Biology Basics — Set 1

Correct Answer: C. Anton van Leeuwenhoek

• **Anton van Leeuwenhoek (C)** = Dutch scientist who first observed living cells using a self-made high-magnification microscope in the 1670s, discovering bacteria and protozoa. • **Key fact** — He ground his own lenses and achieved magnifications up to 270×, far beyond any contemporary instrument. • His meticulous drawings of microorganisms earned him the title 'Father of Microbiology.' • 💡 Option A (Theodor Schwann) is wrong because he co-proposed the cell theory, not discovered living cells; Option B (Robert Brown) is wrong because he discovered the cell nucleus in 1831; Option D (Robert Hooke) is wrong because he observed only dead cork cells and coined the term 'cell.'

Correct Answer: B. Lysosome

• **Lysosome (B)** = Membrane-bound organelle filled with powerful hydrolytic enzymes capable of digesting all major biological macromolecules. • **Key fact** — Named 'suicidal bag' by Christian de Duve because rupture of its membrane releases enzymes that digest the cell itself — a process called autolysis. • Lysosomes are also central to autophagy, where they recycle damaged organelles to keep the cell healthy. • 💡 Option A (Golgi apparatus) is wrong because it modifies and packages proteins, not digests waste; Option C (Mitochondria) is wrong because it produces ATP energy; Option D (Ribosome) is wrong because it synthesizes proteins.

Correct Answer: B. Cellulose

• **Cellulose (B)** = A complex polysaccharide made of long chains of glucose units linked by β-1,4-glycosidic bonds, forming the rigid framework of plant cell walls. • **Key fact** — Cellulose microfibrils are arranged in layers, giving plant cells exceptional tensile strength to resist osmotic pressure. • Unlike starch, cellulose cannot be digested by most animals because they lack the enzyme cellulase. • 💡 Option A (Chitin) is wrong because it forms the cell walls of fungi and the exoskeletons of insects, not plants; Option C (Peptidoglycan) is wrong because it is found in bacterial cell walls; Option D (Glycogen) is wrong because it is the energy-storage carbohydrate found in animal liver and muscle.

Correct Answer: B. Protista

• **Protista (B)** = One of the five kingdoms in Whittaker's system, containing mostly unicellular eukaryotic organisms that don't fit neatly into plant, animal, or fungal categories. • **Key fact** — Amoeba moves by pseudopods and engulfs food, while Paramecium uses cilia for locomotion — both are classic Protista examples studied in exams. • Protista serve as the evolutionary bridge between simple prokaryotes (Monera) and complex multicellular eukaryotes. • 💡 Option A (Plantae) is wrong because it includes multicellular photosynthetic organisms like mosses and flowering plants; Option C (Fungi) is wrong because it contains multicellular decomposers like mushrooms and moulds; Option D (Monera) is wrong because it contains prokaryotes — bacteria and cyanobacteria — which lack a true nucleus.

Correct Answer: D. Ribosome

• **Ribosome (D)** = Tiny non-membrane-bound organelle made of rRNA and proteins that reads mRNA instructions and assembles amino acids into proteins. • **Key fact** — Ribosomes are found either free in the cytoplasm (making proteins for the cell itself) or attached to the rough endoplasmic reticulum (making proteins for export). • Every living cell — from bacteria to human neurons — contains ribosomes, making them the universal protein factory of life. • 💡 Option A (Vacuole) is wrong because it stores water, salts, and waste materials; Option B (Lysosome) is wrong because it digests waste using hydrolytic enzymes; Option C (Centrosome) is wrong because it organizes spindle fibers during cell division.

Correct Answer: B. Chloroplast

• **Chloroplast (B)** = Double-membrane organelle containing chlorophyll that captures sunlight and converts it into chemical energy (glucose) through photosynthesis — making it the food-producing 'kitchen' of the cell. • **Key fact** — Chloroplasts contain their own DNA and ribosomes, supporting the endosymbiotic theory that they were once free-living photosynthetic bacteria. • The inner membrane is folded into stacked disc-like thylakoids where light reactions occur, and the surrounding stroma where the Calvin cycle runs. • 💡 Option A (Leucoplast) is wrong because it is a colorless plastid that stores starch, oils, or proteins; Option C (Mitochondria) is wrong because it generates ATP through cellular respiration, not photosynthesis; Option D (Chromoplast) is wrong because it stores red, orange, and yellow pigments for color, not food production.

Correct Answer: A. Genus

• **Genus (A)** = The taxonomic rank directly above Species in the biological hierarchy, grouping closely related species that share a recent common ancestor. • **Key fact** — In binomial nomenclature (e.g., Homo sapiens), the first word is the genus name — always capitalized and italicized. • The correct order is: Kingdom → Phylum → Class → Order → Family → Genus → Species, placing Genus between Family and Species. • 💡 Option B (Phylum) is wrong because it sits between Kingdom and Class, far above Family; Option C (Order) is wrong because it sits between Class and Family, above Family not below it; Option D (Class) is wrong because it sits between Phylum and Order, two levels above Family.

Correct Answer: C. Centrosome

• **Centrosome (C)** = A microtubule-organizing center consisting of two centrioles surrounded by pericentriolar material, found mainly in animal cells. • **Key fact** — During cell division, the centrosome duplicates and each copy migrates to opposite poles of the cell, then nucleates spindle fibers (microtubules) that pull chromosomes apart. • Without properly functioning centrosomes, chromosomes cannot be distributed equally to daughter cells, leading to chromosomal abnormalities. • 💡 Option A (Ribosome) is wrong because it synthesizes proteins, not spindle fibers; Option B (Lysosome) is wrong because it breaks down cellular waste using digestive enzymes; Option D (Mitochondria) is wrong because it produces ATP through cellular respiration.

Correct Answer: A. Taxonomy

• **Taxonomy (A)** = The branch of biology concerned with naming, describing, and classifying all living organisms into hierarchical groups based on shared characteristics. • **Key fact** — Developed systematically by Carl Linnaeus in the 18th century, taxonomy gives every organism a universal two-part scientific name accepted worldwide. • Modern taxonomy now integrates molecular data (DNA sequences) alongside morphological traits for more accurate classification. • 💡 Option B (Ecology) is wrong because it studies the relationships between organisms and their environment; Option C (Histology) is wrong because it studies the microscopic structure of tissues; Option D (Cytology) is wrong because it studies the structure and function of individual cells.

Correct Answer: B. Monera

• **Monera (B)** = The only kingdom in Whittaker's five-kingdom system composed entirely of prokaryotes — organisms whose cells lack a membrane-bound nucleus and membrane-bound organelles. • **Key fact** — Prokaryotes reproduce primarily by binary fission, have circular DNA floating freely in the cytoplasm, and include bacteria and cyanobacteria (blue-green algae). • Monera are the most ancient and abundant life forms on Earth, thriving in extreme environments from hot springs to deep ocean trenches. • 💡 Option A (Protista) is wrong because it contains unicellular eukaryotes like Amoeba which have a true nucleus; Option C (Animalia) is wrong because it contains multicellular eukaryotic animals; Option D (Fungi) is wrong because fungi are eukaryotes with membrane-bound nuclei.