CBSE Class 12th Biology Practice Paper Set 1

Salmonella typhi is the bacterium that causes typhoid fever. One of the diagnostic symptoms of typhoid fever is a sustained high fever. This means that the person affected by the disease will have a fever that lasts for a prolonged period of time without any significant fluctuations. Therefore, the correct answer is Salmonella typhi and sustained high fever.

The correct answer is Apis mellifera. This is the most common species of bees used in apiculture, also known as honey bee. Apis indica is not a commonly used species for apiculture.

The umbilical cord serves multiple functions during pregnancy. It supplies oxygen to the fetus, ensuring its proper development. It also delivers essential nutrients to the fetus, which are necessary for its growth. Additionally, the umbilical cord helps to withdraw blood that is rich in carbon dioxide and depleted in nutrients from the fetus, keeping it healthy. Therefore, all the given statements about the functions of the umbilical cord are correct.

BOD (Biochemical Oxygen Demand) is a measure of the amount of oxygen required by microorganisms to decompose organic matter in water. In polluted water, there is a higher concentration of organic pollutants, which leads to an increased demand for oxygen by microorganisms. Therefore, BOD is more in polluted water. On the other hand, potable water is treated to remove organic pollutants, resulting in a lower concentration of organic matter and a lower demand for oxygen. Hence, BOD is less in potable water.

Codominance is the correct answer because in the ABO blood group gene, both the A and B alleles are expressed equally and simultaneously in individuals who inherit both alleles. This means that both the A and B antigens are present on the surface of red blood cells, resulting in the AB blood type. This is different from complete dominance, where one allele is completely dominant over the other, and incomplete dominance, where a blend of the two alleles is observed. Epistasis refers to the interaction between different genes, which is not applicable in this case.

Cyanobacteria are known to be biofertilizers because they have the ability to fix atmospheric nitrogen into a usable form for plants. This process helps in increasing the fertility of the soil by providing a nutrient source for plants. Additionally, cyanobacteria also add organic matter to the soil through their growth and decomposition, further enhancing soil fertility. Therefore, the correct option is "They add organic matter to the soil and help in increasing its fertility."

The given answer is correct because all of the provided statements accurately describe the salient features of the double helix structure of DNA. The first statement mentions that the structure is composed of two polynucleotide chains with a sugar-phosphate backbone and bases projecting inside. The second statement states that the pitch of the helix is 3.4nm and there are approximately 10 base pairs in each turn. The third statement correctly states that nucleotides are linked together through phosphodiester bonds. Therefore, all of the above statements are true and describe the features of the double helix structure of DNA.

Banana is considered a good example of parthenocarpy because it produces seedless fruit in the absence of successful fertilization. Parthenocarpy is a phenomenon where fruits develop without the need for pollination or fertilization. In the case of bananas, the fruit develops from the ovary without the need for the ovules to be fertilized. This can occur naturally or can be induced through artificial means such as hormone treatments. The resulting fruit is seedless, as there was no fertilization to produce viable seeds.

The dominant traits in this scenario are white and purple flowers. This is because one of the garden pea plants produced axial white flowers, indicating that the white flower trait is dominant. Additionally, another plant of the same species produced terminal violet flowers, indicating that the purple flower trait is also dominant.

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A molecule that can act as a genetic material must be chemically and structurally stable to ensure that it can carry and transmit genetic information accurately. Additionally, it should be able to generate its replica through processes like DNA replication. Therefore, the correct answer is i, iv.

ADA deficiency in humans is caused by the deletion of the gene for ADA, which affects the functioning of the immune system. ADA (adenosine deaminase) is an enzyme that plays a crucial role in the development and maturation of immune cells. Without ADA, toxic metabolites accumulate in the body, leading to severe combined immunodeficiency (SCID). SCID is a disorder characterized by a weakened immune system, making individuals highly susceptible to infections. Therefore, the deletion of the ADA gene directly affects the functioning of the immune system.

This statement is incorrect because Darwin's theory of natural selection is based on the idea that individuals in a population do have heritable variations. These variations are passed on from one generation to the next through genes, and they provide the raw material for natural selection to act upon. Without heritable variations, there would be no genetic diversity in a population, and natural selection would not be able to drive the evolution of species.

Natural selection is the process by which organisms with advantageous traits are more likely to survive and reproduce, leading to the passing on of those traits to future generations. In this scenario, the insect becoming resistant to a parasite is a result of natural selection. The insects that have a genetic variation that makes them resistant to the parasite are more likely to survive and reproduce, passing on this resistance to their offspring. Over time, the population of insects will become predominantly resistant to the parasite due to the selective pressure exerted by the parasite.

The secondary oocyte is surrounded by two structures when it is released from the ovary: the zona pellucida and the corona radiata. The zona pellucida is a glycoprotein layer that surrounds the oocyte and plays a crucial role in fertilization. The corona radiata, on the other hand, is a layer of granulosa cells that surround the oocyte and provide protection and nourishment. Therefore, the correct answer is "b & c only".

