RowQ
The Vault
RowQ
The Vault
CBSE Class 9 Biology · 12 questions · 29 marks
A single cell can manage on its own, but a mango tree or a human being cannot be run by identical cells all doing the same job. Groups of similar cells settle into a shared task and become a tissue — xylem that pipes water upward, muscle that shortens on command, nerve that carries a signal in milliseconds. Learning tissues means learning why a tree can stand tall without a skeleton and why a cut on your skin heals but a cut nerve often does not.
A gardener trims the growing tip of a hedge so that it becomes bushier instead of taller. Which tissue has been removed?
Answer
Apical meristem is correct — it sits at the tip of the shoot and is responsible for increase in length, so removing it stops upward growth and encourages side branches to develop. Lateral meristem increases girth, intercalary meristem lies at the base of leaves and internodes, and sclerenchyma is a dead supporting tissue that does not divide.
The husk of a coconut is rough and fibrous because it is rich in which tissue?
Answer
Sclerenchyma is correct — its cells are dead, long and narrow with walls thickened by lignin, which makes coconut husk tough and fibrous. Parenchyma is soft packing tissue, collenchyma gives flexibility, and aerenchyma is an air-filled parenchyma found in aquatic plants.
Which type of muscular tissue keeps working rhythmically throughout life without ever tiring?
Answer
Cardiac muscle of the heart is correct — its branched, uninucleate cells contract and relax rhythmically and involuntarily for a lifetime without fatigue. Striated and skeletal muscles are voluntary and tire quickly, while smooth muscle works involuntarily but does not maintain a continuous rhythmic beat.
Which connective tissue joins one bone to another at a joint?
Answer
Ligament is correct — it is a strong, highly elastic connective tissue that holds two bones together and keeps a joint stable. A tendon joins muscle to bone, cartilage cushions the ends of bones, and areolar tissue fills spaces between organs.
Assertion (A): The walls of the alveoli in the lungs are made of a single layer of very thin, flat cells. Reason (R): Squamous epithelium provides a mechanically tough barrier that resists wear and tear.
Answer
A is true but R is false — alveolar walls really are lined with a single layer of extremely thin, flat squamous epithelial cells, but the reason given is wrong. Simple squamous epithelium is delicate rather than tough, and its thinness exists precisely to allow rapid diffusion of oxygen and carbon dioxide across it. Resistance to wear and tear is the role of stratified squamous epithelium, such as that found in the skin.
Give three differences between meristematic tissue and permanent tissue in plants.
Answer
First, meristematic tissue consists of actively dividing cells, whereas permanent tissue is made of cells that have lost the power of division and have differentiated for a fixed function. Second, meristematic cells are small, roughly isodiametric, with thin walls, dense cytoplasm, a prominent nucleus and no vacuoles or only very small ones, while permanent cells are larger, often have thickened walls and usually possess a large vacuole. Third, meristematic tissue occurs only at specific growing regions such as root and shoot tips and the cambium, whereas permanent tissue makes up the bulk of the plant body and includes tissues such as parenchyma, sclerenchyma, xylem and phloem.
Water lilies and other floating aquatic plants have large air spaces in their stems and leaves. Name this modified tissue and state its function.
Answer
The tissue is aerenchyma, a modified form of parenchyma in which large air cavities are present between the cells. These air-filled spaces make the plant body light and buoyant so that leaves and stems float on the water surface, and they also store and circulate gases such as oxygen to submerged parts where diffusion from water alone would be too slow.
Compare the structure and working of striated muscle with that of smooth muscle.
Answer
Striated muscle cells are long, cylindrical, unbranched and multinucleate, and they show alternating light and dark cross bands under a microscope. They are attached to bones, are under conscious control, contract rapidly and powerfully, and tire quickly — for example, the muscles used to lift a bag. Smooth muscle cells are spindle-shaped with tapering ends, contain a single nucleus and show no cross bands. They occur in the walls of hollow organs such as the intestine, blood vessels and urinary bladder, work involuntarily and slowly, and can keep contracting for long periods without fatigue — for example, the wave-like peristalsis that pushes food along the gut.
Why is blood considered a connective tissue even though it is a flowing liquid?
