Bio F4 Chap 15

Question 1

Explain the functions of progesterone and its effects on pregnancy.

Answer 1

• prevents uterus contraction and new follicle development
• induces the enlargement of internal structures such as the ureter and uterus in preparation for carrying a baby to term

Question 1

What could possibly happen if gametogenesis does not take place?

Answer 1

• gametogenesis produces haploid gametes, that is, gametes that contain half the number of chromosomes of the parent cells
• when the male and female gamete fuse, the new individual will have the same number of chromosomes as the parent cell (diploid)
• if the gametogenesis does not occur, no gametes will be produced
• no zygotes will be produced and consequently this leads to the extinction of the particular species

Question 2

Explain what would happen to the corpus luteum if fertilisation does not occur.

Answer 2

• corpus luteum degenerates causing progesterone and oestrogen to stop secreting
• without the stimulation of progesterone and oestrogen, the endometrial wall collapses and menstruation takes place

Question 3

In your opinion, what is the best way to overcome premenstrual syndrome?

Answer 3

• intake of balanced diet
• frequent exercise
• get enough sleep
• always active

Question 4

Explain the early developmental process of the embryo.

Answer 4

• the zygote divides many times by mitosis
• the zygote forms a solid ball of cells called morula
• morula forms a hollow sphere known as blastocyst
• blastocyst then develops into an embryo

Question 5

State what might happen if maternal blood mixes with foetal blood.

Answer 5

• the placenta is formed from the mother’s endometrial tissue and embryonic tissue that allows materials to diffuse across it
• if there’s a mixture of foetus’ and mother’s blood, agglutination may occur if the mother’s blood group is different from that of the foetus

Question 6

State the characteristics of conjoined twins.

Answer 6

• the physical part Siamese twins is still joined together, usually at the chest, abdomen or pelvis
• may also share one or two internal organs

Question 7

What are the causes of impotency?

Answer 7

• hormone imbalance
• sex organ deformed or infected
• health issues such as cardiovascular diseases or diabetes
• immune system

Question 8

Why must insects go through ecdysis?

Answer 8

• the shedding of the external of skeleton to allow growth and development

Question 9

The foetus has its own blood circulation system, separate from its mother. Explain why.

Answer 9

• to protect the fine blood vessels of the foetus from bursting due to the high blood pressure of the mother
• to prevent the mother’s and foetus blood from mixing which may cause agglutination

Question 10

A pair of identical twins were separated at birth. Once they reached adulthood, they found out that they both have different body sizes. Explain the factors that would cause this.

Answer 10

• both grew up in different conditions
• their food intake was different and both carried out different daily activities

Question 11

Explain why pregnant mothers must stop smoking.

Answer 11

• chemicals such as nicotine and carbon monoxide diffuse across the placenta into the foetus
• nicotine may affect foetus growth
• carbon monoxide competes with oxygen to combine with haemoglobin
• this reduces the oxygen content received by the foetus and may cause miscarriage

Question 12

State the changes that occur to a zygote from fertilisation up to birth.

Answer 12

• the zygote divides repeatedly by mitosis
• this cellular division produces a ball of cells, but the cell size is retained at this stage
• further development produces a solid ball of cells called morula
• the morula will form a blastocyst, a hollow sphere consisting of cells
• after a few days, the blastocyst will implant itself on the endometrium (uterine wall) of the mother
• this is where the blastocyst continues its development as an embryo
• after two months, the embryo is called foetus with most body parts identifiable
• the foetus is known as a baby after birth

Question 13

A woman took contraceptive pills to prevent pregnancy. The pill inhibits secretions of the Follicle Stimulating Hormone (FSH) from the pituitary gland. Explain the effects of taking contraceptive pills on the menstrual cycle.

Answer 13

• level of FSH is low (in the blood)
• No development of follicle and Graafian follicle is not formed
• less oestrogen secreted (by ovary)
• pituitary (gland) is not / less stimulated to secrete (enough) LH
• no ovulation

Question 14

Explain the effects of oestrogen and LH imbalance.

