Biology Basics — Set 2

Correct Answer: B. Vacuole

• **Vacuole (B)** = A large, fluid-filled membrane-bound sac that occupies up to 90% of a mature plant cell's volume, storing water, mineral salts, sugars, and waste products. • **Key fact** — By absorbing water and pressing outward against the cell wall, the vacuole creates turgor pressure — the force that keeps non-woody plants upright and crisp. • Animal cells have smaller, temporary vacuoles for specific tasks, while plant cells typically have one large central vacuole that dominates the cell interior. • 💡 Option A (Mitochondria) is wrong because it generates ATP through cellular respiration; Option C (Golgi body) is wrong because it packages and ships proteins to their destinations; Option D (Nucleus) is wrong because it houses DNA and controls gene expression.

Correct Answer: A. Singer and Nicolson

• **Singer and Nicolson (A)** = Proposed the Fluid Mosaic Model in 1972, describing the cell membrane as a dynamic fluid bilayer of phospholipids in which protein molecules are embedded like tiles in a mosaic. • **Key fact** — The 'fluid' part means phospholipids and proteins can move laterally within the bilayer; the 'mosaic' part refers to the varied proteins scattered throughout the membrane. • This model explains selective permeability — how the membrane allows some substances to pass freely while blocking others. • 💡 Option B (Watson and Crick) is wrong because they described the double-helix structure of DNA in 1953; Option C (Schleiden and Schwann) is wrong because they co-proposed the cell theory stating all living things are made of cells; Option D (Robert Brown) is wrong because he discovered the cell nucleus in 1831.

Correct Answer: C. Chromoplast

• **Chromoplast (C)** = A type of plastid that synthesizes and stores carotenoid pigments — carotene (orange-red) and xanthophyll (yellow) — giving tomatoes, carrots, and ripe fruits their characteristic colors. • **Key fact** — Chromoplasts develop from chloroplasts during fruit ripening, which is why tomatoes turn red as they mature — chlorophyll breaks down and chromoplast pigments are revealed. • These bright colors attract animals for pollination and seed dispersal, serving an important ecological function. • 💡 Option A (Leucoplast) is wrong because it is a colorless plastid that stores starch or oils, not pigments; Option B (Anthocyanin) is wrong because it produces purple, blue, or red colors in flower petals, not the orange-red of tomatoes or carrots; Option D (Chlorophyll) is wrong because it is the green pigment responsible for photosynthesis, not the orange-red coloration.

Correct Answer: A. Lamarck and Treviranus

• **Lamarck and Treviranus (A)** = Independently coined the word 'Biology' in 1802 to name the unified science of living organisms — Jean-Baptiste Lamarck in France and Gottfried Treviranus in Germany. • **Key fact** — The word comes from Greek: 'bios' (life) + 'logos' (study), and their simultaneous coinage established biology as a distinct scientific discipline separate from natural philosophy. • Lamarck also proposed early evolutionary ideas (inheritance of acquired traits), though Darwin later replaced this framework with natural selection. • 💡 Option B (Linnaeus) is wrong because he developed the binomial nomenclature classification system, not the word 'Biology'; Option C (Aristotle) is wrong because he is called the 'Father of Biology' for his early zoological observations, but lived over 2,000 years before the term was coined; Option D (Darwin) is wrong because he proposed the theory of evolution by natural selection in 1859, decades after 'Biology' was already named.

Correct Answer: A. Golgi Apparatus

• **Golgi Apparatus (A)** = A stack of flattened membrane-bound sacs (cisternae) that receives proteins from the endoplasmic reticulum, modifies them, sorts them, and packages them into vesicles for delivery — functioning like a cellular post office. • **Key fact** — The Golgi adds sugar chains, phosphate groups, and other tags to proteins that act as 'address labels,' directing each vesicle to the correct destination inside or outside the cell. • Named after Italian scientist Camillo Golgi, who discovered it in 1898 using silver staining — a find for which he shared the Nobel Prize in 1906. • 💡 Option B (Endoplasmic Reticulum) is wrong because it synthesizes proteins (rough ER) and lipids (smooth ER) but does not package and address them for delivery; Option C (Ribosome) is wrong because it only assembles amino acids into proteins, with no packaging function; Option D (Nucleolus) is wrong because it produces ribosomal RNA and assembles ribosome subunits.

