Write your answer in about 150 words for each of the following: (a) Write about different ways by which biodiversity is being…

(a) Threats to biodiversity Biodiversity is threatened when the processes that maintain species, genetic and ecosystem diversity are disrupted. Habitat destruction is the dominant cause: deforestation, wetland drainage, urbanisation and agricultural conversion fragment populations, reduce carrying capacity and increase extinction risk. Invasive species such as Lantana camara and Parthenium hysterophorus outcompete natives, alter fire regimes and pollination networks, and can drive endemic species into IUCN Red List categories such as Vulnerable, Endangered or Critically Endangered. Pollution adds further pressure; eutrophication depletes oxygen in water bodies, while persistent toxins cause biomagnification through food chains, affecting predators. Population overgrowth intensifies all these impacts by increasing demand for land, water and energy. Overexploitation, including overfishing, illegal wildlife trade and poaching, removes individuals faster than populations can replace them, as seen in tigers, rhinoceroses and many marine fish stocks. These five pressures are often summarised as H-I-P-P-O, and they interact cumulatively.

(b) hnRNA processing In eukaryotes, hnRNA is not immediately functional; it must be processed in the nucleus to become stable, exportable and translatable mRNA. First, a 5′ methylguanosine cap is added to the 5′ end, protecting the transcript from exonucleases, helping ribosome recognition and assisting nuclear export. Next, the 3′ end is cleaved and a poly-A tail is added by poly-A polymerase, increasing stability and aiding translation. The central step is splicing: introns are removed and exons joined by the spliceosome, a complex assembled from snRNPs (U1, U2, U4, U5 and U6) and proteins. The spliceosome recognises conserved GU at the 5′ splice site and AG at the 3′ splice site, following the GU-AG rule, and catalyses two transesterification reactions. Alternative splicing, in which different exons are included or excluded, allows one gene to produce multiple mRNAs and proteins, increasing functional diversity without increasing gene number. The mature mRNA is then exported to the cytoplasm for translation.

(c) Continental drift The statement is justified by vicariance biogeography. When Gondwanaland fragmented, roughly between 180 and 30 million years ago, populations of organisms that were once continuous were separated by newly formed oceans and land barriers. Alligatorids illustrate this: Alligator mississippiensis in North America and Alligator sinensis in China occupy disjunct regions, yet their similarity and fossil record indicate a common ancestral distribution before continental separation. Similarly, lungfishes are relictual and disjunct: Protopterus in Africa, Lepidosiren in South America and Neoceratodus in Australia occur on former Gondwanan landmasses. Their limited dispersal ability and ancient lineage make long-distance oceanic dispersal unlikely. Thus, the present distribution is better explained by continental drift and subsequent isolation than by active dispersal. The pattern supports vicariance, where geographic barriers split ancestral ranges, leading to endemic lineages on different continents. This explains why related but non-contiguous species are found on separated continents, and why their distributions mirror former continental connections rather than current dispersal routes.

(d) RFLP RFLP analysis is based on natural variation in restriction fragment lengths. DNA is digested with restriction endonucleases that cut at specific recognition sequences. If a point mutation, insertion or deletion creates or destroys a restriction site, the resulting fragment lengths differ between individuals. These polymorphic fragments are separated by gel electrophoresis, transferred to a membrane by Southern blotting, and detected with a labelled probe complementary to a known DNA sequence. Because fragment patterns are inherited, RFLP can be used for DNA fingerprinting, as developed by Alec Jeffreys, for paternity testing, genetic mapping, and disease diagnosis, such as sickle-cell anaemia and Huntington’s disease. In forensic science, RFLP was historically important, but modern profiling, including in the Nirbhaya case, uses STR analysis rather than RFLP. Thus, RFLP remains a foundational molecular tool for identifying genetic variation and linking DNA to specific loci.

(e) Receptor-mediated endocytosis Receptor-mediated endocytosis is a selective uptake mechanism in which extracellular ligands bind specific cell-surface receptors. In the LDL pathway, apolipoprotein B-containing LDL particles bind LDL receptors, causing receptor clustering in clathrin-coated pits. Dynamin then pinches off the coated vesicle, which uncoats and fuses with an early endosome. In the acidic endosome, LDL dissociates from the receptor; the receptor is recycled to the plasma membrane, while LDL is delivered to lysosomes for cholesterol release. Similar pathways operate for transferrin and insulin. The advantages are high specificity, efficient concentration of ligands against a concentration gradient, protection of selected ligands and receptors from unnecessary lysosomal degradation, and maintenance of cellular cholesterol homeostasis. This controlled recycling also prevents wasteful loss of receptors and allows cells to regulate uptake according to metabolic need. Defects in LDL receptor function can cause familial hypercholesterolaemia, showing the physiological importance of RME.