Q.(a) Write the causes for infertility in males and females. OR

(a) Infertility in males and females arises from a range of physical, hormonal, infective and genetic causes affecting gamete production or the reproductive tract. (b) Because invasive alien species escape the natural checks of their native range, they can outcompete and displace endemic species, causing irreversible biodiversity loss -- as documented cases like Lake Victoria's cichlids show.

(a) Infertility, the inability of a couple to conceive despite regular unprotected intercourse over a reasonable period, can stem from causes in either partner. In males, common causes include a low sperm count (oligospermia) or complete absence of sperm in the semen (azoospermia); poor sperm motility or a high proportion of abnormally shaped sperm, which reduces their ability to reach and fertilise an egg; physical blockage of the sperm-carrying ducts (such as the vas deferens), preventing sperm from being ejaculated; hormonal imbalances affecting testosterone, FSH or LH levels, which are needed for normal spermatogenesis; a varicocele (enlarged veins in the scrotum, which can raise testicular temperature and impair sperm production); infections such as mumps orchitis (inflammation of the testis following mumps infection); and certain genetic disorders (such as Klinefelter's syndrome). In females, common causes include blockage of the fallopian tubes, frequently resulting from pelvic inflammatory disease or untreated sexually transmitted infections, which prevents the egg and sperm from meeting; disorders of ovulation, in which the ovaries fail to release an egg regularly; hormonal imbalances disrupting the menstrual/ovarian cycle; structural abnormalities of the uterus, such as fibroids, which can interfere with implantation; endometriosis (growth of uterine-lining-like tissue outside the uterus); and a natural, age-related decline in the number and quality of eggs as a woman grows older. …