IB biology- Reproduction- Unit 6

10 IB, reproduction

1: : What is asexual reproduction?

The formation of a new but identical individual from a single organism.

2: : What is binary fission?

A parent cell divides so that each new cell contains a complete set of DNA identical to that of the parent. Occurs in unicellular organisms that do not have a true nucleus. Example: Bacteria.

3: : What is budding?

A bud grows on the parent organism. The bud grows for a while and eventually breaks away forming an independent organism. Occurs in invertebrate animals such as sponges and hydra.

4: : What is sporulation?

The parent organism produces spores. Spores are stored in the sporangium until they are mature and ready to be dispersed. Spores can grow into a new individual through mitotic cell division. Occurs in bread mold.

5: : What is regeneration?

An organism divides in half and regenerates the parts it is missing. New limbs can also be grown this way. Occurs in invertebrates such as planarians and sea stars.

6: : What is parthenogenesis?

Growth and development of embryos occurs without fertilization. Occurs in Daphnia, which under ideal conditions use parthenogenesis to reproduce rapidly.

7: : What is meiosis?

Meiosis is a special type of cell division that occurs only in reproductive organs. Meiosis makes reproductive cells called gametes (egg or sperm).

8: : What are the two functions of meiosis?

Halving the chromosome number and producing genetic variety.

9: : What is the diploid number of chromosomes?

The diploid (2n) number of chromosomes is 46, which is the number of chromosomes in all cells in the human body except gametes.

10: : What is the haploid number of chromosomes?

The haploid (n) number of chromosomes is 23, which is the number of chromosomes in gametes.

11: : What are the phases of meiosis?

The phases of meiosis are prophase, metaphase, anaphase, and telophase. Meiosis involves two sequences of these phases: Meiosis I (reduction division) and Meiosis II (further division).

12: : What happens during interphase in meiosis?

During interphase, the cell grows and replicates DNA. After replication, each chromosome is made up of a pair of identical sister chromatids held together by a centromere.

13: : What occurs during prophase I?

Homologous chromosomes align forming a bivalent. Homologous chromosomes contain the same genes but can have different alleles. The nuclear membrane disappears, spindle fibers begin to form, and crossing over occurs.

14: : What is crossing over?

Crossing over is the exchange of genetic material between non-sister homologous chromatids. This process forms chromatids that are a mixture of paternal and maternal alleles.

15: : What happens during metaphase I?

Spindle fibers attach to the centromere of each chromosome. Spindle fibers pull each bivalent to the center of the cell, and random assortment occurs.

16: : What is random assortment?

The bivalents line up on the equator of the cell randomly, resulting in gametes that contain either maternal or paternal chromatids, or a mixture of both.

17: : What occurs during anaphase I?

The homologous chromosomes separate and move to opposite poles of the cell. The centromere does not split, so sister chromatids are held together, moving one chromosome to each pole.

18: : What happens during telophase I?

The chromosomes begin to uncoil, spindle fibers disappear, and the cytoplasm is divided. The nuclear membrane begins to form around the pairs of homologous chromosomes.

19: : What occurs during prophase II?

The phases of meiosis II are identical to the phases of mitosis. The nuclear membrane disappears, spindle fibers are formed, and chromatin coils and becomes visible.

20: : What happens during metaphase II?

Spindle fibers attach to the centromere of each chromosome and move the chromosomes to the middle of the cell.

21: : What occurs during anaphase II?

Spindle fibers pull sister chromatids to opposite poles of the cell.

22: : What happens during telophase II?

The nuclear membrane reappears, spindle fibers disappear, the cytoplasm divides, and new cells are formed. The result is four non-identical haploid cells.

23: : What is spermatogenesis?

Spermatogenesis is the process of sperm production and development that takes place in the testes of the male. The final product is four haploid sperm cells.

24: : Where does spermatogenesis occur?

Spermatogenesis occurs in the seminiferous tubules of the testes.

25: : What are spermatogonia?

Spermatogonia are diploid germinal epithelium cells in the seminiferous tubules that divide (mitosis) regularly to produce more diploid cells, which enlarge and become primary spermatocytes.

26: : What happens to primary spermatocytes during meiosis?

Primary spermatocytes divide by meiosis. The first meiotic division produces two haploid cells called secondary spermatocytes. The second meiotic division produces four spermatids.

27: : What role do Sertoli cells play in spermatogenesis?

Sertoli cells, also known as nurse cells, assist in the differentiation of immature spermatids into spermatozoa by providing nourishment.

28: : Where does sperm maturation and storage occur?

Sperm maturation and storage occur in the epididymis.

29: : Which hormones control sperm production?

Sperm production is controlled by three hormones: Follicle-Stimulating Hormone (FSH), Testosterone, and Luteinising Hormone (LH).

30: : What is the role of FSH in sperm production?

FSH stimulates meiosis in spermatocytes to produce haploid cells.

31: : What is the role of Testosterone in sperm production?

Testosterone stimulates the maturation of secondary spermatocytes into mature sperm cells.

32: : What is the role of LH in sperm production?

LH stimulates the secretion of testosterone by the testes.

33: : What is semen?

Semen is a nutrient-rich fluid in which sperm cells are released at ejaculation. It is produced by the seminal vesicles and the prostate gland.

34: : What is the composition of semen?

70% of semen is fluid from the seminal vesicles, rich in fructose to provide energy for sperm and containing mucus to protect sperm from the acidic environment of the vagina. The prostate gland produces an alkaline fluid.

35: : How is semen mixed with sperm cells?

Semen is mixed with sperm cells as they leave the epididymis and move along the vas deferens (spe

36: : What is oogenesis?

Oogenesis is the process of egg production and development that takes place in the ovary of the female.

37: : Where does oogenesis occur?

Oogenesis occurs in the ovaries of the female.

