CBSE(NCERT) GRADE 12 BIOLOGY 2024 SET1

During biological treatment of sewage, the masses of bacteria held together by fungal filaments to form mesh like structures are called

Which one of the following statements is correct in the context of observing DNA separation by agarose gel electrophoresis ?

A phenomenon where a male insect mistakenly identified the patterns of a orchid flower as the female insect partner, and tries to copulate and thereby pollinates the flower is said to be :

Identify the correct labellings in the figure of a fertilised embryo sac of an angiosperm given below :

Match the following genes of the lac operon listed in column ‘A’ with their respective products listed in column ‘B’:

Assertion (A): AIDS is a syndrome caused by HIV. Reason (R): HIV is a virus that damages the immune system with DNA as its genetic material. Select the correct option.

Assertion (A): In molecular diagnosis, single stranded DNA or RNA tagged with radioactive molecule is called a probe. Reason (R): A probe always searches and hybridises with its complementary DNA in a clone of cells.

Assertion (A): In birds the sex of the offspring is determined by males. Reason (R): Males are homogametic while females are heterogametic.

Assertion (A): Communities that comprise of more species tend to be more stable. Reason (R): A higher number of species results in less year to year variation in total biomass.

(a) “Farmers prefer apomictic seeds to hybrid seeds.” Justify giving two reasons. OR (b) Mention one advantage and one disadvantage of amniocentesis.

(a) 5' – G A A T T C – 3' 3' – C T T A A G – 5' Name the restriction enzyme that recognises the given specific sequence of bases. What are such sequence of bases referred to as ? (b) What are the arrows in the given figure indicating ? Write the result obtained thereafter.

Observe the population growth curve and answer the questions given below: (a) State the conditions under which growth curve ‘A’ and growth curve ‘B’ plotted in the graph are possible. (b) Mention what does ‘K’ in the graph represent.

Explain how are plants benefitted by their association with “Glomus species”.

If the base adenine constitutes 31% of an isolated DNA fragment, then write what will be the expected percentage of the base cytosine in it. Explain how did you arrive at the answer given.

Identify a, b, c, d, e and f in the table given below : Sl. No. Organism Bioactive Molecule Use 1. Monascus purpureus a b 2. c d Antibiotic 3. e Cyclosporin A f

Identify a, b, c, d, e and f in the table given below:

(a) Tropical regions harbour more species than the temperate regions. How have biologists tried to explain this in their own ways ? Explain.

(b) (i) What does an ecological pyramid represent ? (ii) The Ecological pyramids may have an ‘upright’ or an ‘inverted’ shape. Justify with the help of suitable examples.

(a) What are transgenic animals ? (b) Name the transgenic animal having the largest number amongst all the existing transgenic animals. (c) State any 3 reasons for which these types of animals are being produced.

If the cells in the leaves of a maize plant contain 10 chromosomes each, write the number of chromosomes in its endosperm and zygote. Name and explain the process by which an endosperm and a zygote are formed in maize.

(a) Why does DNA replication occur within a replication fork and not in its entire length simultaneously ? (b) “DNA replication is continuous and discontinuous on the two strands within the replication fork.” Explain with the help of a schematic representation.

Name the hormones and their source organ, which are responsible for menstrual cycle at puberty.

Explain the processing of heterogeneous nuclear RNA (hnRNA) into a fully functional mRNA in eukaryotes. Where does this processing occur in the cell ?

For successful pregnancy, at what phase of the menstrual cycle an early embryo (upto 3 blastomeres) should be implanted in the Uterus (IUT) of a human female who has opted for Assisted Reproductive Technology (ART) ? Support your answer with a reason.

The world is facing accelerated rates of species extinction largely due to human activities. Explain any three human activities responsible for accelerated rates of species extinction.

Name the hormone and its source organ responsible for the events occurring during proliferative phase of menstrual cycle. Explain the event.

In a human female, the reproductive phase starts on the onset of puberty and ceases around middle age of the female. Study the graph given below regarding menstrual cycle and answer the questions that follow : (a) Name the hormones and their source organ, which are responsible for menstrual cycle at puberty. 1 (b) For successful pregnancy, at what phase of the menstrual cycle an early embryo (upto 3 blastomeres) should be Implanted in the Uterus (IUT) of a human female who has opted for Assisted Reproductive Technology (ART) ? Support your answer with a reason. 1 (c) Name the hormone and its source organ responsible for the events occurring during p

In a human female, the reproductive phase starts on the onset of puberty and ceases around middle age of the female. Study the graph given below regarding menstrual cycle and answer the questions that follow :

In a normal human female, why does menstruation only occurs if the released ovum is not fertilised ? Explain.

Read the following passage and answer the questions that follow : “Mosquitoes are drastically affecting the human health in almost all the developing tropical countries. Different species of mosquitoes cause very fatal diseases so much so that many humans loose their life and if they survive, are unable to put in productive hours to sustain their life. With the result the health index of the country goes down.”

Name the form in which Plasmodium gains entry into (i) human body (ii) the female Anopheles body.

(a) (i) Draw a schematic diagram of the cloning vector pBR 322 and label (1) Bam HI site (2) gene for ampicillin resistance (3) ori (4) rop gene. (ii) State the role of rop gene. (iii) A cloning vector does not have a selectable marker. How will it affect the process of cloning? (iv) Why is insertional inactivation preferred over the use of selectable markers in cloning vectors?

Why do the symptoms of malaria not appear in a person immediately after being bitten by an infected female Anopheles ? Give one reason. Explain when and how do the symptoms of the disease would appear.

(a) (i) Draw a diagram of a human sperm. Label any four parts and write their functions. (ii) In a human female, probability of an ovum to get fertilized by more than one sperm is impossible. Give reason.

Explain the events which occur within a female Anopheles mosquito after it has sucked blood from a malaria patient.

(a) Natural selection operates in different ways in nature. (i) Identify the type of natural selection depicted in the graph above. (ii) In England after industrialisation, the population of dark winged moths were more favoured than white winged moth. Explain. (iii) Anthropogenic action can enhance the rate of evolution. Explain with the help of an example.

Name a species of mosquito other than female Anopheles and the disease, for which it carries the pathogen.

(b) (i) Name the nematode (scientific name) that infects the roots of tobacco plant and reduces its yield. (ii) Name the vector that is used to introduce nematode-specific genes into the host plant (tobacco). (iii) How do sense and anti-sense RNAs function? (iv) Why could parasite not survive in a transgenic tobacco plant?

(b) (i) With the help of labelled diagram only, show the different stages of embryo development in a dicot plant. (ii) Endosperm development precedes embryo development. Justify.

(b) (i) Why did Hershey and Chase use $^{35}S$ and $^{32}P$ in their experiment? Explain. (ii) State the importance of (1) blending and (2) centrifugation in their experiment. (iii) Write the conclusion they arrived at the end of their experiment.