Why do ventricles have thicker walls than atria?

What are the differences between the transport of materials in xylem and phloem?

What prevents backflow of blood inside the heart during contraction?

How does the transportation of water occur at night in the absence of transpiration?

Consider the following statements about the human heart:
$(i)$ The left atrium receives oxygenated blood from the body.
(ii) The left ventricle pumps oxygenated blood to the body, and the right ventricle pumps deoxygenated blood to the lungs.
(iii) The left atrium transfers blood to the right ventricle.
(iv) The right atrium receives deoxygenated blood from the body, and the left ventricle pumps oxygenated blood to the body.
Which of the following statement$(s)$ is/are true?

List the three kinds of blood vessels of the human circulatory system and write their functions in tabular form.