NEET BIOLOGY BY SHASHI SIR

13.2.4 Population Interactions   Can you think of any natural habitat on earth that is inhabited just by a single species? (No) There is no such habitat and such a situation is even inconceivable.  For any species, the minimal requirement is one more species on which it can feed.  Even a plant species, which makes its own food, cannot survive alone; it needs soil microbes to break down the organic matter in soil and return the inorganic nutrients for absorption.  And then, how will the plant manage pollination without an animal agent?  It is obvious that in nature, animals, plants and microbes do not and cannot live in isolation but interact in various ways to form a biological community.  Even in minimal communities, many interactive linkages exist, although all may not be readily apparent.  Interspecific interactions arise from the interaction of populations of two different species. They could be beneficial, detrimental or neutral (neith...

8.5.4 Prevention and Control The age-old adage of ‘prevention is better than cure’ holds true here also.  It is also true that habits such as smoking, taking drug or alcohol are more likely to be taken up at a young age, more during adolescence.  Hence, it is best to identify the situations that may push an adolescent towards use of drugs or alcohol, and to take remedial measures well in time.  In this regard, the parents and the teachers have a special responsibility. Parenting that combines with high levels of nurturance and consistent discipline, has been associated with lowered risk of substance (alcohol/drugs/tobacco) abuse.  Some of the measures mentioned here would be particularly useful for prevention and control of alcohol and drugs abuse among adolescents  (i) Avoid undue peer pressure -  Every child has his/her own choice and personality, which should be respected and nurtured.  A child should not be pushed unduly to perf...

8.5.3 Effects of Drug/Alcohol Abuse The immediate adverse effects of drugs and alcohol abuse are manifested in the form of reckless behaviour, vandalism and violence. Excessive doses of drugs may lead to coma and death due to respiratory failure, heart failure or cerebral hemorrhage. A combination of drugs or their intake along with alcohol generally results in overdosing and even deaths.   Alcohol + Barbiturate = increases depresent effects Alcohol + Antihistamines = cause drowiness Alcohol + Valium = increase sedative effects Alcohol + Hashish = decrease coordination Alcohol + Aspirin = damage to gastro-intestinal mucosa The most common warning signs of drug and alcohol abuse among youth include. Drop in academic performance, unexplained absence from school/college,  lack of interest in personal hygiene, withdrawal, isolation, depression,  fatigue, aggressive and rebellious behaviour,  deteriorating relationships with family and friends,  l...

8.5.1 Adolescence and Drug/Alcohol Abuse Adolescence means both ‘a period’ and ‘a process’ during which a child becomes mature in terms of his/her attitudes and beliefs for effective participation in society.  The period between 12-18 years of age may be thought of as adolescence period.   In other words, adolescence is a bridge linking childhood and adulthood.  Adolescence is accompanied by several biological and behavioural changes.  Adolescence, thus is a very vulnerable phase of mental and psychological development of an individual.  Curiosity, need for adventure and excitement, and experimentation, constitute common causes, which motivate youngsters towards drug and alcohol use.  A child’s natural curiosity motivates him/her to experiment.  This is complicated further by effects that might be perceived as benefits, of alcohol or drug use.  Thus, the first use of drugs or alcohol may be out of curiosity or experimentation, but la...

8.3 AIDS The word AIDS stands for Acquired Immuno Deficiency Syndrome.  This means deficiency of immune system, acquired during the lifetime of an individual indicating that it is not a congenital disease. ‘Syndrome’ means a group of symptoms.  AIDS was first reported in 1981 and in the last twenty-five years or so, it has spread all over the world killing more than 25 million persons.  AIDS is caused by the Human Immuno deficiency Virus (HIV), a member of a group of viruses called retrovirus , which have an envelope enclosing the RNA genome.   Human Immuno deficiency Virus (HIV) Structure & its Genome:   It is roughly spherical with a diameter of about 120  nm , around 60 times smaller than a  red blood cell . It is composed of two copies of positive- sense   single-stranded   RNA  that codes for the virus's nine  genes  enclosed by a conical  capsid  composed of 2,000 copies...

8.2.7 Immune System in the Body  The human immune system consists of lymphoid organs, tissues, cells and soluble molecules like antibodies.  As you have read, immune system is unique in the sense that it recognises foreign antigens, responds to these and remembers them.  The immune system also plays an important role in allergic reactions, auto-immune diseases and organ transplantation.  Lymphoid organs:   These are the organs where origin and/or maturation and proliferation of lymphocytes occur.   The primary lymphoid organs  The primary lymphoid organs  are bone marrow and thymus w here immature lymphocytes differentiate  into antigen-sensitive lymphocytes.  The location of various lymphoid organs in the human body is shown in Figure below-                                                   ...

8.2.5 Allergies   When you have gone to a new place and suddenly you started sneezing, wheezing for no explained reason, and when you went away, your symptoms dissappeared.  Did this happen to you? Some of us are sensitive to some particles in the environment.  The above-mentioned reaction could be because of allergy to pollen, mites, etc., which are different in different places.  The exaggerated response of the immune system to certain antigens present in the environment is called allergy.  The substances to which such an immune response is produced are called allergens.  The antibodies produced to these are of IgE type.  Common examples of allergens are mites in dust, pollens, animal dander, etc.  Symptoms of allergic reactions include sneezing, watery eyes, running nose and difficulty in breathing.   Allergy is due to the release of chemicals like histamine and serotonin from the mast cells.   For determining the cause...

8.2.3 Active and Passive Immunity  When a host is exposed to antigens, which may be in the form of living or dead microbes or other proteins, antibodies are produced in the host body.   This type of immunity is called  Active Immunity .  Active immunity is slow and takes time to give its full effective response.  Injecting the microbes deliberately during immunisation (Artificial Active Immunity) or infectious organisms gaining access into body during natural infection induce active immunity ( Natural active immunity) .  When ready-made antibodies are directly given to protect the body against foreign agents, it is called passive immunity ( Artificial passive immunity) .  Do you know why mother’s milk is considered very essential for the newborn infant?  The yellowish fluid colostrum secreted by mother during the initial days of lactation has abundant antibodies (IgA) to protect the infant ( Natural passive immunity) .  The foetus...