CBSE Class 12 Biology Question Paper (Outside Delhi 2017) with Solutions

Students can use CBSE Previous Year Question Papers Class 12 Biology with Solutions and CBSE Class 12 Biology Question Paper (Outside Delhi 2017) to familiarize themselves with the exam format and marking scheme.

CBSE Class 12 Biology Question Paper (Outside Delhi 2017) with Solutions

Time Allowed: 3 Hours
Maximum Marks : 70

General Instructions:

1. All questions are compulsory.
2. Question number 1 to 5 are very short answer questions and carry 1 mark each.
3. Question number 6 to 10 are short answer questions and carry 2 marks each.
4. Question number 11 to 22 are also short answer questions and carry 3 marks each.
5. Question number 23 is a value based question and carry 4 marks.
6. Question number 24 to 26 are long answer questions and carry 5 marks each.
7. Use log tables, if necessary. Use of calculator is not allowed.

Section – A

Question 1.
Our government has intentionally imposed strict conditions for M.T.P. in our country. Justify giving a reason.
Answer:
Our government has imposed strict conditions for M.T.P. to avoid its misuse. Such restrictions are very important to prevent sex determination before birth of a child and illegal female foeticides in our country. MTP are considered relatively safe during the first trimester, i.e., upto 12 weeks of pregnancy.

Note
MTP stands for medical termination of pregnancy is defined as the intentional or voluntary termination of pregnancy before full term. It is done to got rid of unwanted pregnancies failure of the contraception used during coitus or rapes.

Question 2.
State the fate of a pair of autosomes during gamete formation.
Answer:
The homologous pair of autosomes will separate from each other and will move to different gametes during gamete formation.

Question 3.
What role does an individual organism play as per Darwin’s theory of natural selection ?
Answer:
As per Darwin’s theory of natural selection, an individual organism in a population is responsible for passing on the variation and favourable mutations to the next generations by taking part in a successful event of sexual reproduction.

Question 4.
Suggest a method to ensure an anamnestic response in humans.
Answer:
Anamestic response is the secondary immune response which is produced when the body encounters the same antigen which is entered previously in the body. As the body recognises the pathogen, immune system starts producing antibodies against the foreign antigens for subsequent encounter and this response is very intense.

Question 5.
What is biopiracy?
Answer:
Biopiracy is the term used to refer to the use of bio-resources by multinational companies and organisations without proper authorisation from the countries and people concerned without compensatory payment. For example, basmati is a type of fragrant rice variety grown in India. But some US based companies crossed this Indian basmati rice with their local variety and produced Texmati – a new American fragrant rice variety and used it commercially.

Section – B

Question 6.
A mature embryo-sac in a flowering plant may possess 7-cells, but 8-nuclei. Explain with the help of diagram only.
Answer:
A mature embryo sac in a flowering plant possess 7 cells, but have 8 nuclei. This can be understood with the help of diagram given below:

Question 7.
Describe the structure of a nucleosome.
OR
Mention the evolutionary significance of the following organisms :
(a) Shrews
(b) Lobefins
(c) Homo habilis
(d) Homo erectus
Answer:
DNA is organized into bead structure called nucleosome. There is a set of positively charged, basic proteins called histones, which are rich in basic amino acids – lysine and arginine. They have positively charged side chains. Histones organize into unit of 8 molecules called histone octamer. Negatively charged DNA is wrapped around this positively charged octamer to form nucleosome. One histone octamer has 8 histones. One nucleosome (DNA + histone octamer) attaches to other nucleosome with the help of linker DNA associated with HI protein.

A typical nucleosome contains 200 bp of DNA helix. Nucleosome forms chromatin in the form of bead on string. Chromatin condense/super coil at metaphase stage to form chromosomes. Packaging of chromatin to chromosomes occurs with the help of additional set of proteins called NHC (non-histone chromosomal) proteins.

