Explanation

• Thymine is a pyrimidine nitrogenous base found in DNA.
• But normally absent in RNA, where uracil takes its place.
• The two pyrimidine bases in RNA are uracil (U) and cytosine (C).
• Adenine (A) and guanine (G) are purine bases found in both DNA and RNA.
• DNA contains A, T, G, C.
• RNA contains A, U, G, C.

Last verified on 25-10-2026

Explanation

• N-formyl methionine (fMet) is the initiating amino acid in protein synthesis in bacteria, including E. coli.
• Chloroplasts and mitochondria have bacterial-like ribosomes and generally use fMet to initiate protein synthesis.
• Eukaryotic cytoplasmic ribosomes usually begin protein synthesis with ordinary methionine (Met), not formylated methionine.

Last verified on 01-11-2026

Explanation

• During DNA replication, helicase unwinds the double-stranded DNA.
• This unwinding creates tension and excessive twisting (supercoiling) ahead of the replication fork.
• Topoisomerases temporarily cut one or both DNA strands, allow the DNA to relax, and then rejoin the strands.
• DNA gyrase is a type of topoisomerase found in bacteria that helps remove positive supercoiling and introduces negative supercoiling.
• Topoisomerases prevent DNA tangling and help replication proceed smoothly.

Last verified on 01-11-2026

Explanation

• Mitochondria produce most of the ATP (adenosine triphosphate) in eukaryotic cells through aerobic cellular respiration.
• ATP is the main energy-carrying molecule of the cell.
• It provides energy for various cellular activities.

Additional information:

• ATP is also produced in the cytoplasm during glycolysis.
• In plant cells, chloroplasts also produce ATP during photosynthesis.
• It is mainly for use within the chloroplast.

Last verified on 27-10-2026

Explanation

• Quill feathers (flight feathers) are found on the wings and tail and provide lift, thrust, and steering.
• Contour feathers cover the bird’s body and give it a streamlined shape that reduces air resistance.

Last verified on 01-11-2026

Explanation

• Birds (class Aves) are endothermic, meaning they maintain a relatively constant body temperature.
• Their bones are generally lightweight and contain air spaces, helping reduce body weight for flight.
• Feathers and several skeletal adaptations support flight and insulation.

Last verified on 01-11-2026

Explanation

• The clitellum is a thickened, glandular band present in sexually mature earthworms.
• It secretes mucus during reproduction and produces material that forms the cocoon for eggs.
• Earthworms belong to the phylum Annelida and class Clitellata.

Last verified on 27-10-2026

Explanation

• A pellicle is a supportive outer covering found in certain unicellular organisms.
• It helps maintain their shape while allowing flexibility to varying degrees.
• Amoeba verrucosa is identified as having a thicker, wrinkled, pellicle-like covering.

Last verified on 27-10-2026

Explanation

• Karl Theodor Ernst von Siebold proposed that protozoans are unicellular organisms.
• He classified protozoans as single-celled animals in his work on invertebrates (1845).
• Protozoans perform essential life functions within a single cell.

Last verified on 01-11-2026

Explanation

• Tropical rainforests are among the most threatened ecosystems because of deforestation, agricultural expansion, logging, and human settlements.
• They contain exceptionally high biodiversity, so habitat destruction puts many plant and animal species at risk.
• The Amazon, Congo, and Southeast Asian rainforests are major tropical rainforest regions.

Last verified on 01-11-2026