Bihar Board 12th Biology Important Questions Long Answer Type Part 3

Bihar Board 12th Biology Important Questions Long Answer Type Part 3 are the best resource for students which helps in revision.

Bihar Board 12th Biology Important Questions Long Answer Type Part 3

Question 1.
Write an explanatory note on the efforts for conservation of biodiversity in India.
Indian region has contributed significantly to the global biodiversity. If is die centre of diversity of animal species, crop plants, fruit plants and vegetables, edible diascroeas, alocasia, colocasia; spices and condiments etc. It also represents a secondary centre of domestic for some animals and plants. Efforts are being made for conservation of biodiversity in India through following biodiversity management systems:

(i) The in situ conservation of biodiversity is being carried out through sphere Reserves, National Parks, Wildlife Sanctuaries and other protected as by the Ministry of Environment and Forests.

(ii) The joint forest management systems involve forest departments and local communities. This enables the tribal people and local communities to have access to non-wood forest products and at the same time protect the forest resources.

(iii) The 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.

(iv) Botanical and zoological gardens are established to have large collections of plants and animal species in different climatic regions of India.

(v) The landraces and diverse food and medicinal plants are also being conserved by the tribal people and women working individually or with various non-Govt. agencies.

Question 2.
How do plants adapt to water scarcity and saline environments.
Adaptations to Water Scarcity: The plants of hot deserts are adapted to survive in dry conditions of soil and high temperatures. The plants which evade dry conditions are known as ephemerals. These have the following adaptations:

  • They have deep tap roots which can reach up to water table level in arid climates as in Prosopis (mesquite), palms and some species of Acacia.
  • Stomata are sunken in Oleander (Nerium).
  • Leaves are deciduous, leathery with waxy cuticle in order to perform low respiration.
  • In Cacti, leaves are reduced to spines and stems are modified into fleshy and spongy structures., Some cacti have expandable stems for storing water and have spreading root systems in the surface layer of the soil.

Adaptation in Saline Environments: Halophytes are plants of saline environment which are adapted to grow in high concentration of salt in soil or water. They occur in tidal marshes and coastal dunes, mangroves and saline soils.
(i) Halophytic plants, under hot and dry conditions, may become succulent and dilute the ion concentration of salts with water which they store in cells of stems and leaves.

(ii) Managroves which grow in marshy conditions can excrete salts through the salt glands on the leaves. Some mangroves can expel salts from roots by pumping excess salts back into soil.

(iii) Dunaliella species (green and halophytic algae found in hyper saline lakes) can tolerate saline conditions by accumulating glycerol in the cells, which helps in osmoregulation.

(iv) Avicennia and Rhizophora (red mangrove) have special adaptations like pneumatophores, prop and stilt roots and vivipary (seeds germinate while on the tree). The presence of pneumatophores (the respiratory roots) helps to take up oxygen from the atmosphere and transport it to the main roots. Prop and stilt roots in many species of mangroves support to the plants in wet substratum. Vivipary permits plants to escape, the effect of salinity on seed germination.

Question 3.
What is mutualism? Give its examples both from plants and animals.
Mutualism: It is a relationship between two organisms where both are benefited for food, shelter and substratum for attachment. Mutualism may or may not involve close physical association, between the in disiduals of pairs of species. It is a functional association, not merely living together, li may be obligate (species are completely dependent upon each other) or facultative (one species may survive even in the absence of the other partner species). The condition in which there is a close physical association between the individuals of a pair of species is also called symbiosis (living together). It is mainly an obligator association.

Example: (i) The association of Trichonympha and termite is symbiotic Trichonympha lives in the gut of termites and digests the cellulose of wood for them and in turn, termite provides food, shelter and constant internal environment to the Trichonympha.

(ii) The relationship between water fern, Azolla and nitrogen fixing bacteria (Anabaena) is symbiotic. Azolla is a small, fast growing aquatic fern which carries cyanobacteria (Anabaena azolla) in its leaf cavities. It fixes nitrogen from the air and gives it to Azolla and ultimately to soil and in turn, Azolla provides nutrition to the Anabaena.

(iii) The fungal symbiotic association with algae is called lichens. The algae manufacture the food by the process of photosynthesis and shares with fungi. On the other hand, fungus provides are structural covering and anchorage to the algae. It also traps the moisture in the atmosphere and gives it to algae for photosynthesis.

(iv) Nitrogen fixing bacteria (Rhizobium) live in root nodules of legumes where the bacterium derives nutrition from the host plant but fixes the atmospheric nitrogen and makes it available to the plants.