Note
In a nucleus, some of the region of chromatin are loosely packed (and stains light) and are referred to as euchromatin The chromatin that is more densely packed and stains dark are called heterochromatin.

OR

(a) Shrews were the first mammals. These were the long-tailed insectivorous, squirrel-like creatures, which gave rise to the primitive primates, namely lemurs and tarsiers in the beginning of the tertiary period (Palaeocene epoch).

(b) The discovery of Coelacanth (lobefins) first amphibians is significant as they prove that amphibian have evolved from fish-like organisms. Lobefins were the ancestors of modern day frogs and salamanders.

(c) Homo habilis were the first human-like primate who lived in Africa about 2 million years ago. Their brain capacities were between 650- 800cc and they had bipedal locomotion, moved erect and probably didn’t eat meat.

(d) Homo erectus were the next primates evolved from Homo habilis about 1.5 mya. They had a large brain capacities around 900cc and they had an erect posture. They probably ate meat.

Question 8.
In an agricultural field there is a prevalence of the following organisms and crop diseases which are affecting the crop yield badly :
(a) Write rust
(b) Leaf and stripe rust
(c) Black rot
(d) Jassids
Recommend the varieties of crops the farmers should grow to get rid of the existing problem and thus improve the crop yield.
Answer:

S. No.	Crop Disease/ Organism	Resistant Crop Variety
(a)	White rust	Pus a Swarnim
(b)	Leaf and stripe rust	Himgiri
(c)	Black rot	Pusa Shubhra
(d)	Jassids	Pusa Sem 2

Normal varieties of crops are prone to infection by various pathogens result in poor growth of crops. To get rid of existing problems, the farmers should grow improved hybrid varieties as these are resistance to fungi, bacteria and viral diseases.

Question 9.
How does the application of the fungal genus, Glomus, to the agriculutural farm increase the farm output?
Answer:
Glomus belongs to the genus fungi that are found in symbiotic relationship with the roots of the seed plants (mycorrhiza). Phosphorus is absorbed by the fungi from the soil and passed into the plants and in return derives sugar from the plant cell for survival. Thus the application of the fungal genus, Glomus, to the agricultural farm increases the farm output due to increased phosphorus availability to the crops.

Question 10.
Plenty of algal bloom is observed in a pond in your locality.
(a) Write what has caused this bloom and how does it affect the quality of water
(b) Suggest a preventive measure.
Answer:
(a) Cause – Algal blooms are caused due to the excessive nutrients present in the water bodies. This high availability of nutrients like phosphorus and nitrogen is caused by the chemicals present in fertilisers that get dissolved in the soil and eventually get washed away to the water bodies.

Affect – These algal blooms may shade out plants that would normally live lower in the water column result in a loss of biodiversity. Eutrophication can also result in the development of hypoxic conditions. This oxygen deficiency may cause the death of aquatic organisms. They ultimately degrade the quality of water.

Note
Eutrophication is the natural aging of the lake by biological enrichment of its water.

(b) Farmers in areas that are affected by algal blooms need to find alternative ways to fertilize the soil like using manures and techniques such as vermicomposting. Also, people must use cleaning agents and detergents that are biodegradable and that do not contain phosphates. To further reduce the amount of nutrients that are causing an overgrowth of algae in lakes and streams, strict laws need to be created that regulate the dumping of waste water.

Section – C

Question 11.
(a) List the three states the annuals and biennial angiosperms have to pass through during their life cycle.
(b) List and describe any two vegetative propagules in flowering plants.
Answer:
(a) Vegetative, reproductive and senescent phases are the phases associated with annual and biennial plants.

(b) Roots and leaves are two vegetative parts of the plants which can be used for vegetative propogation. Root propagule include the propagation of a new plant through its fleshy roots, such as in the case of sweet potato and dahlia.

Vegetative propagation through leaves includes case of Bryophyllum. Adventitious buds arising from notches present at margins of leaves helps Bryophyllum to propagate vegetatively. When these buds are shed and fall on ground, they grow to form new plants.

