Plant Tissue and Animal Tissue – Long Answer Questions (CBSE Class 9 Biology)
Medium Level (Application & Explanation)
Q1. Explain the role of meristematic tissue in plant growth. Describe the types of meristems and give examples of where they are found.
Answer:
- Meristematic tissue consists of actively dividing, undifferentiated cells responsible for plant growth. These cells are small, have thin walls, dense cytoplasm, and large nuclei.
- Apical meristems are found at the tips of roots and shoots and cause primary growth — increase in length. For example, root apices form new root cells, enabling roots to penetrate soil.
- Lateral meristems, such as the cambium, are found along the sides of stems and roots and cause secondary growth — increase in girth (thickness). Trees thicken because of cambial activity.
- Intercalary meristems occur at the base of leaves or internodes (common in grasses) and help in rapid elongation and regrowth after grazing.
- Overall, meristematic tissues are the source of new cells that later differentiate into permanent tissues like xylem, phloem, and epidermis, enabling continuous growth and repair.
Q2. Describe the structure and functions of xylem and phloem. How do these tissues differ in their roles?
Answer:
- Xylem and phloem are the two main components of the plant’s vascular tissue responsible for transport.
- Xylem is made of vessels, tracheids, xylem parenchyma, and xylem fibers. Vessels and tracheids are dead, hollow, and thick-walled, allowing unidirectional transport of water and dissolved minerals from roots to leaves. Xylem also provides mechanical support.
- Phloem consists of sieve tubes, companion cells, phloem parenchyma, and phloem fibers. Sieve tubes are living cells that transport organic food (mainly sugars) from leaves (source) to sinks (growing parts, storage organs) in both upward and downward directions. Companion cells help sieve tubes with metabolic activities.
- Key differences: xylem transports water/minerals and is mainly dead at maturity; phloem transports food and is living. Xylem flow is passive (transpiration pull), while phloem uses active processes (pressure-flow mechanism).
Q3. How do plant tissues adapt to arid (dry) environments? Use examples such as cacti to explain anatomical modifications.
Answer:
- Plants in arid areas show tissue-level adaptations to conserve water and reduce evaporation. In cacti:
- Succulent parenchyma stores large quantities of water in leaves or stems. These parenchyma cells have large vacuoles that keep water for drought periods.
- The epidermis is thick and often covered with a waxy cuticle, reducing water loss. Stomata may be fewer and sunken to lower transpiration.
- Collenchyma and sclerenchyma provide robust support for swollen stems that store water. Sclerenchyma gives mechanical strength to heavy, water-filled tissues.
- Many cacti have reduced leaves, with photosynthesis done by modified stems containing chlorenchyma (chloroplast-rich parenchyma), limiting surface area to reduce water loss.
- These tissue adaptations result in efficient water storage, reduced transpiration, and strong support, enabling survival in deserts.
Q4. Compare parenchyma, collenchyma, and sclerenchyma in terms of structure and function. Mention one example use for each tissue in plants.
Answer:
- Parenchyma: Cells are living, with thin primary walls and large central vacuoles. They are loosely packed, allowing storage, photosynthesis, and gaseous exchange. Example: palisade parenchyma in leaves conducts photosynthesis; cortex parenchyma stores food.
- Collenchyma: Cells are elongated, living, with unevenly thickened primary walls rich in pectin and cellulose. They provide flexible support in growing parts without restricting growth. Example: collenchyma beneath the epidermis in young stems and petioles supports leaves.
- Sclerenchyma: Cells have thick, lignified secondary walls and are usually dead at maturity. They give rigid mechanical support and protection. Example: sclereids in seed coats and nut shells; fibers in jute and flax used for making ropes and textiles.
- In summary, parenchyma handles metabolic and storage roles, collenchyma provides flexible support, and sclerenchyma gives rigid strength.
Q5. Explain the four major types of animal tissues (epithelial, connective, muscle, nervous) and highlight two clear differences between animal tissues and plant tissues.
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Answer:
- Epithelial tissue: Sheets of closely packed cells that cover body surfaces and line cavities. Functions include protection, absorption, secretion (e.g., skin, intestinal lining).
