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Key Answers) 1 II PUC BIOLOGY ASSIGNMENT – 11 (KEY ANSWERS) 1. With a schematic representation, explain the life cycle of HIV. (5) The HIV (retro virus) gains entry into the body through sexual contact with an infected person. The virus then enters macrophages. In macrophages RNA genome of the virus replicates to form viral DNA with the help of reverse transcriptase enzyme. The viral DNA is incorporated into the host DNA and direct infected host cells (macrophages to produce viral particle. Therefore macrophages act as HIV factory. Simultaneously HIVB enters into T-lymphocytes (TH – Helper T-cells) where it replicates and produces progeny viruses. The progeny viruses released into the blood, attack the other helper T-lymphocytes. This is repeated leading to progressive decrease in the number of helper T – lymphocytes in the body. Due to decrease in the number of T – lymphocytes, the person suffers from infections such as Mycobacterium, viruses, fungi and even parasites like Toxoplasma. The person becomes immune deficient. This lead to his death. 2. The cells of malignant tumors are considered as dangerous. – Give reason. (1) Malignant tumors grow very rapidly, damage surrounding normal tissues and spread to other parts through blood stream where they get lodged and transform the normal cells into cancer cells. ASC INDEPENDENT P. U. COLLEGE Page 1 of 6 3. Explain the salient features of double helix model of DNA. (5) WATSON AND CRICK MODEL OF DNA (Double helix model) * Rosalind Franklin is best known for her work on the X-ray diffraction images (1952) of DNA, which led to the discovery of the DNA double helix model (1953) for which Francis Crick, James Watson, and Maurice Wilkins shared the Nobel Prize in Physiology or Medicine in 1962. * DNA is made up of two polynucleotide chains. The backbone of the chain is made up of sugar – phosphate and the bases project inside. * The bonds between the nucleotides are called phosphodiester bonds. * DNA is double stranded and obeys Chargaff’s rule and has complementary base pairing. Hence, DNA has constant Nucleotide ratio * The chains have anti-parallel polarity. It means, if one chain has polarity 5’→3’, the other has 3’→5’. * The bases in two strands are paired through hydrogen bond forming base pairs (bp). * Adenine forms two hydrogen bonds with thymine (A=T) from opposite strand and vice-versa. Similarly, guanine is bonded with cytosine with three hydrogen bonds (C≡ G). As a result, approximately uniform distance between the two strands of the helix. * The chains are coiled in a right handed fashion. (B-DNA). The pitch of the helix (i.e., one complete 360 ̊turn is called Gyre) is 34 Å and there are roughly 10 base pairs in each gyre (Turn). Therefore, the distance between successive base pairs in a helix is approximately equal to 3.4 Å. * The plane of one base pair stacks over the other in double helix. This, in addition to H – bonds, confers stability of the helical structure. ASC INDEPENDENT P. U. COLLEGE Page 2 of 6 4. What is reproduction? Mention its significance. (2) The process by which the organisms produce young ones of their own kind or species is called reproduction. Significance of reproduction: It helps in the continuation of species generation after generation. It enables species to live generation after generation. 5. Write the structure of morphine and cannabinoid molecule. (2) 6. State concept of abiogenesis and biogenesis. (2) Theory of abiogenesis (Theory of spontaneous generation) states that “Living things arises spontaneously from non - living things.” This theory was developed by Aristotle. Later this theory was disproved by Francisco Redi, John Needam, Lazzaro Spallanzani and Louis Pasteur. Theory of Biogenesis states that “Life exists from pre – existing life.” 7. What is drug abuse? Describe the suitable example of drugs that are commonly used. (5) When drugs are taken for purpose other than the medicinal use in abnormal amosunts or frequency that impairs one’s physical and physiological functions is called drug abuse. Drugs that are commonly abused are as follows: OPIOIDS: Opioids are the drugs which bind to opioid receptors in the central nervous system and gastro – intestinal tract. These are derivatives of morphine. Extracted from the latex of poppy plant Papaver somniferum. Ex. Heroin commonly called smack is a white bitter crystalline compound obtained from acetylation of morphine. It is a depressant and slows down body functions. Morphine is an effective sedative and pain killer and is useful in patients, who have undergone surgery. CANNABINOIDS: These are a group of chemicals, which interact with cannabinoid receptors in the brain. They are obtained from Cannabis sativa. The inflorescence, leaves, flowers, latex are used in various combinations to produce cannabinoids such as marijuana, hashish, charas, and ganja. They affect cardio-vascular systems of the body. COCA ALKALOIDS OR COCAINE: These are obtained from Erythroxylum coca (Coca plant). It interferes with the transport of neurotransmitter dopamine. Example: Cocaine commonly called coke or crack. HALLUCINOGENS: The well known plants with hallucinogenic properties are Atropa belladonna, Datura. Drugs like barbiturates, Amphetamines, Benzodiazepines and LSD (Lysergic Acid Dietheylamide) are used as medicines to help patients with mental illness like depression and insomnia are often abused. 