Biology arose in a twofold manner - firstly, as a practicing art towards exploring and improving a variety of usable plant and animal products as well as towards maintaining good health; secondly, as an academic pursuit out of curiosity to know about humans and other living beings and to understand their position on the planet Earth.

Evolution of Life | Functions of Plants | Functions of Animals | Reproduction & Heredity

Excessive Intake of Food

If a person continues to eat more food than required by his body, he soon becomes overweight and bulky. Excess of carbohydrates and fats instead of providing energy get accumulated in the body.

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Mineral Deficiency Diseases

1. Anaemia (Iron deficiency)

Iron is important for the formaiton of the respiratory pigment hemoglobin present in blood. Deficiency of iron results in reduction of red blood cells. This reduces the oxygen carrying capacity of blood.

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Protein Energy Malnutrition (PEM)

Generally, the growing children suffer from protein energy malnutrition as the required amount of proteins needed for their growth and development is not available. A number of children in the age group of 1-5 years suffer from this disease.

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Meaning of Health and Disease

According to the World Health Organisation (WHO), health is defined as:

Health is a state of complete physical, mental, and social well being and not merely absence of disease or infirmity.

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Sexually Transmitted Diseases

The diseases that are transmitted through sexual contact are known as sexually transmitted diseases. Sexually transmitted diseases are those diseases that are transmitted via the mucous membrane and secretions of the sexual organ, throat and the rectum. Syphilis, gonorrhoea, and AIDS are some sexually transmitted diseases.

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Non-Communicable Diseases

1. Diabetes mellitus

The disease can be diagnosed by blood test or urine test.

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Diseases Caused by Worms

1. Filariasis

Pathogen: Filarial worm (Wucheraria bancrofti)

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Diseases Caused by Protozoans

1. Malaria

Pathogen: Malarial parasite (different species of Plasmodium)

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Diseases Caused by Bacteria

1. Tuberculosis

Pathogen: A bacterium (Mycobacterium tuberculosis)

Mode of transmission: airborne-discharged through sputum, cough and sneeze, of the infected person.

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Diseases Caused by Viruses

1. Chicken pox

Pathogen: Chicken pox virus (voricella)

Mode of transmission: By contact or through scabs

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Modes of Spread of Communicable Diseases

Communicable diseases spread from the infected person to a healthy person.

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Types of Diseases

Any malfunctioning process which interferes with the normal functioning of the body is called a disease. Disease may be defined as a disorder in the physical, physiological, psychological or social state of a person caused due to nutritional deficiency, physiological disorder, genetic disorder, pathogen or any other reason.

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Balanced Diet

Balanced diet consists of all the nutrients in varying amounts. To maintain proper health, one needs the right type of food in right quantity. The need generally varies with age, sex, type of work and state of body.

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Energy Requirements of Body

The body needs energy to carry on various activities of life. This energy is obtained by eating food. The energy requirement of an individual depends on various factors like age, sex, amount of work done (occupation), special needs like pregnancy and lactation.

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Water and Roughage


Water is an important constituent of diet. 75% of an infant body and 60% of an adult body is nothing but water.

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Minerals are micronutrients required in varying amounts for proper functioning, normal growth and keeping good health of body. They are inorganic elements, occurring in the form of their salts like calcium, potassium, sodium, phosphorus, iron, etc. They do not supply energy to our body but are essential for protection against diseases and also have role in body functions.

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Vitamins are complex chemical substances required by the body in very small amounts. They do not yield energy but act as biocatalysts in the body. They are essential for good health and protect the body from various diseases. They are essential for the utilization of other nutrients that we take in the diet.

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Proteins are extremely large molecules composed of many amino acids. Proteins are complex organic compounds rich in carbon, hydrogen, oxygen, nitrogen and sometimes phosphorous and sulphur also.

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Fats are members of lipids. Like carbohydrates, fats are also made up of carbon, hydrogen and oxygen. However fats contain more carbon and hydrogen and less oxygen.

