Write the differences between: (a) Blood and Lymph (b) Open and Closed system of circulation (c) Systole and Diastole (d) P-wave and T-wave

(a) Blood and lymph:-
Blood-
1. Blood is a red-coloured fluid that contains RBCs.
2. It contains plasma, RBCs, WBCs, and platelets. It also contains proteins.
3. Blood transports nutrients and oxygen from one organ to another.
lymph-
1. Lymph is a colourless fluid that lacks RBCs.
2. It contains plasma and lesser number of WBCs and platelets. It lacks proteins.
3. Lymph plays a role in the defensive system of the body. It is a part of the immune system.

(b) Open and closed systems of circulation:-
Open system of circulation-
1. In this system, blood is pumped by the heart, through large vessels, into body cavities called sinuses.
2. The body tissues are in direct contact with blood.
3. Blood flows at low pressure. Hence, it is a slower and less efficient system of circulation.
4. The flow of blood is not regulated through the tissues and organs.
5. This system is present in arthropods and molluscs.

Closed system of circulation-
1. In this system, blood is pumped by the heart, through a closed network of vessels.
2. The body tissues are not in direct contact with blood.
3. Blood flows at high pressure. Hence, it is a faster and more efficient system of circulation.
4. The flow of blood can be regulated by valves.
5. This system is present in annelids, echinoderms, and vertebrates.

(c) Systole and diastole
Systole:-
1. It is the contraction of the heart chambers to drive blood into the aorta and the pulmonary artery.
2. Systole decreases the volume of the heart chambers and forces the blood out of them.

Diastole:-
1. It is the relaxation of the heart chambers between two contractions. During diastole, the chambers are filled with blood.
2. Diastole brings the heart chambers back into their original sizes to receive more blood.

(d) P-wave and T-wave:-
1. In an electrocardiogram (ECG), the Pwave indicates the activation of the SA node.
2. During this phase, the impulse of contraction is generated by the SA node, causing atrial depolarisation.
3. It is of atrial origin.

T-wave:-
1. In an electrocardiogram (ECG), the T-wave represents ventricular relaxation.
2. During this phase, the ventricles relax and return to their normal state.
3. It is of ventricular origin.

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