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.
The pancreas is connected directly into the small intestines and gallbladder.
Enzymes that are produced by the pancreas are secreted directly into the small
<span>intestine.</span>
The correct answer is option Covalent bonds.
The water is a molecule formed by the covalent interaction between one oxygen and two hydrogen molecule. The chemical formula of the water is 
. In the water molecule, each hydrogen atom shares an electron with the oxygen. The oxygen is more electronegative so, it pulls the electron towards it, and gains a partial negative charge and the hydrogen gains a partial positive charge. The partial positive charge of hydrogen in one molecule attracts the partial negative charge in other molecule and forms inter molecule hydrogen bonding.
You should use an electric telescope so the cells of the microorganisms can be seen
