Hair is primarily composed of a protein called, keratin. Some regions of the polypeptide chain may take on a twisting shape. The twisting of the polypeptide chain is an example of which protein structure level?

quaternary

primary

secondary

tertiary

the dark variety, as they are not visible on the dark tree barks

explanation:

the most common type of reef is the fringing reef. this type of reef grows seaward directly from the shore. they form borders along the shoreline and surrounding islands.

measuring light intensity

light meters can be used to measure light intensity. the meter is held at the soil surface and pointed in the direction of the maximum light intensity, and then the meter is read.

errors can be made when measuring light intensity by accidentally shading the light meter. the reliability of the results can be checked by taking many samples.

these muscles maintain the blood pressure in the vessels. the smooth muscles are innervated by nerves of the autonomic nervous system. when the muscles contract, they cause vasoconstriction of the vessels and increase blood pressure. when the muscles relax, they enable vasodilation of the   blood vessels hence reduce blood pressure.