Question 12.
Draw a labelled diagrammatic sectional view of a human seminiferous tubule.
Answer:
Diagrammatic sectional view of a seminiferous tubule (enlarged)

Note
Seminiferous tubules is lined by two types of cells such as sertoli cells and male germ cells. The male germ cells undergo meiotic divisions in sperm formation whereas sertoli cells provide nutrition to the germ cells.

Question 13.
During a medical investigation, an infant was found to possess an extra chromosome-21. Describe the symptoms the child is likely to develop later in the life.
Answer:
Down’s syndrome is a genetic disorder caused due to the presence of an additional copy of chromosome number 21 (trisomy of 21). The affected individual will have:

1. short statured with small round head
2. furrowed tongue
3. partially open mouth
4. Simian crease is prominent in the middle of the palm and broad palm
5. retarded physical, psychomotor and mental development
6. IQ is less than 25.

Note
Down’s syndrome was first described by Langdon Down in 1866.

Question 14.
A number of passengers were severely burnt beyond recognition during a train accident. Name and describe a modem technique that can help hand over the dead to their relatives.
Answer:
The technique that will help the authorities to establish the identity of the dead is known as DNA fingerprinting. Basis of DNA Fingerprinting – DNA fingerprinting is a method for comparing the DNA sequences of any two individuals. 99.9% of the base sequences in all human beings are identical. It is the remaining 0.1% that makes every individual unique.

In this, certain specific regions called repetitive DNA sequences that are different in every individual, that are used for comparative study. This repetitive DNA is separated from the bulk DNA as different peaks during density gradient centrifugation in which, bulk DNA forms major peak and the other small peaks are referred to as satellite DNA. These sequences show high degree of polymorphism and tbrm the basis of DNA fingerprinting.

Methodology of DNA fingerprinting- The DNA fingerprinting technique involves following steps:

1. Extraction – DNA is extracted from cells in a centrifuge.
2. Amplification – Many copies of extracted DNA are made by polymerase chain reaction.
3. Restriction Digestion — DNA is cut into fragments with enzymes into precise sequences.
4. Separation of DNA sequences — The cut DNA fragments are passed though electrophoresis set up containing agarose gel and the separated fragments can be seen under UV radiation.
5. Southern Blotting – The separated sequences are transferred onto a nylon membrane.
6. Hybridisation – The nylon membrane is immersed in a bath and radioactive labelled VNTR probes are added.
7. Autoradiography – The membrane is pressed onto an X-ray film and dark bands develop the probe sites which resemble bar codes.

After autoradiography, different bands are obtained which are characteristics of an individual. The presence of similarities between the casualties and their relatives determines their relatedness on the basis of which the dead bodies can be handed over to their respective relatives.

Note
The VNTR belongs to a class of satellite DNA referred to as mini satellite. A small DNA sequence which is arranged tandenly in many copy numbèrs the copy number varies from chromosome to chromosome in an individual.

Question 15.
p ² + 2pq + q ² = 1, Explain this algebraic equation on the basis of Hardy Weinberg’s principle.
Answer:
Hardy Weinberg’s principle states that allele frequencies are stable and is constant from one generation to other generation. The gene pool remains constant called genetic equilibrium. Sum total of all the allele frequencies is one. Suppose there are two alleles ‘A’ and ‘a’ in a population.

Their frequencies are p and q, respectively. The frequency of AA individual in a population is p ² . It can be explained that the probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual is simply the product of the probabilities, i.e., p ² . In the same way, the frequency aa is q ² and for Aa is pq.
p ² + 2pq + q ² = 1

where, p ² represents frequency of homozygous dominant genotype, 2pq represents the frequency of the heterozygous genotype and q ² represents the frequency of homozygous recessive.

