CBSE Class 12 Biology Solved Practice Paper for 2018 Board Exam: Set I
Class 12 Biology solved practice paper for CBSE board exam 2018 is available here. This solved paper contains important questions of NCERT textbook and NCERT Exemplar. These questions are expected to be asked in CBSE Class 12 Biology board exam 2018.
Completely solved paper for Class 12 Biology board exam 2018 is available here. This paper based on latest CBSE Class 12 Biology Syllabus and most of the questions given in this paper are from NCERT Textbook and NCERT Exemplar. There is a high probability that these questions might be asked in Biology board exam 2018. This paper is scheduled to be held on 27 March 2018.
General Instructions for the paper:
(i) There are a total of 26 questions and five sections in the question paper. All questions are compulsory.
(ii) Section A contains questions number 1 to 5, very short-answer type questions of 1 mark each.
(iii) Section B contains question number 6 to 10, short-answer type I questions of 2 marks each.
(iv) Section C contains question number 11 to 22, short-answer type II questions of 3 marks each.
(v) Section D contains question number 23, value based question of 4 marks.
(vi) Section E contains question number 24 to 26, long-answer type questions of 5 marks each.
Some questions and their solutions from the solved paper are given below:
Question: Although potato tuber is an underground plant part, it is considered as a stem. Mentions two reasons.
The two reasons are:
(a) The tuber has nodes and internodes.
(b) Leafy shoots appear from the nodes.
Question: Name the part of gynoecium that determines the compatible nature of pollen.
Question: Name the common function that cotyledons and nucellus perform.
Question: Which are the three cells found in a pollen grain when it is shed at the three-celled stage?
One vegetative cell and two male gametes.
Question: Name the common function that cotyledons and nucellus perform.
Question: Suggest four important steps to produce disease resistant plant through conventional plant breeding technology.
1. Selection of parent plants with desired combination of characters.
2. Hybridization of selected parent plants to obtain progeny carrying the desired characters of both parent plants.
3. Selection of superior recombinant offspring.
4. Testing of selected recombinants followed by their release for commercial production.
Question: Name a genus of baculovirus. Why they are considered good biocontrol agents?
Nucleopolyhedrovirus. Being species specific selective and narrow spectrum biocontrol agents, these viruses do not exert any harmful impact on crops, animals and human and non target insects. For example, Nucleopolyhedrovirus targets mainly moths and butterflies.
Question: Comment on the RCH programme of the government to improve the reproductive health of the people.
Creating public awareness regarding reproduction related aspects and providing facilities to build up a healthy society with added emphasis on the health of mother and child are the basic aims of the RCH programmes.
Question: In order to obtain the F1 generation, Mendel pollinated a true-breeding, say, tall plant with a true-breeding dwarf plant. But for getting the F2 generation, he simply self-pollinated the tall F1 plants. Why?
Genotype of 50% of the offspring would resemble one parent and the rest the other parent. All the F1 offsprings of the cross are heterozygous so allowing self pollination is sufficient to raise F2 offspring. Also he intended to understand the inheritance of the selected trait over generations.
Question: Sometimes cattle or even human beings give birth to their young ones that have extremely different sets of organs like limbs/position of eye(s) etc. Why?
There is a disturbance in co-ordinated regulation of expression of sets of genes associated with organ development.
Question: Describe the role of Agrobacterium tumefaciens in transforming a plant cell.
Agrobacterium tumefaciens harbours a mega plasmid called Ti-plasmid. This has a T-DNA region flanked by left border and right border sequence. The T-DNA gets transferred and integrates with the host plant DNA. This property of Ti-plasmid has been exploited for cloning of gene of interest and stably integrating them in the plant genese. Therefore, by using Ti-plasmid or its derivatives, recombinant plant cells with desired genes of interest stably integrated in the plant genome has been successfully produced.
Question: How can we improve the success rate of fertilisation during artificial insemination in animal husbandry programmes?
The technology is called MOET or Multiple Ovulation Embryo Transfer. During the procedure, a cow is given hormonal treatment so that more than one ovule (6-8 eggs) is produced per cycle. After mating or artificial insemination the embryos at 8-32 celled state are transferred to different surrogate mother cows. The method has been successfully used for cattle, sheep, buffalo etc.
Question: Suggest two features of plants that will prevent insect and pest infestation
(i) increasing hair growth on aerial parts of plants.
(ii) Rendering the flowers nectar less.
(iii) Enabling plants to secrete insect killing chemicals (toxins)
Question: (a) State the cause of depletion of ozone layer.
(b) Specify any two ill-effects that it can cause in the human body.
(a) Ultraviolet radiations act upon chlorofluorocarbons (CFCs) releasing Cl atoms in the stratosphere. These Cl atoms combine with O3 and degrade it.
(b) Ill-effects of Ozone Depletion:
(i) UV-B damages DNA and proteins of living organisms causing mutation.
(ii) It causes skin aging, skin cell damage and skin cancers.
Question: What would happen if histones were to be mutated and made rich in amino acids aspartic acid and glutamic acid in place of basic amino acids such as lysine and arginine?
If histone proteins were rich in acidic amino acids instead of basic amino acids then they may not have any role in DNA packaging in eukaryotes as DNA is also negatively charged molecule. The packaging of DNA around the nucleosome would not happen. Consequently, the chromatin fibre would not be formed.
Question: Embryo sacs of some apomictic species appear normal but contain diploid cells. Suggest a suitable explanation for the condition.
It is true that many apomicts posses normal looking embryo sacs. The only possibility of the embryo sac possessing diploid cells is due to failure of meiotic division at the megaspore mother cell stage. Since, the megaspore mother cell has a dipoid nucleus, if it undergoes mitosis instead of meiosis, all the resulting nuclei and cells will be diploid in nature.
Question: What role does pituitary gonadotrophins play during follicular and ovulatory phases of menstrual cycle and also explain the shift in steroidal secretions.
Menstrual cycle is regulated by hypothalamus through the pituitary gland. At the end of menstrual phase, the pituitary FSH gradually increases resulting in follicular development within the ovaries. As the follicles mature, Estrogen secretion increases resulting in a surge in (FSHe and LH) The surge of LH15 responsible for ovulation. LH also gonadotropins induces luteinisation. This leading to the formation of corpus luteum. Corpus luteum secretes progesterone and source estrogen which help in maintaining the interine endometrium for implantation.
Question: Why are coral reefs not found from West Bengal to Andhra Pradesh but found in Tamil Nadu on the east coast of India?
High salinity, optimal temperature and less siltation are essential to colonise corals. If siltation and fresh water inflow are very high, the corals don’t colonise. In contrast when the siltation and fresh water inflow by the rivers are very less, the coral do colonise.
Other important questions and solutions are available in the PDF.