8. What is animal husbandry? (1) Animal husbandry is the agricultural practice of breeding and raising livestock. It deals with the care and breeding of livestock like buffaloes, cows, pigs, horses, cattle, sheep, camels, goats etc., that are useful to humans. 9. Why human males are called heterogametic? (1) Males produce two different types of gametes either with X – chromosome or with Y – chromosome, therefore males are heterogametic. 10. What is: Chargaff’s rule, Palindromic sequence of DNA, Complementary base pairing. (3) CHARGAFF’S RULE: States that the number of purine residues and the number of pyrimidine residues are equal in DNA. That is number of adenine residues is always equal to thymine and the number of cytosine residues is always equal to guanine. A+G/T+C = 1 and A+T\G+C = Constant. ASC INDEPENDENT P. U. COLLEGE Page 3 of 6 PALINDROMIC SEQUENCES OF DNA: The sequences of DNA that reads the same in both 5’→3’ and 3’→5’ directions is called palindraomic sequences of DNA. COMPLEMENTARY BASE PAIRING: In DNA, always a purine pairs with a pyrimidine. It is very specific that Adenine pairs with thymine and vice-versa by two hydrogen bonds, Guanine pairs cytosine and vice-versa by three hydrogen bonds is called complementary base pairing. 11. Mention the nucleosides and nucleotides of DNA and RNA. (4) NUCLEOSIDES OF RNA: Adenosine, guanosine, cytidine and uridine NUCLEOSIDES OF DNA: Deoxyadenosine, deoxyguanosine, deoxycytidine and deoxythymidine NUCLEOTIDES OF RNA: AMP, GMP, CMP and UMP NUCLEOTIDES OF DNA: dAMP, dGMP, dCMP and dTMP 12. What is the pitch of DNA a helix? (1) 34Å 13. List the adaptations of entamophilous and anemophilous flowers. (4) 14. Pollen grains are useful and also harmful. – Substantiate your statement with reasons. (3) Pollen grains are rich in nutrients. In western countries, a large number of pollen products in the form of tablets and syrups are used as food supplements. Pollen consumption has been claimed to increase the performance of athletes and race horses. So pollen grains are useful. Pollen grains of many species cause several allergies and bronchial afflictions in some people often leading to chronic respiratory disorders such as asthma, bronchitis etc. Plants like Parthenium (carrot grass) came into our country as a contaminant with imported wheat, has become ubiquitous in occurrence and causes pollen allergy. Hence, the pollen grains are harmful to. 15. Explain pollen-pistil interaction. (3) All the events from pollen deposition on the stigma until pollen tube entry into the ovules are together referred to as pollen – pistil interaction. It is a dynamic process involving pollen recognition followed by promotion or inhibition of pollen. Plant breeders use this knowledge gained in this area to get desired hybrid by manipulating pollen – pistil interaction This is mediated by the chemical components of the pollen interacting with those of the pistil. \After compatible pollination, the pollen grain germinates on the stigma to produce a pollen tube through one of the germ pore. The contents of the pollen grain move into the pollen tube. The pollen tube grows the tissue by the sugary secretion of stigma, style and reaches the ovary. ASC INDEPENDENT P. U. COLLEGE Page 4 of 6 16. Distinguish between nucleoside and nucleotide. (2) 17. What is theory of panspermia? (1) Panspermia theory states that units of life called spores were distributed throughout the universe; were transferred to different planets including earth, later they developed into life. 18. Name the gases present and absent in the pre-biotic atmosphere? (2) Hydrogen, Carbon dioxide, Methane, Water vapour is the gases present in the pre-biotic atmosphere. Molecular oxygen was the only gas that was absent in the pre-biotic atmosphere. 19. With reference to AIDS, answer the following questions: a) Mention the causative agent? Retrovirus named HIV (Human Immuno - deficiency Virus) b) Mention the transmission of HIV infection. Transmission of HIV infection generally occurs by Sexual contact with infected person By transfusion of contaminated blood and blood products By sharing infected needles as in the case of intra-venous drug abusers From the infected mother to her child through placenta. c) What type of cells is attacked by HIV? Helper T – lymphocytes are attacked by HIV d) Indicate the diagnostic test and confirmatory test. ELISA (Enzyme Linked Immuno-Sorbent Assay) e) Name the other infection that takes place due to the decrease in the specific type of cells? (5) Mycobacterium, viruses, fungi and even parasites like Toxoplasma. 20. Write short notes on cancer detection and diagnosis.
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