HSC EV Biology 2nd Paper 9th Chapter Note. Continuance of Human Life. Sexual reproduction produces the variations which are necessary for a species to maintain homeostasis or balance. As a species, humans have a high degree of variation and this variation has helped us to populate the entire planet. Our reproductive system is one of the main reasons why we have been so successful as a species. In males, the reproductive system begins to form when the fetus is eight weeks old and is fully functional at the end of puberty (around 13 years of age). Puberty is the stage when reproductive hormones are formed and reproductive development begins.
Viable sperm is able to be produced by the end of puberty. The male reproductive system is made up of a number of parts. Both the testes and penis are outside the body cavity of the male. Within the seminiferous tubules, Sertoli cells, support, regulate and nourish the developing sperm. Once formed, sperm move to the epididymis where they become mature and motile. During sexual arousal, the soft tissue of the penis fills with blood making the penis erect. The sperm then moves out of the epididymis through a tube called the sperm duct or vas deferens.
This is necessary for sexual reproduction because each parent must give only half of the required genetic material, otherwise, his offspring would have too much DNA, which can be a problem. These different types of cell division are discussed below. Organisms can be classified as unicellular (consisting of a single cell; including bacteria) or multicellular (including plants and animals). While the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion (1013) cells. Most plant and animal cells are visible only under a microscope, with dimensions between 1 and 100 micrometers.
HSC EV Biology 2nd Paper 9th Chapter Note. Continuance of Human Life
A cell is the smallest working unit of all living organisms on our planet earth, which is capable of performing life functioning. Hence it can also be defined as a fundamental unit of life. The term cell was first observed and identified by an English physicist Robert Hook in the year 1665. There were many theories developed for the cell. Later in the year 1839 a two German scientist – Schwann and Schleiden provided few basic principles of the cell.
A microscopic living organism. Examples include bacteria, protozoa, and some fungi and parasites. Viruses are also called microbes. Microbes are tiny forms of life that surround us — too small to be seen by the naked eye. They are found in water, in the soil, and in the air. The human body is also home to millions of these microbes, also called microorganisms. Some microbes make us sick, others are important for our health.
An electrochemical cell consists of two half-cells. Each half-cell consists of an electrode and an electrolyte. The two half-cells may use the same electrolyte, or they may use different electrolytes. The chemical reactions in the cell may involve the electrolyte, the electrodes, or an external substance (as in fuel cells that may use hydrogen gas as a reactant). In a full electrochemical cell, species from one half-cell lose electrons (oxidation) to their electrode while species from the other half-cell gain electrons (reduction) from their electrode.
There are many cells in an individual, which performs several functions throughout life. The different types of the cell include- prokaryotic cell, plant and animal cell. The size and the shape of the cell range from millimeter to microns, which are generally based on the type of function that it performs. A cell generally varies in their shapes. A few cells are in spherical, rod, flat, concave, curved, rectangular, oval and etc. These cells can only be seen under a microscope.
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