38: : What are oogonia?

Oogonia are diploid germinal epithelial cells within the ovaries that divide by mitosis to produce more diploid cells.

39: : What happens to oogonia during oogenesis?

Oogonia enlarge to form primary oocytes, which are also diploid. Primary oocytes begin meiosis but stop at prophase I.

40: : What is a primary follicle?

A primary follicle is a structure formed by a primary oocyte surrounded by follicle cells.

41: : What happens during each menstrual cycle?

During each menstrual cycle, a few follicles continue meiosis I, but only one completes it, producing two haploid cells: a secondary oocyte and a polar body.

42: : What is the role of the polar body?

The polar body degenerates and does not develop further.

43: : What happens to the secondary oocyte after ovulation?

The secondary oocyte begins meiosis II but stops in prophase II. The follicle cells divide and produce a fluid that causes the follicle to swell and rupture, releasing the secondary oocyte.

44: : What happens after fertilization?

After fertilization, the secondary oocyte completes meiosis II to become a mature ovum and expels another polar body.

45: : What is the corpus luteum?

The corpus luteum is the empty follicle that develops after ovulation and produces progesterone.

46: : What is the role of progesterone?

Progesterone increases the uterine lining and causes FSH and LH to drop, preventing the release of another egg.

47: : What happens if the egg is not fertilized?

If the egg is not fertilized, the corpus luteum breaks down, causing progesterone levels to drop and menstruation to occur.

48: : What happens if the egg is fertilized?

If the egg is fertilized, the sperm travels up the oviduct, and fertilization occurs in the oviducts, forming a zygote.

49: : What is internal fertilization?

Internal fertilization occurs when sperm cells are transferred into the female body during copulation. It is common in reptiles, birds, and mammals.

50: : What is external fertilization?

External fertilization occurs when both male and female gametes are released into the water, where fertilization takes place. It is common in aquatic species.

51: : What is the advantage of internal fertilization?

Internal fertilization increases the chance that gametes will meet, so these species have to produce fewer gametes. The fertilized ovum can be enclosed in a protective covering or remain in the female’s body during development.

52: : What is the acrosome reaction?

The acrosome reaction occurs when the sperm binds to the zona pellucida, releasing enzymes that digest the zona pellucida, allowing the sperm to penetrate the egg membrane.

53: : What is the cortical reaction?

The cortical reaction involves the release of cortical granules from the egg, causing the binding proteins on the egg membrane to be digested, preventing further sperm from binding and hardening the zona pellucida.

54: : What is the blastocyst?

The blastocyst is an almost hollow ball of cells formed by the zygote as it travels down the oviduct towards the uterus. The outer cells become the placenta, while the inner cell mass becomes the embryo.

55: : What is implantation?

Implantation is the process where the blastocyst attaches itself to the endometrium lining of the uterus, occurring 6-10 days after fertilization.

56: : What is the role of human chorionic gonadotropin (HCG)?

HCG signals the ovary to maintain the corpus luteum, which produces progesterone and estrogen through the first trimester.

57: : What is gastrulation?

Gastrulation is the process during the second week of pregnancy where cells in the embryo become arranged in three layers called germ layers: ectoderm, mesoderm, and endoderm.

58: : What is the placenta?

The placenta is an organ that develops during pregnancy, providing nutrients and oxygen to the fetus and removing waste. It is made up of the maternal endometrium and chorionic villi.

59: : What is the umbilical cord?

The umbilical cord connects the embryo to the placenta, carrying fetal blood to the placenta and back to the fetus.

60: : What are the three trimesters of pregnancy?

The human gestation period is divided into three trimesters: the first trimester (1-12 weeks), the second trimester (13-25 weeks), and the third trimester (26-40 weeks).

61: : What is the amnion?

The amnion is a fluid-filled sac that surrounds and protects the embryo. It provides a cushioning environment and helps maintain a stable temperature.

62: : What is the chorion?

The chorion is the outermost membrane that surrounds the embryo. It contributes to the formation of the placenta and helps protect the embryo.

63: : What is the uterus?

The uterus is a muscular organ in the female reproductive system where the fertilized egg implants and develops into an embryo and fetus. It provides a nurturing environment for fetal development.

64: : What role do progesterone and estrogen play during pregnancy?

Progesterone and estrogen maintain the endometrium (uterine lining), suppress the menstrual cycle, and promote the growth of breast tissue.

65: : What signals the onset of labor?

The levels of progesterone and estrogen produced by the placenta begin to fall, signaling the onset of uterine contractions known as labor.

66: : What role do prostaglandins play during labor?

Prostaglandins are secreted by the endometrium and initiate uterine contractions.

67: : What role does oxytocin play during labor?

Oxytocin, released by the pituitary gland, stimulates uterine contractions. It is controlled by positive feedback, where a small contraction triggers the release of more oxytocin.

68: : What are the three stages of birth?

The three stages of birth are the dilation stage, expulsion stage, and placental stage.

69: : What happens during the dilation stage of birth?

The cervix dilates due to uterine contractions and oxytocin, lasting about 2-20 hours. The amnion breaks, releasing fluid.

70: : What happens during the expulsion stage of birth?

Uterine contractions become forceful, pushing the baby through the cervix into the birth canal. The baby's head rotates to make it easier to pass through the birth canal.

71: : What happens during the placental stage of birth?

The placenta and umbilical cord are expelled from the uterus, usually happening between 10-15 minutes after the baby is born.

72: : What hormone increases after birth to stimulate milk production?

Prolactin, from the anterior pituitary, increases after birth to stimulate milk production by the mammary glands.

73: : How is milk released from the mammary glands?

As the baby suckles, prolactin secretion is maintained, and oxytocin is released from the posterior pituitary, causing milk to be released from the milk ducts.