In population genetics studies, the Hardy-Weinberg equation can be used to measure whether the observed genotype frequencies in a population differ from the frequencies predicted by the equation. If there is any difference in the frequencies, it indicates the extent of evolutionary change.

Question 16.
(a) What precaution(s) would you recommend to a patient requiring repeated blood transfusion?
(b) If the advise is not followed by the patient, there is an apprehension that the patient might contract a disease that would destroy the immune system of his/ her body.
Explain with the help of schematic diagram only how the immune system would get affected and destroyed.
Answer:
(a) If a patient requires repeated blood transfusion, he must ensure that the donor’s blood has been screened for HIV and other pathogens before blood transfusion.

(b) If this advice is not being followed by the patient he might contract AIDS (Acquired Immunodeficiency Syndrome). AIDS is a serious health problem in which the immune system of the patient gets weakened greatly. It is caused by a virus named HIV (Human Immunodeficiency Virus). It is a retrovirus, which attacks the helper T-cells of the body and greatly reduce their number. These helper T-cells are responsible for stimulating the antibody production by B-cells Thus, reduction in their number results in the loss of natural defence of our body. HIV can attack and replicate inside the host cell by using reverse transcription method, which is shown below:

Diagrammatic Representation of replication of reterovirus:-

Note
Infected cell can survive while viruses are being replicated and released.

Question 17.
(a) What is inbreeding depression?
(b) Explain the importance of “selection” during inbreeding in cattle.
Answer:
(a) Inbreeding refers to the mating of more closely related individuals within the same breed for 4-6 generations. This results in the reduction in the fertility and productivity of an organism. This is called inbreeding depression.

(b) Inbreeding is done to evolve a pureline and to express desirable superior genes in any animal. To carry out this, superior males and superior females are selected for mating which contain those desirable characteristics. In case of cattle, a superior female is a cow or buffalo that produces more milk per lactation and a superior male is the bull which gives rise to superior progeny as compared to those of other males. The improvement in traits occur due to homozygosity. The harmful recessive genes which have come together due to homozygosity are eliminated through selection.

Question 18.
Describe how do ‘floes’ and ‘activated sludge’ help in Sewage Treatment.
Answer:
During sewage treatment the bacteria naturally present in sewage helps in the process. After primary treatment the effluent is passed into large aeration tanks where vigorous growth of useful aerobic microbes form floes. Floes are masses of bacteria associated with fungal filaments to form mesh like structures. These microbes consume major part of the organic matter in the effluent reducing biochemical oxygen demand of the effluent.

After this effluent is passed into a settling tank where these floes are allowed to sediment and called activated sludge. This is passed to anaerobic sludge digesters where other kinds of anaerobic bacteria digest the bacteria and fungi of sludge. During this digestion the bacteria produces a mixture of gases like methane, hydrogen sulphide, carbon dioxide forming biogas which is used as a fuel.

Question 19.
Explain the role(s) of the following in Biotechnology.
(a) Restriction endonuclease
(b) Gel – electrophoresis
(c) Selectable markers in pBR322
Answer:
(a) Restriction endonuclease – These are molecular scissors or biological scissors that recognizes and cuts double stranded DNA at specific points. They are used in biotechnology to form recombinant molecules which are composed of DNA from different sources. To insert a foreign DNA into an intact DNA, it must be cut from its source and the intact DNA also must be cut open. Both these processes are carried by using the same restriction endonucleases.

(b) Gel electrophoresis is a molecular biology technique which is used for the separation of DNA fragments. DNA fragments are produced by cutting with restriction.

DNA fragments are negatively charged molecules they can be separated by forcing them to move towards the anode under an electric field through a medium. The smaller, the fragment size, the farther it moves.

Note
Ethidium bromide is an intercalating agent which is used to visualise the separated DNA fragments followed by exposure to UV radiation.

