Nervous + endocrine, plant hormones MCQs

Q1. Which of the following statements about the parts of a neuron is INCORRECT?

• A.Axons are short and receive impulses from other neurons
• B.Dendrites are short and receive impulses from other neurons
• C.The cell body contains the nucleus and most cell organelles
• D.The axon terminal releases neurotransmitter into the synaptic cleft

Answer: A. Axons are short and receive impulses from other neurons

What does the chapter say about this? The first option is INCORRECT - axons are typically LONG and CARRY impulses AWAY from the cell body to the next neuron or effector. It is the dendrites that are short and receive impulses. The other three options describe the cell body, dendrites and axon terminal correctly. Pick: A) Axons are short and receive impulses from other neurons.

Q2. Which of the following is the correct sequence of plant hormone activity that allows a dormant seed to germinate?

• A.Imbibition of water → fall in ABA → rise in gibberellin → enzyme synthesis (alpha-amylase) → mobilisation of stored food → seedling growth
• B.Rise in ABA → fall in gibberellin → seed dormancy ends → growth begins
• C.Rise in ethylene → fall in cytokinin → root emergence
• D.Rise in auxin → root elongation → photosynthesis → fall in ABA

Answer: A. Imbibition of water → fall in ABA → rise in gibberellin → enzyme synthesis (alpha-amylase) → mobilisation of stored food → seedling growth

What is the textbook's take? Seed germination begins with water uptake (imbibition), which dilutes/breaks down the dormancy hormone ABA. Gibberellin levels rise and induce synthesis of hydrolytic enzymes such as alpha-amylase in the aleurone layer, mobilising stored starch into sugars that fuel embryo growth. The other options reverse the antagonism between ABA (promotes dormancy) and gibberellin (breaks dormancy). Pick: A) Imbibition of water → fall in ABA → rise in gibberellin → enzyme synthesis (alpha-amylase) → mobilisation of stored food → seedling growth.

Q3. Which of the following correctly describes auxin redistribution in a horizontally placed shoot?

• A.Gravity causes auxin to accumulate on the lower side; the lower side elongates more and the shoot curves upward (negative geotropism)
• B.Gravity causes auxin to accumulate on the upper side; the upper side elongates more and the shoot curves downward
• C.Auxin distribution is unaffected by gravity in shoots
• D.Auxin is destroyed on the lower side, so the shoot grows straight upward

Answer: A. Gravity causes auxin to accumulate on the lower side; the lower side elongates more and the shoot curves upward (negative geotropism)

What's the underlying rule? When a shoot is laid horizontal, statoliths in cells of the shoot sense gravity and trigger lateral transport of auxin to the lower side. In SHOOTS, more auxin means more elongation, so the lower side elongates faster and the shoot bends upward - negative geotropism. The same auxin concentration in ROOTS does the opposite (inhibits elongation on the lower side), giving positive geotropism. Pick: A) Gravity causes auxin to accumulate on the lower side; the lower side elongates more and the shoot curves upward (negative geotropism).