Ans: A tissue is a group of cells that are similar in structure and work together to perform a specific function. In multicellular organisms, different types of tissues lead to division of labour — each group of cells is specialised for a particular job, such as support, transport, or protection. This division of labour increases the efficiency of the body and allows it to carry out complex life processes that a single cell could not perform alone.

Ans: Meristematic tissues are plant tissues made up of actively dividing cells. They are responsible for the growth of the plant in length, girth, and regrowth after cutting. The structural features that allow continuous division are:

• Cells are small with thin cell walls — easier and faster to divide.
• They have a large and prominent nucleus — the control centre for division.
• Dense cytoplasm with many organelles — supports active metabolism.
• Vacuoles are absent — vacuoles store mature contents; their absence keeps the cells ready to divide.
• Cells are tightly packed with little or no intercellular space.

Ans: Plants have three types of meristematic tissues:

• Apical meristem: Located at the tips of roots and shoots. Causes the plant to grow in length (height of stem, depth of roots).
• Lateral meristem: Located along the circumference (in a ring) of stems in dicot plants. Divides and adds cells inward and outward, causing increase in girth (diameter/thickness of stem). Produces the annual rings visible in cut tree trunks.
• Intercalary meristem: Located at the base of internodes or just above the nodes of stems. Enables plants to regrow after being cut, mowed, or grazed. For example, grass grows back after mowing because of intercalary meristem at its nodes.

Ans: When the tip of a young plant is cut, the apical meristem at the shoot tip is removed. This stops the plant from growing in length. However, the plant has intercalary meristem present at the nodes of the stem (points where leaves and branches arise). After the tip is cut, these meristematic cells at the nodes become active and produce new side branches, making the plant appear bushy. This is also why hedges become bushy after trimming and why grass regrows after being grazed.

Ans: Differentiation is the process by which meristematic cells lose their ability to divide and become specialised to perform specific functions. After continuous cell division in the meristematic tissue, some newly formed cells remain meristematic while others undergo structural and functional changes. These changed cells form permanent tissues that are specialised for functions such as support, storage, transport, or protection. Once differentiated, these cells generally cannot divide again.

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Ans: A fresh twig bends without breaking because it contains collenchyma tissue. Collenchyma cells have unevenly thickened cell walls due to the deposition of pectin, a flexible chemical similar to rubber. This gives the fresh twig flexibility and the ability to bend. In a dry twig, the cells lose water, the pectin dries out, and the tissue becomes brittle. The dry twig then contains more sclerenchyma (thick, lignified, dead cells) that are rigid and snap instead of bending.

Ans: Both xylem and phloem are complex permanent tissues (made of more than one type of cell) involved in transport within the plant.

Ans: Epithelial tissue forms the outer covering of the body (skin) and lines internal organs such as the mouth, lungs, blood vessels, and intestine. Its cells are closely packed with very little space between them.

• Exchange function: Epithelium in the lining of blood vessels and lungs is a single thin layer, which allows rapid diffusion of oxygen, carbon dioxide, and other materials.
• Protection function: Epithelium in the skin, mouth, and oesophagus has many layers of flat, tightly packed cells that protect underlying tissues from mechanical injury, friction, and entry of microbes.
• Absorption function: In the lining of the small intestine, cells are tall and pillar-like, often with hair-like structures, for efficient uptake of nutrients.

Ans: Both observations are explained by the role of blood, a connective tissue, and its components:
Cut on skin → Redness and swelling: When tissue is injured, White Blood Cells (WBCs) rush to the infected area to fight bacteria. This causes inflammation — redness, warmth, and swelling. Platelets help form a clot to stop bleeding.
Exercise → Red face: During exercise, muscles need more oxygen. The brain signals the heart to beat faster, increasing blood flow throughout the body, including to the skin of the face. This increased blood flow (carrying red haemoglobin-rich RBCs) makes the face appear red.

Ans: Connective tissue is a type of animal tissue that connects, supports, and binds other tissues and organs together. It has cells embedded in a matrix (which can be fluid, jelly-like, or rigid).

• Blood: Transports nutrients, gases (oxygen, CO₂), hormones, and waste between different parts of the body.
• Bone: Provides structural strength and support; protects delicate organs (e.g., skull protects the brain).
• Cartilage: Provides flexibility and cushions the ends of bones at joints for shock absorption.
• Tendon: Connects muscles to bones and transmits the force of muscle contraction to produce movement.
• Ligament: Connects bone to bone at joints; provides stability and prevents excessive or dislocating movement.

Ans: The shoulder has a ball and socket joint — the rounded top of the upper arm bone fits into a shallow hollow of the shoulder bone. This structure allows movement in all directions: forward, backward, sideways, and circular rotation.
The elbow has a hinge joint — like a door hinge, it allows movement only in one direction (bending and straightening). The shape of the bones at the elbow restricts movement to a single plane. This is why the shoulder has a much wider range of motion than the elbow.

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Ans: Neurons (nerve cells) are the cells of nervous tissue, specialised to receive, process, and transmit messages. Each neuron has three main parts:

• Cell body: Contains the nucleus and controls cell activities. It is the main processing centre of the neuron.
• Dendrites: Short, branch-like extensions from the cell body. They receive signals from other neurons or sensory receptors and carry them toward the cell body.
• Axon: A single, long fibre extending from the cell body. It carries messages away from the cell body to other neurons or to muscles/glands. At its end are axon terminals that transmit the message to the next cell.

Ans: When an elephant strips the bark, it damages the epidermis (outer protective layer of the plant) and the phloem (which lies just beneath the bark and is responsible for transporting food from leaves to the rest of the plant). Damaging the epidermis exposes the inner tissues to mechanical injury, infection, and water loss. Damage to phloem disrupts the downward transport of food from leaves to roots. If phloem is completely girdled (removed all around), the roots will be starved of food and the tree may eventually die. If the lateral meristem below is also damaged, new bark will not regenerate and the tree loses its girth-growth capacity.