(v) Mycorrhizae are mutualistic relationship between fungi and roots of higher plants. The fungus helps in mineral nutrition of the plants with which they are associated and obtains, in turn, carbohydrates from plants.

(vi) The relationship between sea anemone and shell of hermit crab is facultative mutualism. The sea anemone grows on the back of the crab providing camouflage and protection (the sea anemone has stinging cells) and in, turn, the sea anemone is transported about reaching new food sources. This type of mutualism is also called protocooperation.

Question 4.
How can biotechnology contribute to sustainable agriculture?
Or, Elaborate as to how biotechnology can be helpful in achieving sustainable agriculture.
Biotechnology contributes to sustainable agriculture by developing biofertilizers, biopesticides, disease and insect resistant varieties and single cell proteins:

(i) Biofertilizers: These are the living organisms which bring about soil nutrients enrichment due to their biological activity. The main sources of biofertilizers are bacteria, cyanobacteria and fungi. The symbiotic bacteria like Rhizobiufn is found in the root nodules of legumes and they bear the capability of fixing atmospheric nitrogen. The free living Azotobacter can fix atmospheric nitrogen and make it available to crops. Similarly, some cyanobacteria (Anabaena Azolla) form symbiotic association with the fern Azolla.

Insoluble forms of soil phosphorus are converted into soluble forms by certain micro-organisms. This makes phosphorus available to the plants Mycorrhiza is the symbiotic association of fungal hyphae and roots of higher plants. These fungi solubilize phosphorus, produce plant growth promoting substances and protect host plants from soil pathogen.

Biofertilizers are a low cost input and they do not pollute the environment. They also reduce the dependence on chemical fertilizers.

(ii) Disease and insect resistant varieties: Genetic engineering has enabled the development of crop varieties which are resistant to certain insects and diseases. This approach has produce varieties resistant to diseases caused by bacteria and fungi as well. Development of disease and insect resistant varieties has expected to minimize the use of chemical for their control and as a result, pollution.

(iii) Single cell protein: Single cell protein is microbial biomass rich in high quality protein. These serve as valuable food and feed supplements. It reduces the pressure on agricultural production systems for the supply of the required proteins. In addition, SCP production based on industrial effluents helps to reduce environment pollution.

Question 5.
Briefly describe the applications of biotechnology in the field of medicine.
Biotechnology has a wide range of applications in the field of medicine. Its applications in medicine include the prevention of disease, early diagnosis of disease, treatment of disease, genetic counselling, gene therapy and forensic medicine.

These are briefly discussed as under:
(1) Development of Vaccine for Immunity: Vaccines are chemical substances prepared from the proteins (antigens) of the other animals which confer immunity to a particular virus. The development of vaccines through P biotechnology includes the following three ways:

(a) Separation of pure antigen using a specific monoclonal antibody interferons (protein having a property of inhibiting viral infection and cell proliferation) have been purified by using monoclonal antibodies. These are? used for the treatment of cancer.

(b) Synthesis of antigen with the help of cloned gene. These are the examples of vaccines produced by the cloned gene – vaccine for hepatitis B virus and vaccine for malaria.

(c) Synthetic peptides as vaccine. These are the vaccines for smallpox, rabies, poliovirus and for cancer and foot and mouth disease virus (FMDV).

(2) Diagnosis of diseases: For the diagnosis of various diseases the biotechnology has provided two very effective and sensitive tools: monoclonal antibodies and DNA probes. These are being prepared and made available for the diagnosis of a variety of diseases e.g. diseases caused by the protozoans and helminths, sexually transmitted diseases, congenital diseases.

(3) Treatment of diseases: Various drugs for the treatment of various diseases are also manufactured using biotechnology. Treatment of a disease can also be affected via gene therapy. Various drugs produced through biotechnology are – Insulin, Interferons, growth hormones (prototrophin in USA and somatonorm in UK), human blood clotting factor VIII : C, immunogenic proteins etc.

The ultimate goal of the gene therapy is the gene replacement therapy. At present, the current strategy for gene therapy largely centres around gene augmentation i.e., replacement of the defective or missing gene by introducing a foreign gene. Live adino viruses are being used, in the US military personnel as the vaccine to cure lung disorders.

In 1993, adopting IVF technology (in vitro fertilization technology), Dr. A. Handyside of London got success in producing a genetically engineered female baby (C. O. Brein), whose parents transmitted the genetic disease (crystic fibrosis) in earlier four babies, who died later on. But this genetically engineered body is neither sufferer nor carrier of the disease.

(4) Forensic Medicines: Forensic medicine is used for the identification of criminals such as murderers and rapists; reuniting the lost children; solving disputed problems of parentage; etc with the help of DNA finger printing.

