Bihar Board 12th Biology Important Questions Long Answer Type Part 2

Bihar Board 12th Biology Important Questions Long Answer Type Part 2

BSEB 12th Biology Important Questions Long Answer Type Part 2

Question 1. Differentiate between them:
(i) Antibodies and antigens
(ii) Interferons and antibodies
(iii) Benign tumour and Malignant tumour
(iv) B-cells and T-cells.
Answer:
(i) Antibodies and antigens:

Antibodies	Antigens
1. Antibody is a molecule synthesized by an animal to combat foreign material.	1. Antigen is usually a foreign material that elicits antibody formation.
2. Each antibody is a protein molecule.	2. Antigen is a protein or polysaccharide molecule.
3. Antibody occurs on the surface of a plasma cell and also in body fluids.	3. Antigen may occur on the surface of a microbe or as a free molecule.
4. Antibody directly joins an antigen to destroy the latter.	4. Antigen binds to a macrophage to reach a helper T-cell to initiate immune response.

(ii) Interferons and antibodies:

Interferons	Antibodies
1. Are produced by any microbe infected cell.	1. Are produced by plasma B-cells only.
2. Leave the infected cell and enter a nearby healthy cell to dispose of the microbes.	2. Pass into the circulate in blood any lympth to dispose of antigens.
3. Induce the healthy cell to synthesize antimicrobial proteins that check microbial.	3. Selectively bind to antigens that are immobilised for easy attack by phagocytes.
4. Are quick in action but give a temporary protection against microbes.	4. Are slow in action but give a long-lasting protection against antigens.
5. Act inside the cells.	5. Act outside the cells.
6. Form the body’s second line of defence.	6. Form the body’s third line of defence.

(iii) Benign tumour and Malignant tumour:

Benign tumour	Malignant tumour
1. These remain confined in the organ affected.	1. These spread from one organ to other organs of the body.
2. These are enclosed in a connective tissue sheath.	2. These are not enclosed in connective tissue sheath.
3. These have less growth rate.	3. These have rapid growth rate.
4. Cancer cells are more adhesive.	4. Cancer cells are less adhesive.
5. No metastasis.	5. Metastasis is generally present.

(iv) B-cells and T-cells:

B-cells	T-cells
1. B-cells form humoral or antimediated immune system (AMIS).	1. T-cells form cell-mediated immune system (CMIS).
2. They are differentiated in bone marrow.	2. They are differentiated in thymus gland.
3. They defend against some virus, encapsulated bacteria and toxins that enter the blood and lymph.	3. They defend against viruses, protists, fungi and some bacteria which enter the cells.
4. They form by division plasma cells.	4. They form by division lymphoblasts of three types: killer, helper and suppressor cells.
5. Plasma cells do not move to the site of infection.	5. Lymphoblasts move to the site of infection.
6. Plasma cells secrete antibodies that pass into the blood and lympth and dispose of the antigens.	6. Killer cells on reaching the site of infection secrete perforin that kills microbes by puncturing their cell membrane.
7. Plasma cells do not react against transplants and cancer cells.	7. Killer cells react against transplants and cancer cells also.
8. Plasma cells have no inhibitory role on immune system.	8. Suppressor cells inhibit the immune system from attacking body’s own cells.

Question 2.
(i) Give a schematic representation of events during inflammatory reaction.
(ii) Write down the role of lymphatic system.
(iii) What is the role of macrophages?
Answer:
(i)

(ii) Lymphatic system have following roles:

• It drains excess tissue fluid from the extracellular spaces back into the blood.
• Some of the fluid from the digestive tract is absorbed into the lumph. The lymphatic vessels store this fluid temporarily and release it gradually so that the kidneys do not face a sudden pressure of urine excretion.
• It carries carbon dioxide and nitrogenous waste materials that diffuse into the tissue fluid to the blood.
• It takes lymphocytes and antibodies from the lymphatic nodes to the blood.
• It transports fats digested and absorbed in the intestine to the blood in the form of chylomicron droplets.
• It destroys the invading microorganisms and foreign particles in the lymphatic nodes.
• It maintains the quality and quantity of the blood by restoring the fluid and solutes that leave it.
• It brings plasma protein macromolecules synthesized in the liver cells and hormones produced in the endocrine glands to the blood. These molecules cannot pass into the narrow blood capillaries but can diffuse into lymphatic capillaries.

(iii) Macrophages have following roles/functions:

• Defence: Wandering macrophages (also called histiocytes) dispose of microbes in the connective tissue. Fixed macrophages destroy microbes in the blood and lymph.
• Giant Cell Formation: Many macrophages may fuse to form a large multinucleate giant cell to capture a foreign body too big for a single macrophage to engulf.
• Scavenging: Macrophages also dispose of dead tissue cells and noncellular foreign matter.
• Antigen Display: Macrophages carry the antigens of the engulfed microbes on their surface to display them to the lymphocytes in the lymphatic nodes. This activates the immune system.
• Secretion of Endogenous Pyrogen: Macrophages secrete interleukin-1 (IL-1), also called endogenous pyrogen. It plays a role in inflammatory response, in causing fever, and in activation of other phagocytic cells as well as the T-cells and B-cells to produce their effect.

Question 3. What is interspecific hybridisation? Explain the term by giving an example.
Answer: A cross between two different related species is called interspecific hybridisation. The progeny is different from both the parents. Sometimes the progeny combines the desirable features of both the parents. Examples is production of mule by a cross between female horse (mare) and male donkey.

It inherits size from horse and sure footedness, great endurance to hardship from donkey. It is more useful on high hills. However with all its hybrid vigour, the mule is sterile and unable to reproduce.