Answer 14

Oestrogen:
- restores and repairs the endometrial tissue and stimulates endometrial thickening
- causes more LH to be secreted
- imbalance between these two hormones leads to no ovulation and no thickening of endometrial tissue

Question 15

Explain the blood composition that flows through the blood vessel at Q.

Answer 15

• the veins in the umbilical cord transport oxygen and nutrient-rich blood from the mother to the foetus
• the arteries in the umbilical cord transport blood rich in CO2 and nitrogenous waste materials such as urea from the foetus to the mother to be expelled

Question 16

Explain how placenta helps in foetal immune response.

Answer 16

• antibodies diffuse from the mother to the foetus
• when the antibodies enter the foetus’ bloodstream, the antibodies will act against pathogen
• this provide immunity to the foetus and prevents disease infection

Question 17

A woman having problems getting pregnant needed an injection of hormone X from a specialist. Hormone X has the same function as the luteinizing hormone (LH). After aa certain period, the woman was pregnant. Explain how the hormone X injection can help the woman to get pregnant.

Answer 17

• since the role of hormone X is similar to hormone LH, hormone X is able to stimulate follicle development together with FSH that stimulates ovulation
• the woman has a possibility of becoming pregnant
• ovum is fertilised by sperm to form a zygote
• after ovulation, Graafian follicle forms a corpus luteum
• corpus luteum is stimulated to secrete progesterone and oestrogen
• progesterone and oestrogen stimulate the endometrial tissue to become thick, folded and rich with blood capillaries as a preparation for zygote implantation

Question 18

During ejaculation, approximately 300 million sperms are released. From this amount, only about 300 sperms arrive at the secondary oocyte, and only one will be successful in fertilising the ovum. If only one sperm reaches the secondary oocyte, fertilisation will not take place. Explain why.

Answer 18

• to fertilise an ovum the protective layer outside the ovum must be digested by the enzyme found in the sperm acrosome
• one sperm is not enough to digest the protective layer
• the presence of many sperms is sufficient to digest the protective layer to enable one sperm to fertilise the ovum

Question 19

Describe how changes in different hormone levels in one menstrual cycle prepare a woman for pregnancy.

Answer 19

For an individual with a 28-day menstrual cycle, the changes in the levels of various hormones in preparation of conception is shown below.
- from day 0 to 7, right after menstruation, the pituitary gland is stimulated to secrete follicle stimulating hormone (FSH)
- FSH causes one or more Graafian follicle to develop in the ovary
- FSH stimulates follicle cells to secrete oestrogen
- from day 8 to 14, the concentration of oestrogen increases and reaches its maximum level on day 12
- oestrogen acts to restore and repair the endometrial tissue
- oestrogen also stimulates the pituitary gland to secrete luteinising hormone (LH)
- LH stimulates ovulation on day 14
- from say 15 to 21, the Graafian follicle that develops into a corpus luteum will be stimulated by LH to secrete progesterone
- the rising progesterone level stimulates the endometrium to expand, become thicker and more vascular
- from day 22 to 28, if fertilisation occurs, the progesterone level will continue rising to ensure further uterine development
- progesterone inhibits FSH and LH production, hence the menstrual cycle and ovulation does not take place in a woman who is pregnant
- this will prevent the development of other follicles in the ovary during pregnancy

Question 20

The umbilical cord is the lifeline between the foetus and its mother. Cord blood is blood left in the umbilical cord and placenta after birth. After a baby is born, cord blood is kept as it is a source of stem cells rich in hematopoietic stem cells. Is it important for parents to keep the cord blood for their children’s future?

Answer 20

• the stem cells of the umbilical cord have the potential to be turned into various types of cells
• umbilical cord stem cells can be used to treat various life-threatening diseases such as heart attack and stroke
• stem cell blank is one way of keeping umbilical cord blood so that the concerned individual can get their own stem cell for cellular therapy in the future