(e) pBR322 has two antibiotic resistance genes, one for ampicillin and other one for tetracycline. Antibiotic resistance serves as selectable marker. If the foreign DNA is ligated at the site of tetracycline resistance gene in pBR322 vector, the recombinant plasmid will lose tetracycline resistance due to insertion of foreign DNA but can still be selected out from non-recombinants by plating the transformants on ampicillin containing medium.

The transformants growing on ampicillin containing medium are then transferred on a medium containing tetracycline. The recombinants will grow in ampicillin containing medium but not on the tetracycline-containing medium. However, the non-recombinants will grow on both. Thus by using antibiotic resistant genes as selectable markers, we
can differentiate between recombinants and non-recombinants.

Note
Insertional inactivation results in the β-galactosidase enzyme. The presence of a chromogenic substrate gives blue coloured colonies if theplasmid in bacteria does not have an inert. Presence
of insert results into insertional inactivation of the β- galactosidase and colonies do not produce any colour and are identified as recombinant Colonies.

Question 20.
Write the steps you would suggest to the undertaken to obtain a foreign-gene-product.
Answer:
Recombinant DNA technology allows DNA to be produced via artificial means. The procedure has been used to change DNA in living organisms and may have even more practical uses in the future. Recombinant DNA technology works by taking DNA from two different sources and combining that DNA into a single molecule.
To obtain rDNA steps involved are:

(a) The DNA fragment containing the gene sequence to be cloned (also known as (‘insert’) is isolated.
(b) Insertion of these DNA fragments into a host cell using a ‘vector’ (carrier DNA molecule).
(c) The rDNA molecules are generated when the vector self replicates in the host cell.
(d) Transfer of the rDNA molecules into an appropriate host cell.
(e) Selection of the host cells carrying the rDNA molecule using a marker.
(f) Replication of the cells carrying rDNA molecules to get a genetically identical cells population or clone.

Question 21.
Why do lepidopterans die when they feed on Bt cotton plant? Explain how does it happen.
Answer:
Bt cotton is an insect resistant plait which resist attack of Lepidopterans insects. The plant Bt toxin gene cause death of insect larvae by causing cdl lysis and swelling of epithelium of midgut. Bt toxin is biologically produced by bacterium called Bacillus thuriltgiensis (Bt).

This toxin is insecticidal protein crystal (cry proteins) produced in bacteria (inactive form in bacteria) during a particular phase of growth. Inactive protein (protoxin) is converted into active form of toxin due to alkaline pH of gut of insect which solubilize crystals. The attivated toxin binds to surface of midgut epithelial cell and creates pores that cause cell swelling and lysis and eventually death of the insect.

Note
Genes cry Lie and cry II Ab control the cotton bollworm while cry IAb controls corn borer.

Question 22.
“In-situ’ Conversation can help endrangered/threatened species. Justify the statement.
OR
Name and describe any three causes of bio-diversity losses.
Answer:
In situ Conservation

• It is the conservation and protection of biodiversity in natural habitat. Population is conserved in surroundings, where they have developed their distinctive features. Example: National parks, biosphere reserves, wildlife sanctuaries, etc.
• It also includes the introduction of plants and animal species back into agriculural, horticultural and animal husbandry practices so that they are cultivated/ reproduced and reused by the farmers.
• It also maintains genetic diversity of crop plants/ flowers by saving seeds for next planting season.
• Biodiversity is permanently protected.
• Facilitates scientific research of the site.
• It may be possible to improve the ecological integrity of the area and restore it if it has been damaged by poaching etc.

OR

Three causes of biodiversity losses are:

1. Habitat destruction- It is considered as the primary cause of biodiversity loss. It leads to the extinction or decrease in the number of animals living in that particular habitat. Urbanisation, industrialization, clearing forest for agriculture, filling wetlands, caused extinction of endemic species.

2. Alien species invasion- Non-native species introduced for economic and other uses, invaded and drive away the local species. Exotic/alien species have proved harmful to both aquatic and terrestrial ecosystem.