Question 4. Name the ways through which breeders create desired genetic variations in plants. Write short notes on any four of those.
Answer: The different ways through, which breeders create genetic variations in plants are (a) Domestication, (b) Germplasm collection, (c) Plant introduction, (d) Selection, (e) Hybridisation, (f) Polyploidy, (g) Mutation, (h) Genetic engineering.

(i) Plant introduction: When a variety of any plant species is taken from one area into a new area (where it was not grown before) it is called as plant introduction. Plant introductions from other countries are valuable sources of germplasm. These provide us with many valuable crops. Example – potato, tomato, cauliflower, grapes, guava etc. are introduced crops. Soyabean is a recently introduced crop.

Introductions have also provided us with improved varieties of the existing crops. Example ‘Sonara-64’ variety of wheat and ‘Taichung Native I’ variety of rice are introductions. These are dwarf varieties and provided the starting material for ‘Green revolution’ in our country.

(ii) Hybridization: process of crossing of two species having desirable characters is known as hybridisation. This method produces genetic variations in the next progeny. It is a scientific improvement of plants by crossing of two varieties. It can also be called as the mating between lines of different genotypes. One parent is male and the other female, when they are crossed together the hybrids are produced. They are called F₁ seeds.

In F₂ generation there will be segregation, recombination and independent assortment. Hybridization may be between different varieties of same species, then it is termed as intervarietal hybridisation. If a crop species is mated with other different but related species it is called interspecific hybridisation. Such variations are very important for plant breeding.

(iii) Mutation: Mutation is defined as “a sudden and heritable change in a character of an organism.” It may arise due to a change in any of the following: (a) chromosome structure, (b) chromosome number, and (c) base sequence of the concerned gene. Mutations occur in nature spontaneously at a very low rate. They are called spontaneous mutations. Mutant alleles are generally recessive. They produce harmful effects. Only about 0.1% of the mutant alleles are beneficial.

Mutations may be induced by mutagens which may be physical (X-rays, gamma rays, UV-radiations etc.), chemical (ethyl methane sulphonate (EMS) and sodium azide etc.); Mutation breeding is used in plant breeding to develop improved varieties.

(iv) Polyploidy: The condition in an organism, in which the number of complete chromosome sets is higher than the diploid number is called polyploidy. For example monoploids have ‘n’ (sign); diploids have 2n; triploids have 3n (3 chromosome sets) and so on.

Autopolyploidy: The variation of the number of chromosome sets arising within a species is called autopolyploidy. For example, in sexually reproducing organisms egg may be fertilized by more than one sperm, and resulting failure, mitosis and failure of meiosis during gamete formation. Autopolyploidy variety of tea in India.

Allopolyploidy is produced in two steps – two different species are hybridized to produce F1. Then F1 is doubled in chromosome numbers, e.g. wheat, oat, tobacco.

Question 5. Describe the main sources of biofertilizers, giving suitable examples.
Answer: Biofertilizers are organisms which enrich the soil with nutrients. The main sources of biofertilizers are bacteria, cyanobacteria and fungi. These are discribed as follows:
(i) Legume-Rhizobium symbiosis: Leguminous plants show symbiotic relationship with nitrogen fixing bacteria Rhizobium.

(ii) Azolla-Anabaena symbiosis: Anabaena are cyanobacteria, which lives in symbiosis with fern Azolla. Anabaena fixes atmospheric nitrogen. Azolla and cyanobacteria Nostoc are added to rice fields to increase the yield. Azolla grows rapidly in the fields, finally decays and add nitrogen content to the soil.

(iii) Free living bacteria: These are asymbioitc, aerobic and anaerobic bacteria which fix atmospoheric nitrogen under poor aeration conditions. They require Hydrogen gas to fix nitrogen. For example – Azotobacter, Bacillus, Clostridium etc.

(iv) Cyanobacteria: Cyanobacteria or blue green algae are widely used as biofertilizers. They have thick walled heterocysts which fix atmospheric nitrogen. For example Anabaena, Nostoc, Aulosira. These are capable of photosynthesis and can supply nitrogen to entire rice crop. These are simple to use and very cost effective.

(v) Mycorrhiza: Some fungus live symbiotically in the roots of higher plants. These fix atmospheric nitrogen and are termed as Mycorrhiza. These may be of two types: Ectomycarrbiza, where fungus hyphae penetrate into cortex of roots. This increases the surface area for absorption of water and minerals like N, P and K. These also solubilise some insoluble organic compounds. For example they are found in Eucalyptus, pine, oaks etc. Endomycorrhiza: The fungus lives in the intercellular spaces of the cortical cells of the roots. For example legumes, cereals, grasses, citrus, rubber, tea etc.

(vi) Microphos Biofertilizers: Some microorganisms solubilize bound phosphate of soil and make it available for plant absorption. For example Pseudomonas striata and Bacillus polymyxa and fungi – Aspergillus.

(vii) Loose association of Nitrogen fixing bacteria: Some bacteria live in close contact with the roots of grasses and cereals, called associative symbiosis. They fix nitrogen, which is absorbed by the plant and the bacteria get nourishment in return, For example Azospirillum lipoferum with the roots of Maize and Brazilian grasses.

Question 6. Write short notes on the following:
(a) Baker’s yeast
(b) Brewer’s yeast
(c) Batch process
(d) Continuous process.
Answer:
(a) Baker’s yeast: Saccharomyces cerevisiae is used in baking industry for desirable changes in flavour and texture of the baked products, it is called baker’s yeast. The baker’s yeast is prepared by growing the stock strain on molasses and then centrifuged and washed. These yeasts ferment the sugar in the dough, CO₂ and alcohol escape during baking so the baked products become soft and porous.

