CBSE 12 Biology Question Paper-2023 Set-1

A human ovum completes its second meiosis :

Choose the option that gives the correct number of pollen grains that will be formed after 325 microspore mother cells undergo microsporogenesis.

Given below are two columns. In Column I the names of four contraceptive devices are given and in Column II the modes of action of the contraceptives are given. Select the option where the contraceptive devices are correctly matched with their respective modes of action. Column I (Contraceptive devices) P. Lippes loop Q. Multiload 375 R. Subcutaneous Norplant S. Saheli Column II (Modes of action) i. Inhibition of ovulation ii. Phagocytosis of sperms in uterus iii. Causes thickening of cervical mucous iv. Makes cervix hostile to sperms

The first gene-sequenced crop is :

Identify the region 'X', the factor 'Y' and the enzyme 'Z' involved in the process of transcription in prokaryote as shown in the schematic representation given below.

Three genes R, S and T are located on the same chromosome. If the recombinant percentage between R and S is 20%, R and T is 35% and S and T is 15% respectively, can you predict the correct order of these genes on the chromosome? Which of the following shows the correct sequence of the genes on the chromosome?

The graph plotted below is based on the data collected by biology students with respect to the levels of oxygen at the specific points in the river flowing outside their city. Which point in the graph indicates the entry of untreated sewage in the river?

The status of the human population reflected in the human age pyramid given below is:

Which one of the following products was produced as a result of DNA manipulation in the first transgenic cow 'Rosie'?

Which one of the following processes results in the production of recombinants in future generations?

Given below are two columns. In Column I is the list of four enzymes and in Column II is the list of functions of the given enzymes. Which one of the following options shows the enzymes matched with their respective functions correctly? Column I (Enzyme) P. DNA ligase Q. Restriction exonuclease R. Taq polymerase S. Restriction endonuclease Column II (Function) i. Removes nucleotides from the ends of DNA ii. Extends the primer on DNA template iii. Joins DNA fragments iv. Cuts DNA at specific sites

The first clinical gene therapy was given to a four-year-old girl with:

Which of the following is true with respect to the process of polymerisation of DNA?

Name the phase of cell cycle when DNA replicates:

Which of the following is an example of an incomplete dominant trait?

When a DNA molecule with heavy nitrogen (N15) is replicated in a medium containing normal nitrogen (N14), what will be the composition of the DNA molecules after two generations?

The principle of gene therapy is to:

A student finds a plant whose flowers are brightly coloured and fragrant, and which produces a large amount of nectar. The student can conclude that this plant is pollinated by:

A couple has three daughters. The probability of them having a boy as a fourth child is:

The technique of growing plants in a nutrient solution, without soil, is known as:

Which of the following is a vestigial organ in humans?