Star is a brilliantly glowing sphere of hot gas whose energyis produced by an internalnuclear fusion process. Stars are contained in galaxies. A galaxy contains not only stars, but clouds of gas and dust. These clouds are callednebulae, and it is in a nebula where stars are born. In the nebula is hydrogen gas which is pulled together by gravityand starts to spin faster. Over millions of years, more hydrogen gas is pulled into the spinning cloud. The collisions which occur between the hydrogen atoms starts to heat the gas in the cloud. Once the temperature reaches 15,000,000 degrees Celsius, nuclear fusion takes place in the center, or core, of the cloud. The tremendous heat given off by the nuclear fusion process causes the gas to glow creating a protostar. This is the first step in the evolution of a star. The glowing protostar continues to accumulate mass. The amount of mass it can accumulate is determined by the amount ofmatter available in the nebula. Once its mass is stabilized, the star is known as a main sequence star. The new star will continue to glow for millions or even billions of years. As it glows, hydrogen is converted into helium in the core by nuclear fusion. The core starts to become unstable and it starts to contract. The outer shell of the star, which is still mostly hydrogen, starts to expand. As it expands, it cools and starts to glow red. The star has now reached the red giant phase. It is red because it is cooler than the protostar phase and it is a giant because the outer shell has expanded outward. All stars evolve the same way up to the red giant phase. The amount of mass a star has determines which of the following life cycle paths the star will take.
Many scientists are concerned that the Ogallala aquifer in the United States is being depleted at an alarming rate. The statement that is correct and would state the most likely be a major effect of this aquifer running dry is choice A. It states that many crops would die because irrigation water would be limited.
Zit sure has to be B. Pollution
Answer:
1- Presence of phenotypic variation
2- some phenotypic variation due to genetic variation
3- the given trait has an impact on fitness
Explanation:
The evolutionary theory by natural selection proposed by Darwin in his publication “On the origin of species” (1859) is based on a series of assumptions that enable to understand the amazing biodiversity on the Earth. First, individuals are not identical among them, i.e., there exists variation in the traits among the members of a given population, species, etc. Second, phenotypic variation leads to differential survival and reproduction of the organisms that are best fitted to the environment (i.e., competence among the members of the population). Finally, phenotypic traits are passed from generation to generation (i.e., phenotypic variation is inheritable), thereby favoring offspring from parents more adapted to the environment.