(b) Brewer’s yeast: The yeasts used in brewing industry for making alcoholic drinks are called brewer’s yeast. Beer produced is undistilled product of grain-mesh fermentation brought about by Saccharomyces cerevisiae and S. Carisbergensis. Wine is an undistilled product of fruit-juice fermentation brought by Saccharomyces ellipsoidens.

(c) Batcl process: This is type of fermentation process where a large volume of nutrient medium (volume upto 2,25.000 litres) is inoculated and allowed to proceed when maximum yield is obtained. Then the fermentation is stopped, the product is recovered and the fermentation tank (bioreactor) is cleaned, resterilized and used again.

(d) Continuous process: In this type of fermentation process, the fresh nutrient medium is added either continuously or at intervals along with continuous or at intervals withdrawl of a swall portion of fermentation product from the medium.

Question 7. Give a brief explanation of population growth pattern.
Answer: There are mainly two primary reasons for increase in human population. These are:
(i) Decline in death rate,
(ii) Increase in longevity.

However, in the civilized world of today, it is unfortunate that man himself is an enemy of man. He harms his fellow men through hoarding, adulteration, deprivation, exploitation, subjugation, violence and war.

World human population growth rate is about 2% on the basis of 1973 census. It was 0.8% per year for the developed countries and nearly 2.591 of developing countries. At this current rate of growth human population is doubling itself every 35 years. If the 6.0 billion people in the world today (1997) continue to increase at the present rate, their combined mass of more than 338 million tonnes will exceed the mass of the earth (which is about 6.5 billion trillion tonnes) in a period of about 1550 years. Thus, the human population explosion as shown in Fig. has become a serious global concern.

Whether our earth planet will have the carrying capacity of such a large mass of human population is a big question. Earth will soon become severely overcrowded and uninhabitable. Will the human beings then take the extraterrestrial migration and colonies other planets? About 56% of the total world population resides in. Asia alone.

Japan is the most thickly populated country and Australia is the most thinly populated country in the world. In India, Kerala is the most thickly populated state.

According to 1991 census, population of India is 843 million. The sex ratio is 929 females per 1,000 males. The literacy rate is 52.11% population growth rate in India is 2.14%.

Population beyond certain limit experiences acute food storage and many individuals face death from starvation or malnutrition. Accordingly if the present trend of human population growth continues, all available natural resources will be too meagre to meet the needs. When all these sources fall far below the need of a common man, a severe competition is bound to ensue, which may lead to large number of socio-economic problems such as energy crisis, ecodegraddation, hunger, poverty, famine, soil erosion, floods, deforestation, unemployment, shortage of raw materials, medical aid, housing, drinking water, clothing and lack of educational facilities. Danger of epidemic diseases will increase. These conditions may result into misery, poor health and increase of urban slums. Overpopulation is the main cause of economic backwardness in our country.

Question 8. How can be know whether a population is flourishing or declining?
Answer: The size of a population keeps changing in time, depending on various factors including food availability, predation pressure and reduce weather. These changes in the population density can give us some idea what is happening to the population – whether it is flourishing or declines. However, the density of a population in a given habitat during a given period, fluctuates due to changes in four basic processes. These are as follows:

• Natality: Number of births during a given period in the population that are added to the initial density.
• Mortality: The number of deaths in the population during a given period.
• Immigration: Number of individuals of the same species that have come into from elsewhere during the time period under consideration.
• Emigration: Number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

Question 9. Describe a biotic community (near your home or school) stating the relationships that exist between the common species comprising it.
Answer: Biotic community: It includes all the living things present in a particular area having various food relationships. A biotic community is organised into three kinds of living things producers, consumers and decomposers. All the three interact with each other in relation to their food and dependent upon each other for their food. Now let us take the example of a biotic community i.e., pond found near the vicinity of the school. In the pond we can identify all the three components mentioned below:

1. Autotrophs: These are green plants which grow and live in water. The common examples of autotrophs (green plants) found in a freshwater pond are: Hydrilla, Vallisneria, water weeds, lotus and other species of aquatic plants. These plants capture the sun’s energy (high energy) and with the help in their green parts produce food with the help of CO₂ and H₂O. This process is called photosynthesis. These plants manufacture their food themselves, so they are termed as autotrophs.

2. Consumers: Consumers present in the pond are small animals, insect larvae, Cyclops, protozoan, snails. These organisms feed on aquatic plants and get their energy. On these small animals, feed bigger fishes which form consumer No. 3, finally birds, mammals and even man feed on them.

3. Decomposers: These are microorganisms such as bacteria and fungi which help in the decay of dead living things (organic matter) These help in the recycling of the materials in the bioshpere.

Question 10. Briefly describe tropical forest biomes.
Answer: Tropical forest are of two types: Tropical rain forests, and Tropical deciduous forests.

Tropical rain forests or evergreen forests occur near the equator. In India they are along the Western Ghats in the north-eastern region. The climate is warm and moist, and with no seasonal variations. Rainfall is high (200 cm or more) and uniform with no dry periods, sunlight is strong, soil is rich in minerals and humus. They have excellent conditions for plant growth throughout the year. Life is abundant with about 71 to 80% of world’s insect species and 80-85% of birds species. The dense vegetation is vertically stratified into 4 to 5 strata, each storey in inhabited by different animals. The soil is highly leached. Nutrients are stored in tall vegetation and soil storage is low. Tropical rain forests have highest standing crop biomass among all the biomes.

Tropical deciduous forests: These are distributed in northern and southern parts of India. The climate is warm, with alternate wet and dry periods. Rainfall is high around 100 to 200 cm per annum. Sunlight is strong, soil is rich in mineral and humus. In wet period, the forest is green with dense foliage and thick herbaceous layer. The epiphytes and climbers are fewer than tropical rain forests. The trees shed their leaves during dry seasons. They have trees like sal, teak, mahua, amla, jamun, senwl etc. These forests are rich in animal population too. The common animals are deer, elephants, pigs, lion, birds, reptiles, insects and worms.

