CBSE(NCERT) GRADE 12 BIOLOGY 2025 SET1

proportion of bases in a double-stranded DNA ?

IUD used by females as contraceptive device is :

RNA was considered as the first genetic material. Out of the evidences listed below, point out the correct evidence :

Regulation of lac operon by repressor is referred to as which of the following type of regulation ?

Which of the following options is a Stop codon ?

chromosomes, i.e. 45 with XO is known as :

The bioactive molecules are matched with their source organism and functions. Select the incorrect pair :

Which one of the following exhibits ZW (female) and ZZ (male) chromosome type of sex-determination ?

Species which have diverged after origin from common ancestor giving rise to new species, adapted to new habitats and ways of life is called :

Which of the following given options serves as an inoculum in sewage treatment plants ?

Select the correct option about plasmid from the given options :

Assertion (A) : Pollen grains are well preserved as fossils. Reason (R) : Fossils are formed only from bones and teeth of animals.

Assertion (A) : The template strand has the polarity of 5' to 3' and sequences are same as RNA (except thymine at the place of uracil). Reason (R) : The strand that is referred to as coding strand does not code for anything.

Assertion (A) : Antibiotics are chemical substances, which are produced by some microbes and can kill or retard the growth of other disease-causing microbes. Reason (R) : All micro-organisms like fungi, bacteria, protozoans are used to produce antibiotics.

Assertion (A) : Single-stranded portions of RNA are known as sticky ends. Reason (R) : DNA fragments with the same kind of ligases.

(a) (i) What is the ploidy of primary spermatocytes and secondary spermatocytes ? (ii) Point out one difference in first meiotic division of spermatogenesis and oogenesis. OR (b) (i) Mention the function of trophoblast in the human embryo. (ii)

(a) How does polygenic inheritance show deviation from Mendelian inheritance ? OR (b) Explain briefly the two non-Mendelian patterns of inheritance that are observed in blood groups of humans.

How does polygenic inheritance show deviation from Mendelian inheritance?

Explain briefly the two non-Mendelian patterns of inheritance that are observed in blood groups of humans.

What function is performed by tears shed by our eyes ? Which type of barrier is this in the process of immunity ? Give another similar example.

Name and explain in brief one method which is used to introduce alien DNA into an animal cell and plant cell respectively.

(a) Describe the population logistic growth model and provide its equation. OR (b) Explain this process of decomposition of detritus till the formation of humus.

Describe the population logistic growth model and provide its equation.

Give any three adaptations found in wind-pollinated plants.

Describe the structure of the uterus wall and functions performed by any of its two layers.

What is a replication fork? How does it aid replication of long strands of DNA?

What is polymorphism in DNA? Give any two applications of DNA polymorphism.

Though baculoviruses are pathogens, they are used as biological control agents. Give three reasons why they are preferred.

Mention a method that can detect a pathogen at very low concentrations even when symptoms are not visible. Which two diseases are detected by this method?

Distinguish between predator and prey. Mention any two significant roles that predators play in nature.

Read the following passage and answer the questions that follow. In a given population, the frequency of occurence of alleles of a gene or a locus is supposed to remain fixed and even remain the same through generations. Hardy-Weinberg principle stated it using algebraic equations. Certain factors are known to affect Hardy-Weinberg equilibrium. These are gene migration, genetic drift, etc. When migration of a section of population to another place and population occur, gene frequencies change in the original as well as in the new population. Sometimes the change in allele frequency is so different in the new sample of population that they become a different species. (a) Define Hardy-Weinberg equilibrium. (b) What do you understand by Founder effect? (c) (i) Gene migration can affect Hardy-Weinberg OR (c) (ii) How can mutations result in evolution? Explain.

Read the following passage and answer the questions that follow. Generally all of us have been vaccinated at various ages according to a schedule. Certain vaccines are taken only once and yet protection is provided for a long time or even for a lifetime in some cases. (a) What name is given to such a type of immune response? Also name the property which is responsible for it. (b) What are the types of this immune response? Describe briefly. (c) (i) What are the special types of blood cells that help to achieve this type of immunity and how? OR (c) (ii) What is anamnestic response?

(a) The study of plants shows that: (i) Angiosperms or seed-producing plants have the widest distribution. Describe how the presence of seed is advantageous to angiosperms. Mention any three points. (ii) Differentiate between perisperm and pericarp. (iii) What is Polyembryony? Give an example.

(b) (i) Name the source of gonadotropins in human females. Explain the changes brought about in the ovary by these hormones during menstrual cycle. (ii) Name any two specific hormones which are produced by placenta only during pregnancy. (iii) Where are the stem cells located in the human embryo? What is their significance?

Describe five benefits of genetically modified organisms.

Describe the structure of Insulin. How does maturation of Insulin occur? What reaction can occur in a person who is given insulin from an animal source?

(a) (i) Explain with an example how mutualistic interaction involves co-evolution. (ii) What is endemism? Name any two hotspots found in India.

Differentiate between perisperm and pericarp.

What is Polyembryony ? Give an example.

Name the source of gonadotropins in human females. Explain the changes brought about in the ovary by these hormones during menstrual cycle.

Name any two specific hormones which are produced by placenta only during pregnancy.

Where are the stem cells located in the human embryo ? What is their significance ?

Explain with an example how mutualistic interaction involves co-evolution.

What is endemism ? Name any two hotspots found in India.

If the population density (N) at a particular time (t) is 500, what would the population density be at another specified time $(t+1)$ with the following data ? Natality = 100 Mortality = 50 Immigration = 300 Emigration = 250

Differentiate between in situ conservation and ex situ conservation.