly separate processes involving different organisms.

Key Concept:Antibiotic Discovery

d) Alexander Fleming
[Solution Description] Alexander Fleming discovered Penicillin, marking a significant event in medical history.

Key Concept:Identification

a) Bacillus thuringiensis (Bt)
[Solution Description] Bacillus thuringiensis (Bt) is commonly used to control caterpillar populations. It can be applied directly or genetically engineered into plants to provide pest resistance.

Key Concept:Concept Integration, Critical Analysis

c) Azospirillum and Azotobacter
[Solution Description] Sandy soils are characterized by poor nutrient retention and require bacteria that not only fix nitrogen but also help improve soil structure. Azospirillum enhances root surface area, aiding in nutrient absorption, while Azotobacter fixes nitrogen effectively in varied environments. Together, they improve soil fertility by increasing nitrogen levels and enhancing plant access to nutrients. Their combined application can significantly boost nitrogen availability in challenging soil conditions like sandy soils.

Key Concept: Fungal Symbiosis

c) Arbuscular mycorrhizae

[Solution Description] Mycorrhizal fungi form associations with plant roots, facilitating the uptake of nutrients such as phosphorus. The arbuscular mycorrhizal (AM) fungi, belonging to the Glomeromycota phylum, are particularly efficient at absorbing phosphorus and transferring it to their host plants.

Nobel Prize Recognition

d) Fleming, Chain, and Florey
[Solution Description] The Nobel Prize in Physiology or Medicine in 1945 was awarded to Alexander Fleming, Ernst Boris Chain, and Howard Florey for their work on the discovery and development of Penicillin.

Key Concept:By-product Use

b) Fertilizer
[Solution Description] After the biogas production process, the leftover slurry is rich in nutrients and can be effectively used as a fertilizer.

Key Concept:Basic Identification

d) Aspergillus niger
[Solution Description] The organism used for the production of citric acid is Aspergillus niger. It is a filamentous fungus that is commonly employed in the industrial production of citric acid through fermentation.