Question 11. Diagrammatically show how energy flows from one trophic level to another trophic level.
Answer: Energy is lost as heat from each successive trophic level. This can be shown as follows:

Sun serves as a source of energy in the biosphere. Producers trap a small amount of this energy and transfer it to other members of food chain (consumers and decomposers). Thus producers have highest energy level. The pyramid of energy is always straight i.e., it decreases from bottom to top.

Question 12. Give an account of factors affecting rate of decomposition.
Answer: Factors affecting decomposition – Rate of decomposition of detritus is regulated by climatic factors and chemical quality of detritus. The key role is played by temperature and soil moisture through their regulatory effect on the activities of soil microbes. Detritus decomposes are rapidly, within a few weeks or month, in a climate characterized by higher temperature (>25°C) and moist conditions (e.g. in humid tropical regions.

Low temperature (<10°C) sharply reduces decomposition rate even if moisture is in plenty. In regions of high latitude (or altitude) complete decomposition of detritus can take several years or decades. The composition rate is low under prolonged soil dryness even if the temperature remains high as in tropical deserts.

Accumulation of some substance in the detritus increases decomposition rate. Chemical quality of detritus is determined by the relative proportions of water soluble substances, sugars, polyphenols, lignin and nitrogen. Under same climatic conditions decomposition rate is slower if the detritus is rich in substances such a lignin and chitin. The nitrogen-rich detritus (having low amounts of lignin) decomposes relatively, quickly. The actual rate of decomposition of detritus in natural conditions depends upon the integrated effect of environmental conditions and detritus quality also.

Question 13. Give major characteristics of desert biome.
Answer: Deserts are located in rain shadow areas, where dry air from the equator falls upper atmosphere. Their main characteristics are:

• Prolonged scarcity of rainfall
• Period of dryness and evaporation from soil higher
• The annual rainfall is below 70mm to 120mm
• There is variation of temperature during day and night
• There is no permanent or temporary flowing water. The sunlight is strong and abundant
• The soil is sandy or rocky
• The desert biome has less life and organisms which have adaptation to extreme temperature and arid conditions can only survive
• The desert plants nuclide ephemeral annual herbs which grow during rainy season, succulent xerophytes like cactus, euphorbias, thorny shrubs, small trees like Prosopis, Salvador, Tamarix. The most common grass in deserts in Cenchrus
• Animals in desert biome are arthropods, scorpions, spiders, insects, rattlesnake, lizards, camels, jackrabbit, desert rat, cactus woodpecker, roadrunners, burrowing owl. Mostly animals are small and nocturnal
• The biomass and primary productivity levels in deserts are low.

Question 14.
(a) How is biodiversity distributed along major environmental gradients?
(b) What are the main strategies for conservation of the wildlife?
Answer:
(a) Gradients of biodiversity: The biodiversity varies with change in latitude or altitude. The biodiversity increases from the poles to the equator. In the temperate region the climate is severe with short growing period for plants. In topical rain forest the conditions are favourable for growth throughout the year. Speciation occurs during favourable conditions.

Mean number of vascular species per 0.1 ha sample area in tropical rain forests varies from 118 – 236. This is only in the range of 21 – 48 species in the temperate zones. Such correlation between diversity and latitude exists for a wide variety of taxonomic groups, like ants, birds, butterflies, and moths.

There is a decrease in species, diversity from lower to higher altitudes on a mountain. A 1000m increase in altitude results in a temperature drop of about 6.5°C. Drop in temperature and greater seasonal variability at higher altitudes are a major factor to reduce biodiversity. The latitudinal and altitudinal gradients of species diversity are two master gradients. More complex and diverse flora and fauna will be in complex and heterogenous physical environment.

(b) Strategies for conservation of wild life:

• Wild life protection in natural as well as artificial habitats.
• Endangered, vulnerable and rare species should be given preference over others in the conservation programmes.
• To provide proper habitat to the wild animals, air, water and land should be properly managed.
• Wild varieties of plants and animals should be preserved for various breeding programmes.
• The feeding areas, breeding grounds, resting sites etc. of wild animals should be kept intact for animals safe growth and reproduction.
• Instead of a single species, whole ecosystem should be safeguarded.
• Areas should be protected for migratory animals.
• National parks and Sanctuaries should be set up to take care of wild animals.
  Hunting should be prohibited, especially during breeding season.
• People should be educated and children should be inspired about the need and modes of conservation of wild life.
• International trade on wild plants, animals and their products should be regulated by law.

Question 15. Write short notes on the following:
(a) Wild life sanctuary
(b) Biosphere reserves
(c) Genetic diversity
(d) India’s effort in biodiversity conservation.
Answer:
(a) Wild Life Sanctuary: In a sanctuary, protection is given only to the fauna and operations such as harvesting of timber, collection of minor forest products and private ownership rights are permitted so long as they do not interfere with the well-being of animals. There are presently 368 Sanctuaries in India covering over 1,07,310,13 square kilometres, amounting to 3.2 percent of India’s total geographical area.

(b) Biosphere reserves: Biosphere reserves are a special category of protected areas of land and/or coastal environments wherein people are an integral component of the system. The concept of biosphere reserve was launched in 1975 as a part of the UNESCO’s MAB (man and biosphere) programme. There are 13 biosphere reserves in India which are notified as National Parks. Each biosphere reserve has a core, buffer and a transition zone.

