The Reproductive System — ICSE Class 10 Biology Important Questions

Answer: (c) Fallopian tube (oviduct).

The ovum released from the ovary is fertilised by a sperm in the upper part of the fallopian tube; the resulting zygote then moves to the uterus for implantation.

Answer: (c) Testosterone.

The testes make sperms and secrete testosterone, which controls the development of male secondary sexual characters such as a deep voice and facial hair.

Answer: (c) Day 14.

Ovulation, the release of the mature ovum from the ovary, occurs at about the middle of the cycle, roughly on the 14th day of a 28-day cycle.

Answer: (c) Acrosome of the head.

The acrosome is a cap over the front of the sperm head; it releases enzymes that dissolve the outer covering of the ovum so the sperm can enter and fertilise it.

Answer: (a) When no fertilisation occurs the corpus luteum breaks down and progesterone, which was maintaining the uterine lining, falls; the lining is therefore shed as the menstrual flow, so R correctly explains A.

(i) Gestation: the period of development of the foetus inside the uterus, from fertilisation (implantation) to birth; about $280$280 days (about $9$9 months) in humans.

(ii) Parturition: the birth of the baby at the end of gestation, by strong contractions of the uterus (helped by the hormone oxytocin).

The sperm has a head (with the acrosome cap in front and the nucleus behind), a middle piece packed with mitochondria that supply energy, and a long tail (flagellum).

Function of the tail: it lashes from side to side to propel the sperm and help it swim towards the ovum.

The sperm travels along the following path:

Testis (seminiferous tubules, where sperms are formed) $\rightarrow$→ epididymis (sperms are stored and mature) $\rightarrow$→ vas deferens (sperm duct) $\rightarrow$→ joined by fluid from the seminal vesicle and prostate gland to form semen $\rightarrow$→ urethra $\rightarrow$→ out through the penis.

Thus the sequence is: testis, epididymis, vas deferens, urethra, penis.

Both are haploid gametes, but the sperm is adapted for movement and the ovum for nourishing the future zygote.

Ovary produces ova and secretes the hormones oestrogen and progesterone.

Fallopian tube (oviduct) carries the ovum and is the site of fertilisation.

Uterus is where the fertilised egg implants and the foetus develops.

Cervix is the narrow neck of the uterus that opens into the vagina and guards the entrance to the uterus.

Vagina receives the sperms and serves as the birth canal at delivery.

The menstrual cycle is the roughly 28-day cycle of changes in the ovary and uterus, controlled by hormones. Its main events are:

1. Menstruation (days 1-5): the thickened lining (endometrium) of the uterus, unused because fertilisation did not occur, breaks down and is shed with blood through the vagina.

2. Follicular phase and repair (about days 6-13): the pituitary hormone FSH makes an ovarian follicle grow; the growing follicle secretes oestrogen, which repairs and thickens the uterine lining.

3. Ovulation (about day 14): a surge of the pituitary hormone LH causes the mature follicle to burst and release the ovum into the fallopian tube.

4. Luteal phase (about days 15-28): the empty follicle becomes the corpus luteum, which secretes progesterone; progesterone maintains the thick, blood-rich uterine lining so it is ready to receive an embryo.

5. If fertilisation does not occur, the corpus luteum degenerates, progesterone falls, and the lining is shed again, starting the next cycle. If fertilisation occurs, progesterone continues and menstruation stops.

(i) The process is implantation (the embedding of the embryo into the uterine wall).

(ii) The disc-shaped connecting structure is the placenta.

(iii) Two functions of the placenta:

• It supplies oxygen and nutrients (glucose, amino acids) from the mother's blood to the foetus.
• It removes carbon dioxide and nitrogenous wastes from the foetal blood into the mother's blood; it also secretes hormones that maintain pregnancy.

(iv) The amniotic fluid (inside the amnion). It protects the foetus from shocks and injury, keeps its temperature steady and lets it move freely.