Chapter 3: Tissues in Action

Cells are the basic units of life, and tissues are groups of cells working together to perform specific functions. Understanding how tissues are structured helps us know how organs function, how diseases arise (like cancer, where cell division goes uncontrolled), and how the body maintains itself. This knowledge has direct applications in medicine, such as developing treatments for tissue damage, growing replacement tissues (tissue engineering), and understanding how drugs affect the body. For human welfare, it enables advances in agriculture (crop improvement), medical diagnosis, and therapies like skin grafting.

Plant tissues differ from animal tissues mainly because plants are stationary and must synthesise their own food through photosynthesis, while animals move and obtain food from external sources. Plants have rigid cell walls and tissues like sclerenchyma for support, and meristematic tissues for continuous growth, which are absent in animals. Animal tissues are more diverse (epithelial, connective, muscular, nervous) to support locomotion, digestion, and coordination. The different lifestyles and modes of nutrition drive these structural and functional differences in tissues.

In multicellular organisms, different cells are specialised to perform different tasks — this is called division of labour. Cells of similar type group into tissues (e.g., muscle tissue for movement), tissues form organs (e.g., heart), and organs form organ systems (e.g., circulatory system). This hierarchy allows each unit to be highly efficient at its specific task, much like specialised workers in a factory. The structure of each tissue is directly suited to its function — for example, xylem cells are hollow and dead to allow smooth water transport, while nerve cells are long with branches to rapidly transmit signals.

Observation: Roots in Jar A (uncut) continue to grow steadily in length each day. Roots in Jar B (tips cut on Day 3) stop growing or grow much more slowly after the tips are removed.

Inference: Root growth occurs only from the tip region, which contains actively dividing meristematic cells (apical meristem). When the tip is removed, the source of new cells is lost and growth stops. This confirms that apical meristem at the root tip is responsible for the increase in root length.

When a blood vessel is injured, tiny cell fragments called platelets (thrombocytes) rush to the site of the wound. Platelets release chemical signals that trigger a cascade of reactions involving proteins in the blood plasma, ultimately producing fibrin — a tough protein that forms a mesh over the wound. Red blood cells get trapped in this mesh, forming a clot (scab) that plugs the wound and stops further bleeding. This is a protective mechanism of blood, a fluid connective tissue, to prevent excessive blood loss and infection.