(c) Genetic diversity: It is the genetic variations found amongst members of the same population and geographically separated population of the species. On the basis of genetic differences, all the individuals of the same species become different from one another. Environment plays major role in imparting diversity of living organisms. For eg. there are various races of human beings like Mongoloid, Negrito etc. The differences can be in alleles, in entire genes or in chromosomal structures.

(d) India’s effort in biodiversity conservation: India has contributed a lot to the global biodiversity. India is a homeland of 167 cultivated species and 320 wild relatives of crop plants. It is the centre of diversity of animal species (Zebu, Mithun, chicken, water buffalo, camel); crop plants (rice, sugarcane, banana, tea, millet); fruit plants and vegetables (mango, jackfruit, cucurbits), edible diasporas, alocasia, colocasia, spices and condiments (cardamom, black pepper, ginger, turmeric); bamboos, brassicas, and tree cotton.

The in situ conservation of biodiversity is being, carried out through Biosphere reserves, National parks, Wild Life Sanctuaries and other protected areas by the Ministry of Environment and Forests. The joint forest management systems involve forest departments and local communities.

National Bureau of Plant, Animal and Fish Genetic Resources has a number of programmes to collect and conserve the germplasm of plants and animals in seed gene banks, and field, gene banks for in vitro conservation.

The land races and diverse food and medicinal plants are also being conserved.

Question 16. With an example explain the importance of organic farming.
Answer: Organic farming is a cyclical, zero-waste procedure, where waste products from one process are cycled in as nutrients for other processes. This enchances the maximum ultilization of resource and increases the efficiency of production. For example, a farmer of Sonipat, Haryana, Ramesh Chandra Dagar, includes bee-keeping, dairy management, water harvesting, compositing and agriculture in a chain of processes, which support each other and allow an extremely economical and sustainable venture.

Cattle excreta (dung) are used as dung in place of chemical fertilizer for crops. Crop waste is used to create compost, which can be used as a natural fertilizer or can be used to generate natural gas for satisfying the energy needs of the farm.

Question 17. What are the major cause of species losses in a geographical region?
Or, What kinds of threats to the biodiversity may lead to its loss?
Answer: These are:
(i) Habitat loss and fragmentation: The destruction of habitat is the primary cause of loss of diversity. It occurs due to cutting down of trees, filling a wet land, ploughing a grassland or by burning a forest.

This causes the change in the natural habitat and kills or forced out many plants, animals and micro-organisms. A forest patch surrounded by croplands, orchards, plantations or ubran areas is an example of fragmented habitats. With the fragmentation of a large forest tract, the species occupying the deeper parts of forests get disappeared.

(ii) Disturbance and pollution: Communities are largely affected by natural disturbance such as fire, tree fall and defoliation as well as by man made disturbances. Man disturbs the community by using large number of synthetic compounds, releasing of radiation or spilling over of oil in the sea. The lead poisoning and eutrophication cause mortality of species and reduce the species diversity.

(iii) Introduction of exotic species: New species that enter a geographical region are called exotic or alien species. Introduction of such species may cause disappearance of native species through changed biotic interactions e.g, Nile perch, an exotic predatory fish introduced into lake victoria threatens the entire ecosystem of the lake by eliminating several native species of the small Cichlid fish species that were endemic to this freshwater aquatic system. Similarly, Lantana Camara has invaded many forest lands in different parts of India and strongly competes with the native species.

(iv) Co-extinctions: When a species becomes extinct, the plant and animal species associated with it also become extinct. When a fish species become extinct, its assemblage of parasites also meets the same fate.

Question 18. Why should we conserve biodiversity?
Or, What are the uses of biodiversity?
Answer: Uses:
(i) Source of food and improved varieties: Biodiversity has a prime role in agriculture as a source of new crops, material for breeding improved varieties and new biodegradable pesticides. The wheat, com and rice are the three main major carbohydrate crops which yield two third of the food substaining the human population.

The commercial domestic species are crossbreed with their wild relatives to improve their traits. The genes of wild species are used to confer new properties such as diseases resistance or improve yield in domesticated species e.g., rice grown in Asia is protected from diseases by genes received from a single wild rice species (Oryza nivara) from India.

(ii) Drugs and medicines: Several important pharmaceuticals are obtained from plant based substances and these substances are developed into variable drugs like Morphine, Quinine and Taxol etc. Morphine (Papaver somniferum) used as an analgesic; Quinine (Chinchona ledgeriana) used for the treatment of malaria and Taxol, an anti-cancer drug obtained from the bark of the yew tree (Taxus brevifolia, T. baccata). 25% of the drugs in the pharmacy are derived from a mere 120 species of plants.

(iii) Asthetic and cultural benefits: Biodiversity has great aesthetic value. Examples of aesthetic rewards include ecotourism, bird watching, wildlife, pet keeping and gardening etc. In majority of Indian villages and towns, plants like Ocimum sanctum (Tulsi) and Ficus religiosa (Peepal) are considered sacred and worshipped by the people. Several birds and even snakes have been considered scared.

(iv) Ecosystem services: Biodiversity is essential for maintenance of gaseous composition of the atmoshphere, climate control by forests and oceanic systems, natural pest control, pollination of plants by insects and birds, formation and protection of soil, conservation and purification of water and nutrient cycling etc.

Question 19. Describe the model of DNA as give by Watson and Crick.
Answer: DNA is found in all animal cells. In eukaryotes it is usually found with protein as nucleoprotein but in some prokaryotes it occurs independently. DNA is also present in mitochondria.

Structure: DNA is considered as the herediatry meterial which carries the genes. It is a large molecule built out of smaller molecules called monomer units or nucleotides. The monomer nucleotide of DNA has two parts a backbone consists of a sugar molecule, deoxyribose and phosphate group. The backbone is a long chain of sugar-phosphate and atached to each sugar residue is a side chain of a base. The bases are of four different kinds. A purine base- adenine or guanine A pyrimidine base-Cytosine or thymine.

