Test Yourself For CBSE Class XII Board 2024: Solve Class XII Biology Questions From Previous SQPs

CBSE Class XII Boards is around the corner. This is surely the time to focus rather than panicking. Concentrate on studies, and you will definitely achieve your goal.

At this time, constant revision of what you have studied is crucial. The questions below will test your preparedness level, and also give an idea of the kind of questions that may be asked.

The following questions of Class 12 Biology have been taken from past sample questions papers of CBSE so, rest assured about the authenticity. The answers have been provided at the end.

Q1. The figure below shows the structure of a plasmid:

CBSE Sample Question Paper 2022-23

A foreign DNA was ligated at BamH1. The transformants were then grown in a medium containing antibiotics tetracycline and ampicillin. Choose the correct observation for the growth of bacterial colonies from the given table:
(1 mark)

Q2. In a certain species of insects, some have 13 chromosomes, and the others have 14 chromosomes.The 13 and 14 chromosome bearing organisms are:
(1 mark)
a) males and females, respectively
b) females and males, respectively
c) all males
d) all females

Q3. Name the technique by which Gene expression can be controlled with the help of RNA molecule.
(1 mark)

Q4. The prophase I stage of meiosis plays a vital role in r-DNA formation. Justify with reason.
(1 mark)

Q5. The graph given below indicates the administration of the first (L) and second dose (M) of a vaccine. The corresponding response of the body is indicated by X and Y. Interpret the graph and explain the reason for such a response shown by the body:
(2 marks)

CBSE Sample Question Paper 2023-24

Q6. Why does the lac operon shut down some time after the addition of lactose in the medium where E.coli was growing? Why low level expression of lac operon is always required?
(2 marks)

Q7. In the figure given below, parts A and B show the level of hormones which influence the menstrual cycle. Study the figure and answer the questions that follow:
(2 marks)

CBSE Sample Question Paper 2022-23

(a) Name the organs which secrete the hormones represented in parts A and B.

(b) State the impact of the hormones in part B on the uterus of the human female during 6 to 15 days of menstrual cycle?

Q8. Suggest and explain the assisted reproductive techniques which will help a couple to have children, where the female had a blockage in the fallopian tube and the male partner had a low sperm count.
(3 marks)

Q9. Give three reasons as to why the prokaryotes are not given any figures for their diversity by the ecologists.
(3 marks)

Q10. Oil spill is a major environmental issue. It has been found that different strains of Pseudomonas bacteria have genes to break down the four major groups of hydrocarbons in oil. Trials are underway to use different biotechnological tools to incorporate these genes and create a genetically engineered strain of Pseudomonas - a ＆super-bug＊, to break down the four major groups of hydrocarbons in oil. Such bacteria might be sprayed onto surfaces polluted with oil to clean thin films of oil.?
(5 marks)

(a) ?List two advantages of using bacteria for such biotechnological studies?

(b) For amplification of the gene of interest PCR was carried out. The PCR was run with the help of polymerase which was functional only at a very low temperature. How will this impact the efficiency of the PCR? Justify.

(c) If such bacteria are sprayed on water bodies with oil spills, how will this have a positive or negative effect on the environment? Discuss.

ANSWERS

Ans 1.
(b) No growth, growth

Ans 2.
a) males and females, respectively

Ans 3.
RNA interference

Ans 4.
The prophase I stage of meiosis plays vital role in r-DNA formation because crossing over occurs at this stage which helps in recombination.

Ans 5.
On administration of the first dose of the vaccine (L), the body shows a response of low intensity (X) as the immune system comes in contact with the antigenic protein of the weakened/inactivated pathogen for the first time. This is called primary immune response.

On subsequent encounter with the same antigenic protein in the second dose (M), the body elicits a highly intensified secondary response (Y). Because of the memory of the first contact with the antigen, the secondary immune response is faster and stronger, leading to more effective pathogen elimination in comparison to the primary immune response.

Ans 6.
After addition of lactose, complete breakdown of lactose to glucose and galactose takes place. Therefore, there is no more lactose to bind to the repressor protein and the lac operon shuts down.

A very low level of expression of lac operon has to be present in the cell all the time, otherwise lactose cannot enter the cells.

Ans 7.
(a) A 每Pituitary gland; B: Ovary
(b) Endometrium of the uterus regenerates through proliferation.

Ans 8.
As the male partner is suffering from low sperm count, Intracytoplasmic sperm injection technique should be used to directly inject sperm into the ovum.

As the female partner is having blockage in the fallopian tube, In vitro fertilization, followed by embryo transfer (ET) will help her conceive. In this case, sperms from the male partner will be collected and injected into the ovum of the female partner to form zygote under simulated conditions in the laboratory and embryo with more than 8 blastomeres will be transferred into the uterus IUT 每 intra uterine transfer, to complete its further development.

Ans 9.
Prokaryotic organisms＊ diversity is not given any figures by ecologist because of following reasons.

• Classification and identification of vast diversity of microbes is very difficult and cannot be efficiently done with use of currently available methods.
• For many microorganisms, it is difficult to culture them under laboratory condition.
• According to current biochemical and molecular techniques, it is estimated that microbes diversity can range in billions with microbes inhabiting diverse habitat on earth, with enormous diversity present in air, water and soil. Hence, more advanced molecular and biochemical techniques are needed to classify and identify this enormous diversity of microbes.

Ans 10.

(a) You can easily grow a large quantity of the bacteria/no ethical issues/have plasmids/ can easily transform (any 1)

(b) PCR will not amplify the gene. (? Mark) If the polymerase enzyme denatures at low temp, it will not be able to withstand high temperature which is essential for separating/opening/unwinding/ denaturing DNA strand to open. Thus subsequent step of extending the primers using the nucleotides provided in the reaction and the genomic DNA as template will not occur.

(c) Positive effect: oil spills can be treated and the environment becomes better/ cleaner/ water becomes more potable/ safe for aquatic forms/ safe for water birds like sea gulls. (any one 1)

Negative effect: the bacteria can mutate/ can harm other organisms/ can conjugate with other non-virulent forms and make them super bugs with detrimental effect/ unpredictable/ for a longer duration it may reduce the dissolved oxygen and leading to mortality of aquatic organisms (any one 1)

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