Full explanation of NCERT Exploration Activity 3.2 for Class 9 (Chapter 3: Tissues in Action). This activity bridges everyday experiences — a cut that clots, a swollen infected wound, a flushed face after exercise — to the specific roles of RBCs, WBCs, platelets, and plasma in the blood. Includes a complete explanation of Table 3.3 and a brief recap of why blood is a connective tissue. Aligned with CBSE syllabus 2026–27.
Q. What does Activity 3.2 ask you to do?
Activity 3.2 is not a laboratory experiment — it is a reflective observation activity. NCERT Exploration asks you to think about three everyday experiences involving your body and connect each one to a specific component of blood. The goal is to show that the biology you are studying in class is not abstract — it explains things that happen to your body every day.
To connect three common personal experiences — a cut that stops bleeding, a swollen infected wound, and a flushed or red face during exercise — to the specific functions of the four components of blood (plasma, RBCs with haemoglobin, WBCs, and platelets), demonstrating that blood as a connective tissue supports, defends, and transports throughout the body.
Q. Fill in and explain Table 3.3 from NCERT Activity 3.2.
| Experience | Blood Component Responsible | Scientific Explanation |
|---|---|---|
| You get a cut and the bleeding stops within a few minutes | Platelets (thrombocytes) + plasma protein fibrinogen | When a blood vessel is damaged, platelets rush to the site and clump together. They trigger a clotting cascade in which the plasma protein fibrinogen is converted into insoluble fibrin threads that form a mesh — the clot. This seals the broken vessel and stops bleeding. |
| An infected wound swells, becomes red and warm, and may produce pus | WBCs (white blood cells / leucocytes) | When bacteria or foreign particles enter the body, WBCs migrate to the site in large numbers. They engulf and destroy the pathogens (phagocytosis) or release antibodies. The increased blood flow to the area causes redness and warmth; swelling results from fluid accumulation. Pus is a collection of dead WBCs, bacteria, and tissue fluid — a sign that WBCs have been fighting the infection. |
| Your face turns red and you breathe faster during vigorous exercise | RBCs carrying haemoglobin; increased blood circulation; plasma | During exercise, active muscles consume more oxygen and produce more carbon dioxide. The brain responds by increasing heart rate and breathing rate. More blood — carrying RBCs loaded with haemoglobin and oxygen — is pumped to the muscles. The skin blood vessels dilate to help dissipate excess heat, which is why the face turns red. Plasma carries the dissolved carbon dioxide and nutrients throughout this increased circulation. |
Q. What are the four blood components and their functions as demonstrated by this activity?
Red blood cells (RBCs / erythrocytes) are the most numerous cells in blood. They contain the red iron-based protein haemoglobin, which gives blood its characteristic red colour and is responsible for transporting oxygen from the lungs to all body tissues. Mature mammalian RBCs have no nucleus, freeing up space for more haemoglobin. During exercise, as this activity shows, the demand for oxygen increases and RBCs must circulate faster.
Platelets (thrombocytes) are small, irregularly shaped cell fragments with no nucleus. Their sole role is blood clotting. When a blood vessel is cut, platelets aggregate at the wound site within seconds and trigger the clotting cascade. Without functional platelets, even a minor cut could lead to dangerous, uncontrolled bleeding.
White blood cells (WBCs / leucocytes) are the body's mobile defence force. They are larger than RBCs, contain a nucleus, and are colourless (no haemoglobin). When infection occurs, WBC count rises dramatically as the bone marrow produces more of them. They cause the classic signs of inflammation — redness, warmth, swelling — and produce pus at the site of infection, as this activity clearly shows.
Plasma is the pale yellow, watery fluid matrix of blood (~55% of blood volume). It carries dissolved nutrients, hormones, carbon dioxide, waste products, and the plasma proteins (including fibrinogen for clotting). All three experiences in this activity involve plasma: it carries the clotting proteins to a wound, transports defensive molecules during infection, and carries dissolved CO₂ and nutrients during exercise.
Q. Why is blood classified as a connective tissue?
Students often find it surprising that blood is grouped with connective tissue — after all, it is a liquid that flows. However, blood meets the exact definition of connective tissue: it consists of cells widely separated from each other and embedded in a large amount of non-living matrix (in this case, the liquid matrix called plasma).
Just as the matrix of bone is hard (mineralised with calcium and phosphorus) and the matrix of cartilage is jelly-like, the matrix of blood is fluid (plasma). The physical state of the matrix is what differs — the defining feature (cells in a non-living matrix) remains the same. Blood also fulfils the connective tissue function of connecting all parts of the body by flowing through blood vessels to transport materials to and from every tissue.