Biology Test - 56

The premolars also called premolar teeth, are transitional teeth located between the canine and molar teeth. It is four in number and are absent in infants which is actually replaced by the molars in the later stages. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth. Premolars can be considered transitional teeth during chewing or mastication.

In the lac operon of E.coli due to the activity of regulator gene synthesis of repressor molecules occurs. These repressor molecules get attached to the operator gene and thus check mRNA synthesis and because of this no protein synthesis occurs.

Tubuloglomerular feedback control is useful for GFR.

Tubuloglomerular feedback – Two components:

•  Afferent arteriole feedback mechanism.
• Usually referred as “Tubuloglomerular feedback”.
• Efferent arteriole feedback mechanism.

Afferent arteriolar feedback mechanism:

• Transmitter involved – Adenosine causing Ca²⁺ channel opening.

Efferent arteriolar feedback mechanism:

• Activates renin-angiotensin system generating angiotensin II→ efferent arteriole constriction → ed GFR.
• Feedback depends on juxtaglomerular apparatus & its specialized cells.
• Macula densa – Specialized epithelium of distal tubule in close contact with afferent arteriole

The lion-tailed macaque or the wanderoo, is an Old World monkey endemic to the Western Ghats of South India. The lion-tailed macaque ranks among the rarest and most threatened primates. Their range has become increasingly isolated and fragmented by the spread of agriculture and tea, coffee, teak and cinchona, construction of water reservoirs for irrigation and power generation, and human settlements to support such activities.

The two DNA chains are held together by hydrogen bonds between their nitrogenous bases. Adenine (A), a purine of one chain lies exactly opposite thymine (T), a pyrimidine of the other chain. Similarly, cytosine (C), a pyrimidine lies opposite guanine (G), a purine.

Three hydrogen bonds occur between cytosine and guanine (C - G) at positions 1′ 2′ and 6′ and two hydrogen bonds between adenine and thymine A−T at positions 1′ and 6′

The zona granulosa and theca cells of Graafian follicle remaining in the ovary after ovulation and some surrounding capillaries and connective tissue evolve into the corpus luteum (a temporary endocrine gland). The corpus luteum produces progesterone and, in the event of fertilization, provides the required progesterone until the placenta is formed. In the absence of fertilization, the life span of the corpus luteum is 14 days. It then degenerates into a corpus albicans, which is mainly a scar tissue.

In forceful expiration, VRG neurons get fired.

Medullary respiratory group:

Principal areas in medulla oblongata concerned with respiratory regulation.

Ventral respiratory group (VRG):

• Mainly concerned with forceful expiration.
• Minimal activities w.r.t inspiration.
• Contributes to both expiration & inspiration.

Dorsal respiratory group (DRG):

• Mainly concerned with inspiration.
• Descend & terminate on spinal motor neurons innervating primary inspiratory muscles.
• Diaphragm & External intercostal muscles.

The bones of forelimbs of whale, bate, cheetah, and man are similar in structure because they are homologous organs. The organs which have the same fundamental structure but are different in functions are called homologous organs. These organs follow the same basic plane of organization during their development. But in the adult condition, these organs are modified to perform different functions as an adaptation to different environments. The homologous structures are a result of divergent evolution. Homology indicates common ancestry.

The first clinical gene therapy was done for the treatment of SCID (Serve Combined Immuno Deficiency resulting form deficiency of ADA). The first clinical gene therapy was given in 1990 to a 4-years old girl with adenosine deaminase (ADA) deficiency. This enzyme is very important for the immune system to function. ADA deficiency can lead to severe combined immune deficiency (SCID).

Frogs have a third eye lid that covers their eyes so they can keep them open underwater. The eyelid is called the nictitating membrane and also helps the eyes to stay moist when they are not in the water.