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Meghna Thapar 5 years, 9 months ago
Evidences of evolution:
Some of the important sources which provide evidences for evolution are:
(a) Analogous Organs: Organs which performs similar function but are different in structure and origin.
Example - wings of a bird and wings of an insect.
The presence of analogous organs indicates that even the organisms having organs with different structures can adapt to perform similar functions for their survival under hostile environmental conditions. Thus, the presence of analogous organs in different animals provide evidence for evolution by telling us that though they are not derived from common ancestors, they can still evolve to perform similar functions to survive, flourish and keep on evolving in the prevailing environment.
(b) Homologous Organ: Organs which have different functions but similar structure and origin.
Example - fore arm of frog, lizard, bird and human.
The presence of homologous organs in different animals provides evidence for evolution by telling us that they are derived from the same ancestor who had the 'basic design' of the organ on which all the homologous organs are based.
(c) Fossils: The remains of dead animals or plants that lived in the remote past are known as fossils. The fossils provide evidence of evolution. For example, a fossil bird called Archaeopteryx looks like a bird but it has many features which are found in reptiles. This is because Archaeopteryx has feathered wings like those of birds but teeth and tail like those of reptiles. Therefore, Archaeopteryx is a connecting link between the reptiles and birds and suggests that birds have evolved from reptiles. Thus, fossils provide evidence that the present plants and animals have originated from the previously existing ones through the process of continuous evolution.
Posted by Gauri Shankar Shah Shah 5 years, 9 months ago
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Meghna Thapar 5 years, 9 months ago
The prevention of pregnancy in women (by preventing fertilisation) is called contraception. There are four methods of contraception:
- Barrier method: In barrier method of contraception, the physical devices such as condoms are used by males and females.
- Chemical method: In chemical methods of preventing pregnancy, the females use two types of pills – oral pills and vaginal pills.
- Intra-Uterine Contraceptive Devices – The use of intra-uterine contraceptive devices like Copper-T is very effective in preventing pregnancy. A Copper-T is placed inside the uterus by a doctor to prevent unwanted pregnancies.
- Surgical method: These methods are available for males as well as for females. Vasectomy is done in males and tubectomy is done in females.
Posted by Harsh Verma 5 years, 9 months ago
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Meghna Thapar 5 years, 9 months ago
The rapid, automatic response to a stimulus which is not under the voluntary action of the brain is called reflex action.
Reflex arc is the neural pathway that mediates a reflex action.
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Functions of blood:
(i) It carries oxygen from the lungs to different parts of the body.
(ii) It carries carbon dioxide from the body cells to the lungs for breathing out.
(iii) It carries digested food from the small intestine to all the parts of the body.
(iv) It carries waste product called urea from the liver to the kidneys for excretion in the form of urine.
(v) It protects the body from diseases.
The functions of lymph are:
(i) It takes part in the nutritive process of the body.
(ii) It protects the body by killing the germs drained out of the body tissues with the help of lymphocytes contained in the lymph nodes, by making antibodies.
(iii) It helps in removing the waste products like fragments of dead cells etc.
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An autosome is any chromosome that is not a *** chromosome (an allosome). However, an allosome is a *** chromosome that differs from an ordinary autosome in form, size, and behavior.
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When a girl is born, the ovaries already contain thousands of immature eggs. On reaching puberty, some of these start maturing. One egg is produced every month by one of the ovaries. The egg is carried from the ovary to the womb through a thin oviduct or fallopian tube. The two oviducts unite into an elastic bag-like structure known as the uterus. The uterus opens into the ****** through the cervix. The sperms enter through the vaginal passage during sexual intercourse. They travel upwards and reach the oviduct where they may encounter the egg. The fertilised egg, the zygote, gets implanted in the lining of the uterus, and starts dividing.
The release of an ovum from an ovary is called ovulation. In human females, the ovaries start releasing ovum once every 28 days from the age of puberty. Fertilisation is possible if mating takes place during the middle of menstrual cycle because in a normal healthy girl the ovulation takes place on the 14th day of the beginning of menstrual cycle of 28 days. The embedding of embryo in the thick lining of the uterus is called implantation.
The lining thickens and is richly supplied with blood to nourish the growing embryo. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta.
Placenta is a disc like special tissue which develops between the uterus wall and the embryo after implantation. Its function is the exchange of nutrients, oxygen and waste products between the embryo and the mother. It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The developing embryo will also generate waste substances which can be removed by transferring them into the mother’s blood through the placenta. The time period from the fertilisation up to the birth of a baby is called gestation. The average gestation period in humans is about 9 months (about 38 weeks).The child is born as a result of rhythmic contractions of the muscles in the uterus.
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In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how fast light travels through the material. It is defined as. where c is the speed of light in vacuum and v is the phase velocity of light in the medium.
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Meghna Thapar 5 years, 9 months ago
In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how fast light travels through the material. It is defined as. where c is the speed of light in vacuum and v is the phase velocity of light in the medium.
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