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Carbohydrates are the chemical compounds made up of carbon, hydrogen and oxgyen. They release energy on biological oxidation with the help of cellular enzymes. They are the cheapest source of energy.

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Macronutrients and Micronutrients

Nutrition is the sum of the processes by which an organism takes in, metabolizes and utilizes food substance for its various biochemical activities. Nutrients are the organic or inorganic substances which help in survival and in maintaining proper health. A nutrient supplies energy to the body, builds and repairs body tissues and regulates the body metabolism.

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Classification of Food

Food is the basic necessity of life. Regular supply of food is essential for human beings in order to keep fit and to carry on all the life processes. Food is any substance which performs the following functions in the body:

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Genes and Protein Synthesis

The genes of an individual is the genotype, and the expression of genes results in the phenotype. There are different structural proteins like Haemoglobin in blood, enzymes e.g. pepsin, almost all of which are proteins.

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DNA Replication

DNA duplicates itself with complete fidelity for passing on genetic information to the next generation of cells. Replication may be defined as a mechanism for transmission of genetic information generation after generation.

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RNA: Ribonucleic Acid

Apart from DNA, RNA or Ribonucleic acid is the other important nucleic acid present inside the cell.

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Structure of DNA

Chemical Nature of DNA

DNA (Deoxyribonucleic acid) is a polynucleotide, a macromolecule made of units called nucleotides. Each nucleotide consists of three sub units:

  1. a pentose (5 carbon) sugar called deoxyribose
  2. 4 nitrogenous bases: Adenine (A), and Guanine (G) are purine bases and Thymine (T) and Cytosine (C) are pyrimidine bases
  3. a phosphate group (PO4) positioned on the sugar
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Discovery of DNA as Genetic Material

That genes, located on chromosomes, are the hereditary material was known to scientists in the early twentieth century. That genes are segments of DNA became evident from the work of Griffith on bacterial transformation.

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One Gene One Enzyme Hypothesis

The British biochemist and physician Archibald Garrod had mentioned in his book named "Inborn errors of metabolism" that there are inherited genetic disorders such as phenylketonuria and alkaptonuria which are caused by the absence of particular enzymes.

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Human Genome

In the last over hundred years, genetics and molecular biology have gone far ahead and the progress has been very rapid. Today there is hope for cure of genetic disorders through gene therapy. This is because in 2003, most of the genes on human chromosomes have been mapped or located on the 23(n) chromosomes.

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Amniocentesis in a technique by which hereditary disorders due to defects in genes can be detected.

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Genetic Disorders in Humans

Any change from the normal number or structure of chromosomes causes abnormalities.

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Human Karyotype

Human karyotype is the arrangement of human chromosomes in seven groups according to the types of chromosomes and their size. It is prepared by arranging chromosomes seen at mitotic metaphase in descending order with the longest pair of chromosomes drawn first, and the sex chromosomes are drawn the last.

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Criss-Cross Inheritance

The genes which are located on X chromosome (sex chromosome), are called sex linked genes. These genes show criss-cross inheritance.

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Sex Determination in Humans

Sex of the unborn individuals is determined in different ways in different kinds of organisms. In some diploid organisms, specific chromosomes have a role in sex determination. Such chromosomes are called sex chromosomes and the rest of the chromosomes of a set are called autosomes.

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Linkage and Crossing Over

Bateson and Punnett performed a dihybrid cross with true breeding varieties of sweet pea (Lathyrus sativus) and instead of 9:3:3:1 ratio in F2 generation they got the ratio 7:1:1:7. It means that the characters controlled by the two genes chosen for the experiment do not follow the principle of independent assortment as postulated by Mendel. Instead they tend to be inherited together or are linked together. Thus genes present on the same chromosome tend to be inherited together and are said to be linked. This phenomenon is called linkage.

