Biology Basics — Set 4

Correct Answer: C. Cell wall

• **Cell wall** = A rigid outer layer made of cellulose that surrounds plant cells, providing structural support and shape. • **Key fact** — Animal cells rely only on the flexible cell membrane for boundary, so they lack this hard cellulose wall entirely. • Plant cells also uniquely have chloroplasts and a large central vacuole that animal cells do not possess. • 💡 Option A (Mitochondria) is wrong because both plant and animal cells have mitochondria for energy production; Option B (Cell membrane) is wrong because all living cells — plant and animal — have a cell membrane; Option D (Nucleus) is wrong because both plant and animal cells possess a membrane-bound nucleus.

Correct Answer: C. Genus and Species

• **Genus and Species** = The two-part scientific naming system called Binomial Nomenclature, introduced by Carl Linnaeus, uses Genus (capitalised) followed by species (lowercase). • **Key fact** — For example, humans are named *Homo sapiens* where *Homo* is genus and *sapiens* is species; this name is universally recognised across all languages. • Scientific names are always written in italics or underlined, ensuring no ambiguity between languages or regions. • 💡 Option A (Family and Genus) is wrong because Family is a higher rank not used in naming; Option B (Kingdom and Phylum) is wrong because these are the broadest classification levels, far above the naming system; Option D (Class and Order) is wrong because these ranks are also above the species level and not part of binomial nomenclature.

Correct Answer: A. Smooth Endoplasmic Reticulum

• **Smooth Endoplasmic Reticulum (SER)** = A network of membranous tubules without ribosomes, specialised for synthesising lipids, steroids, and phospholipids. • **Key fact** — SER is abundantly found in liver cells where it detoxifies drugs and poisons, and in steroid-producing cells like adrenal glands. • Unlike Rough ER, SER has no ribosomes on its surface, which is why it appears smooth and is dedicated to non-protein synthesis tasks. • 💡 Option B (Golgi body) is wrong because Golgi apparatus modifies and packages proteins for secretion, not lipid synthesis; Option C (Rough ER) is wrong because Rough ER is studded with ribosomes and specialises in protein synthesis and folding; Option D (Ribosome) is wrong because ribosomes are sites of protein synthesis, not lipid production.

Correct Answer: C. Rudolf Virchow

• **Rudolf Virchow** = A German physician who in 1855 added the crucial third principle of Cell Theory: *Omnis cellula e cellula* — every cell arises from a pre-existing cell. • **Key fact** — This principle demolished the idea of spontaneous generation for cells and established that life is continuous, always originating from prior life. • Virchow's contribution completed the Cell Theory framework built earlier by Schleiden (1838) for plants and Schwann (1839) for animals. • 💡 Option A (Schleiden) is wrong because Matthias Schleiden proposed that all plants are made of cells but did not address cell origin; Option B (Schwann) is wrong because Theodor Schwann extended cell theory to animals but did not propose cellular origin from pre-existing cells; Option D (Robert Hooke) is wrong because Hooke only first observed and named cells in cork in 1665, long before the question of cell origin was studied.

Correct Answer: A. Cytoplasm

• **Cytoplasm** = The jelly-like, semi-fluid substance enclosed within the cell membrane, composed of water, salts, and dissolved organic molecules. • **Key fact** — Cytoplasm acts as the medium in which all cell organelles are suspended, and it is the site of many metabolic reactions like glycolysis. • The fluid portion of cytoplasm excluding organelles is called cytosol, and it constantly moves within the cell in a process called cytoplasmic streaming. • 💡 Option B (Vacuole) is wrong because vacuoles are membrane-bound sacs for storage of water and waste, not the bulk semi-fluid material; Option C (Nucleus) is wrong because the nucleus is a distinct membrane-bound organelle containing DNA, not the general semi-fluid filling; Option D (Cell wall) is wrong because the cell wall is the rigid outermost layer found only in plant cells, not a substance inside the cell membrane.

