CBSE Class 9 Science Exemplar Chapter 6: Tissues NCERT Solutions

Solution: The correct option is (b) Sclerenchyma.

Explanation:

Parenchyma cells are living tissues with thin cell walls, a large central vacuole, and dense cytoplasm. They are found in the soft parts of plants like the pith and cortex.

Sclerenchyma tissue is characterized by its dead cells, which possess very thick cell walls due to the deposition of lignin. This provides rigidity and strength. Sclerenchyma is commonly found in the veins of leaves, the hard outer coverings of seeds and nuts, and surrounding vascular bundles.

Collenchyma tissue consists of living cells that are elongated and have unevenly thickened cell walls, particularly at the corners. They provide mechanical support to growing stems and leaves and are often found just below the epidermis.

Epithelial tissues are protective and covering tissues found in animals, forming the outer layer of skin and lining internal organs and cavities.

Solution: The incorrect sentence is (a) Parenchymatous tissues have intercellular spaces.

Explanation:

Parenchyma tissues primarily function as packing tissue and for storage in plants. While some parenchyma cells might have small intercellular spaces, it is not a defining characteristic, and in many cases, they are closely packed. In contrast, collenchymatous tissues often have intercellular spaces. Therefore, stating that parenchymatous tissues *have* intercellular spaces as a general rule is considered incorrect in this context, especially when compared to other tissues that definitely possess them.

Sentence (b) is correct: Collenchymatous tissues are indeed characterized by irregular thickening at their corners.

Sentence (c) is incorrect: Apical and intercalary meristems are types of meristematic tissues, responsible for growth, not permanent tissues.

Sentence (d) is generally correct: Meristematic cells, especially in their active dividing state, are small and dense with a large nucleus and often lack prominent vacuoles, which develop later as cells differentiate into permanent tissues.

Solution: The increase in the girth of a stem is due to the activity of the (b) lateral meristem.

Explanation:

Apical meristems are located at the tips of roots and shoots and are responsible for the increase in length (primary growth). Intercalary meristems, found at the nodes or bases of leaf stalks, also contribute to elongation. Vertical meristem is not a standard botanical term for growth in length. The lateral meristem, which includes the vascular cambium and cork cambium, is responsible for secondary growth, leading to an increase in the diameter or girth of stems and roots.

Solution: The cell that does not have a perforated cell wall among the given options is (a) Tracheids.

Explanation:

Tracheids are elongated, spindle-shaped cells found in xylem. They are dead cells and their primary function is water transport. While they have pits, they do not possess perforations in their cell walls like vessels do.

Companion cells are associated with sieve tubes in the phloem and are living cells involved in the transport of sugars.

Sieve tubes are part of the phloem and are responsible for translocation of sugars. They have sieve plates, which are perforated areas, but not complete perforations in the same way as vessels.

Vessels are also found in xylem and are the main water-conducting elements. They are formed from a series of vessel elements arranged end to end, and their end walls are perforated, forming continuous tubes.

Solution: The type of epithelial cells responsible for absorbing digested food materials in the intestine is (b) Columnar epithelium.

Explanation:

Columnar epithelial cells are tall and pillar-like, with their nuclei located towards the base. They form the lining of organs such as the stomach, small intestine, and large intestine. Their elongated shape and the presence of microvilli on their surface significantly increase the surface area available for absorption. They are specialized for absorption and secretion of substances.

Stratified squamous epithelium provides protection against abrasion and is found in the skin and lining of the mouth. Spindle fibres are components of muscle tissue. Cuboidal epithelium is involved in secretion and absorption in glands and kidney tubules.

Solution: The possible reason for the dislocation of two long bones in the hand is a (c) Ligament break.

Explanation:

Ligaments are strong, fibrous connective tissues that connect bones to other bones at joints. They provide stability to the joint and prevent excessive movement. When a person experiences a dislocation, it means the bones forming the joint have been forced out of their normal alignment. This often occurs due to the stretching or tearing (break) of the ligaments that hold the joint together.

Tendons are also fibrous connective tissues but they connect muscles to bones, facilitating movement. A break in a tendon would affect muscle action. Skeletal muscles are contractile tissues responsible for movement. Areolar tissue is a loose connective tissue found throughout the body, filling spaces between organs and tissues, and is not primarily responsible for joint stability.