Botany: Solved Previous Year Question Paper for NCERT/ CBSE Class 12th Botany
(Long Answer Type Questions)
Question: What is Semiconservative DNA Replication? Describe the mechanism of the same with suitable diagrams.
Ans: Semiconservative DNA replication is the process by which a double-stranded DNA molecule is duplicated in a way that each of the ensuing double-stranded DNA molecules has one strand that is an exact clone of the original DNA molecule and one new strand. DNA replication is a crucial step for maintaining genetic information that takes place during cell division.
Semiconservative DNA replication works in the manner described below:
1. The enzyme helicase unwinds the double-stranded DNA molecule into two single strands that are connected by hydrogen bonds.
2. The enzyme primase binds to the individual strands and produces short RNA primers.
3. The new DNA strand is created when the enzyme DNA polymerase attaches to the RNA primers. To the initial single strand of the double-stranded DNA molecule, the newly created DNA strand is complementary.
4. Up until it reaches the end of the double-stranded DNA molecule’s initial single strand, the enzyme DNA polymerase keeps generating the new DNA strand.
5. The freshly generated DNA strand’s sugar-phosphate backbone is joined to the host protein by the enzyme DNA ligase.
Question: Define multiple alleles with the help of a suitable example.
Ans: When two or more alleles are present at the same locus or gene, the situation is referred to as multiple alleles. The cat coat colour gene is one illustration of this. For this gene, there are three distinct alleles: black (B), orange (O), and white (W). Any of these allele combinations, such as BB, BW, WW, and so on, are possible in cats. As a result, the coats have a variety of colours, from black to white.
Question: Explain the phenomenon of multiple allelism.
Ans: The word “multiple allelism” refers to the possibility of two or more distinct alleles existing at the same locus in a population. Two alleles at the locus, one from each parent, are carried by every member of the population. The set of alleles a person possesses is known as their genotype, and alleles are different variants of a gene. When a locus contains more than two alleles, multiple allelism develops, which allows for the possibility of more genotypes. There are different levels of each allele’s frequency in the population, and the alleles can be dominant, recessive, or codominant.
Question: What are Negative Interactions? Describe various negative interactions found among organisms.
Ans: Negative interactions are ones in which at least one of the interacting organisms suffers. Competition, predation, parasitism, and disease are typically used to describe these relationships.
1. Competition: In competition, two or more creatures vie for the same scarce resources, such as food, water, space, or mates. The competition may be immediate, such as when two animals fight over food, or indirect, such as when two plants compete with one another for sunlight.
2. Predation: Predation is the interaction of two animals in which one, the predator, seeks and consumes the other, the prey.
3. Parasitism: Parasitism is a sort of interaction in which one creature, the parasite, resides on or within another organism, the host, and gains advantages from the host without giving anything back.
4. Disease: Disease is the result of a relationship between two species in which one of the organisms, the pathogen, wreaks havoc on the host organism. These microorganisms include bacteria, viruses, fungi, and other types.
Question: Give an account of energy flow in an ecosystem.
Ans: The process of photosynthesis, in which plants absorb the sun’s energy and transform it into chemical energy, is the first source of energy flow in an ecosystem. Then, as herbivores consume plants and predators consume other animals, this energy is transferred throughout the food chain. Some of the energy that moves through the food web is used to power the metabolic activities of the organisms, while some of it is wasted as heat energy. Unused energy eventually finds its way back into the atmosphere as waste products like carbon dioxide. These waste products are broken down by decomposers, such as bacteria, fungi, and other microbes, which return nutrients to the soil for plants to once again absorb and utilise. The continual repetition of this cycle of energy flow ensures the ecosystem’s continued health and balance. (Short Answer Type Questions)
Question: Write short notes on:
Ans: (i) Hydrophilly: Pollination by water is known as hydrophily. The female reproductive organs of plants receive pollen that has been distributed by the water. Water pollination occurs frequently in a wide range of different plant species as well as in aquatic plants like water lilies.
(ii) Entomophilly: Pollination by insects is referred to as entomophily. Pollinators, including bees, butterflies, and other insects, move pollen from one flower to another so that plants can reproduce successfully.