According to watson and crick (1953) the structure of DNA is as follows:

• DNA molecule consists of two long strands of nucleotides which are spirally coiled around a central axis. Due to this coiling arrangement deep and shallow grooves are formed.
• The length of the one turn is 34A0 and in each turn there are 10 nucleotides. So the distance between successive nucleotides in any chain is 3.4 A0 the width of DNA molecule is 20A.
• In each strand deoxyribose sugar and phosphate groups are arranged alternately.
• Either a purine or pyrimidine base is attached with deoxyribose.
• Purine base of one strand is connected with pyrimidine base of the other by hydrogen bonds.
• Adenine always pairs with thymine (A-T) and guanine with cytosine (G-C).

Fig. 1. Model to show the way in which two phosphate sugar chains /(ribbons) may be arranged in a double helix form held together by base to form 1 unit of structure of DNA (10 A° = 1 nm)

Fig. 2. DNA molecule (diagrammatic) representation of two complementary chains of nucleotides.

Replication of DNA: Three methods have been reported for DNA replication.

(i) Conservative method: If DNA replicates by this method then both the strands of one of the DNA will have completely old material and the other will have completely new chemical substance. But experiments have disproved it.

(ii) Dispersive method: According to this method the two long double helix will break at many places to form many small pieces. Each will replicate and these will pair at random. This is also not accepted.

(iii) Semiconservative method: In this case one strand of each DNA molecule will have new and the second strand will have old material Meselson and Stahl (1958) proved by experiments the DNA replication takes place only by semiconservative method which are as follows

• DNA molecule is uncoil and two strands are seprated by breaking the hydrogen bonds.
• The separated strands now begin to synthesize the complementary strand or synthesize the RNA. This is done with the help of an enzyme called DNA polymerase.

Question 20.
(i) What is meant by semi conservative replication of DNA?
(ii) Describe the main aspects on the experiment conducted by Meselson and Stahl to show that DNA replication is indeed semi conservative.
Or, What did Meselson and Stahl demonstrate by their experiments with DNA? How they achieve it?
Answer:
(i) Semi-conservative replication: During replication, the two strands of DNA unwind at its one end by the breakage of H-bonds between the bases. These strands act as template for the formation of new strand, by allowing complementary bases to arrange themselves on the exposed bases. This leads to the formation of new DNA where one strand is parental and other is synthesized new one. This type of DNA replication is called as semi-conservative.

(ii) Meselson and Stahl grew Escherichia coli bacteria in N¹⁵ medium heavy isotope of nitrogen) for several generations so that all their DNA strands may become labeled with N¹⁵. These bacteria were then changed to another medium containing usual N¹⁴. and were analyzed for radioactivity. After first generation, each DNA helix showed the presence of N¹⁵ in one of the two strands and N¹⁴ in the second strand. This reveals to the semi-conservative nature of DNA.

These semi-conservative strands were then again grown in normal N¹⁴ medium and then analyzed for second generation. It showed two DNA with N¹⁵ and N¹⁴ strands and two with N¹⁴ on both the strands.

The density of most of DNA is almost the same as the density of the concentrated solutions of cesium chloride (CsCl). If a mixture of E. coli DNA containing N¹⁵ (heavy DNA) andE. coli DNA containing N¹⁴ (light DNA) is subject to CsCl equilibrium density gradient centrifugation, the DNA separates into different bands. After one generation of growth in N¹⁴ – medium, the DNA bands at a intermediate (hybrid) density.

Such hybrid DNA contains N¹⁵ in one strand and N¹⁴ in the other strand. After two generations of growth in N¹⁴ – medium, half of the DNA bands at the hybrid density and half bands at the light density. This clearly indicates that DNA replication is indeed semi-conservative.

Question 21. Describe about gametogenesis in human.
Answer: The gametes formation is called gametogenesis. It is of two types: (A) Spermatogenesis, (B) Oogenesis.
(A) Spermatogenesis: Sperms or male gametes formation is called spermatogenesis. It takes place in seminiferous tubules of testes Spermatogenesis completes in three phases that are:

1. Multiplication phase
2. Growth phase
3. Maturation phase.

1. Multiplication phase: Seminiferous tubule is lined by a layer of cuboidal epithelial cells called germinal epithelium. At a time any one cell of germinal epithelium divides regularly by mitosis. The cells formed are called spermatocytes or spermatogonia that is diploid. From sperm mother cell mans spermatocytes form and thus called multiplication phase.

2. Growth phase: All spermatocytes grow in size by interphase. The developed cells are called primary spermatocyte. That is also diploid.

3. Maturation phase: Primary spermatocytes divide by first meiotic on forming two secondary spermatocytes. These cells are haploid both Secondary spermatocytes divide by Ilnd meiotic on forming 4 spermatids. Spermatids are haploid. Spermatids develop into sperm by spermileosis or spermiogenesis.

(B) Oogenesis: Ova or female gametes formation is called Oogenesis. Ova formation takes place in ovary. Oogenesis is divided into three phases i.e., (a) Multiplication phase, (b) Growth phase, (c) Maturation phase.

(a) Multiplication phase: Ovary is lined by a layer of cuboidal epithelial cells called germinal epithelium. At a time any one cell of germinal epithelium divides mitotically forming follicles. Follicles are diploid. The dividing cell is called ovum mother cell.

(b) Growth phase: Among follicles any one follicle grows in size by interphase. The developed follicle is called primary follicle that is diploid. Other follicles surround the developed follicle and nourish.

