Answer:
Because they aren't made out of cells, they don't grow, they don't make their own energy, and they can't keep themselves in a stable state. Hope that helps! :)
Answer:
The most common mode of spread for respiratory viruses is via (C) respiratory droplet transmission. Virus-laden droplets (generated by coughing, sneezing, or talking) are propelled from an infected person directly onto the mucosal surfaces of a host.
Explanation:
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The immune system is spread throughout the body and involves many types of cells, organs, proteins, and tissues. Crucially, it can distinguish our tissue from foreign tissue — self from non-self. Dead and faulty cells are also recognized and cleared away by the immune system.
If the immune system encounters a pathogen, for instance, a bacterium, virus, or parasite, it mounts a so-called immune response. Later, we will explain how this works, but first, we will introduce some of the main characters in the immune system.