Friday 6 December 2013

What causes shortsightedness or myopia?


What causes shortsightedness or myopia?
Symptom: A person with shortsightedness cannot see objects which are far away but can see objects which are nearby.
Reason for the defect: The light rays from the object move through the eye and get converged before the retina. As image of the object is not formed on the retina we cannot see the object.
Causes for the defect:  The lens is too convex or too curved is one of the reason for this defect. Another reason for this defect is the eye ball may become lengthened from front  to back.
How to rectify this defect?
A spectacle with concave lens has to be used for rectifying this defect.  Concave lens is a diverging lens which makes the light rays to travel further and make them to meet on the retina. The power of the lens has to be noted with a negative sign. Shortsightedness or myopia is mainly caused in school going  children.

Monday 1 October 2012

ICSE, ISC -Board's Examination Preparation Guiding Blog

Quick Revision Material for ICSE Board's Biology Examination

I am providing here quick revision material for ICSE Board's examination preparing students. If the student is thorough with this material, the student will find it easy to answer both section I as well as section II questions with utmost perfection. I am a Biology teacher teaching Biology in a reputed school for more than 20 years.

1. Important days to remember:

World Population Day: July 11th
World Health Day: April 7th
World Environment Day: June 5th
World AIDS Day: December 1st
International Ozone Day: September 16th
World Red Cross Day: May 8th

2. Gestation period: 280 days
Life span of RBC or Erythrocytes: 120 days
Life span of WBC or Leukocytes: 14 days
Life span of platelets or Thrombocytes: 3-5 days
Total spinal nerves in human body: 31 pairs
Total number of vertebrae in human body: 33
Number of muscles which attach eye ball to eye sockets: 3 pairs or 6 extrinsic muscles or rectris muscles
Menstrual cycle: 28 days

3. Diseases caused by:

Bacteria: Cholera, Tetanus, Leprosy, Tuberculosis, Gonorrhea, Syphilis, Diphtheria, Pneumonia

Viruses: Common cold, Influenza, Mumps, Poliomyelitis, Rabies, Small Pox, Measles, Yellow fever, AIDS

Fungi: Ring worm, Athlet's Foot

Protozoa: Malaria, Amoebic dysentry, Sleeping sickness

Deficiency diseases: Marasmus, Kwashiorkar, Xerophthalmia, Anaemia

4. Disinfectants: Cresol, Phenol, 40%Lysol, Formalin, Lime, Bordeaux mixture, DDT

Antiseptics: Carbolic acid, Iodine, Benzoic acid, Mercurochrome, Boric acid

Antibiotics: Penicillin, Streptomycin, Terramycin, Erythromycin, Ampicillin

5. Abbreviations

ATP: Adenosine Triphosphate (Cellular currency)

ADP: Adenosine diphosphate

NADP: Nicotinamide Adenosine dinucleotide phosphate

RUBP: Ribulose bisphosphate (CO2 acceptor in Dark reaction of Photosynthesis)

CFC's: Chlorofuorocarbons (causes bone holes)

GH: Growth hormone

FSH: Follicle stimulating hormone

ADH: Antidiuretic hormone or vasopressin

TSH: Thyroid stimulating hormone

ACTH: Adrenocorticotropic hormone

LH: Lutenizing hormone

DDT: Dichloro diphenyl trichloroethane

AIDS: Acquired Immuno Deficiency Disease

HIV: Human Immuno Virus

IUDC: Intrauterine devices

MTP: Medical termination of pregnancy

BOD: Biological Oxygen Demand

CNG: Compressed Natural Gas

WHO: World Health Organization

GHIH: Growth Hormone Inhibiting Hormone

DTP: Diphtheria, Tetanus, Pertussis (Whooping cough)

BCG: Bacillus of Calmette and Guerin




                                                  Endocrine Glands
1.      Glands are of two types- Exocrine glands and Endocrine glands.
.Exocrine glands are duct (having tube) glands- secrete enzymes.
.Endocrine glands are ductless (tube lacking) glands secrete enzymes.
2.      Hormones are chemical messengers which are produced at one part of our body and have influence at some other parts (target organs) of our body.
Characteristics of hormones:
1.      Hormones are always poured or secreted into blood by endocrine glands.
2.      Hormones always act away from the source of their secretion.
3.      Hormones are produced in  trace quantity but they have wide influence  all over our body.
4.      Same hormone produced in different species will have the same influence.
5.      Hormones cannot be stored in our body but  will be excreted after their action.
6.      Hormones regulate physiological process by chemical means.
7.      Chemically hormones are peptides (insulin), amine (adrenaline), steroids (testosterone).
8.      Secretion of a hormone less (hypo/under secretion) or more (hyper/over secretion) leads to some defects in the body.
1.     THYROID GLAND:   
Location: A butterfly shaped gland present below larynx and above trachea. The two wings of thyroid gland are connected by a bridge like region called isthmus.
Hormones secreted: Thyroxine and Calcitonin
Principal activities of Thyroxine hormone:-
1.      Regulate basal metabolism ( Cellular oxidation resulting in heat production).
2.      It influences general growth of the body, ossification of bones, mental development and body heat content.
Hypo secretion or under secretion (Hypothyroidism) of this hormone leads to three defects.
a.      Simple Goiter: Thyroid gland present below the neck region become swollen.
Symptom: Abnormal swelling of thyroid gland present below the neck region.

Reason: Lack of iodine in diet. Iodine helps in the synthesis of thyroxine hormone by thyroid gland.
People live in hilly plains most commonly suffer from this defect due to iodine gets leached away from the sloppy soils. Hence the food produced from these crops lack iodine mineral.
b.      Cretinism: It is a defect caused in child or at infancy.
Symptoms: Dwarfism, Mental retardation.
c.       Myxoedema:  disease caused in old people. Person become sluggish. Swelling can be Iseen in face and hands.
Over secretion /Hyper secretion (Hyperthyroidism) leads to Exophthalmic Goiter.
Symptoms: 1. Eyes protrude out.
2.     Metabolic and heart beat rate increases.
3.     Shortness of breath
4.     Goiter in the neck.
2.PANCREAS:
This gland acts as both exocrine and endocrine gland. Pancreas is present below the stomach region. Pancreas as an exocrine gland it secret enzymes and as an endocrine gland secrete hormones. Patches of endocrine cells present in pancreas together known as Islets of Langerhans.  
a.      Beta cells of Islets of Langerhans secret Insulin.
Principal activities of Insulin hormone:
1.      Insulin promotes proper utilization of glucose by our body cells.
2.      Insulin converts excess glucose present in blood to glycogen and store it in liver.
b.      Alpha cells of  Islets of Langerhans secret Glucagon.  
Glucagon converts glycogen present in liver to glucose and put into blood circulation.
c.       Delta cells of Islets of Langerhans secrete Somatostatin. This hormone control secretions of both insulin and glucagon hormones.