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Chromosomal Theory of Inheritance

Sutton and Boveri in 1902 observed that chromosomes from two parents come together in the zygote as a result of the fusion of two gametes and again separate out during meiosis at the time of formation of gametes. Chromosomes are filamentous bodies present in the nucleus and seen only during cell division. Gametes have half (n) number of chromosomes or are haploid and zygote is diploid or has (2n) or double the number of chromosomes when compared to chromosome number in the gametes.

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Important Terms in Genetics

Factor: The unit of inheritance and expression of a particular character is controlled by inheritable units called factor (gene) which are present in pairs in parental cells and singly in the gametes.

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Mendel’s Principles of Inheritance

Based on the results of Mendel's experiments, Mendel postulated the following laws of heredity.

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Mendel’s Experiments on Garden Pea

Sir Gregor Johann Mendel (1822 to 1884) was Austrian monk who used garden pea (Pisum sativum) for his experiments on plant breeding and published his results in 1865. However, his work was independently rediscovered in 1900, long after Mendel’s death, by Tschermak, Correns and DeVries. But since Mendel was the first to suggest principles underlying inheritance he is regarded as the founder or father of genetics.

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Heredity and Variation

Whenever an infant is born in a family, the relatives begin to wonder about the resemblance of the infant’s eyes, facial features, complexion, colour of hair with those of the parents, siblings and grand parents. The source of such resemblances and differences are in the genes that are passed down form parents to children and so on generation after generation. This inheritance of genes is termed heredity the study of reasons of heredity is Genetics.

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Medical Techniques in Reproduction

There are many new medical techniques in the field of reproduction to help infertile males and females produce babies.

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Fertilization, Pregnancy and Development of Embryo

Fertilization and implantation

Spermatoza remain viable in the female genital tract from 24 to 72 hours. For fertilization, sperms are introduced into the female body. One sperm fuses with the ovum in the fallopian tube.

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Menstrual Cycle in Human Females

In a human female, the fertility period extends from the age of puberty, i.e. about 12-13 years up to menopause, i.e. 45-50 years. The stage of puberty is marked by the appearance of secondary sexual characteristics.

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Female Reproductive System

The female reproductive system consists of the following organs: a pair of ovaries, a pair of fallopian tubes, uterus, vagina and external genitalia.

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Male Reproductive System

The reproductive system in male consists of the following organs: a pair of testes, a pair of epididymis, a pair of vasa deferentia, urethra, penis and accessory glands.

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Human Reproductive System

Humans reproduce sexually. Reproduction in humans is in two parts:

  1. Reproductive system
  2. Fertilization, pregnancy and development of the embryo
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Plant Movements

Movements of plants are completely different from body movement. Except some unicellular plants, all other higher plants cannot move from place to place as their roots are fixed in the soil. Still they show movement by folding the buds, opening and closing the flowers, and bending towards sun light. These movements in plants are very slow and you have to wait and observe them carefully and patiently to notice these movements.

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Aging of Plants

Like animals, plants also have fixed life span and after completing that perioid, they die. Before death several degradation processes occur in their body like yellowing of leaves and fading of flower colour. It is due to loss in structure and function of an organ or the whole plant. The deteriorative processes which ultimately lead to complete loss of organization and functioning of the plant or its parts is known as Senescence.

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The temperature affects growth and development of plants. For flowering in some plants, a particular temperature is required. Studies show that if temperature is reduced to a particular point then flowering occurs at an early stage. For example by applying a temperature ranging between 1-10°C to certain variety of wheat, rice and cotton, growth of seedlings is accelerated and flowering occurs earlier. This method of inducing early flowering in plants at low temperature is called vernalisation.

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Some plants like spinach and wheat produce flowers in summer while others like and dahlia and cosmos flower in winter. Plants that flower in summer require longer duration of light per day than those flowering in winter. The duration of light plays an important role in flowering of plants. This effect of duration of light on the growth of plants is known as photoperiodism.

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