List of top Biology Questions asked in CBSE CLASS XII

State any two criteria for determining biodiversity hotspots
Name the main type of antibody produced by the immune system in response to this disease.
Which two main inflammation-causing chemicals are produced by the mast cells in such an immune response?
Many children in the metro cities are suffering from a very common exaggerated response of the immune system to certain weak antigens in the air. (i) What is the term used for the above mentioned disease?
Expand PID. Name any two common viral infections transmitted through sexual contact in human females.
Arrange the given important steps of decomposition in their correct order of occurrence in the breakdown of complex organic matter and explain the fourth step in the process.
\( \fbox{Catabolism}\) \(\fbox{Leaching} \fbox{Fragmentation} \fbox{Mineralisation} \fbox{Humification}\)
Assertion (A): In some species of asteraceae and grasses, seeds are formed without fertilization.
Reason (R): Formation of fruit without fertilization is called parthenocarpy.
The animals that evolved into the first amphibians during evolutionary history were:
Assertion (A): In humans, filariasis is characterized by inflammation of the lower limbs.
Reason (R): Filarial worm usually lives in the lymphatic vessels of the lower limbs.
Assertion (A): Isolated single cells can be fused to produce somatic hybrids.
Reason (R): Cells selected for somatic hybridisation have desirable characters.
Bacteria growing anaerobically on cellulosic material produce large amounts of which gases? Select the correct option.
If a natural population of 60 individuals is in Hardy-Weinberg equilibrium for a gene with two alleles B and b, with the gene frequency of allele B of 0.7, the genotype frequency of Bb will be:
Human Immunodeficiency Virus is a member of the group of viruses known as:
Given below are few statements with reference to the human male reproductive system:
1. Paired seminal vesicles, prostate gland and bulbourethral gland constitute the male accessory glands.
2. Secretions of the male accessory glands constitute the seminal plasma.
3. Secretions of the bulbourethral glands help in the lubrication of the penis.
4. Enlarged end of the the penis is known as foreskin.
5. Seminal plasma is rich in fructose, calcium and certain enzymes.
Choose the option with all true statements from the given options:
Inheritance of which of the following traits is shown in the cross given below?

Autosomal recessive trait

Choose the correct option from the following:
Some of the important goals of HGP are given below. Choose the correct goal of HGP.
In a DNA, the percentage of thymine is 20. What is the percentage of guanine in it?
Select the statements that are true for the embryo of the flowering plants from the given options:
1. The zygote forms a proembryo and subsequently heart-shaped, globular and mature embryo.
2. Most zygotes divide to form embryo only after a certain amount of endosperm is formed.
3. The embryo develops at the micropylar end of the embryo sac.
4. A typical dicotyledonous embryo consists of an embryonal axis and a scutellum.
Choose the correct option from the following:
When a pure tall pea plant (\textit{Pisum sativum}) with green pod is crossed with a dwarf pea plant with yellow pod, how many dwarf pea plants, out of 16, will be produced in the F\textsubscript{2 generation?}

Assertion (A): Streptococcus pneumoniae and \(\textit{Haemophilus influenzae}\) are responsible for causing infectious disease in human beings. 
Reason (R): A healthy person acquires the infection by inhaling the aerosols released by an infected person.

If Meselson and Stahl’s experiment is continued for 80 minutes (till III generation), then what would be the ratio of DNA containing \( N^{15}/N^{15} : N^{15}/N^{14} : N^{14}/N^{14} \) in the medium?

Study the items of Column-I and those of Column-II:

Choose the option that correctly matches the items of Column-I with those of Column-II:

Which of the following features correctly show the mechanism of sex-determination in honey-bees?
(i) A zygote formed from the union of a sperm and an egg develops into a male.
(ii) Males have half the number of chromosomes as that of females.
(iii) The females are diploid having 32 chromosomes.
(iv) Males have a father and can produce sons.
Choose the correct option:
In molecular biology, who proposed that genetic information flows in one direction?

Which one of the following options shows the correct evolutionary order of the plants mentioned below?
(i) Fern
(ii) Ginkgo
(iii) Zostrophyllum
(iv) Gnetales