In the light reaction of photosynthesis, which photosystem is involved in the photolysis of water?
A. Photosystem I (PSI)
B. Neither PSI nor PSII
C. Both PSI and PSII
D. Photosystem II (PSII)
Answer: Option D
Solution (By JKExamLibrary)
Photosystem II (PSII), also known as P680, is the first photosystem in the non-cyclic electron transport pathway (Z-scheme). It is responsible for the photolysis of water, a process where water molecules are split into oxygen, protons (H+), and electrons. This oxygen is released as a byproduct of photosynthesis.
Explanation:
The cranium (skull) is composed of several bones fused together, encasing and protecting the brain. Vertebrae protect the spinal cord, sternum protects the heart and lungs anteriorly, pelvis supports abdominal organs and connects to legs. The cranium also provides attachment for muscles.
In plant physiology, the 'Transpiration pull' theory, also known as the cohesion-tension theory, was proposed to explain the ascent of sap in tall trees. The key forces involved are:
A.Root pressure and capillarity
B.Cohesion between water molecules, adhesion to xylem walls, and tension created by transpiration
Explanation:
The cohesion-tension theory, primarily proposed by Dixon and Joly (and later supported by Denison), is the most widely accepted mechanism for the ascent of sap in tall trees. It relies on the physical properties of water. Transpiration from the leaves creates a negative pressure (tension) in the xylem. This tension pulls the water column upwards. The water column remains unbroken due to the high cohesive force between water molecules (hydrogen bonding) and the adhesive force of water to the hydrophilic walls of the xylem vessels and tracheids. This creates a continuous, passive pull from the top.
Explanation:
Follicle-stimulating hormone (FSH) from the anterior pituitary promotes the growth and maturation of ovarian follicles and stimulates estrogen secretion. LH triggers ovulation, estrogen proliferates endometrium, progesterone maintains it.
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