(c) Maturation Phase: The primary follicle divides by 1st meiotic on. forming one larger cell and one smaller cell. The larger cell is called secondary spermatocyte containing n. The smaller cell is called polar body that is also n. Secondary follicle divides by Ilnd meiotic on forming a larger cell Ovum (n) and a smaller cell polar body (n). Polar body formed after Ist meiotic on may or may not divides by IInd meiotic on.

Thus in Oogenesis one Ovum and two or three polar bodies form from one primary follicle.
Actually IInd meiotic on takes place during fertilization.

Question 22. Describe in brief about sexually transmitted diseases.
Answer: There are some diseases known those are transmitted through sex. These diseases are also called veneral diseases. These diseases are – Syphilis, Gonorrhoea, Hepatitis B, genital herpes, genital warts, Trichomoniasis, AIDS, Chlamydiasis, vaginitis. In these diseases – Syphilis, Gonorrhoea, Vaginitis are the bacterial diseases, Hepatitis B, genital herpes, AIDS are the viral diseases. Trichomoniasis is a protozoan disease.

Hepatis B and AIDS are also transmitted by blood transfusion, use of used needle, syringe, blade etc. These diseases are also transmitted from infected mother to foetus. AIDS develops by HIV. HIV infection is very dangerous.

Except HIV, Hepatitis-B & genital herpes all other diseases are completely curable if detected in early and treated by doctor. The early symptoms of most diseases are minor live itching, fluid secretion, slight pain, swelling etc ground genital organ. Due to social stigma the patient does not consult doctor for treatment. This leads to complcation like pelvic inflammatory diseases, abortions, infertility and even cancer. Such complication are very harmful and cause of death.

These diseases are found among 15 – 24 yrs age. These diseases should be treated properly in early stage for prevention we should take precautions like –

• Should avoid sex with unknown partner.
• Should avoid prostitution.
• Should use condom for prevention during coitus.
• Should consult doctor if doubt.

Question 23.
(i) What is meant by sedimentary cycle?
(ii) Depict diagrammatically the phosphorus cycle or sulphur cycle.
Answer:
(i) Sedimentary Cycle: It involves cycling and recycling of reservoir of various minerals such as phosphorous or sulphur etc. of lithosphere or soil between living and non-living.

(ii) Phosphorus Cycle: The crystalline rocks are the major natural source of phosphorus which on their weathering add phosphates to the soil. Phosphates are also put into in the form of artificial fertilizers. These phosphates get dissolved in water and are absorbed by plants via the roots. These are then passed to animals through food chains. These phosphates are returned back to the soil when bacteria and fungi decompose their excreta or their dead bodies (plants and animals). However, sometimes inorganic phosphates molecules are released on the decomposition of the organic phosphate molecules. These are then incorporated with metals like aluminium, iron or calcium and from the compounds which remain unavailable to plants and is, thus, lost to the cycle, Phosphorus present in bones and teeth is also resistant to decay and may remain outside the natural cycle for a considerable time.

Fig. Phosphorus Cycle

Question 24. What is ecological spectrum? Describe it with labelled diagram.
Answer: Ecological spectrum deal about distribution of species in a ecosystem and their habitat readiness. For better understanding of ecological spectrum must be required study about species area relationship which are diagrammatically represented as follows-

Famous German naturalist Alexander Von Humbolt during deep observation demonstrated that within a region, species richness increased with increasing explored area, but only up to a limit. In fact, the relation between species richness and area for a wide variety of taxa turns out to be a rectangular hyperbola. On a logarithmic scale, the relationship is a straight line described by the equation.
log S = log C + Z log A
where S = Species richness,
Z = Slope of the line,
C = Y-intercept.

Question 25. Describe briefly on the Carbon Dioxide cycle.
Answer:
(a) Carbon Dioxide Cycle: Atmospheric carbon dioxide is virtually the exclusive carbon source and with water one of the two major oxygen sources for the construction of living matter. The gas enters the living worlds through photosynthesis in which it is a fundamental raw material. Photosynthesis incorporates CO₂ into organic substances and these are partly used in the construction of more living matter.

The CO₂ content of the atmosphere is replenished not only through biological combustion or respiration but also through non-living combustion of real gases. In the first case CO₂ is a byproduct and is returned to the environment immediately in the second it is a decay product returned after death. The release of CO₂ into the air in forest libres and in the burning of industrial fuels actually. Constant living delayed competition of carbon cycle.

The combustible substances in wood, coal, oil and natural gas all are organic compounds that are manufactured through Photosynthesis.

Question 26. What is meant by ecosystem and what are the types?
Or, Describe the pond an example of fresh water ecosystem.
Answer: Odum has defined ecosystem as the basic fundamental unit of ecology which includes both the oranisms and the nonliving environment, each influencing the properties of the other and each is necessary for the maintenance of life.

Types of Ecosystem:
(a) Terrestrial ecosystem:

1. Cropland ecosystem
2. Grassland ecosystem
3. Forest ecosystem
4. Desert ecosystem

(b) Fresh water ectirsystem:

• Pond ecosystem
• Lake ecosystem
• River ecosystem

(c) Marine ecosystem: Pond as an example of ecosystem – The freshwater pond as a whole represents a complete self maintaining and regulating ecosystem. The pond could be defined as a body of shallow standing water characterised by relatively quiet waters and abundant vegetation with thousands of microorganism, large plants and animals. In the pond ecosystem all the four basic units of an ecosystem are well represented. These are:

1. Abiotic substances: These are non-living components of the pond ecosystem and include basic inorganic and organic compounds such as water, carbon dioxide, oxygen, calcium, nitrogen and phosphorous, salts and their compounds, amino and humic acids etc. Only a small amount of these vital nutrients is found in soluble state in the pond water, but a much larger proportion is held in reserve solid form especially in the bottom sediments, as well as in the organism themselves. The rate of release of nutrients from the solids the solar input and the cycle of temperature, day length and other climatic conditions regulate the rate of function of the entire ecosystem of pond on day to day basis.

