Botany: Solved Previous Year’s Question Paper for NCERT/ CBSE Class 12th Botany Paper Code (HSE2KROXI)
(Long Answer Type Questions)
Question: Describe the structure of DNA as proposed by Watson and Crick.
Ans: The double helix is the term given to the Watson and Crick model for DNA structure.
1. It is made up of two nucleotide strands that are spirally wound around one another.
2. Four nitrogenous bases—adenine (A), thymine (T), guanine (G), and cytosine (C)—hold the two strands together.
3. Weak connections between base pairs of nucleotides keep the strands together. The bases adenine (A) and thymine (T) are paired on one strand, and guanine (G) and cytosine (C) are paired on the other.
4. The hydrogen bonds that link the base pairs together create the “rungs” of the ladder-like structure.
5. Replication and genetic coding are made possible by the ability to separate the strands and use them to build new DNA molecules.
6. The strands are antiparallel, which means that one runs in a direction of 5′ to 3′ and the other in a direction of 3′ to 5′.
7. These bases are paired together in a specific way: A pairs with T and G pairs with C. This structure allows the strands to bond together and forms the double helix.
Question: Give an account of ecological succession on bare rock.
Ans: The process by which bare rock is gradually colonised over time by plants and other animals is known as ecological succession. This process begins with bacteria and lichens colonising the rock, which can endure in the harsh, nutrient-poor environment offered by the rock. As these organisms start to decompose the rock, they release nutrients into the environment that other organisms can consume. As the lichens develop, they offer a barrier that helps to keep moisture and nutrients in the soil, enabling other plants to colonise the region. Mosses, grasses, and shrubs are among the vegetation that eventually starts to colonise the rock. A more conducive environment for bigger species, such as birds and mammals, is created as the plants expand. More plant species can invade the area as a result of these animals’ contribution to soil fertilisation through their waste. A mature ecosystem with a diverse range of plant and animal species can eventually evolve.
Question: What kind of threats to biodiversity may lead to its loss?
Ans: Threats to biodiversity that can result in its extinction include habitat loss, pollution, invasive species, climate change, over-exploitation, and environmental changes brought on by humans.
1. Habitat Loss: Human activities like urbanisation, deforestation, and agricultural development are serious threats to biodiversity because they destroy and fragment ecosystems.
2. Climate Change: Climate change is affecting species’ life cycles, producing a shift in their ranges, and altering their abundance and distribution.
3. Pollution: Pollution, such as that in the air, water, and ground, can harm or destroy habitats and result in the extinction of species.
4. Invasive Species: These non-native species have the potential to outcompete native species for resources, reducing biodiversity.
5. Overharvesting: Taking too many species for commercial purposes might result in population decreases and put species in jeopardy.
(Short Answer Type Questions)
Question: Describe the structure of a typical monosporic embryo sac found in flowering plants.
Ans: An embryo sac in a monosporic spore typically has 8 cells and 7 cell layers. The egg cell makes up the top layer. The two synergids make up the second layer. Three antipodal cells make up the third layer. The two core cells make up the fourth layer. The one-celled main endosperm nucleus is the fifth layer. The two polar nuclei make up the sixth layer. The secondary endosperm cell is located in the seventh layer. The embryonal cell, which gives rise to the embryo, is the eighth and final cell.
Question: What is Biofortification?
Ans: Biofortification is the process of enhancing the nutritional value of crops. Through agronomic techniques, traditional plant breeding, or contemporary biotechnology, This procedure can be used to boost the number of vital micronutrients in food crops, including iron, zinc, and vitamin A. In those who rely on those crops as their main source of food, this can assist to enhance nutrition and lower the risk of micronutrient deficiencies.
Question: distinguish between ectoparasite and endoparasite?
Ans: Ectoparasites, including fleas, ticks, and lice, are parasites that inhabit the exterior of their host’s body. Endoparasites, such as tapeworms, roundworms, and protozoa, are parasites that reside inside the bodies of their hosts.
(Very Short Answer Type Questions)
Question: What is Micropropagation?
Ans: Micropropagation is a method of plant propagation used to quickly create lots of seedlings that are all genetically similar. It entails taking a little amount of plant tissue and growing it under carefully monitored circumstances in a sterile setting. It can be used to create plants with desired characteristics, such as better yield or disease resistance.
Question: What is BOD? What does it mean if a water sample has more BOD?
Ans: Biological oxygen demand is referred to as BOD. It is a measurement of how much-dissolved oxygen aerobic microorganisms require to decompose organic materials in a specific water sample. A greater BOD value in a water sample indicates the presence of more organic matter in the sample, which may be a sign of higher pollution levels.
Question: What do you mean by Cloning?
Ans: Cloning is the technique of making a biological thing, tissue, or cell an identical copy. It is utilised to construct duplicates of plants, animals, and even humans and can be done naturally or artificially. Cloning is a technique used in biotechnology to create genetically identical copies of cells, organs, and even whole species.
Question: Distinguish between Habitat and Ecological Niche.
Ans: An ecological niche is an organism’s function and place within its environment, whereas a habitat is the actual physical environment in which it lives. The ecological niche is an organism’s specialised place in the ecosystem, whereas the habitat offers the resources necessary for survival such as food, water, and shelter. A bird, for instance, might fit under the category of an insectivorous seed eater despite living in a forest.
Question: Define Porogamy.
Ans: Porogamy is a sort of marriage in which a woman weds multiple husbands at the same time. The husbands are brothers, hence it is a type of polygamy.
(Objective Type Questions)
Question: Parthenogenesis is the presence of more than one embryo the seed.
Question: During DNA replication, one new strand is formed in the continuous stretch in the 5′-3′ direction. It is called a strand formed from okazaki fragments and is termed is Strand.
Ans: The strand formed from Okazaki fragments is the lagging strand.
Question: The number of young ones produced by an organism due to its lifetime is called ……