Botany: Solved Previous Year’s Question Paper for NCERT/CBSE  Class 12th Botany Paper Code (RKDO18 —–20303-X)

 (Long Answer Type Questions) 

Question: State the principle of independent assortment. Explain the same with dihybrid cross. 

Ans: The principle of independent assortment states that the segregation of one pair of alleles during meiosis is independent of the segregation of another pair of alleles. In other words, the alleles of one gene do not influence the alleles of another gene.

For example, in a dihybrid cross, you would have two traits, each with two alleles. For example, if we used the traits of seed shape (round or wrinkled) and seed color (yellow or green), then the dihybrid cross would consist of four alleles. The principle of independent assortment states that the alleles of seed shape and seed color would be sorted and passed on independently to the offspring. In other words, the allele for round seed shape would be sorted independently of the allele for yellow seed color.

Question: (i)What is primary productivity ? 

(ii) Why does it vary in different ecosystems ? 

(ii) State the relationship between gross and primary productivity. 

Answer: (i) Primary productivity is the rate at which energy is converted into organic matter by living organisms such as plants within an ecosystem.

(ii) It varies in different ecosystems due to the availability of resources, environmental factors such as temperature and light intensity, and the presence of other organisms.

(iii) The relationship between gross and primary productivity is that gross productivity is the total amount of energy produced by an ecosystem, while primary productivity is the amount of energy converted into organic matter. Gross productivity is the sum of all primary production, as well as respiration processes such as decomposition and consumption.

Question: State the function of a reservoir in a nutrient cycle. Explain the simplified model of carbon cycle in nature. 

Answer: A reservoir in a nutrient cycle is a location where nutrients are stored in large amounts. Reservoirs play a crucial role in cycling of nutrients through an ecosystem, as they act as a storehouse that can supply nutrients during times of scarcity or when they are in high demand. For example, in the carbon cycle, reservoirs such as the atmosphere, oceans, and living organisms store carbon in large volumes.

 The simplified model of the carbon cycle in nature involves the following steps:

1. Carbon dioxide is taken in by plants through photosynthesis and stored in their tissues.

2. Animals consume plants and store the carbon in their bodies.

3. When animals die, their bodies decompose and release carbon dioxide back into the atmosphere, which completes the cycle.

4. Carbon dioxide can also be released by burning fossil fuels and other human activities.

5. Eventually, carbon dioxide is taken back up by plants and the cycle continues.

(Short Answer Type Questions) 

Question: What do you mean by population interaction? Differentiate between: (i) Mutalism and Competition 

(ii) Parasitism and Predation 

Answer: Population interaction is the interaction between populations of different species living in the same habitat. This includes interactions such as competition, predation, parasitism, and mutualism.

(i) Mutualism is a type of population interaction where two different species interact in a positive way and both benefit from the interaction. An example of this is the relationship between pollinators and flowering plants.

 Competition is a type of population interaction where two different species compete for the same resources. An example of this is two different species of fish competing for food in the same body of water.

(ii) Parasitism is a type of population interaction where one species benefits at the expense of the other. An example of this is the relationship between a tick and a mammal.

Predation is a type of population interaction where one species hunts and consumes another species. An example of this is a lion hunting and killing an antelope.

 (Very Short Answer Type Questions) 

Question: What are the harmful effects of ozone depletion in stratosphere dr living organisms ? 

Answer: Ozone depletion in the stratosphere can have a number of harmful effects on living organisms. One of the most serious effects is an increase in the amount of ultraviolet radiation that reaches the Earth’s surface. This is because ozone in the stratosphere acts as a shield, preventing dangerous UV radiation from reaching the surface. In addition to increasing the risk of skin cancer and other forms of skin damage, increased UV radiation can also cause genetic damage to plants and animals, which can lead to long-term health consequences for both humans and other species. Ozone depletion can also cause changes in global climate patterns, with potentially negative impacts on food production, ecosystems, and human health.

Question: What is the function of histones in DNA packaging? 

Answer: Histones are proteins that help package and organize DNA in the nucleus of eukaryotic cells. They act like spools around which the DNA winds, allowing it to fit into a much smaller space. Histones also help regulate gene expression by controlling access to DNA, as well as providing a structural scaffold for proteins that modify chromatin structure.

Question: Reteroviruses do not follow central dogma. Comment. 

Answer: Retroviruses are unique in that they are able to reverse transcribe their genetic material from RNA to DNA, which is then integrated into the host cell’s genome. This is an example of an exception to the central dogma of molecular biology, which states that genetic information flows from DNA to RNA to protein.

 (Objective Type Questions) 

Question: (i) Define hot spot. 

Ans: Hot spots are areas of high biodiversity, defined as areas that contain a large number of species and a high degree of endemism (species which are only found in that region).

(ii) Organization responsible for maintaining red data book is: 

(a) IUCN 

(c) CITES 

 (b) WWP 

(d) IBWL 

Answer: (a) IUCN

(iii) Bl-toxin is: 

(a) Intracellular lipid 

(b) Intracellular crystalline protein 

(c) Extracellular crystalline protein 

(d) Glycoprotein 

Answer: (c) Extracellular crystalline protein

(iv) Which of the following is not biofertilizer ? 

(a) Nostoc 

(b) Mycorrhiza 

 (c) Agrobacterium 

 (d) Rhizobium 

(a) Nostoc

 (v) In typical embryo soul the nuclei are arranged as: 

(a) 3 + 2 + 3 

(b) 3 + 3 + 2 

(c) 2 + 3 + 3 

(d) 2 + 4 + 2 

Answer: (c) 2 + 3 + 3

(Long Answer Type Questions) 

Question: What do you mean by semiconservative mode of replication? Explain the mechanism of same with suitable diagrams.

Ans: Already discussed 

(Short Answer Type Questions) 

Question: How does pollen mother cell develop into mature pollen grain ? Illustrate the stages with well labelled diagram

Ans: Already discussed 

Question: Define Apomixes. Explain its significance. How can it be commercially used ?

Ans: Already discussed 

Question: State the importance of Biofortification.

Ans: Already discussed 

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