Class XII – Biology – Paper – 1

Ans. c) 10%

Ans. c) Exponential growth

Ans. b) All of these

Ans. c) LNG-20

Ans. c) Embryonic stem cells

Ans. d) Symbiosis

Ans. d) The two genes are linked and present on the same chromosome

Ans. c) A-electrodes, B-NH₃ + H₂ + H₂O +CH₂, Ccold water, D-vacuum, E-U trap

Ans. b) Detritus is rich in lignin and chitin.

Ans. b) The parents are heterozygous

Ans. d) Biological response modifier

Ans. d) Blunt ends

Ans. b) Both A and R are true but R is not the correct explanation of A.

Ans. a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

Ans. c) A is true but R is false.

Ans. b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

Ans. No, as GMO may pose some threat to environment or living organism. I will ask her to approach GEAC as GEAC is responsible for approval of proposals relating to release of genetically engineered organisms and products into the environment including experimental field trials. 

Values

• Sense of responsibility.

• Understanding.

Ans. Valine: GUU, Proline: CCU

Ans. Nucleotides of DNA strand: TAC AAA TAC GGA CAA AGA ATT

Ans. UAA: Stop

Ans.

Synergids and egg cell are the components of egg apparatus.

Ans. A- Leydig’s cell

B- Sertoli cell

C- Spermatogenesis (Formation of sperms)

D- Spermiogenesis (Transformation of spermatid into sperm)

Ans. Bacillus thuringiensis produces an endotoxin which when ingested and released in the gut of the larvae of insect pest disrupts its gut lining and thus caterpillars are killed. By killing the caterpillars, it helps in pest control.

Ans. Lactic Acid Bacteria (LAB) or Lactics constitute a diverse group of microorganisms associated with plants, meat, and dairy. They are used in the manufacture of dairy products such as acidophilus milk, yogurt, buttermilk, and cheeses.

Role of LAB in human stomach:

lactic acid bacteria have a number of well-established benefits. They can improve lactose digestion, play a role in preventing and treating diarrhea and act on the immune system, helping the body to resist and fight infection. It play a very beneficial role in checking disease-causing microbes

Ans. Out of 64 codons 61 code for amino acids and rest 3 codons do not code for any amino acids. These function as stop codons.

Ans. Unambiguous and specific codon These code for only one amino acid, thus, making the genetic code unambiguous and specific e.g. UUU

Ans. Some amino acids are coded by more than one codon, so the code is degenerate, e.g. serine is coded by 6 codons.

Ans. The codon is nearly universal. Some exceptions to the rule are mitochondrial codon and in some protozoans, e.g. UUU.

Ans. Initiator codon AUG has a dual function. It codes for methionine and also acts as an initiator.

Ans. Test cross: A cross in which an individual with an unknown dominant phenotype is crossed with a recessive individual for that trait. So it is helpful in knowing the genotype (whether it is homozygous or heterozygous for the dominant trait) of an unknown individual.

Condition I: If the unknown is homozygous tall (TT) then crossing with dwarf recessive (tt) gives all tall offsprings (Tt).

Condition II: If the unknown is heterozygous tall (Tt), then crossing with dwarf results in 50% tall (Tt) and 50% dwarf (tt) progeny.

Ans. Commensalism: In ecology, commensalisms is a class of relationship between two organisms where one organism benefits but the other is unaffected.

Ans. Parasitism: It is a relationship between two organisms where the larger animal is at harm and the smaller animal is benefited.

Ans. Camouflage: Camouflage is a method of crypsis – avoidance of observation – that allows an otherwise visible organism or object to remain indiscernible from the surrounding environment through deception. The best example of camouflage is shown by the garden lizard which changes its colour as per its surroundings.

Ans. Mutualism: It is relationship between two organisms where both organisms are benefited. For example, some birds pick worms and insects from big animals skin to get food. This helps the bigger animal to get rid of insects and worms.

Ans. Interspecific competition: Interspecific competion, in ecology, is a form of competition in which individuals of different species compete for the same resource in an ecosystem (e.g. food or living space).

Ans. Deletion of the gene for ADA in an individual leads to ADA deficiency disorder Adenosine Deaminase (ADA) enzyme is crucial for immune system to function.

Ans. Gene therapy is helpful in the treatment of ADA deficiency. The treatment involves the following steps:

a. Lymphocytes from the blood of patient are grown on a culture outside the body.

b. A functional ADA, cDNA (using a retroviral vector) is then introduced into these lymphocytes.

c. Such genetically engineered lymphocytes are returned to the blood of patient.

d. Periodic infusion of such genetically engineered lymphocytes is required by the patient.

Ans. When we consider a large area to assess the species-area curve, we need to understand the advantages offered by the large areas. A larger area means more resources and a higher number of plants. This will provide more food to sustain more individuals. Thus, species richness increases with an increase in the explored area. This explains the occurrence of the steeper slope when we draw the species-area curve for a large area.

Ans. The term genetic diversity refers to the diversity of genes within a species. It is important for the following reasons:

(i) Greater the genetic diversity among organisms of a species, the more chances it has in surviving environmental perturbations.

(ii) Species with higher genetic variations tend to be more resistant to diseases. They also show greater adaptibility to changing environmental conditions. On the other hand, genetically uniform populations are highly prone to diseases and harsh environment.