The explanation for the given correct answer is that the wings of a cockroach and a bird are analogous because they have different origins (they evolved independently) but are functionally similar (both are used for flying). This suggests that evolution has led to the development of similar structures in different organisms to perform similar functions, even though they may have different origins.

Cleistogamy is a type of self-pollination in plants where the flowers remain closed and do not require external pollinators for fertilization. This allows for the production of seeds even in the absence of pollinators. Therefore, the statement that "It produces assured seed set even in the absence of pollinators" is correct.

Parthenogenesis refers to the process of producing a complete individual from an unfertilized egg. In this reproductive strategy, the egg develops and grows without being fertilized by sperm. This phenomenon is observed in certain species, such as some insects, reptiles, and fish. It allows for the production of offspring without the need for a male partner and can be advantageous in certain environments or situations where males are scarce or absent.

Blood tests for malaria should be done when the temperature is high because the malaria parasite, Plasmodium, is more active and replicates faster in warmer temperatures. This increases the chances of detecting the presence of the parasite in the blood sample. Additionally, high temperatures are often associated with fever, which is a common symptom of malaria. Therefore, conducting blood tests when the temperature is high increases the accuracy of diagnosing malaria.

The main function of a catalytic converter is to reduce the emission of other dangerous compounds. This is achieved by converting harmful pollutants in the exhaust gases into less harmful substances through a series of chemical reactions. Unleaded petrol is desirable because it does not contain lead, which can damage the catalytic converter and reduce its effectiveness in reducing emissions.

Lysine and arginine are both amino acids that contain positively charged side chains. These positive charges on the side chains of lysine and arginine enable histones to acquire a positive charge. This positive charge allows histones to interact with and bind to the negatively charged DNA molecule, forming the nucleosome structure.

The correct answer is "leaves and the raisin of cannabis plant and it directly affects the cardiovascular system." Ganja, also known as marijuana, is derived from the cannabis plant. When consumed, it can have various effects on the body, including an increased heart rate and blood pressure, which directly affects the cardiovascular system.

DNA polymerases from thermophilic organisms are used in the polymerase chain reaction (PCR) because the priming and extension steps of PCR must be carried out at high temperatures to prevent the single strands of DNA from reannealing. Thermophilic DNA polymerases are able to function at these high temperatures, allowing for efficient and accurate DNA amplification during PCR.

The acrosome is located in the head part of the sperm and its function is to provide mobility to the sperm and to promote meiosis following fertilization. Meiosis is a crucial process that leads to the formation of gametes, such as sperm and eggs. The acrosome contains powerful enzymes that are needed for the sperm to penetrate and fertilize the egg by breaking down the protective layer called the zona pellucida. Therefore, the acrosome plays a vital role in the reproductive process by enabling the sperm to reach and fertilize the egg.

During seed germination, the seed coat needs to rupture for the embryo to emerge. This rupture is caused by the massive imbibition of water by the seed. When water is absorbed, it causes the seed to swell and the pressure exerted by the swelling seed leads to the rupture of the seed coat. This allows the embryo to grow and develop into a new plant.

The correct answer is "Developing immunity that is protection against infection plus recognizes and removes old, malformed, or damaged red blood cells". The spleen plays a crucial role in the immune system by producing and storing immune cells, such as lymphocytes, which help fight against infections. Additionally, the spleen acts as a filter, removing old, malformed, or damaged red blood cells from circulation. Therefore, this answer accurately describes the two different roles of the spleen in the human body.

The correct answer is that β-Galactosidese is coded by "z" genes and is responsible for the hydrolysis of lactose into galactose and glucose. This enzyme plays a crucial role in lactose metabolism by breaking down lactose, a disaccharide, into its monosaccharide components. The "z" genes encode for the synthesis of β-Galactosidese, which is essential for the utilization of lactose as a carbon source by the cell.

The correct answer is "i, iii".

Statement i states that the testes are present in a pouch which helps to maintain the lower temperature required for spermatogenesis. This is true because the testes need to be kept at a slightly lower temperature than the rest of the body for the production of sperm.

Statement iii states that the testes have Leydig cells which synthesize and secrete androgen hormones. This is also true because Leydig cells are responsible for producing testosterone, which is an androgen hormone.

Therefore, the correct answer is "i, iii" because both statements are true.

Rhode Island Red is a breed of chicken that is known for its hardiness, versatility, and ability to lay a good number of brown eggs. It is a popular breed among backyard chicken keepers and small-scale farmers due to its excellent meat quality and ability to thrive in various climates. Rhode Island Reds are also known for their calm and friendly temperament, making them a great choice for families and beginners in chicken keeping.

The incorrect option is i, ii. This is because colostrum does not provide minerals, but it does produce immunoglobulin and cytokines, with IgA being in the highest proportion. Additionally, colostrum transfers growth factors like epidermal and epithelial growth factor, making it nature's perfect first food.