Tissues — Set 1

Correct Answer: A. Apical meristem

• **Apical meristem** = actively dividing, undifferentiated tissue at stem and root tips that drives primary elongation growth • **Key fact** — apical meristem cells are small, isodiametric, have dense cytoplasm, thin walls, and no large vacuoles, enabling rapid mitosis • These cells remain totipotent (can form any tissue type), which is why they are used in plant tissue culture for cloning • 💡 Option B (Permanent tissue) is wrong because permanent tissues are already differentiated and no longer divide; Option C (Lateral meristem) is wrong because it increases girth/width, not length; Option D (Intercalary meristem) is wrong because it sits at internodes of grasses, enabling regrowth after grazing, not tip elongation

Correct Answer: B. Collenchyma

• **Collenchyma** = simple permanent tissue of living cells with unevenly thickened corners due to extra cellulose and pectin deposits • **Key fact** — pectin at cell corners allows bending without breaking, making collenchyma the main flexible-support tissue of young dicot stems, petioles, and leaf midribs • Unlike sclerenchyma, collenchyma cells are living and can still elongate as the plant grows • 💡 Option A (Sclerenchyma) is wrong because it has dead, heavily lignified cells making it rigid, not flexible; Option C (Chlorenchyma) is wrong because it is parenchyma modified for photosynthesis with no mechanical role; Option D (Parenchyma) is wrong because parenchyma has uniformly thin walls and serves storage, not support

Correct Answer: C. Tendon

• **Tendon** = dense regular connective tissue of tightly packed collagen fibres that attaches skeletal muscle to bone • **Key fact** — tendons are nearly inextensible, transmitting the full force of muscle contraction to bone; the Achilles tendon connecting calf muscles to the heel bone is the thickest in the body • Tendons contain tenocytes between collagen bundles and have poor blood supply, which is why they heal very slowly • 💡 Option A (Cartilage) is wrong because cartilage cushions joints and forms ear or nose frameworks, not muscle-bone junctions; Option B (Areolar tissue) is wrong because it is loose connective tissue filling gaps between organs with no tensile function; Option D (Ligament) is wrong because ligaments connect bone to bone, not muscle to bone

Correct Answer: A. Xylem

• **Xylem** = complex vascular tissue that transports water and dissolved minerals from roots upward to leaves • **Key fact** — xylem contains tracheids and vessel elements that are dead at functional maturity with lignified walls, allowing unobstructed water flow via the cohesion-tension mechanism • Water travels through xylem pulled upward by transpiration at leaves without any energy expenditure by the plant • 💡 Option B (Phloem) is wrong because phloem transports sugars and organic molecules made in leaves down to all parts of the plant; Option C (Epidermis) is wrong because epidermis is the protective outer layer of plant organs, not a conducting tissue; Option D (Cambium) is wrong because cambium is meristematic tissue producing secondary xylem and phloem, not a conduit for water

Correct Answer: C. Histology

• **Histology** = the branch of biology that examines the microscopic structure and arrangement of tissues using staining and microscopy • **Key fact** — the word comes from Greek 'histos' (tissue) + 'logos' (study); Marcello Malpighi is regarded as the founder of histology • Haematoxylin and eosin (H&E) is the most common histological stain, colouring nuclei blue-purple and cytoplasm/ECM pink • 💡 Option A (Physiology) is wrong because physiology studies how systems function, not their microscopic structure; Option B (Anatomy) is wrong because anatomy deals with gross body structure visible to the naked eye; Option D (Cytology) is wrong because cytology studies individual cells in isolation, not organised tissue groups

Correct Answer: B. Adipose tissue

• **Adipose tissue** = specialised loose connective tissue of adipocytes (fat cells) that store triglycerides as long-term energy reserves • **Key fact** — white adipose tissue (WAT) stores energy and insulates the body; brown adipose tissue (BAT) generates heat via non-shivering thermogenesis using uncoupling protein UCP1 • Adipose tissue constitutes about 15-25% of healthy body weight and cushions organs such as the kidneys • 💡 Option A (Areolar tissue) is wrong because areolar tissue is loose connective tissue that binds organs together, not a fat-storage depot; Option C (Nervous tissue) is wrong because it consists of neurons and glial cells for signal transmission, not energy storage; Option D (Epithelial tissue) is wrong because it covers and lines body surfaces and does not store fat

Correct Answer: B. Active cell division

• **Active cell division** = the defining characteristic of meristematic tissue; cells continuously undergo mitosis to produce new cells for growth • **Key fact** — meristematic cells are small, isodiametric, have dense cytoplasm, a prominent nucleus, thin cell walls, and no large central vacuoles • They remain totipotent (able to develop into any tissue type), which is exploited in plant tissue culture for cloning entire plants • 💡 Option A (Dead cells) is wrong because dead cells cannot undergo mitosis; meristematic cells are always metabolically active; Option C (Large vacuoles) is wrong because large central vacuoles develop only in mature permanent cells, not in rapidly dividing meristematic cells; Option D (Thick cell walls) is wrong because thick lignified walls are a feature of mature sclerenchyma, not thin-walled dividing meristematic cells

Correct Answer: C. Columnar epithelium

• **Columnar epithelium** = epithelial tissue of tall pillar-shaped cells lining absorptive and secretory surfaces like the small intestine • **Key fact** — the apical surface of intestinal columnar cells bears microvilli forming the brush border, increasing absorption surface area about 600 times compared to a smooth surface • Goblet cells interspersed among columnar cells secrete mucus that protects the intestinal lining from digestive enzymes and acid • 💡 Option A (Ciliated epithelium) is wrong because ciliated epithelium lines the respiratory tract where cilia sweep particles out, not the intestinal wall; Option B (Squamous epithelium) is wrong because flat squamous cells form the skin epidermis and blood vessel lining where minimal absorption occurs; Option D (Cuboidal epithelium) is wrong because cube-shaped cuboidal cells line kidney tubules and salivary gland ducts, not the small intestine

Correct Answer: B. Sclerenchyma

• **Sclerenchyma** = simple permanent tissue of dead cells with heavily lignin-thickened walls giving plants extreme rigidity and strength • **Key fact** — the hard husk (coir) of a coconut is made of sclerenchyma fibres; these are among the longest natural plant fibres, used commercially for ropes and floor matting • Sclerenchyma exists as fibres (long, tapering cells) and sclereids or stone cells (short, irregular); stone cells in pears produce the gritty texture • 💡 Option A (Aerenchyma) is wrong because aerenchyma has large air spaces making it light and buoyant, the structural opposite of a hard husk; Option C (Parenchyma) is wrong because parenchyma has living cells with thin walls used for storage and is too soft to form a hard husk; Option D (Collenchyma) is wrong because collenchyma provides flexible support via pectin-thickened corners in living cells, not the extreme stiffness of coconut husk

Correct Answer: A. Blood

• **Blood** = the only fluid connective tissue with a liquid matrix called plasma that contains no collagen or reticular fibres • **Key fact** — plasma makes up about 55% of blood volume and is 90% water; the cellular elements are erythrocytes (RBCs), leucocytes (WBCs), and platelets • Blood is classified as connective tissue because it originates from mesenchyme and has a non-cellular matrix (plasma) binding body systems functionally • 💡 Option B (Bone) is wrong because bone is solid connective tissue with a mineralised matrix of calcium phosphate, not a flowing fluid; Option C (Cartilage) is wrong because cartilage has a firm gel-like matrix reinforced with collagen fibres, not a free liquid; Option D (Areolar) is wrong because areolar tissue is a semi-solid loose connective tissue containing collagen and elastin fibres