Correct Answer: D. Protista

• **Protista** = A diverse kingdom of mostly unicellular eukaryotic organisms that possess a true membrane-bound nucleus unlike bacteria. • **Key fact** — Protists include Amoeba, Paramecium, Euglena, and Plasmodium (malaria parasite); they serve as the evolutionary bridge between prokaryotes and complex multicellular eukaryotes. • Some protists like algae can be multicellular, but the defining characteristic of the kingdom is predominantly unicellular eukaryotic organisation. • 💡 Option A (Fungi) is wrong because fungi are eukaryotic but mostly multicellular (moulds, mushrooms), not unicellular; Option B (Monera) is wrong because Monera includes bacteria and cyanobacteria which are prokaryotic, not eukaryotic; Option C (Animalia) is wrong because all animals are multicellular eukaryotes, not unicellular organisms.

Correct Answer: C. Nucleus

• **Nucleus** = The control centre of the cell that houses DNA and directs all cellular activities including growth, metabolism, and reproduction. • **Key fact** — The nucleus is surrounded by a double-layered nuclear envelope with pores, and contains the nucleolus where ribosomal RNA is produced. • Because the nucleus carries the genetic blueprint and regulates gene expression, it governs every function of the cell — hence called the 'master' or 'brain' of the cell. • 💡 Option A (Ribosome) is wrong because ribosomes are sites of protein synthesis and follow instructions from the nucleus, not give them; Option B (Mitochondria) is called the 'powerhouse of the cell' for energy production, not master; Option D (Golgi body) is wrong because Golgi apparatus only handles packaging and transport of proteins, a specific task not overarching control.

Correct Answer: C. Packaging and secretion

• **Packaging and secretion** = The Golgi apparatus receives proteins from the Rough ER, modifies them (e.g., adds sugar groups), sorts them, and packages them into vesicles for secretion outside the cell or delivery to other organelles. • **Key fact** — Discovered by Camillo Golgi in 1898, it is sometimes called the 'post office of the cell' because it addresses and dispatches molecular cargo to correct destinations. • The Golgi also produces lysosomes by packaging digestive enzymes, linking its function to cellular waste management indirectly. • 💡 Option A (Waste digestion) is wrong because waste digestion is performed by lysosomes, not Golgi apparatus; Option B (Protein synthesis) is wrong because proteins are synthesised at ribosomes on the Rough ER, Golgi only modifies and packages them; Option D (Energy production) is wrong because energy in the form of ATP is produced by mitochondria through cellular respiration.

Correct Answer: D. Lacks a nuclear membrane

• **Lacks a nuclear membrane** = The defining feature of prokaryotic cells is the absence of a membrane-bound nucleus; their DNA floats freely in the cytoplasm in a region called the nucleoid. • **Key fact** — Prokaryotes like bacteria and archaea also lack membrane-bound organelles such as mitochondria and ER, making them structurally much simpler than eukaryotic cells. • Prokaryotes are the oldest form of life on Earth (3.5 billion years old) and reproduce by binary fission, not mitosis. • 💡 Option A (Contains membrane-bound organelles) is wrong because membrane-bound organelles are a feature of eukaryotic cells, not prokaryotes; Option B (Only found in animals) is wrong because prokaryotes are bacteria and archaea found everywhere — soil, water, air — not inside animals only; Option C (Has a well-defined nucleus) is wrong because a well-defined, membrane-enclosed nucleus is the hallmark of eukaryotic cells, the opposite of prokaryotes.

Correct Answer: B. Gregor Mendel

• **Gregor Mendel** = An Austrian monk who conducted breeding experiments on pea plants between 1856–1863 and discovered the fundamental laws of inheritance, earning him the title 'Father of Genetics'. • **Key fact** — Mendel formulated three laws: Law of Dominance, Law of Segregation, and Law of Independent Assortment, which became the foundation of modern genetics. • His work was ignored for 35 years and only rediscovered in 1900 by three scientists independently, confirming the universality of his findings. • 💡 Option A (Charles Darwin) is wrong because Darwin proposed the Theory of Evolution by Natural Selection, not inheritance laws; Option C (Robert Hooke) is wrong because Hooke is credited with discovering cells under a microscope in 1665, not genetics; Option D (Louis Pasteur) is wrong because Pasteur is known for germ theory, pasteurisation, and vaccine development, unrelated to heredity.