(iii) Anemophilly: The process of pollination by the wind is known as anemophilly. Pollen is distributed in the air and transported to plants’ female reproductive systems. Grass and other wind-pollinated plants frequently undergo this kind of pollination.
Question: Enunciate Mendel’s law of segregation with the help of the Monohybrid cross.
Ans: According to Mendel’s law of segregation, the two alleles for a single characteristic segregate (separate) in a monohybrid cross during the development of gametes, resulting in each gamete receiving just one of the two alleles. Because only one of the two alleles for the trait is present in each gamete, when fertilisation takes place, the offspring obtains one allele for the trait from each parent, giving the trait a total of two alleles.
Question: Write an explanatory note on single-cell protein (SCP).
Ans: SCP is a type of food produced from the biomass of microorganisms like bacteria, algae, fungi, and yeast. It is a type of concentrated complete protein that is created by microorganisms grown in a controlled environment on a media-rich in nutrients. SCP is a popular option for vegans and vegetarians because it is a source of protein that may be utilised as a replacement for regular animal-based proteins. Added animal-based proteins in animal diets is another usage for it. SCP is extremely digestible and has vital vitamins, minerals, and necessary amino acids. Additionally, it is a complete protein, meaning it contains all the essential amino acids required by the body for both development and repair. SCP has a wide range of uses, including in industrial, biotechnological, and medical procedures as well as food and animal feed items.
Question: What is Biodiversity? Why has it become important recently?
Ans: The diversity of life on Earth, which includes all varieties of plants, animals, fungi, and microorganisms, is known as biodiversity. It is significant because it improves ecosystem resilience, gives us food and other resources, and helps to control the Earth’s ecology. Recent effects of climate change, pollution, and habitat destruction brought on by human activities have made biodiversity even more crucial. The rapid loss of biodiversity brought on by these activities has an impact on the economy, society, and the health of the planet.
(Very Short Type Questions)
Question: Name the water fern that is an excellent biofertilizer for rice cultivation. What helps the fern to do so?
Ans: Azolla is a water fern that makes a superior biofertilizer for rice farming. Azolla and the cyanobacterium Anabaena azollae, which fixes atmospheric nitrogen and provides it to the fern, have a symbiotic relationship. When this nitrogen-rich fern is introduced to the soil, it functions as a natural fertiliser, increasing the soil’s fertility and the growth of the rice plants.
Question: Why would biopiracy affect India most?
Ans: India might be significantly impacted by biopiracy, especially in the agriculture and pharmaceutical industries. This is because India is home to a wealth of traditional knowledge and biodiversity that could be utilised by foreign businesses and organisations. The theft of biological resources or traditional knowledge without consent or payment to the local communities who created them is known as biopiracy. This can cause profits to be taken out of the local economy, which might cause social and economic unrest. Additionally, biopiracy can deny nearby people access to crucial resources and might prevent them from creating their traditional remedies and farming methods.
Question: What are Threatened Species? Name their three types in order of the danger of extinction they face.
Ans: Animals and plants classified as threatened species are in danger of going extinct, which would mean they would never reappear. According to the threat of extinction they face, threatened species fall into one of three categories:
1) Endangered Species: These species are in danger of going extinct in the wild and are in danger of going extinct completely.
2) Vulnerable Species: Although these species are still rather common if their populations keep falling, they run the risk of going extinct soon.
3) Near-Threatened Species: These species are not now in danger of extinction, but if conservation measures are not adopted to safeguard them, they are likely to do so soon.
Question: A hyaline bisexual and self-fertilized flower that does not open at all is chasmogamous.
Question: Preserving seeds of plants, vegetatively propagating plant cells, sperms, and ova at -196°C (a temperature of liquid nitrogen
is called …
Question: Define the term biome.
Ans: A biome is a large, geographically defined region with biologically related plants and animals. Typically, biomes are categorised according to climate, such as tropical rainforest, temperate forest, desert, grassland, and tundra.
Question: The phenotype ratio obtained by Mendel in his farm so monohybrid cross in the F2 generation was
Ans: 3: 1.