SECTION E

Question 31: (a)

(i) How and why is charging of tRNA essential in the process of translation?

(ii)  State the functionof the ribosome as a catalyst in bacteria during the process of translation.

(iii) Explain the process of binding of ribosomal units to mRNA during

(b) Describe the dihybrid cross upto F2 generation as conducted by Gregor Mendel using pure lines of Garden Pea for characters seed shape and seed colour.

Answer:

(i)The process of activating the inactive amino acids and addition of the activated amino acid to their cognate tRNA is called charging of tRNA. During the charging process, the inactive amino acids in the cytoplasm of a cell are activated in the presence of ATP and is added to the cognate tRNA. This is a crucial step that occurs during the first phase of the translation process because the high energy bond between tRNA and amino acid is used at a later stage in protein synthesis to link the amino acid covalently to the growing polypeptide chain.                                                              

(ii) Ribosomes are made up of structural RNAs and several proteins. One such structural RNA known as 23S rRNA acts as a catalyst in bacteria and is known as the enzyme- ribozyme. It helps in the formation of peptide bonds.                                                                             

(iii) Ribosome exists as two subunits (a large and a small subunit), in its inactive state. When the small subunit encounters an mRNA, the process of translation of the mRNA to protein begins. There are two sites in the large subunit, for subsequent amino acids to bind to and thus, be close enough to each other for the formation of a peptide bond.

(b) The traits in consideration are seed shape and seed colour. Following table shows the various dominant and recessive alleles for these traits.

Pure lines of Garden pea for the characters will have homozygous genotypes. Following is the depiction of the dihybrid cross performed by Gregor Mendel using seed colour and seed shape of the Garden pea as the trait.

In the parent generation, Mendel had performed the cross between homozygous parents (YYRR – yellow and round seeds, yyrr- green and wrinkled seeds). In the first generation, he obtained offsprings which were all heterozygous and exhibited the dominant trait (yellow and round seeds). He performed selfing of the heterozygous offspring.

In the F2 generation he obtained the following ratios:

• Phenotypic ratio: 9:3:3:1
• Genotypic ratio: 1:2:1:2:4:2:1:2:1

Question 32: (a) Bioreactors are the containment vehicles of any biotechnology-based production process.For large scale production and for economicreasons the final success of the biotechnological process depends on the efficiency of the bioreactor.

Answer the following questions w.r.t the given paragraph:

(i)  List the operational guidelines that must be adhered to so as to achieve optimisation of the bioreactor system. Enlist any four.

(ii)  Mention the phase of the growth we refer to in the statement “Optimisation of growth and metabolic activity of the cells”.

(iii) Is the biological product formed in the bioreactor suitablefor the intended immediate use? Give reason in support of your answer.

(b)

(i) ‘EcoRI’ has played very significant role in r-DNA technology.Explain the convention for naming EcoR1. Write the recognition site and the cleavage sites of this restriction endonuclease.

(ii) What are the protruding and hanging stretchesof DNA produced by these restriction enzymes called? Describe their role in formation of r-DNA.

Answer:

(a)

(i)  The list of the operational guidelines that must be adhered to so as to achieve optimisation of growth of the bioreactor system are given below:

a) Monitoring and control of the optimal conditions for achieving the desired product by providing optimum growth conditions (temperature, pH, substrate, salts, vitamins, oxygen).

b) Maintain a sterile or aseptic environment.

c) Optimisation of mixing and aeration.

d) Regular cleaning and maintenance of the bioreactor.                           

(ii)  The phase of the growth referred to in the statement “Optimisation of growth and metabolic activity of the cells” is the exponential phase of growth.

(iii)  The biological product formed in the bioreactor is not suitable for the intended use immediately. It has to further undergo the down streaming process.

This is because the biological product may contain impurities which may hinder the functioning of the product or can cause harmful effects to the consumer. Also if the product is a drug, further clinical trials need to be conducted to ensure the safety and physiological effects of the drug before releasing it into the market.

(b) 

(i) The protruding and hanging stretches of DNA produced by EcoRI are called sticky ends. Sticky ends have over hanging stretches of nitrogenous bases which can pair with complementary bases. Hence, the DNA sequence of our interest which is digested by EcoRI can be ligated with specific vector DNA to create a recombinant DNA.

(ii) EcoRI restriction enzyme is isolated from the bacteria Escherichia coli RY 13 strain. Hence, the letter ‘E’ is derived from the first letter of the genus Escherichia and ‘co’ is derived from the species coli. The letter ‘R’ comes from the strain ‘E. Coli RY 13’. It is followed by a Roman letter ‘I’ as it was the first enzyme to be isolated from the given strain. The recognition site of EcoRI is a palindrome having 5′-GAATTC-3′ sequence. It introduces a cut between G and A nucleotides which creates sticky ends.

Question 33: (a) (i) Explain the monosporic development of embryo sac in the ovule of an angiosperm.

(ii) Draw a diagram of the mature embryo sac of an angiospermic ovule and label any four parts in it.                                                                                                                  

OR

(b) (i) Explain the formation of placenta after the implantation in a human female.

(ii) Draw a diagram showing human foetus within the uterus and label any four parts in it.

Answer:

(a) (i) The process of monosporic development of embryo sac in the ovule of an angiosperm can be divided as:

• Mitotic division of functional megaspore: The nucleus of the functional megaspore undergoes mitotic division to form two nuclei, forming a 2-nucleate embryo sac. This step is followed by two more sequential mitotic nuclear divisions, which result in the 4-nucleate and then the 8-nucleate stages of embryo sac.
• Cell wall formation: Out of eight nuclei, cell walls form around six nuclei and are organised into cells.
• Distribution of cells in embryo sac: The egg apparatus consisting of two synergids and one egg cell are grouped together at the micropylar end. The antipodals consisting of three cells are at the chalazal end. The two nuclei called the polar nuclei are located in the large central cell.

(ii) The labelled diagram of the mature embryo sac of an angiospermic ovule is given below:

(a)  (i) The placenta develops during the first three months of the pregnancy:

• After implantation, finger-like projections called chorionic villi appear on the trophoblast.
• This chorionic villi is surrounded by the uterine tissue and maternal blood.
• The uterine tissue and chorionic villi become interdigitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and maternal body. This structure is called placenta.        

(ii) The labelled diagram of human foetus within the uterus is given below

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