Class 11 Biology Chapter 15 Body Fluids and Circulation – Revision Notes

This chapter follows blood and lymph through a four-chambered, myogenically-beating heart, ending with normal blood pressure values and how to read a basic ECG trace.

Last Updated: September 23, 2026

Blood

• Plasma + formed elements (RBC, WBC, platelets).
• ABO and Rh blood group systems.
• Clotting: fibrinogen → fibrin (via thrombin).

Lymph

• Derived from plasma; fat absorption, immune defence.

Heart

• 4-chambered; myogenic beat via SA node (pacemaker).
• Cardiac cycle: systole/diastole; “lub-dub” from valve closure.

BP and ECG

• Normal BP ~120/80 mmHg.
• ECG: P wave (atrial), QRS (ventricular depolarization), T wave (ventricular repolarization).

One-Line Summary

Blood and lymph circulate through the body via the four-chambered, myogenically-beating heart, with the SA node as pacemaker, transporting gases, nutrients, and immune cells while blood group compatibility governs safe transfusion.

Frequently Asked Questions

What are the main components of blood covered in this chapter?
Blood consists of a fluid matrix called plasma, along with red blood cells that carry oxygen, white blood cells that fight infection, and platelets that help in blood clotting.

What is the difference between systole and diastole in the cardiac cycle?
Systole is the phase during which the heart chambers contract and pump blood out, while diastole is the phase during which the heart chambers relax and fill with blood, together forming one complete heartbeat cycle.

Written by Satish

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