(5) Medicinal uses of moulds: Some of the important medicinal products from moulds are penicillin (Penicillium notatum), citric acid (Aspergillus niger) and gluconic acid fermentation.

Question 6.
Discuss the causes and effects of global warming. What measures need to taken to control global warming.
Or, Account for the causes of green house effect. How does this effect us?
Green House Effect: It is the phenomenon where global warming occurs due to enhanced level of carbon-di-oxide in the atmosphere. It overs due to excessive accumulation of CO2 in the atmosphere, which permits the sunlight to reach the earth’s surface. The earth sends back infrared radiation’s back, into the atmosphere and these get absorbed by the green house gases present in the atmosphere.

The atmosphere radiates part of this energy back to the earth. This downward flux of radiation, called greenhouse flux, keeps the earth warm. So, the atmospheric greenhouse gases forming a blanket over the earth, control the escape of heat from, the earth’s surface to outer space. This leads to increase in the global temperature and this is referred to as Green house effect.

If there is excess increase in concentration of greenhouse gases in the atmosphere, then it would retain more and more of the infrared radiation, resulting enhanced greenhouse effect. Consequently, there will be increase in the global mean temperature which is referred to as global warming.

(a) it will cause melting of polar ice cap and glaciers.

(b) It will also cause rise in sea level and violent tidal waves resulting in flooding of popular coastal plains, increase in the flow of rivers and change in rainfall pattern. It will produce negative impacts on human settlements, tourism, freshwater supplies fisheries, exposed infrastructure, agricultural and drylands and wetlands.

(c) The warming of atmosphere will increase its moisture carrying capacity. The troposphere will warm up and the stratosphere will cool down. This would cause widespread changes in precipitation patterns due to changed pattern of air mass movements.

(d) The climatic conditions will change and this will increase threat to human health particularly in tropic and subtropical countries due to change in ranges of disease vectors, water-borne pathogens etc.

Question 7.
What is biological control? Give its examples.
It is the control of destructive insects (pets) with the utilization of another insects. The biopesticides (predators or beneficial organisms) are multiplied by artificial breeding in the laboratory conditions and then, they are released in the environment to parasitize the pests.

(i) Scale insect is a pest of citrus orchid. Australian lady budge are generally introduced in combating the scale insects that feed on plant sap.

(ii) The aphids are the pest of common vegetables and they are destructed by the use of ladybird or the praying mantis. Similarly, dragonflies are useful to get rid of mosquitoes.

(iii) Soil bacterium, Bacillus thuringiensis acts as a biopesticide. The spores of this bacterium produce the insecticidal cry protein which kill the caterpillars of certain insects. The commerical preparation of B. thuringiensis contains a mixture of spores, cry protein and insert carrier. These are sprayed on vulnerable plant such as Brassicas and fruit trees where they are eaten by the insect larvae.

In the gut of the larvae, the toxin is released and the larvae get killed. The bacterial disease will kill the caterpillars but leave other insects unharmed. The use of biopesticides is reducing the application of chemicals and ultimately helping in sustainable agriculture development.

(iv) Similarly, bioherbicide obtained from fungus Trichoderma is used to control several plant pathogens.

(v) Baculoviruses (Nucleopolyhdedrovirus) are the biological control agents that attack insects and other arthropods. These viruses are excellent candidates for species-specific and have no negative impacts on plants and other organisms or even on non-target insects.

Question 8.
State the hypothesis of Oparin and Haldane about the primordial Earth condition. What do you understand by Haldane’s hot dilute soup? State its significance.
Oparin-Haldane suggested that life comes into existence as a result of chemical evolution which took place on the primordial death under the impact of certain favourable conditions which no longer exist. In the beginning, earth was in the form of hot gases which gradually cooled down and formed the primordial earth. In the ocean of primordial earth, endless chemical reactions occured in the presence of heat, cosmic rays and lightening in reducing atmosphere and formed the complex molecules. These complexes gradually transformed into life.

During the evolution of life, atmospheric water vapour condensed into drops of water and fell as rain. This caused the rolling down of rock surfaces and accumulated to form liquid pools and oceans. In this process, erosion of rocks and washing of minerals into the oceans occurred. This resulted into the production of hot dilute soup.

Significance: Haldane’s hot dilute soup set the stage for combination of various chemical elements. The chemical reactions resulted into the formation of carbohydrates, fatty acids, amino acids and synthesis of other complex substances probably in the sea.

Question 9.
What is meant by analogous organs? Give on example from animals and one from plants?
Analogous organs: The organs that perform the same function but differ in their origin and structure, are called as analogous organs.

