15 extra multiple-choice questions for Plant and Animal Hormones (10th Standard Science, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Who introduced the term 'auxin' in 1931 to describe the plant growth-promoting substance?
- A. Charles Darwin
- B. Kogl and Haagen-SmithCorrect
- C. Frits Warmolt Went
- D. E. H. Starling
Explanation. The term auxin was introduced by Kogl and Haagen-Smith in 1931 to describe plant growth regulators that promote stem and coleoptile elongation.
Q2
Which of the following plant growth regulators is classified as a naturally occurring auxin?
- A. Alpha-Naphthalene Acetic Acid (NAA)
- B. Indole-3-Butyric Acid (IBA)
- C. Phenyl Acetic Acid (PAA)Correct
- D. 2,4-Dichlorophenoxy Acetic Acid (2,4-D)
Explanation. Phenyl Acetic Acid (PAA) and Indole-3-Acetonitrile (IAN) are naturally occurring auxins, whereas NAA, IBA, and 2,4-D are synthetic auxins.
Q3
The delay of leaf senescence and aging in plants brought about by the application of cytokinins is known as:
- A. Bakanae effect
- B. Richmond Lang effectCorrect
- C. Went curvature effect
- D. Apical dominance effect
Explanation. Application of cytokinins delays the aging process in plants by promoting nutrient mobilization; this phenomenon is termed the Richmond Lang effect.
Q4
Artificial induction of sudden stem elongation followed by flowering in rosette plants using gibberellins is referred to as:
- A. Parthenocarpy
- B. Abscission
- C. BoltingCorrect
- D. Senescence
Explanation. Bolting is the rapid elongation of internodes followed by flowering in rosette plants, which can be artificially induced by applying gibberellins.
Q5
Why is abscisic acid (ABA) commonly referred to as the 'stress hormone' in plants?
- A. It speeds up fruit ripening during summer months.
- B. It increases plant tolerance to environmental stress conditions like drought.Correct
- C. It promotes rapid cell division during severe temperature fluctuations.
- D. It stimulates excessive water loss through stomatal pores.
Explanation. Abscisic acid (ABA) increases the tolerance of plants to various environmental stresses, such as drought, by causing stomatal closure to prevent water loss.
Q6
Which plant hormone is a gaseous molecule primarily responsible for fruit maturation and ripening?
- A. Cytokinin
- B. EthyleneCorrect
- C. Gibberellin
- D. Abscisic acid
Explanation. Ethylene is a gaseous plant hormone concerned with the maturation and ripening of fruits such as apples, bananas, and tomatoes.
Q7
Which chemical messenger was the very first hormone discovered in 1902 by Bayliss and Starling?
- A. Insulin
- B. SecretinCorrect
- C. Thyroxine
- D. Adrenaline
Explanation. English physiologists W. M. Bayliss and E. H. Starling first discovered the hormone secretin in 1902 and introduced the term 'hormone' in 1909.
Q8
Which hormone secreted by the anterior pituitary stimulates milk production after childbirth?
- A. Oxytocin
- B. ProlactinCorrect
- C. Vasopressin
- D. Luteinizing hormone
Explanation. Prolactin (lactogenic hormone) initiates mammary gland development during pregnancy and stimulates milk production after childbirth, whereas oxytocin causes milk ejection.
Q9
A deficiency in Vasopressin (Antidiuretic Hormone) leads to which clinical condition?
- A. Diabetes mellitus
- B. Diabetes insipidusCorrect
- C. Simple goitre
- D. Cretinism
Explanation. Deficiency of Antidiuretic Hormone (ADH) or vasopressin reduces reabsorption of water in kidney tubules, resulting in excessive urine output (polyuria) known as Diabetes insipidus.
Q10
Hypothyroidism in adults leading to mental sluggishness, puffiness of the face, and low basal metabolic rate is known as:
- A. Cretinism
- B. Grave's disease
- C. MyxoedemaCorrect
- D. Acromegaly
Explanation. Hypothyroidism in children leads to cretinism, whereas in adults it causes myxoedema, characterized by lethargy, facial swelling, low BMR, and weight gain.
Q11
Tetany, a condition characterized by painful muscle spasms, is caused by hyper-secretion or hypo-secretion of which hormone?
- A. Hyper-secretion of insulin
- B. Hypo-secretion of parathormoneCorrect
- C. Hyper-secretion of thyroxine
- D. Hypo-secretion of growth hormone
Explanation. Hypo-secretion of parathormone reduces blood calcium levels, causing increased neuromuscular excitability and painful muscle spasms termed tetany.
Q12
In the Islets of Langerhans of the pancreas, which specific cells are responsible for secreting glucagon?
- A. Alpha cellsCorrect
- B. Beta cells
- C. Delta cells
- D. Acinar cells
Explanation. Alpha cells of the Islets of Langerhans secrete glucagon (which increases blood glucose), while Beta cells secrete insulin (which decreases blood glucose).
Q13
Aldosterone, the primary mineralocorticoid regulating sodium reabsorption and electrolyte balance, is secreted by which layer of the adrenal cortex?
- A. Zona reticularis
- B. Zona fasciculata
- C. Zona glomerulosaCorrect
- D. Adrenal medulla
Explanation. The adrenal cortex consists of three layers: zona glomerulosa (secretes mineralocorticoids like aldosterone), zona fasciculata (secretes glucocorticoids), and zona reticularis.
Q14
Epinephrine and Norepinephrine are called 'emergency hormones' because they:
- A. Promote glycogen storage in liver cells during rest.
- B. Prepare the body to face stress, fight, fright, or flight situations.Correct
- C. Decrease respiratory rate and slow down heart rate during activity.
- D. Constrict bronchioles and reduce blood pressure.
Explanation. Epinephrine (adrenaline) and norepinephrine are produced by the adrenal medulla during emotional or physical stress to prepare the body for fight, fright, or flight.
Q15
Which hormone secreted by the thymus gland plays a crucial role in promoting the maturation and differentiation of T-lymphocytes?
- A. Thyroxine
- B. ThymosinCorrect
- C. Testosterone
- D. Melatonin
Explanation. The thymus gland secretes thymosin, which stimulates the development and differentiation of T-lymphocytes essential for cell-mediated immunity.
