How does a zygote differ from a mature egg? a. A zygote has more chromosomes. b. A zygote is smaller. c. A zygote consists of more than one cell. d. A zygote divides by meiosis.

Propose an experiment to test the hypothesis that cells from only one region of a frog blastula form the ectoderm. What results from this experiment would support this hypothesis?

After a sperm penetrates an egg, it is important that the vitelline layer separate from the egg so that it can a. secrete important hormones. b. enable the fertilized egg to implant in the uterus. c. prevent more than one sperm from entering the egg. d. attract additional sperm to the egg.

The BMI z-score is a relative measure of body mass index (BMI) that takes into account age. Higher values represent heavier individuals for a given height. The table here shows the BMI z-score of pre- and post-pubertal girls at three ages. Which of the following conclusions can you draw from the data?a. At a given age, there are more girls with low BMI z-scores than with high BMI z-scores.b. At a given age, girls with high BMI z-scores are more likely to have begun puberty than girls with low BMI z-scores.c. Girls 11, 12, and 13 years of age are equally likely to have begun puberty.d. There is no relationship between BMI z-score and age of beginning puberty.

In the 1960s, the U.S. Food and Drug Administration approved a contraceptive that allowed women to plan desired pregnancies and prevent unwanted pregnancies. Oral hormonal contraception ('the pill') uses synthetic hormones similar in structure to progesterone and/or estradiol. What is the pill's mechanism of action?Which of the following is the most effective form of contraception?a. condomb. diaphragmc. withdrawald. the pill

In the 1960s, the U.S. Food and Drug Administration approved a contraceptive that allowed women to plan desired pregnancies and prevent unwanted pregnancies. Oral hormonal contraception ('the pill') uses synthetic hormones similar in structure to progesterone and/or estradiol. What is the pill's mechanism of action?Use your knowledge of the hormonal regulation of reproduction to predict the effect of a daily synthetic progesterone pill on (a) pituitary secretion of LH and FSH, and (b) ovarian secretion of estradiol and progesterone.

A woman had several miscarriages. Her doctor suspected that a hormonal insufficiency was causing the lining of the uterus to break down, as it does during menstruation, terminating her pregnancies. Treatment with which of the following might help her remain pregnant?a. oxytocinb. follicle-stimulating hormonec. luteinizing hormoned. prolactin

In the 1960s, the U.S. Food and Drug Administration approved a contraceptive that allowed women to plan desired pregnancies and prevent unwanted pregnancies. Oral hormonal contraception ('the pill') uses synthetic hormones similar in structure to progesterone and/or estradiol. What is the pill's mechanism of action?Scientists confirmed the pill's mechanism of action by measuring plasma hormone levels in women before and after they went on the pill (* means P<0.05, ** means P<0.01, and *** means P<0.001). Do the data shown here support the hypothesis that the pill affects hormonal signaling?

The embryos of reptiles (including birds) and mammals have systems of extraembryonic membranes. What are the functions of these membranes, and how do fish and frog embryos survive without them?