Answer:
We have just seen that pathogens constitute a diverse set of agents. There are correspondingly diverse ranges of mechanisms by which pathogens cause disease. But the survival and success of all pathogens require that they colonize the host, reach an appropriate niche, avoid host defenses, replicate, and exit the infected host to spread to an uninfected one. In this section, we examine the common strategies that are used by many pathogens to accomplish these tasks.
Explanation:
The first step in infection is for the pathogen to colonize the host. Most parts of the human body are well-protected from the environment by a thick and fairly tough covering of skin. The protective boundaries in some other human tissues (eyes, nasal passages and respiratory tract, mouth and digestive tract, urinary tract, and female genital tract) are less robust. For example, in the lungs and small intestine where oxygen and nutrients, respectively, are absorbed from the environment, the barrier is just a single monolayer of epithelial cells.
Skin and many other barrier epithelial surfaces are usually densely populated by normal flora. Some bacterial and fungal pathogens also colonize these surfaces and attempt to outcompete the normal flora, but most of them (as well as all viruses) avoid such competition by crossing these barriers to gain access to unoccupied niches within the host.
Answer: There are many relationships between the organizational levels of the environment. All of them compliment each other in order to make everything work.The biosphere is what puts everything all together. It is were all live resides. The community,population and organisms are all in the biosphere. The organisms become the population and then the population becomes the community from all the little organisms around. All of these live in biomes and ecosystems. In those areas is where the population and communities live from all the organisms around. Without the biomes and ecosystems there would be no communities nor population and especially no organism's because there'd be no place to call home.
An example of a density-dependent factor is food. Without food the population will die due to starvation. With food the population will strive. A density-independent factor is a disease. The disease will kill of the whole population no matter it's size.
In primary succession is when a newly untouched habitat is occupied. For example a newly grown plant. This plant will soon be taken over by an insect as its temporary home. Once the plant dies the insect leaves. Then the remains of the plant become secondary succession as it is taken over by for example worms in the soil.
Explanation:
Answer:carbon, hydrogen, and sometimes other elements such as nitrogen, sulfur, oxygen, or phosphorus.
Explanation:
