Answers to Hands-on Pg 16

Section B
3a)– Blood flows from arteries to capillaries. There is higher hydrostatic pressure at the arterial end of the cappilaries due to heart’s pumping pressure. The high hydrostatic pressure forces small amounts of water, nutrients, oxygen gas, carbon dioxide gas, hormones (except erythrocytes, platelets and plasma protein) to diffuse out of the blood capillaries into the spaces around the cells. This fluid is called the interstitial fluid.

(b) – Lymphatic system is a one way system consisting of lymphatic capillaries, lymphatic vessels and lymph nodes. Lymph nodes produce lymphocytes. Lymphocytes produce antibodies. Third line of defence occurs when phagocytosis of pathogens by phagocytes fails. Antibodies produced adhere to the surface of the antigens, making them clump together or agglutinate. Some antibodies cause antigens to disintegrate (lysis).
– Some antibodies produce antitoxins to neutralise the toxins produced.

(c) Similarities: Humans, fish and amphibians have closed circulations in which the blood is confined to blood vessels.
Differences:
- Fish has one chambered heart, amphibian has three and human has four chambers.
- Fish has only one atrium but amphibian and human have 2 atria.
- Fish and amphibian have one ventricle but human has 2 ventricles.
– Humans and amphibians have double circulations.
– The fish has a single circulation.
- In the double circulation, blood is pumped from the heart to the lungs and returns from the lungs to the heart which is then re-pumped to the body.
– In the single circulation, deoxygenated blood from the body is pumped to the gills where gaseous exchange takes place.
– Oxygenated blood from the gills flows to the body and returns to the heart.
– Humans have a completely divided heart where oxygenated blood and deoxygenated blood do not mix.
- Lastly, amphibian has incomplete closed circulation but human has complete closed circulation.