Sexual Reproduction, Vision Defects, and Human Biology
Advantages of Sexual Reproduction
In sexual reproduction, more variations are produced. Thus, it ensures the survival of species in a population. The newly formed individual has characteristics of both parents. Variations are more viable in sexual mode than in asexual mode. This is because, in asexual reproduction, DNA has to function inside the inherited cellular apparatus.
The Testes
The testes are the male reproductive organs that are located outside the abdominal cavity within a pouch called the scrotum.
Functions of the testes:
- Produce sperms.
- Produce a hormone called testosterone, which brings about secondary sexual characteristics in boys.
Menstruation
Menstruation is a process in which blood and mucus flow out every month through the vagina. This process occurs every month because one egg is released from the ovary every month and, at the same time, the uterus (womb) prepares itself to receive the fertilized egg. Thus, the inner lining of the uterus gets thickened and is supplied with blood to nourish the embryo. If the egg does not get fertilized, then the lining of the uterus breaks down slowly and gets released in the form of blood and mucus from the vagina.
Reproduction in Unicellular and Multicellular Organisms
In unicellular organisms, reproduction occurs by the division of the entire cell. The modes of reproduction in unicellular organisms can be fission, budding, etc. Whereas in multicellular organisms, specialized reproductive organs are present. Therefore, they can reproduce by complex reproductive methods such as vegetative propagation, spore formation, etc. In more complex multicellular organisms, such as human beings and plants, the mode of reproduction is sexual reproduction.
Fertilization and Embryonic Development
After fertilization, the lining of the uterus 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 the placenta. This is a disc-shaped tissue that is embedded in the uterine wall. The placenta contains villi on the embryo’s side of the tissue and blood spaces on the mother’s side surrounding the villi. This provides a large surface area for food and oxygen to pass from the mother to the embryo and waste products from the embryo to the mother.
Copper-T as a Contraceptive Method
Copper-T is a contraceptive method that prevents the implantation of the zygote inside the uterus. It cannot prevent a woman from sexually transmitted diseases (STDs). STDs are transmitted by contact, which cannot be prevented by Copper-T.
The Atmosphere at High Altitudes
The atmosphere is quite thin at very high altitudes. There is almost no scattering of sunlight, so the sky appears dark to an astronaut.
Vision Defects
Myopia
Myopia is a vision defect in which a person can see nearby objects clearly but cannot see distant objects clearly beyond a certain point. This can be corrected by using concave lenses.
Hypermetropia
Hypermetropia is a vision defect in which a person can see distant objects clearly but cannot see nearby objects clearly. This can be corrected by using convex lenses.
Presbyopia
Presbyopia is similar to hypermetropia; a person having this defect cannot see nearby objects distinctly but can see distant objects without any difficulty. This can be corrected by using bifocal lenses.
Astigmatism
Astigmatism is a defect of vision in which a person cannot simultaneously see both the horizontal and vertical views of an object with the same clarity. This can be corrected by using cylindrical lenses.