NEET BIOLOGY BY SHASHI SIR

 As you are aware, humans are sexually reproducing and viviparous.  The reproductive events in humans include  formation of gametes ( gametogenesis ), i.e., sperms in males and ovum in females,  transfer of sperms into the female genital tract ( insemination ) and  fusion of male and female gametes ( fertilisation ) leading to formation of zygote.  This is followed by formation and development of blastocyst and its attachment to the uterine wall ( implantation ),  embryonic development ( gestation ) and  delivery of the baby ( parturition ).  You have learnt that these reproductive events occur after puberty .  There are remarkable differences between the reproductive events in the male and in the female, for example, sperm formation continues even in old men, but formation of ovum ceases in women around the age of fifty years. 3.1 THE MALE REPRODUCTIVE SYSTEM   The male reproductive system is located in the pelvis region (Figure 3....

  Scientists                                                           Related Fields 1.Ernst Mayr (1904-2004)                            Evolutionary Biologist 2.Matthias Schleiden                                    German Botanist 3.Julius von Sachs                                          German Botanist 4.Theodore Schwann                                    British Zoologist 5.Cornelius van Niel                         ...

  Curious mice By examining mice in different situations, researchers from Netherlands have discovered a new brain circuit that is related to curiosity and novelty-seeking behaviour. The study, published in Science, found that increasing activity in a brain region called Zona Incerta caused increase in interaction with novel objects. They discovered a whole path involving different regions that converts curiosity into action in mice. crd: TH

  6.10 DNA FINGERPRINTING   DNA fingerprinting is a very quick way to compare the DNA sequences of any two individuals. DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called as repetitive DNA, because in these sequences, a small stretch of DNA (TANDEM REPEATS) is repeated many times.  Satellite DNA Repetitive DNA are separated from bulk genomic DNA as different peaks during density gradient centrifugation.  The bulk DNA forms a major peak and the other small peaks are referred to as satellite DNA. Depending on base composition (A : T rich or G:C rich), length of segment, and number of repetitive units, the satellite DNA is classified into many categories, such as micro-satellites, mini-satellites etc.                                 POLYMORPHISM  &  POLYMORPHIC DNA  Polymorphism is a variation at genetic...

  Regulation of Breathing The regulation of breathing is based in the body's acid/base balance. The Central Chemoreceptors (CCR), primarily responsible for the breathing stimulation, are affected by the PaCO 2.  The responsiveness of the peripheral receptors is tied to the level of pH and PaCO 2 . Together these provide the ultimate in servo-control - sensors provide feedback that increase or decrease breathing. Medullary Respiratory Center The rhythmic cycle of breathing originates in the medulla. Higher brain centers (voluntary control), systemic receptors, and reflexes modify the medulla's output. However, no truly separate inspiratory and expiratory centers have been identified. The medulla does contain several widely dispersed groups of respiratory-related neurons that form dorsal and ventral respiratory groups. Fig-Schematic illustration of the respiratory components of the lower brainstem (pons and medulla oblongata). PNC = pneumotaxic center; APC = apneustic center; DR...

  The Antarctic ozone hole forms during the Southern Hemisphere’s late winter as the returning Sun’s rays start ozone-depleting reactions. These reactions involve chemically active forms of chlorine and bromine derived from man-made compounds. The chemistry that leads to their formation involves chemical reactions that occur on the surfaces of cloud particles that form in cold stratospheric layers, leading ultimately to runaway reactions that destroy ozone molecules. In warmer temperatures fewer polar stratospheric clouds form and they don’t persist as long, limiting the ozone-depletion process. @NASA