Correct Answer: B. Autotrophs

• **Autotrophs (B)** = Organisms that synthesize their own organic food from inorganic raw materials using an external energy source — primarily sunlight (photoautotrophs like plants) or chemical reactions (chemoautotrophs like some bacteria). • **Key fact** — Autotrophs are the producers of every food chain; without them, no energy would enter the biotic community since consumers cannot make their own food. • The word comes from Greek 'autos' (self) + 'trophe' (nourishment), meaning 'self-feeders.' • 💡 Option A (Saprotrophs) is wrong because they obtain nutrition by breaking down dead and decaying organic matter using external enzymes; Option C (Parasites) is wrong because they derive nutrition by living on or inside a host organism, harming it in the process; Option D (Heterotrophs) is wrong because they must consume other organisms for energy and cannot make food themselves.

Correct Answer: D. Centriole

• **Centriole (D)** = A cylindrical structure made of microtubule triplets found in pairs within the centrosome of animal cells, playing a critical role in organizing the mitotic spindle during cell division. • **Key fact** — Higher plant cells (angiosperms and gymnosperms) lack centrioles yet can still divide, demonstrating that plants use alternative spindle-organizing mechanisms not dependent on centrioles. • Centrioles are also the base of cilia and flagella, making them important for cell motility in many animal cell types. • 💡 Option A (Cell wall) is wrong because it is present in plant cells, not animal cells; Option B (Mitochondria) is wrong because it is found in both animal and plant cells for energy production; Option C (Chloroplast) is wrong because it is found in plant cells for photosynthesis, not in animal cells.

Correct Answer: C. Cell

• **Cell (C)** = The smallest unit of life that can carry out all fundamental biological processes — metabolism, growth, response to stimuli, and reproduction — independently. • **Key fact** — This principle is part of Cell Theory (Schleiden, Schwann, Virchow): all living things are made of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells. • Single-celled organisms like bacteria and amoeba demonstrate that a single cell can constitute a complete, fully functional living entity. • 💡 Option A (Atom) is wrong because it is the basic unit of matter and chemistry, not life — atoms alone cannot metabolize, grow, or reproduce; Option B (Tissue) is wrong because it is a group of similar cells working together, so it is larger and less fundamental than a cell; Option D (Organ) is wrong because it is composed of multiple tissues, making it a higher-order structure, not the basic unit.

Correct Answer: B. Lipid synthesis

• **Lipid synthesis (B)** = The Smooth Endoplasmic Reticulum (SER) is the primary site for synthesizing phospholipids (needed for all cell membranes), steroids, and cholesterol within the cell. • **Key fact** — The SER also detoxifies harmful substances including drugs and alcohol — liver cells are especially rich in SER for this reason. • Unlike the Rough ER (which is studded with ribosomes for protein synthesis), the SER has a smooth surface with no ribosomes. • 💡 Option A (Protein synthesis) is wrong because protein synthesis occurs on ribosomes attached to the Rough ER, not the Smooth ER; Option C (Energy production) is wrong because energy in the form of ATP is produced by mitochondria through cellular respiration; Option D (DNA replication) is wrong because DNA replication occurs inside the nucleus.

Correct Answer: C. Mitochondria

• **Mitochondria (C)** = Double-membrane organelle that generates most of the cell's ATP through aerobic cellular respiration, earning the nickname 'powerhouse of the cell.' • **Key fact** — Mitochondria have their own circular DNA and ribosomes, supporting the endosymbiotic theory that they evolved from ancient free-living bacteria engulfed by ancestral eukaryotic cells. • A single cell can contain hundreds to thousands of mitochondria — highly active cells like heart muscle cells are packed with them. • 💡 Option A (Ribosome) is wrong because it synthesizes proteins by translating mRNA, producing no energy; Option B (Nucleus) is wrong because it controls gene expression and houses the cell's DNA, not energy production; Option D (Lysosome) is wrong because it digests cellular waste using hydrolytic enzymes.