The type of circulatory system in which blood is confined to vessels is called: MCQ with Answer and Explanation

Explanation:
Progesterone is the primary hormone of the luteal phase (also called the secretory phase) of the menstrual cycle. After ovulation, the ruptured Graafian follicle transforms into the corpus luteum, which secretes large amounts of progesterone. Progesterone prepares and maintains the uterine endometrium (thickening it, increasing blood supply, and stimulating glandular secretion) for the potential implantation of a fertilized egg. If pregnancy does not occur, the corpus luteum degenerates, progesterone levels drop, and menstruation begins.

Explanation:
Oxytocin is a peptide hormone produced by the paraventricular nucleus of the hypothalamus and released by the posterior pituitary. In females, it has two major roles: 1) During childbirth, it stimulates powerful contractions of the uterine smooth muscle, facilitating labor and delivery (this is a positive feedback loop). 2) During lactation, it stimulates the contraction of myoepithelial cells surrounding the alveoli in the mammary glands, causing the ejection (let-down) of milk into the ducts in response to suckling. It does not produce milk; prolactin does that.

Explanation:
In C4 plants, the initial fixation of CO2 occurs in the mesophyll cells. The primary CO2 acceptor is a 3-carbon compound, phosphoenolpyruvate (PEP). The enzyme PEP carboxylase catalyzes the reaction, forming a 4-carbon compound, oxaloacetate (OAA). In C3 plants, the primary acceptor is RuBP, a 5-carbon compound, and the enzyme is RuBisCO.