(i) The wings of an insect are analogous to those of birds and bats because they perform the same function but have dissimilar structure and origin. The wings of an insect are modified outgrowth of the body wall whereas wings of birds and bats are modified forelimbs.

(ii) Potato and sweet potato are analogous organs as both perform the same function of storage of food but they differ in their structure. Potato is an underground-modified stem whereas sweet potato is a modified adventitious root.

(iii) Fins of fishes and flippers of whales are analogous organs because both perform the function of swimming but the flipers of whale are pentadactyl and fins of fishes are not pentadactyl.

(iv) Stings of honey bee and scorpion are analogous structures as both perform the same function. The sting of honey bee is modified ovipositor where as in scorpion, it is modified last abdominal segment.

(v) The eye of an octopus and the eye of a mammal differ in their retinal position but both perform the same function. Similarly, the flippers of penguin (bird) and dolphin (mammal) that perform similar functions in these aquatic animals have originated from different structures of two different lineages.

Question 10.
How do homologous organs, analogous organs and vestigial organs support the theory of organic evolution?
Or, How do morphological and anatomical evidence support organic evolution. Explain with examples.
(i) Homology and analogy: The organs of similar structure and origin but dissimilar in function and form are called as homologous organs and this phenome on is called homology. The presence of homologous organs implies a common evolutionary origin of amphibians, reptiles, birds and mammals from some ancient fish ancestor. The homologous structures seen in successive generations indicate actual relationship and the possessors are the diverse descendants of common ancestry (Divergent evolution).

The organs that perform the same function but differ in their origin and structure, are called as analogous organs and the phenomenon is called analogy. The wings of an insect are analogous to those of birds and bats because they perform the same function but have dissimilar structure and origin. The wings of an insect are modified outgrowth of the body wall whereas wings of birds and bats are forelimbs. These organs have arisen in evolutionary process through adaptation of quite different organisms to a similar mode of life (Convergent evolution).

On the same line, the similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry. These biochemical similarities point to the same shared ancestry as structural similarties among diverse organisms.

(ii) Vestigial organs: These are the reduced and functionless organs which are of no use to the possessor but they still persists generation after generation in reduced form in an individual. They were complete and functional in the anestorseg; appendix in man is considered as the remnant of large intestine (caecum) but it is considered to be storage organ for cellulose digestion in herbivorous mammals. The vestigial organs which used to perform a normal function in the ancestor but during the course of evolution, they have been reduced to vestiges.

(iii) Atavism: It is reappearance of ancestral characters other than parents in the newly born offspring, which have either completely disappeared or reduced. The reappearance of short tail in some babies, multiple mammal in some individuals and dense hairy body etc. are the example of atavism. The reappearance of such ancestral characters favour evolultion.

(iv) Connecting links: The orgaisms which possess the characters of two different groups of organism are known as connecting links eg., duckbilled platypus and spiny anteater serve as a connecting link between the mammals and reptiles. Similarly, lungfishes (Protopterus) is a connecting link between fishes and amphibians.

Question 11.
Describe the model of DNA as give by Watson and Crick.
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).

Bihar Board 12th Biology Important Questions Long Answer Type Part 3, 1
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 12.
(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?
(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.

Bihar Board 12th Biology Important Questions Long Answer Type Part 3, 2

(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 13.
Describe about gametogenesis in human.
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.
Bihar Board 12th Biology Important Questions Long Answer Type Part 3, 3

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.
Bihar Board 12th Biology Important Questions Long Answer Type Part 3, 4

(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 14.
Describe in brief about sexually transmitted diseases.
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 15.
(i) What is meant by sedimentary cycle?
(ii) Depict diagrammatically the phosphorus cycle or sulphur cycle.
(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.
Bihar Board 12th Biology Important Questions Long Answer Type Part 3, 5
Fig. Phosphorus Cycle

Question 16.
What is ecological spectrum? Describe it with labelled diagram.
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.
Bihar Board 12th Biology Important Questions Long Answer Type Part 3, 6

Question 17.
Describe briefly on the Carbon Dioxide cycle.
(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.
Bihar Board 12th Biology Important Questions Long Answer Type Part 3, 7

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 18.
What is meant by ecosystem and what are the types?
Or, Describe the pond an example of fresh water ecosystem.
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.
Bihar Board 12th Biology Important Questions Long Answer Type Part 3, 8

(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 19.
Give an account of foetal membrane and its type.
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.

Bihar Board 12th Biology Important Questions Long Answer Type Part 3, 9

Question 20.
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.
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.


  • 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.