Note
The Nile Perch introduced into lake victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichild fish in the lake. Illegal introduction of the African catfish Clarias gariephinus for aquaculture purposes in posing a threat to the indigenous catfishes in our rivers.

3. Over exploitation of natural resources- Over-exploitation of resources has been one of the major contributor to this. Due to increasing human population, resource demands have increased which has resulted into exploitation of already present resources and development of various forms of energy resources. Development of these energy sources modifies natural habitat and accelerates loss of biodiversity.

Section – D

Question 23.
Public all over India is very much concerned about the deteriorating air quality in large parts of North India. Alarmed by this situation the Resident’s Welfare Association of your locality organized an awareness programme entitled “Bury not bum”. They invited you, being a biology student to participate.
(a) How would you justify your arguments that promote burying and discourage burning? (Give two reasons)
(b) With the help of flow charts, one for each practice depict the chain of events that follow.
Answer:
(a) Following arguments can be put to promote burying and discourage burning:

1. Burning wastes result in generation of various gases like CO ₂ and oxides of nitrogen and sulphur. These gases are very harmful to environment and cause various environmental issues like global warming, acid rain, etc.
2. The gases released during burning have various health hazards also, like nausea, headache, respiratory diseases, etc.

(b) Before burying of wastes, following set of events must be followed:

Section – E

Question 24.
Read the following statement and answer the questions that follow:
“A guava fruit has 200 viable seeds”.
(a) What are viable seeds?
(b) Write the total number of:
(i) Pollen grains
(ii) Gametes in producing 200 viable guava seeds.
(c) Prepare a flow-chart to depict the post-pollination events leading to viable-seed production in a flowering plant.
OR
(a) Arrange the following hormones in sequence of their secretion in a pregnant woman.
(b) Mention their source and the function they perform: hCG, LH, FSH, Relaxin
Answer:
(a) Those seeds that carry a living embryo and are capable of germinating into a seedling under appropriate conditions are termed as viable seeds.

(b) (i) Number of pollen grains required to form 200 seeds will be 200 only as each pollen grain carries to generative cells or male gametes and only one of the two are involved in zygote formation.
(ii) In total 400 gamete cells are required for production of 200 viable zygotes leading to formation of 200 guava seeds.

(c) Flow chart depicting the post pollination events:

OR

(a) The sequence of secretion of the given hormones in pregnant woman is as follows:

1. FSH (Follicle Stimulating Hormone)
2. LH (Luteinizing Hormone)
3. HCG (Human chorionic Gonadotropin)
4. Relaxin

(b)

Hormone	Source	Functions
FSH	Anterior pituitary lobe	Stimulates the growth of ovarian follicles and maturation of primary oocytes
LH	Anterior pituitary lobe	Induces ovulation and maintains corpus luteum
hCG	Chorionic cells of placenta.	Maintains the corpus luteum and stimulates the secretion of proges­terone
Relaxin	Ovary	Helps during child birth by relaxing the pelvic muscles as well as mus­cles of the cervix.

Question 25.
State and explain the “Law of independent assortment” in a typical Mendelian dihybrid cross.
OR
(a) How do the observations made during moth collection in pre and post industrialized era in England support evolution by Natural Selection?
(b) Explain the phenomenon that is well represented by Darwin’s finches other than natural selection.
Answer:
The law of independent assortment states that “when two pairs of traits are combined in a hybrid segregation of one pair of characters is independent of other pair of characters”. This law was proposed by Mendel based on the results of dihybrid crosses, where inheritance of two traits were considered simultaneously. Independent assortment is not applicable for the genes located on the same chromosomes i.e. linked genes.

The following cross between a pure-breeding plant with yellow, round seeds and another pure breeding plant with green, wrinkled seeds, can be taken as an example to explain this law.

The Phenotypic ratio is : 9 : 3 : 3: 1
9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green
Wrinkled yellow and round green are recombinants.
Round yellow and wrinkled green are parental combinations.
The genotypic ratio is:

In this cross, the factors for colour of seeds and those for shape of seeds have segregated independently and each gamete has one factor for each of these two traits.