Answer
A connective tissue is defined by having relatively few cells scattered in an abundant intercellular matrix, and by its role in linking and supporting other tissues. Blood fits this description: its cells — red blood cells, white blood cells and platelets — float in a large volume of fluid matrix called plasma. Functionally it connects every organ of the body by transporting oxygen, digested food, hormones, carbon dioxide and nitrogenous wastes between them, which is why it is classified as a fluid connective tissue.
Describe the components of xylem and phloem and explain how their functions differ.
Answer
Both xylem and phloem are complex permanent tissues, meaning each is made of more than one type of cell working together as a unit. Xylem consists of four elements. Tracheids and vessels are dead, tube-like cells with thick lignified walls that form a continuous pipeline; vessels are wider and more efficient. Xylem parenchyma, the only living component, stores food, and xylem fibres provide mechanical strength. Phloem also consists of four elements. Sieve tubes are living tubular cells whose end walls are perforated like a sieve; each is closely associated with a companion cell that keeps it functioning, since sieve tubes lack a nucleus at maturity. Phloem parenchyma stores food and phloem fibres give support. Their functions differ in three important ways. Xylem conducts water and dissolved minerals absorbed by the roots, whereas phloem conducts the food, mainly sucrose, that leaves manufacture during photosynthesis. Xylem transport is unidirectional, always upward from root to leaf, while phloem transport, called translocation, moves in both directions towards wherever food is needed or stored. Finally, movement in xylem is passive, driven mainly by transpiration pull, while translocation in phloem requires energy from ATP. Because xylem cells are dead and heavily lignified, they also give the plant much of its mechanical strength, which phloem, being largely living tissue, does not.
Explain the different types of epithelial tissue found in the human body, describing where each occurs and why its structure suits that location.
Answer
Epithelial tissue forms a continuous covering over body surfaces and lines internal cavities, acting as a barrier that regulates what passes between the body and its surroundings. Its cells are tightly packed with almost no intercellular material and rest on a basement membrane. Simple squamous epithelium is a single layer of extremely thin, flat cells. It lines the alveoli of the lungs and the walls of blood capillaries, where thinness allows gases and nutrients to diffuse across quickly. Stratified squamous epithelium is arranged in many layers. It forms the outer skin and lines the mouth and oesophagus, where constant friction and abrasion would rapidly destroy a single delicate layer, so a layered arrangement prevents wear and tear. Cuboidal epithelium is made of cube-shaped cells and lines kidney tubules and the ducts of salivary glands. Its shape gives it enough cytoplasm to carry out absorption, secretion and excretion, and it provides mechanical support to the tubules. Columnar epithelium consists of tall, pillar-like cells and lines the inner surface of the intestine, where its height supports the absorption of digested food and the secretion of enzymes and mucus. Ciliated columnar epithelium bears hair-like cilia and lines the trachea and bronchi; the coordinated beating of the cilia sweeps dust and mucus upward and away from the lungs. Glandular epithelium is formed when epithelial cells fold inward to make a multicellular gland, such as a sweat gland or salivary gland, specialised for secretion.
A carpenter named Devan is examining two pieces of timber. He notices that the outer, lighter region of the trunk still conducts sap when the tree is freshly cut, while the dark inner core is completely blocked and no longer carries anything, though it is by far the hardest part of the log. He also observes that when a strip of bark is removed all the way around a young living tree, the tree does not wilt immediately but the region below the cut swells and the tree eventually dies. Answer the following: (a) Which tissue is Devan mainly cutting through in the hard inner core? (b) Which tissue was removed along with the bark? (c) Why did the ringed tree not wilt immediately? (d) Explain why a swelling appeared just above the cut and why the tree finally died.
Answer
(a) The hard inner core is mainly old xylem. Its tracheids and vessels are dead cells with thick lignin-rich walls, which is why this region is the hardest part of the log even after it has stopped conducting sap. (b) Removing a ring of bark takes away the phloem, which lies just inside the bark, along with the cambium; the xylem is deeper inside and remains intact. (c) Water and minerals travel upward through the xylem, which was untouched, so the supply of water to the leaves continued and the tree did not wilt straight away. (d) Phloem carries the food made in the leaves downward to the stem and roots. With the phloem ring cut, this food could not pass the gap and accumulated in the region just above the cut, causing the swelling. Below the cut, the roots were slowly starved of the sugars they need for respiration and growth. Once the roots failed, they could no longer absorb water and minerals, and the whole tree eventually died.
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