Write short notes on each of the following in about 150 words:
(a) What are ecotones? Explain by giving examples. Also write a note on 'edge effect'. (10 marks)
(b) Comment on 'measures of central tendency of data'. (10 marks)
(c) Describe principle,

Question

Write short notes on each of the following in about 150 words:
(a) What are ecotones? Explain by giving examples. Also write a note on 'edge effect'. (10 marks)
(b) Comment on 'measures of central tendency of data'. (10 marks)
(c) Describe principle, working mechanism and applications of gel electrophoresis. (10 marks)
(d) 'Conditioned learning' in animals. (10 marks)
(e) Klinefelter's syndrome and Turner's syndrome in humans. (10 marks)

UPSC Answer Check · Accepted Answer

(a) Ecotones and edge effect 
An ecotone is a transitional zone between two adjacent ecosystems, where their biotic and abiotic conditions overlap. It is often called a tension zone because species from both communities meet, compete, and sometimes hybridise, producing a unique assemblage with higher local diversity. For example, the grassland–forest ecotone in the Terai region of Uttar Pradesh and Bihar shows a gradient from open grasses to dense sal and bamboo forest, with distinct bird, mammal and insect communities. The edge effect refers to the intensified biological activity at such boundaries: light, moisture, temperature and wind change abruptly, creating microhabitats that support more species than either interior ecosystem. Thus ecotones are important for conservation, as they maintain connectivity, gene flow and habitat heterogeneity, but they are also vulnerable to fragmentation and invasive species. Such zones are ecologically dynamic and require landscape-level management to preserve their biodiversity.

(b) Measures of central tendency of data 
Measures of central tendency summarise a data set by a single typical value. The arithmetic mean is common: AM = (x1 + x2 + ... + xn)/n; it is best for normal, symmetrical distributions. The geometric mean, GM = (x1 × x2 × ... × xn)^(1/n), is used for ratios, rates and growth data, such as compound interest, bacterial growth or crop-yield indices. The harmonic mean, HM = n / (1/x1 + 1/x2 + ... + 1/xn), suits rates and reciprocals, for example speed or per-capita consumption. The median is the middle value after arranging data in order; it is preferred for skewed distributions with outliers, such as income or landholding data. The mode is the most frequent value and is useful for discrete, categorical or multimodal data. In Indian agricultural statistics, they analyse rainfall, mandi prices, yields and household consumption; the median suits uneven distributions.

(c) Gel electrophoresis 
Gel electrophoresis separates charged molecules, mainly DNA, RNA or proteins, according to their charge-to-size ratio in an electric field. The sample is loaded into wells in a gel matrix; agarose is used for nucleic acids, while SDS-PAGE uses polyacrylamide with SDS to make proteins migrate mainly by size. When current is applied, negatively charged DNA moves toward the anode, and the gel acts as a molecular sieve: smaller fragments move faster and farther, while larger fragments remain nearer the wells. Over the resolving range, migration distance or mobility varies approximately linearly with the logarithm of molecular weight, allowing size estimation. A simple gel has wells at one end; smaller fragments form bands farther away. Applications include DNA fingerprinting, paternity testing, forensic identification, and wildlife forensics in tiger and poaching cases, where DNA from hair, faeces or carcass helps identify species and individuals.

(d) Conditioned learning in animals 
Conditioned learning is the acquisition of new responses through experience, rather than innate reflexes. In classical conditioning, first described by Pavlov, a neutral stimulus is repeatedly paired with an unconditioned stimulus until it alone evokes the response; for example, a dog learns to salivate at the sound of a bell if the bell is followed by food. In operant conditioning, studied by Skinner, an animal learns to connect its own behaviour with consequences: a rat presses a lever to receive food, and the response is strengthened by reinforcement. Key processes include acquisition, when the association is formed; extinction, when the conditioned stimulus is presented without reinforcement and the response weakens; and generalisation, when similar stimuli elicit similar responses. Indian examples include training elephants in Kerala using repeated cues, rewards and correction, where classical and operant principles operate together. Such learning is important in animal husbandry, wildlife management and behavioural research.

(e) Klinefelter’s and Turner’s syndromes 
Klinefelter’s syndrome is a sex-chromosome disorder in males with karyotype 47,XXY, usually caused by nondisjunction during meiosis. It is the commonest sex-chromosome abnormality in males, with an incidence of about 1 in 500–600 live male births. Affected individuals are phenotypically male but show male hypogonadism, small testes, reduced testosterone, tall stature, gynaecomastia, sparse facial hair and infertility due to impaired spermatogenesis. Turner’s syndrome occurs in females with karyotype 45,X, also due to nondisjunction or structural loss of one X chromosome, with an incidence of about 1 in 2000–2500 live female births. Females are short, have a webbed neck, low posterior hairline, cubitus valgus, lymphoedema, congenital heart defects and primary amenorrhoea because of ovarian dysgenesis. Mosaic forms, such as 46,XY/47,XXY, may show milder features. Turner patients often need growth hormone and oestrogen replacement. Both conditions illustrate how sex-chromosome imbalance affects development, and both require clinical assessment, hormonal management and genetic counselling.

Write short notes on each of the following in about 150 words: (a) What are ecotones? Explain by giving examples. Also write a…

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