OR

(a) Industrial mechanism is an example of the natural selection of a particular form of an organism in an environment which has changed due to the ill effects of pollution created by industrial activities. Bis ton betularia is commonly called peppered moth because of the presence of black dots on creamy-white body. These moths during 1850, were mostly gray (Biston betularia typica) and during day time used to rest on tree-trunks which had lichens grown on them.

They resembled with the background and could not be detected by their predators, mainly birds. During industrial revolution in England, the coal was burnt and the soot got deposited on the tree-trunk. Moreover, sulphur dioxide killed lichens. In such polluted areas all the moths of white coloured now could be spotted by birds. A few black individuals which had mutant gene were selected by nature. Such individuals got more chances of reproduction and the white moth were reduced in number.

After about 100 years (by 1950), more than 90% of the individuals had become black, ‘Melanie form’ (Biston betularia carbonaria). Here biologists could see the evolution occurring before their eyes. This evolution from white to black (Melanie) forms was not due to mutation but due to selection of pre-existing mutant allele by nature (Natural selection).

Now, when electricity is being used in industries, the number of white moths is again increasing. This also indicates that industrial pollution has not eliminated the genes responsible for light colour of the moth. The above hypothesis was also tested by Dr. H. B. D. Kettlewell after releasing equal number of dark and light moths.

(b) ‘Darwin’s Finches’ illustrated adaptive radiation. In this, the species, all deriving from a common ancestor, have overtime successfully adapted to their environment via natural selection. Previously, the finches occupied the South American mainland, but somehow managed to occupy the Galapagos islands, over 600 miles away.

They occupied an ecological niche with little competition. As the population began to flourish in these advantageous conditions, intraspecific competition became a factor, and resources on the islands were squeezed and could not sustain the population of the finches for long.

Due to the mechanisms of natural selection, and changes in the gene pool, the finches became more adapted to the environment. As competition grew, the finches managed to find new ecological niches, that would present less competition and allow them and their genome to be continued.

Thus the finches adapted to take advantage of the various food sources available on the island, which were being used by other species. Over the long term, the original finch species may have disappeared, but by diversifying, would stand a better chance of survival.

All in all, the finches had adapted to their environment via natural selection, which in turn, has allowed the species to survive in the longer term, the prime directive of any species.

Question 26.
(a) What is an age-pyramid?
(b) Name three representative kinds of age-pyramids for human population and list the characteristics for each one of them.
OR
Discuss the role of healthy ecosystem services as a prerequisite for a wide range of economic, environmental and aesthetic goods and services.
Answer:
(a) An age pyramid is a graphical representation of the distribution of various age groups within a population of a region forming the shape of a pyramid when the population (percent individual of a given age or age group) is growing.

(b) For human population, the age pyramid shows age distribution of males and females in a combined diagram. These age groups are pre-reproductive, reproductive and post-reproductive. The shape of the pyramids reflects the growth status of the population, Three types of pyramids namely, pyramid with broad base, bell shaped and an umlike structure indicate rapidly growing population, stable population and a declining population respectively.

OR

Human beings benefit from a multitude of resources and processes that are supplied by natural ecosystem. Collectively, these benefits are known as ecosystem services, for example, healthy forest ecosystems purify air and water, migrate droughts and floods, cycle nutrients, generate fertile soils, provide wildlife habitat, maintain biodiversity, pollinate crops, provide storage site for carbon and also provide aesthetic, cultural and spiritual values. Services can be subdivided into 5 categories –

1. Provisioning : Such as the production of food and water.
2. Regulating: Such as the control of climate and disease.
3. Supporting: Such as nutrients cycle and crop pollination.
4. Cultural: Such as spiritual and recreational benefits.
5. Preserving: Which includes guarding against uncertainty through the maintenance of diversity.