Which of the following statements about the plant stem is correct?
A. It grows downward into the soil.
B. It is usually positively phototropic.
C. It is the main site of photosynthesis in most plants.
D. It bears leaves, flowers, and fruits.
Answer: Option D
Solution (By JKSSB Mock Tests)
Stem bears leaves and reproductive structures. It is positively phototropic (grows towards light). Leaves are the main photosynthetic organs. Roots grow downward.
Explanation:
Acetobacter aceti oxidizes ethanol to acetic acid under aerobic conditions, used in vinegar production. Lactobacillus produces lactic acid, Streptomyces produces antibiotics, E. coli is used in genetic engineering but not vinegar.
Explanation:
Acetylcholine is an excitatory neurotransmitter at neuromuscular junctions and many CNS synapses. GABA and glycine are generally inhibitory in the CNS. Serotonin modulates mood but can have inhibitory or excitatory effects depending on receptors. Neurotransmitters are chemical messengers released from synaptic vesicles into the synaptic cleft to bind to postsynaptic receptors.
In plant physiology, the 'Root pressure' is a positive pressure that develops in the roots due to the active absorption of minerals and the subsequent osmotic entry of water. It is most evident during:
A.Winter when the ground is frozen
B.Early morning or night when transpiration is low and soil moisture is high
Explanation:
Root pressure is a positive hydrostatic pressure generated in the xylem of roots due to the active secretion of ions into the xylem, which lowers the water potential and causes water to enter osmotically from the soil. This pressure can push water up the stem. Root pressure is most evident and measurable during the early morning or at night, when the rate of transpiration from the leaves is very low (or zero) and the soil moisture is high, allowing for maximum water absorption. It is responsible for phenomena like guttation and the exudation of sap from cut stems.
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