Class 9 Science Exploration Chapter 3 MCQ – Tissues in Action

A tissue is formed when cells of similar structure group together to perform a specific function. This division of labour among tissues increases the efficiency of the body and allows complex life processes to be carried out effectively.

Because plants cannot move, they need rigid structures to withstand environmental stresses. Animal cells, without a rigid cell wall, can change shape easily, which supports movement and locomotion — something plants do not need.

Plants have growth zones at the tips of their roots and shoots called apical meristems. These regions contain actively dividing cells responsible for the increase in length (height of stem and depth of roots). When the root tip is removed, growth in length stops, as shown in the onion root experiment.

Annual growth rings are formed by the activity of the lateral meristem. Wide rings indicate favourable growth conditions, while narrow rings indicate unfavourable conditions. By counting these rings, scientists can estimate the tree’s age and understand the climate during each year of its growth.

The lateral meristem is located along the circumference of stems. Its cells divide and produce new cells inward and outward in a concentric manner, increasing the diameter or girth of the stem. This is why the stems of dicot plants become thicker over time.

Intercalary meristems are located at the base of internodes or just above the nodes of certain plants like grasses. When a plant is cut, these meristematic cells divide and allow the plant to regenerate. This is why grass grows back after mowing and hedges become bushy after being trimmed.

As meristematic tissue continuously divides, some newly formed cells lose the ability to divide. These cells then undergo changes in structure and become specialised for specific functions like support, transport, or storage. This process of specialisation is called differentiation, and the resulting cells form permanent tissues.

Meristematic cells are small, have thin cell walls, a large and prominent nucleus, and dense cytoplasm with many organelles. Vacuoles are generally absent and cells are tightly packed. These features support rapid and continuous cell division.

The epidermis is a protective tissue forming the outermost layer of the plant body. It protects against mechanical injury, water loss, and invasion by harmful microorganisms. The transport of food is the function of phloem, not the epidermis.

The epidermis is covered with a waxy layer called the cuticle. In plants living in dry habitats, this cuticle is especially thick to reduce water loss through transpiration. The cuticle also provides protection against mechanical injury and invasion by parasites.

Parenchyma is the most common simple permanent tissue. While its main functions include food storage and photosynthesis in green parts, in aquatic plants it is specialised to contain large air spaces. These air-filled spaces reduce the density of the plant and help it float on water.

Unlike parenchyma which has thin and uniform walls, collenchyma cells have unevenly thickened corners due to the deposition of a chemical called pectin, which gives them flexibility like rubber. This structure allows stems and tendrils to bend without breaking, providing both support and flexibility.

Sclerenchyma cells have thick walls due to the deposition of lignin, which makes them hard, strong, and forms the woody structure of plants. Because of this heavy lignification, most sclerenchyma cells are dead at maturity. This tissue is found in stems, leaf veins, and hard coverings of seeds and nuts like coconut husk and walnut shell.

Xylem and phloem are called complex permanent tissues because each is made up of more than one type of cell working together. Xylem consists of tracheids, vessels, xylem parenchyma, and xylem fibres. Phloem consists of sieve tubes, companion cells, phloem parenchyma, and phloem fibres.

In xylem, tracheids, vessels, and xylem fibres are primarily dead and sclerenchymatous cells. Xylem parenchyma is the only living component of xylem. It helps in the storage of food and aids in the lateral transport of water.

Sieve tubes are the main food-conducting cells of phloem, but they lack a nucleus and are metabolically dependent. Companion cells are specialised parenchyma cells closely associated with sieve tubes. They regulate the cellular functions of sieve tube cells and control the loading and unloading of sugars during food transport.

Epithelial tissue is composed of closely packed cells with very little space between them. This tight arrangement prevents entry of germs, reduces water loss, and provides a continuous protective barrier. Different types of epithelial tissue are structurally adapted for different functions like absorption, secretion, and exchange.

The lining of blood vessels and lungs consists of a single layer of thin, flat cells. Being just one cell thick allows substances like oxygen, carbon dioxide, and other molecules to rapidly diffuse across the membrane — making this structure perfectly suited for exchange functions.

Both blood and bones are connective tissues that connect and support other tissues. The key difference is the nature of their matrix. Blood’s matrix is watery, making it fluid. Bone’s matrix contains calcium and phosphorus compounds, making it hard and rigid. The matrix determines the physical properties of the connective tissue.

Blood contains three main formed elements — Red Blood Cells (RBCs), White Blood Cells (WBCs), and platelets. Platelets are specialised for blood clotting. When a cut or injury occurs, platelets gather at the site and initiate a clotting process that stops the bleeding.

Explanation: Tendons and ligaments are both connective tissues at joints but serve different purposes. Tendons connect muscles to bones — when a muscle contracts, the tendon transmits that force to the bone to produce movement. Ligaments connect bone to bone, providing stability and preventing excessive movement or dislocation.

Voluntary movements are those under conscious control. These are carried out by skeletal muscles, which are attached to the skeleton. Skeletal muscle cells are long, cylindrical, multinucleate (having many nuclei), and striated (showing light and dark bands), making them powerful for controlled movement.

Unlike skeletal muscles which are striated and multinucleate, smooth muscle cells are spindle-shaped, have a single nucleus, and lack striations (they appear smooth). They are responsible for involuntary movements like the movement of food through the intestine and are not under conscious control.

Cardiac muscles are found only in the heart. Their fibres are cylindrical and branched with a single nucleus and have faint striations. Unlike skeletal muscles that tire with use, cardiac muscles are specially structured to work rhythmically and tirelessly throughout life without fatigue, ensuring the heart never stops beating.

A neuron has three main parts — the cell body (which contains the nucleus and controls cell activities), dendrites (which receive signals from other neurons), and an axon (a long fibre that carries messages away from the cell body to the axon terminals, which then transmit the message to other cells).

The shoulder joint is a ball and socket joint, formed by the rounded top of the upper arm bone fitting into a shallow hollow of the shoulder bone. This structure allows the widest range of movement — forward, backward, sideways, and circular — making it the most freely movable joint in the body.

A hinge joint allows movement in only one plane — bending and straightening — just like a door hinge. Both the elbow and the knee are hinge joints. In the knee, a small bone called the kneecap protects this joint.

The skull is a hard protective case for the brain, eyes, and ears. Its bones are connected by fixed joints, which means the bones cannot move relative to each other. This immobility protects the delicate brain from damage even when the rest of the body is moving vigorously.

Totipotency is the ability of a single plant cell to divide, dedifferentiate, and redifferentiate to develop into a complete organism under appropriate conditions. F. C. Steward’s experiment with carrot phloem cells demonstrated this by growing a whole plant from a single cell, showing that each plant cell retains the full genetic information needed for an entire organism.

Between each pair of vertebrae, there is a cartilage disc. Cartilage has a soft, jelly-like matrix that provides flexibility and acts as a cushion, absorbing shocks. This prevents the vertebrae from grinding against each other and protects the spinal cord from injury when we bend, twist, or jump.