1. blood vessel with a thick layer of smooth muscle and elastic fibers is
a. a vein
b. an artery
c. a capillary
d. the vena cava
2. the circulatory, or cardiovascular system, is composed of
a. the lungs, heart and brain
b. the lungs, blood vessels and heart
c. the heart, blood and blood pressure
d. the heart, arteries and veins
3. which cells protect the body by engulfing invaders or producing antibodies?
a. red blood cells
b. plasma cells
c. platelets
d. white blood cells
4. capillaries belong to which body system?
a. skeletal
b. nervous
c. digestive
d. circulatory
5. a blood vessel one cell thick for absorption of nutrients and removal of wastes
a. a vein
b. an artery
c. a capillary
d. the pulmonary artery
6. hemoglobin carries oxygen to the body's cells. which systems contains
a. respiratory
b. circulatory
c. nervous
d. endocrine
7. the cells in cardiac muscle would probably have a high number of
a. mrna molecules
b. golgi apparati
c. lysossomes
d. mitochondria

An artery contains a thick layer of smooth muscles and elastic fibres.

The cardiovascular system consists of heart, arteries and veins.

White blood cells protect the body by engulfing invaders or producing antibodies.

Capillaries belong to circulatory system

A Capillary is a  blood vessel one cell thick for absorption of nutrients and removal of wastes

Respiratory system defines the process in which haemoglobin carries oxygen to the body cells.

The cells in cardiac muscle would probably have a high number of mitochondria

Explanation:

1. Arteries carry blood directly away from the heart and the blood flowing in it is at higher pressure. Because of this high pressure, they have thick tunica media. When blood is coming at high pressure the tunica media contracts,  the lumen becomes narrow.

2. The heart is the main organ or pumping station of the blood, it purifies the blood. The arteries carry oxygenated blood away from the heart to the body while veins bring deoxygenated blood to the heart from the body. Exception are pulmonary veins and pulmonary arteries.

3. White Blood cells are the part of the immune system which destroys the pathogens by the process of phagocytosis.

4. Capillaries are the smallest blood vessels of the body their function is to transfer oxygen and other nutrients from blood to neighbouring tissues.

5. The function of a capillary is to provide oxygenated and deoxygenated bloods from arteries and vein respectively. They also exchange nutrients and removes wastes from neighbouring tissues.

6. Haemoglobin is responsible for carrying oxygen from the lungs to the tissues of the body and also transports hydrogen ions and carbon dioxide to the lungs.

7. The cardiac muscle cell would have the highest number of mitochondria because the constant beating of the heart would require a pool of ATP and it is produced in mitochondria.

i think its white blood cells

i hope this