Which series best illustrates the pathway of blood flow in a closed circulatory system?
a. heart, veins, capillaries, arteries
b. heart, arteries, capillaries, veins
c. heart, veins, arteries, capillaries
d. heart, arteries, veins, capillaries

b. Heart, arteries, capillaries, veins

Explanation:

A closed circulatory system allows blood flow to flow through the heart, arteries, capillaries and veins. This type of circulatory system is characterized by blood always circulating within the blood vessels.

The sequence of prayer, arteries, capillaries and veins can be found in humans, other vertebrates and even in ringworms and mollusks of the Cephalopoda class. Insects also have this type of circulation, but instead of blood they use a substance called hemolymph.

Complete question:

Lipids are important for many cellular functions in our bodies. Like many nutrients, lipids are transported around our bodies via the bloodstream. Unlike many nutrients, lipids require specialized structures called lipoproteins to remain soluble in blood until delivered to target cells. Based on the composition of blood, predict the properties of the outer surface and interior of a lipoprotein that would enable lipid transport through the bloodstream. Select only ONE answer choice.

3. Outer surface = hydrophilic; Interior = hydrophobic

Explanation:

Lipids must be transported via the bloodstream to different target tissues or organs, where they are going to be stored, or used as an energy source, or turned into other products. As lipids are insoluble in water, and most of the blood composition is water (99% of the plasma) they need to be transported in lipoproteins.

Lipoproteins are specialized macromolecules with the main function of packaging the lipids in the plasma and transport them from the intestine and the liver to peripheric tissues. Also, from the peripheric tissues, lipoproteins must carry cholesterol (lipid) to the liver for its elimination as biliary acids.

Lipoproteins have a spherical morphology. Inside there is a hydrophobe core formed of non-polar lipids such as esterified cholesterol and triglycerides. The lipoprotein outer surface is hydrophilic with non-esterified cholesterol, phospholipids, and specific proteins known as apoproteins, APO. It must be hydrophilic in its exterior because it needs to move in the plasma, so it must be in touch with water.