Biology Test 271

The rhizome is a thickened, underground, dorsiventral stem that grows horizontally at a particular depth within the soil. It is brown in colour and shows cymose branching. It can be distinguished from the modified root by the presence of nodes, internodes, terminal buds, axillary buds and scale leaves. The rhizome are perennial and propagate
vegetatively. They store food materials and appear tuberous. E.g., Zingiber
officinale (ginger), Curcuma longa (turmeric), Canna indica, etc

In Vallisneria, the female flower reach the surface of water by the long stalk and the male flowers or pollen grains are released on to the surface of water. They are carried passively by water currents, some of them eventually reach the female flowers and the stigma.

Interstitial cells or Leydig’s cells are the cells interspersed between the seminiferous tubules of the testis. They secrete androgens (e.g., testosterone) in response to stimulation by luteinising hormone from the anterior pituitary gland.

The male sex accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens. The seminiferous tubules of the testis open into the vasa efferentia through rete testis. The vasa efferentia leave the testis and open into epididymis located along the posterior surface of each testis. So, if vasa efferentia gets blocked, the gametes will not be transported from testes to epididymis.

Barr body is a structure consisting of a condensed X chromosome that is found in non-dividing nuclei of female mammals. Amniotic fluid contains fetal skin cells, that are stained to determine the presence of sex chromatin (barr body). The presence of barr body indicates that the developing fetus is female with two X-chromosome.

Lactational amenorrhea method is based on the fact that ovulation and therefore the menstrual cycle do not occur during the period of intense lactation following parturition. This is because breast feeding disrupts the pattern of pulsatile release of GnRH from hypothalamus and hence reduction in gonadotropin releasing hormones. Pills are hormonal preparations (either progestogen or progestogen-estrogen combinations) in the form of tablets which are administrated orally by females. They inhibit ovulation, implantation as well as alter the quality of cervical mucus. Emergency contraceptives are pills that contain levonorgestrel, a type of progestin that helps to prevent pregnancy when taken in few days after sex.

According to Chargaff’s rule, the amount of adenine is always equal to that of thymine and the amount of guanine is always equal to that of cytosine, i.e., A = T and G = C. Also, the purines and pyrimidines are always in equal amounts, i.e., A + G = T + C. Now, given dsDNA has 17% cytosine and hence guanine will be also 17%. So, A + T must be 66%, therefore, percentage of adenine or thymine would be 66/2 = 33%.