Botany: Solved Previous Year Question Paper for NCERT/ CBSE Class 12th (Paper code 81019)
Section – A
Question: What is double fertilization? Who discovered double fertilization in angiosperms? List the post-fertilization changes in the angiospermic ovule.
Ans: The union of two sperm cells from the pollen grain with the egg and the central cell of the embryo sac is known as Double fertilisation and occurs in angiosperms (flowering plants). The endosperm (a tissue that feeds the embryo), is formed by the first fertilisation, and the embryo, is formed by the second fertilisation. Eduard Strasburger, a botanist from Germany, made the discovery.
The angiospermic ovule’s post-fertilization modifications.
1. Free nuclear division of the endosperm and the development of endosperm tissue
2. Ovule maturation
3. The embryo sac’s formation
4. The female gametophyte’s development
Five. Combining male and female gametes
6. The zygote’s formation
7. Endosperm nucleus formation 8. Depositing food stores in the endosperm and embryo
9. The formation of the seed coat
10. Embryonic development and dormancy
Question: What are ecological interactions?
Ans: Ecological interactions are the connections between creatures that share the same habitat. Competition, predation, parasitism, mutualism, and commensalism are just a few of the relationships that can be either positive, negative, or neutral.
Question: Explain predation and parasitism with suitable examples.
Ans: Predation is a two-organism interaction in which there is a predator (the creature that seeks and consumes other species) and prey (the organism that is hunted and eaten). Predators hunt to survive, using their prey as a source of energy and nutrients. Predation includes actions like a lion hunting and devouring a zebra, a hawk consuming a mouse, and a spider devouring an insect.
A Parasitic relationship is one in which one creature (the parasite) depends on another (the host), typically by feeding on it. The host organism is affected by the parasite’s existence since parasites often rely on their host for energy and nutrition. A tick feeding on a deer, a flea feeding on a dog, and a tapeworm feeding on a human are all examples of parasitism.
Question: What are agrochemicals? Name three agrochemicals and explain their effects on the environment.
Ans: Agrochemicals are chemical products that are applied to crops to increase crop yields, improve plant nutrition, and safeguard crops from pests, weeds, and diseases. Three typical agrochemicals include:
1. Herbicides: Herbicides are substances that are used to eradicate or stop the growth of undesirable plants. Herbicides can be extremely harmful to the environment and may contaminate groundwater, soil, and air, although they are excellent at eradicating weeds.
2. Fungicides: Chemicals used to prevent fungal diseases in crops are known as fungicides. They can build up in the soil, water, and food and can be poisonous to helpful organisms.
3. Pesticides: Chemicals known as pesticides are used to manage insects and other pests that eat crops. They have been connected to human health issues including cancer and can harm the environment.
Section – B
Question: List three differences between self and cross-pollination.
Ans: 1. Cross-pollination happens when pollen from one flower’s anther is transmitted to the stigma of another flower, whereas self-pollination happens when pollen from one flower’s anther is transferred to the stigma of another flower.
2. Self-pollination normally results in offspring that share the same genetic makeup as the parent, but cross-pollination frequently results in offspring that have a wider genetic diversity.
3. Self-pollination requires less distance for the pollen to travel, it is frequently more effective than cross-pollination. But because it leads to increased genetic variation, Cross-pollination is regarded to be better for the health of the plant.
Question: Differentiate between co-dominance and incomplete dominance in tabular form.
Ans: Co-dominance is a type of gene expression in which the phenotype exhibits an equal expression of both alleles.
When the offspring’s phenotype combines the phenotypes of the parents, this is referred to as incomplete dominance. Usually, the offspring’s phenotype is a combination of its parents’ two phenotypes. In the case of the flower snapdragon, the progeny may have pink flowers if a red-flowered plant is crossed with a white-flowered plant.
Question: Explain briefly the idea of polygenic inheritance.
Ans: Polygenic inheritance is a system of inheritance in which more than one gene affects an organism’s phenotype; rather than just one gene. It serves as the foundation for many human characteristics, including height, body form, skin tone, eye colour, and hair and eye colour. The effects of the genes may be additive, in which case the phenotype is simply the total of each gene’s effects, or they may interact in more complicated ways.
Question: Explain three applications of tissue culture in plants.
Ans: 1. Plant propagation: Tissue culture is a popular method for plant propagation. Compared to conventional procedures, it is utilised to quickly make clones of a plant.
2. Plant breeding: Tissue culture can be utilised to swiftly and effectively produce a large number of plants with desirable features. This can be used to create new plant varieties with the traits you want.
3. Genetic engineering: Plants can be genetically modified via tissue culture. Plants with higher yields, disease resistance, enhanced nutritional value, and many other desired features can be produced using this method.
Section – C
Question: What is central dogma?
Ans: A theory that defines how genetic information moves from DNA to RNA to proteins is the core dogma of molecular biology. It claims that transcription is the initial step in converting the data stored in DNA into messenger RNA (mRNA). After that, the mRNA is translated into proteins using the translation process. The information does not pass from DNA to proteins and vice versa in this unidirectional genetic information flow.
Question: What are Bt. crops? List one Bt. crop.
Ans: Crops that have been genetically altered to produce proteins from the soil bacterium Bacillus thuringiensis are referred to as Bt. crops (also known as Bt. transgenic crops) (Bt.). Toxic to some insect species, these proteins act as a natural pesticide. Bt corn, which has been altered to produce the Bt protein Cry1Ab, is one example of a Bt crop.
Question: Explain briefly the energy flow in the ecosystem.
Ans: When energy is transferred from one organism to another, this is known as energy flow in ecosystems. Through the food chain, this energy moves from producers like plants that turn sunlight into energy to primary consumers like herbivores who then consume it before passing it on to secondary consumers like carnivores. Additionally, energy is lost along the route during procedures like respiration and excretion, and finally, it escapes into the environment as heat. Ecosystems can maintain their balance and health thanks to this energy flow.
Question: What are biosphere reserves?
Ans: Terrestrial and coastal habitats are protected in biosphere reserves so they can be preserved and used sustainably. They are recognised by the United Nations Educational, Scientific, and Cultural Organization (UNESCO) and are meant to encourage the preservation of biological diversity and the sustainable use of natural resources. Local governments, international organisations, and other groups are among the many stakeholders involved in these reserves. They typically consist of core protected areas, buffer zones, and transition zones where tasks like study, observation, and public outreach are carried out.
Section – D
(i) The dihybrid ratio of 9:3:3:1 proves the law of……
Ans: Mendelian Inheritance.
(ii) Ecology is the study of :
(a) Organism and environment
(b) Man and environment
(c) Soil and water
(d) Husband and wife
(iii) Name two bioherbicides.
Ans: 1. Bacillus subtilis 2. Trichoderma harzianum
(iv) Name the most commonly used bio-weapon.
Ans: Anthrax is the most commonly used bio-weapon.