2. Producer organisms: In a pond the producer organisms are of following main types:
(i) Phytoplankton: These are minute floating plants, usually algae distributed through the pond as deep as light penetrates. When in abundance, phytoplankton give a greenish colour to the ecosystem such as lakes, deep ponds and even oceans. The phytoplankton of a pond usually comprises of Eudorina. Volvox, Clostridium, Microcystis, Anabaena, Oscillatoria, Euglena, Ceratium and Melosira.

(ii) Zooplankton: These animals drift on the water surface through the agencies of water current and include dinofilageliates helizoans and copepods.

(iii) Filamentous algae: These also occur floating in water and include Spirogyra, Oedogonium, Nitelia and Chara.

(iv) Marginal and emergent plants: These are Pomea and Jussiaea, which are found floating on the surface and phragmites, Typha and Acorns, which are rooted .plants or sedges.

(v) Submerged plants: These are Vallisneria, Potamogeton, Naias and Otellia, which are rooted to the bottom. Utricularia and Ceratophylium are rootless submerged plants.

(vi) Surface-floating plants: These are Pistia, Lemna, Wolffic and Eichomia.

3. Macroconsumer organisms: The macro consumers represent animal fauna of pond. These can be categorised into primary consumers or herbivores, secondary consumers or carnivores and tertiary consumers. The primary macro consumers feed directly upon living plant or their remains and are of the following types.

Question 27. Give an account of foetal membrane and its type.
Answer: Foetal membranes are membranous coverings and sacs connected to the embryo. They are four in number Chorion, Amnion, Allantois & Yolksac.

1. Chorion: It is the outermost foetal membrane formed by the trophoblast. It forms chorionic villi and other foetal parts of placenta.
2. Amnion: It lies just outside foetus, formed by inner layer of trophoblast. It gives protection and prevents desiccation of embryo.
3. Allantois: It is a membrane lined small sac which develops from embryonic gut close to yolk sac. It forms umbilical cord of placenta.
4. Yolk sac: It is a membranous lined sac which develops from embryonic gut. The sac contains yolk in egg laying animals. It is non functional in mammals where yolk is not stored. In mammals, in early foetus, yolk forms bipod cells and later on it reduces.

Question 28. What is Acquired immuno Deficiency Syndrome? Write an essay on its pathogen, transmission, etiology, diagnosis and remedy. Write about measures of precaution to be taken against this disease.
Answer: Acquired Immuno Deficiency Syndrome is a kind of secondary immune deficiency disease whose infection takes place by Human Immuno-deficiency Virus. HIV is a kind of retrovirus which contains a protein coat to cover its RNA. The normal immune system of infected human being gets distorted. As a result even ordinary infection leads to lethal condition. According to report of UN AIDS (2000) India is 2nd largest country affected by AIDS next to South Africa. In India, maximum number of AIDS patients are in four states viz-Maharastra, Tamil Nadu, Manipur & Punjab.

In India some of the reasons for intense infection of AIDS are:

• Ignorance & prejudice against the disease
• To understand it as contagious disease
• Reluctance of doctors towards treatment of the disease
• Confidentiality of the treatment
• Unnatural sexual behaviour
• Immoral unprotected sex
• Insufficient facilities of its diagnosis and insufficient funding
• Illiteracy among women.

Mode of transmission: Various modes of transmission of HIV are:

• Unprotected sexual intercourse
• Infected blood transfusion
• Use of contaminated hypodermic needles or syringe
• Infected organ transplantation
• From infected mother to baby during parturition
• Breast feeding by infected-woman.

Diagnosis: ELISA test and Western Blot test are the most effective diagnostic tool to test the AIDS. Other kind of diagnostic methods are dot blot, latex agglutination test, particle agglutination test etc.

Symptoms:

• HIV attacks helper T-cells of adaptive immunity and reduces their number. As a result adaptive immune system of the person becomes very weak.
• Swelling of lymph nodes known as lymphadenopathy.
• Lymphoma
• Excessive loss of platelets in blood leading to internal haemorrhage.
• Deterioration in brain.
• Loss of memory and power of thinking.
• Appearance of several wounds in skin which change to skin cancer.
• Infection of pneumonia in lungs.

Treatment: In Indian medicine company ‘Cipla’ has launched three effective medicines against AIDS Stavudine, Lamivudine, Nevirapine. 2. Another effective medicines are-Protease inhibitor, Azidothymindene (AZT), Sustiva or Efavienz, XQ-9302, Interleukin, Nanoxynol-9 etc. 3. Some of the important effective vaccines against AIDS are-AIDS, VAx, ALVAC, Cananripox vaccines and DNA vaccines etc.

Prevention and control: In india, three are four AIDS reference centres as – All India Institute of Medical Science (AIIMS), New Delhi, National Institute of Virology, Pune; Centre for Advance Research on Virology, Vellore and Natinoal Institute of Communicable Diseases, New Delhi, National AIDS Control Organization (NACO), Delhi was established in 1992. Supreme Court of India has declared marriage of AIDS infected person illegal. NACO has started “Dial-1097” facility in some cities of India on which information and consultancy services against AIDS are free of cost.

Some of the important means to prevent AIDS infection are:

• To avoid illegal and unprotected sexual intercourse.
• To test the blood of donor for AIDS before its transfusion.
• Always use disposable needle and syringe for injection.
• To avoid reuse of razor, blade and inner wear of infected person.
• To create ample management for the awareness of this disease by advertisement, newspapers, magazines, televisions and non government organism (NGOs).
• To implement National AIDS Policy, April 2002.