Viruses enter a host cell when the host cell recognizes and binds the glycoproteins on the virus's surface, then take in the virus by phagocytosis. Thus, d. is the correct answer.
Since options aren't given the responder will display the answer.
They are bonded by atoms.
The atoms in a compound are held together by a chemical bond. The chemical bonds can be either covalent bonds or ionic bonds. Both the bonds are considered very strong bonds. These bonds are mainly formed by sharing of electrons or in the case when one of the elements making the compound donates electron to the other element. The nucleus of each atom attracts to form a strong bond. This property of attraction between the nucleus of the atoms actually helps in forming the chemical bonds.<span>
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Microtubules are macromolecules that build both, cilia and flagella.
<span>Microtubules are cytoskeletal fibres that are formed by polymerization of α,β-tubulin and they are important components of cilia, flagella and some other cellular structures. Cilia and flagella are very similar in their organization, both have a central bundle of microtubules-axoneme. Axoneme is compound of nine outer doublet microtubules which surround a central pair of singlet microtubules. Even thought cilia and flagella are structurally similar, they are differentiated based on their function and/or length. Flagella are longer and the primary role of the flagella is locomotion. On the other hand, shorten cilia often has the function in sensing the extracellular environment.</span>
