Ch 13 Reproduction in humans

Question 1

Seminal fluid

Answer 1

1. Provides a medium for sperms to swim in
2. Contains sugars that act as an energy source for sperms
3. Contains mucus for lubrication
4. Alkaline, helps neutralize acidic urine in male’s urethra and acidic secretions in female’s vagina

Question 2

Sperms

Answer 2

acrosome: contains enzymes for penetration into the ovum during fertilization
nucleus: contains a haploid number of chromosomes
packed with many mitochondria: release energy for swimming
tail: beats to drive the sperm forward

Question 3

Ova

Answer 3

cytoplasm: contains food reserves for the early development of the embryo
nucleus: contains a haploid number of chromosomes

Question 4

Follicle development and ovulation

Answer 4

1. Increased levels of female sex hormones stimulate follicles to develop
2. The follicle grows in size and moves towards the surface of the ovary
3. The mature follicle bursts to release the ovum into the funnel of the oviduct
4. The ovum is transported along the oviduct by the beating action of the cilia on its inner wall and the peristaltic contraction on its muscular wall
5. The ruptured follicle becomes the yellow body
6. The yellow body degenerates if fertilization does not occur

Question 5

Menstrual cycle

Answer 5

1-5:
If fertilization does not occur, the yellow body degenerates. The thickened uterine lining breaks down. The uterine lining and the unfertilized ovum are discharged through the vagina. Some follicles in the ovary start to develop.
6-13:
Follicles continue to develop. The uterine lining thickens and the blood supply increases to prepare for the implantation of an embryo
14:
Ovulation occurs
15-28:
The ruptured follicle becomes the yellow body, which releases a hormone to increase and maintain the thickness of the uterine lining. The uterine lining becomes very thick. It is ready to receive an embryo

• If fertilization occurs and the woman gets pregnant, the degeneration of the yellow body is delayed. The uterine lining does not break down. It continues to thicken. Menstruation does not occur until the baby is born

Question 6

Fusion of sperm and ovum

Answer 6

1. When sperms meet an ovum in the oviduct, they try to penetrate it.
2. The sperms release enzymes from their acrosomes to digest a path through a jelly coat of the ovum
3. The head of one of the sperms successfully passes through the cell membrane and enters the cytoplasm of the ovum. The midpiece and tail are left outside. The jelly coat of the ovum changes to prevent the entry of other sperms
4. The nucleus of the sperm fuses with the nucleus of the ovum

Question 7

Implantation

Answer 7

1. Ovulation occurs
2. Fertilization gives rise to a zygote
3. The zygote is moved down the oviduct by the beating action of cilia and the peristaltic contraction of the muscular wall of the oviduct. The zygote divides repeatedly to form an embryo
4. The embryo implants into the uterine lining

Question 8

Amniotic fluid

Answer 8

1. acts as a cushion to protect the embryo from mechanical injury
2. provides a stable environment for the development of embryo
3. prevents the embryo from desiccation
4. allows the embryo to move around easily
5. lubricates the vagina during childbirth

Question 9

Separation of embryo’s blood and maternal blood

Answer 9

1. avoid breakage of embryo’s blood vessels by the high blood pressure of maternal blood
2. avoids clumping of blood in case the blood types of the embryo’s blood and the maternal blood are incompatible
3. prevents the entry of certain pathogens or toxins from the maternal blood into the embryo’s blood

Question 10

Adaptation of the placenta to exchange of materials

Answer 10

1. The finger-like embryonic villi greatly increase the surface area for the exchange of materials
2. The walls of the embryo’s capillaries and the embryonic villi are very thin. This provides a short distance for the diffusion of materials
3. There are a lot of blood vessels which can carry materials away rapidly. A steep concentration gradient of materials between the embryo’s blood and the maternal blood is maintained

Question 11

Prenatal care

Answer 11

1. Have a balanced diet
2. Do gentle exercise regularly
3. Have prenatal check-ups
4. Do not smoke
5. Do not drink alcohol
6. Do not take drug without seeking the doctor’s advice

Question 12

Identical twins

Answer 12

1. One ovum is fertilized by a sperm
2. One zygote is formed
3. The zygote divides into two cells
4. Each cell undergoes mitotic cell division repeatedly to form a ball of cells
5. The two embryos develop into two genetically identical individuals

• same genetic make-up
• same sex
• same blood group
• look very much alike

Question 13

Fraternal twins

Answer 13

1. Two ova are fertilized by different sperms
2. Two zygotes are formed
3. Each of the zygotes divides into two cells
4. The cells undergo mitotic cell division repeatedly to form a ball of cells
5. The two embryos develop into two genetically different individuals

• different genetic make-up

Question 14

Birth process

Answer 14

1. Cervix dilates. Amnion breaks and amniotic fluid flows out
2. Muscles of uterine wall and abdominal wall contract strongly to push the foetus out through the vagina
3. Placenta detaches and is pushed out of the body

Question 15

Benefits of breast-feeding

Answer 15

1. Breast milk provides essential nutrients and antibodies for the baby
2. Breast-feeding helps the recovery of the mother’s uterus and reduces the risk of breast cancer and ovarian cancer in the mother
3. Breast-feeding enhances mother-child bonding