Answer:
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: water 
Physical property is defined as the property of a substance which becomes evident during physical changes. Water is liquid at room temperature whereas hydrogen and oxygen are gases at room temperature.
Chemical property is defined as the property of a substance which becomes evident during chemical changes. Water reacts with metals to form bases, hydrogen reacts with metals to form hydrides and oxygen reacts with metals to form oxides.
Mitosis is the process of cell division, where one parent cell divides to produce two genetically identical daughter cells. This process is vital in growth and tissue repair.
The reason that tissue from the fetal stage is helpful in studying mitosis is because mitosis is continuously and rapidly occurring in this phase of life in humans. The high rate of mitosis is due to the need for the fetus to grow rapidly and develop the necessary parts for it to be born.
False, if too many individual organisms die, the speices might die out
Answer:
A: Oxygen levels are low and, therefore, more red blood cells are produced, giving the athletes an advantage when competing at lower altitudes.
Explanation:
<em>At high altitudes, the partial pressure of oxygen is lower compared to lower altitudes</em>. The body system try to adjust to lower oxygen level by undergoing several physiological changes. Depending on the duration spent in high altitude, the body can either try to adjust in the short term or acclimatize for a longer term.
One of the processes the body undergoes during acclimatization is an increase in red blood cell production. The kidney secretes erythropotein in response to inadequate oxygen in body tissues, and this makes the liver to increase erythrocyte production.
The increase in red blood cell production correspondingly increases the oxygen-carrying capacity of the blood as a result of increased hemoglobin. This condition persists for a few weeks even after the body returns to lower altitude where oxygen is adequate. Increased oxygen capacity means the rate of energy production (through respiration) within the body will also increase
<em>Hence, those who acclimatize to high altitude usually experience increased capillary density, tissue perfusion and improved athletic performance at lower altitudes. </em>
The correct option is A.
