During birth, an infant is normally stimulated to breathe by_________________.
surfactant
CO2 accumulating in the infant's blood
prostaglandins
an increased O2 level in the infant's new environment
The Correct Answer is B
A. Surfactant reduces surface tension in the alveoli, aiding in lung expansion, but it does not directly stimulate breathing.
B. CO2 accumulating in the infant's blood: The accumulation of CO2 in the infant's blood is a significant stimulus for the first breath after birth. High levels of CO2 trigger the infant's respiratory centers to start breathing.
C. Prostaglandins are involved in labor and delivery but do not directly stimulate breathing in the newborn.
D. An increased O2 level in the infant's new environment: Increased O2 levels do not directly stimulate breathing; rather, the accumulation of CO2 is the primary stimulus.
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Correct Answer is A
Explanation
A. Luteinizing hormone (LH); testosterone: Luteinizing hormone (LH) stimulates the interstitial cells (Leydig cells) of the testes to produce and secrete testosterone.
B. Follicle-stimulating hormone (FSH); androgen-binding protein (ABP): Follicle-stimulating hormone (FSH) stimulates the Sertoli cells to produce androgen-binding protein (ABP), but it does not stimulate the interstitial cells to secrete testosterone.
C. Luteinizing hormone (LH); androgen-binding protein (ABP): Luteinizing hormone (LH) stimulates the secretion of testosterone, not androgen-binding protein (ABP). ABP is stimulated by FSH.
D. Luteinizing hormone (LH); estrogen: Luteinizing hormone (LH) stimulates the secretion of testosterone, not estrogen. Estrogen is primarily produced in females and also in males in smaller amounts.
Correct Answer is A
Explanation
A. Two haploid (n) cells; four haploid (n) cells: At the end of meiosis I, the result is two haploid cells, each with half the number of chromosomes of the original cell. At the end of meiosis II, these two haploid cells divide again to form a total of four haploid cells.
B. Two diploid (2n) cells; one haploid (n) cell: This option is incorrect because meiosis I produces two haploid cells, not diploid cells, and meiosis II produces four haploid cells, not one.
C. Two diploid (2n) cells; four haploid (n) cells: This option is incorrect because meiosis I does not produce diploid cells; it produces two haploid cells. At the end of meiosis II, the result is four haploid cells, which is correct, but the description of meiosis I is incorrect.
D. Two haploid (n) cells; one diploid (2n) cell: This is incorrect because meiosis I results in two haploid cells, and meiosis II results in four haploid cells, not one diploid cell.