(a) What is meant by biodiversity? Explain various means of in situ conservation of biodiversity. (20 marks) (b) Describe two…

(a) Biodiversity and in situ conservation

Biodiversity is the variability among living organisms from all sources: diversity within species (genetic), between species, and of ecosystems (Convention on Biological Diversity, 1992).

In situ conservation protects species in their natural habitats, so that evolution, gene flow and ecological interactions continue and viable populations are maintained. Its means in India, which has over 1,000 protected areas, are:

• National parks: areas of high ecological value under the Wildlife (Protection) Act, 1972, with no grazing, hunting or forestry; for example Jim Corbett (the first, 1936), Kaziranga and Gir.
• Wildlife sanctuaries: protected areas where limited human use, such as regulated collection of forest produce, may continue; for example Bhitarkanika (Odisha).
• Biosphere reserves: large multi-use areas under UNESCO's Man and the Biosphere programme, with a core zone, buffer zone and transition zone; Nilgiri (1986, the first), Sundarbans and Nanda Devi. India has 18.
• Conservation and community reserves: added by the 2002 amendment of the Act; conservation reserves are government land linking protected areas, and community reserves are community or private land managed by local people.
• Sacred groves: forest patches protected by local belief, as in the Khasi Hills, the Western Ghats and the orans of Rajasthan.
• Wetland and marine reserves: Ramsar wetlands such as Chilika and Keoladeo, and the Gulf of Mannar Marine National Park (the first marine national park, 1982), protect aquatic ecosystems.
• Species projects: Project Tiger (1973) and Project Elephant (1992) protect threatened species along with their habitats.
• Biodiversity heritage sites: fragile areas notified under the Biological Diversity Act, 2002, such as Nallur Tamarind Grove in Karnataka.

In situ conservation is cheaper than ex situ methods, protects whole ecosystems with their co-evolved interactions, and lets populations keep adapting to change.

(b) Laws of learning and types of learning

Thorndike's two basic laws:

• Law of effect: a response followed by a satisfying consequence is strengthened, and one followed by discomfort is weakened.
• Law of exercise: a stimulus–response connection becomes stronger with repeated use and weaker with disuse. Thorndike himself later gave up this law, since practice alone does not strengthen a connection, and found punishment less effective than reward.

Types of learning:

• Habituation: the simplest, non-associative learning; the response to a harmless stimulus declines when it is repeated, is specific to that stimulus, and returns after a strong new stimulus (dishabituation). Examples: gill withdrawal of Aplysia to repeated touch, birds ignoring a scarecrow. It saves energy.
• Trial and error learning: the animal tries many responses and gradually keeps the rewarded one. A hungry cat in Thorndike's puzzle box scratches and bites at random until it chances on the latch (a loop or lever) that opens the door to food; the escape time falls over successive trials. A rat learning to press a lever for food is another example.
• Latent learning: learning without reinforcement that shows only when motivation appears. In the experiment of Tolman and Honzik (1930), rats given food in the maze only from day 11 improved sharply the next day and matched rats rewarded from the start, showing that they had already learned the maze layout (a cognitive map).

(c) Polymerase chain reaction (PCR)

PCR, invented by Kary Mullis in 1983 (Nobel Prize in Chemistry, 1993), amplifies a chosen DNA segment in vitro.

Principle: a DNA polymerase extends two primers, complementary to the 3′ ends of the two strands of the target, using dNTPs. As the enzyme is heat-stable, strand separation, primer binding and copying can be repeated in cycles in a thermocycler, and the target doubles in each cycle.

The mixture holds template DNA, two primers, dNTPs, Taq DNA polymerase (from Thermus aquaticus) and buffer with Mg²⁺.

Mechanism (one cycle, repeated 25–35 times):

1. Denaturation at 94–95 °C: the double helix melts into single strands.
2. Annealing at 50–65 °C, a few degrees below the primer melting temperature: primers bind to the flanking sequences.
3. Extension at 72 °C: Taq adds nucleotides to the 3′ end of each primer, copying the target.

After n cycles the target can reach 2ⁿ copies; 30 cycles give about a billion-fold amplification (2³⁰ ≈ 1.07 × 10⁹). The product is checked by agarose gel electrophoresis.

Uses:

• Diagnosis of infections (tuberculosis, HIV, COVID-19 by RT-PCR) and of genetic diseases such as sickle-cell disease, including prenatal testing.
• Forensic DNA fingerprinting and paternity tests.
• Gene cloning, sequencing and mutagenesis; gene-expression studies by qPCR.
• Ancient DNA and wildlife species identification.

Variants include RT-PCR (RNA template), real-time or quantitative PCR, nested PCR and multiplex PCR.