Ans. During the pre-industrialisation all the white-winged moths survived due to white coloured lichens on trees, but during postindustrialisation, white-winged moths were unable to survive as predators could spot the moth against contrasting background, and the dark-winged moths survived, this showed that in a mixed population of white and dark-winged moths those who can adapt better will survive.

Ans. The excess use of herbicides and pesticides has resulted in the selection of resistant varieties that developed due to the chance or random mutation.

Ans. 1) (i) Brush your teeth every day, To keep the doctor away.

(ii) Take care of your body, it’s the only place you have to live.

2) Diseases like typhoid and amoebiasis.

Values

• Responsibility.

• Sensitivity towards public. Hygiene

• Problem solving.

Ans. The primary oocyte is a diploid cell whereas secondary oocyte is a haploid cell. The primary oocyte is formed when oogonia are at the prophase-I of the meiotic division in the foetal ovary whereas secondary oocyte is formed from primary oocyte after meiosis – I division to produce ova in females during the stage of puberty.

Ans. The secondary follicle is then transformed into a tertiary follicle characterized by antrum, which is a fluid-filled cavity. At this phase, the primary oocyte grows in size inside the tertiary follicle to complete the first meiotic division. The tertiary follicle finally transitions to form the Graafian follicle.

Ans. large number of primary follicles degenerate in females during the period from birth to puberty by the process called follicular atresia. As a result, about 60000-80000 primary follicles are left in each ovary at puberty.

Ans. After ovulation, the remaining cells of Graafian follicle are stimulated by LH to develop corpus luteum (an endocrine gland which secrete progesterone hormone).

Ans. Period of illness: The number of disease-causing microorganisms reaches its maximum during the period of illness so, there are maximum chances of a person transmitting a disease/infection at this stage.

Ans. Time period between infection and appearance of its symptoms is known as incubation period. AIDS/any other correct example T lymphocytes are attack by the pathogen of this disease.

Ans.

Ans. Period of illness

B lymphocytes/B cells produces antibodies.

Ans.

Ans. The three method of pollen transfer in plant are

1. Autogamy

2. Geitonogamy

3. Xenogamy

Ans. 1. Water lily: achieve successfully pollination by insects/wind.

2. Vallisneria: Female flowers on long stalks reach water surface male flowers or pollen released on water and carried by water current to female flowers to achieve pollination.

Ans. Genetic: Self-incompatibility/prevents self-pollen (same flower or other flowers of same plant) from fertilizing the ovules by inhibiting pollen germination, pollen tube growth in pistil. Physiological: Pollen release and stigma receptivity are not synchronized, either pollen matures earlier and stigma later or pollen matures later than stigma.

Ans. Ans. A functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter is called an operon. An operon is generally transcribed into polycistronic mRNA. A single mRNA which codes for more than one protein is called polycistronic mRNA. An operon is made up of 3 basic DNA components:

i. Promoter: A nucleotide sequence that enables a gene to be transcribed is called a promoter. It is recognized by RNA polymerase, which then initiates transcription.

ii. Operator: A segment of DNA to which a repressor binds is called the operator.

iii. Structural genes: The genes that are co-regulated by the operon are called structural genes. Inducible Operon: When the operon is regulated by an inducer, it is called an inducible operon. An inducer can switch on or off the operon. Lac operon is an example of an inducible operon. Lactose is a substrate of enzyme beta-galactosidase and is the inducer of the lac operon.

Ans. Process of transcription in Prokaryotes are as follows

DNA – dependent RNA polymerase that catalyses the process of transcription, three steps: initiation, elongation, and termination, Initiation: RNA polymerase binds to promoter, associated with initiation – factor ( ) at 5’ end of DNA, Elongation: nucleoside phosphates serve as substrate following the rule of complementarity, RNA polymerase help in opening the helix and continuous elongation, Termination: Terminator factor ( ), nascent RNA falls off along with RNA polymerase

Ans. In the above bacterial cell, i.e. A is plasmid B is chromosomal DNA. The plasmid is used as a vector in rDNA technology.

Ans. If the enzyme EcoRl acts on both linear DNA and plasmid DNA, each having three recognition sites, the restriction enzyme will generate 3 fragments from plasmid DNA (as it is circular) and 4 fragments from linear DNA.

Ans. Selection of recombinants due to inactivation of antibiotics is a laborious process as it requires:

i. a vector with two antibiotic resistance marker. ii. preparation of two kinds of media plate with one antibiotic each. Transformed cells are first plated on that antibiotic plate which has not been insertional inactivated (ampicillin) and incubated overnight for growth of transformants. For the selection of recombinants, these transformants are Replica plated on second antibiotic (tetracycline) plate (which got inactivated due to insertion of a gene). Non-recombinants grow on both the plates (one carrying ampicillin and the other carrying tetracycline) while recombinants will grow only on ampicillin plate. This entire exercise is laborious and takes more time (two overnight incubation) as well. However. if we choose the second option (insertional inactivation of a marker that produces colour in the presence of a chromogenic compound), we can distinguish between the recombinants and nonsubstrate recombinants on a single medium plate (containing one antibiotic and the chromogenic compound) after overnight growth.