- Connective tissue: Cells embedded in an extracellular matrix (fibres and ground substance). It supports and binds tissues (e.g., bone, cartilage, blood, adipose).
- Muscle tissue: Composed of contractile cells or fibers that produce movement. Types: skeletal (voluntary), cardiac (heart), and smooth (involuntary in organs).
- Nervous tissue: Made of neurons and neuroglia; it transmits electrical signals for coordination and control (brain, spinal cord, nerves).
- Two differences from plant tissues: animal cells lack cell walls and often form mobile, contractile systems (muscles), while plant tissues have rigid cell walls (cellulose) and specialized tissues for photosynthesis and water transport (xylem & phloem).
High Complexity (Analytical & Scenario-Based)
Q6. A houseplant shows stunted growth, yellowing leaves, and weak stems after transplanting. Analyze which plant tissues might be damaged and explain how this causes the observed symptoms.
Answer:
- Root meristem or root hairs may be damaged during transplanting, reducing water and mineral uptake. Without sufficient water and nutrients, leaves turn yellow (chlorosis) and growth slows.
- Xylem vessels could be disrupted, impairing water transport to leaves and stems, leading to wilting and weak stems. Poor water supply also affects turgor pressure, reducing stem rigidity.
- Phloem damage would reduce sugar transport from leaves to growing regions and roots, causing energy shortage and stunted growth.
- Meristematic regions (apical meristems) at shoot tips might be injured, directly stopping length growth and leaf formation.
- Finally, cambium injury in woody plants can disrupt secondary growth, weakening stem strength. Repair involves re-establishing vascular connections and healthy meristem activity, which can take days to weeks.
Q7. Compare regeneration after nerve injury and muscle injury in animals. Explain why recovery rates and outcomes differ at the tissue level.
Answer:
- Muscle tissue (especially skeletal muscle) has a limited capacity to regenerate because muscle fibers are long and multinucleated. Satellite cells (muscle stem cells) can divide and repair small injuries, so minor damage often heals with partial restoration of function. Severe injuries may lead to fibrosis (scar tissue), reducing contractility.
- Nervous tissue shows poor regeneration in the central nervous system (brain and spinal cord) because mature neurons have limited ability to divide and the environment is inhibitory to regrowth. In contrast, peripheral nerves have better, but still slow, regeneration due to Schwann cells guiding axon regrowth.
- Differences arise because muscle repair uses resident stem cells and extracellular matrix remodeling, whereas neuronal repair requires axon regeneration and synapse reformation, processes that are more complex and often blocked in the CNS. Thus, muscles recover faster and more completely in mild injuries; nerve injuries often cause long-term deficits.
Q8. Why can many plants regenerate lost parts (like roots, stems, or whole plants from cuttings) while animals rarely regenerate complex organs? Discuss cellular and tissue-level reasons.
Answer:
- Plants retain meristematic tissues (undifferentiated, totipotent cells) throughout life, enabling continuous cell division and dedifferentiation where mature cells can revert to dividing states. This cellular totipotency allows formation of new organs (roots, shoots) from cut tissues.
- Plant cells are enclosed by cell walls and remain in a flexible developmental program; hormones like auxins and cytokinins can redirect differentiation to form new tissues. Vascular tissues can reconnect to restore transport.
- Animals have limited populations of true totipotent cells after embryonic stages. While some tissues (like liver) regenerate partly, most specialized animal cells (neurons, cardiac muscle) do not readily revert or divide. Animal tissue repair often results in scar formation rather than full organ replacement.
- Also, plant cells communicate and reorganize via meristems and hormonal gradients, enabling organogenesis, a capacity largely absent in mature animal tissues—hence plants regenerate more completely.
Q9. Explain the tissue interactions necessary for successful grafting (joining two plants). Which tissues must unite and why is the cambium important?
Answer:
- Successful grafting requires close contact and fusion of the vascular tissues, mainly cambium layers of both rootstock and scion. Cambium is a lateral meristem that produces new xylem and phloem; when cambial layers align, they form a continuous meristem that generates vascular tissue across the graft union.
- Initially, healing involves formation of a callus (parenchyma) from cells near the cut surfaces. This callus bridges the gap and provides a matrix for cambial cells to proliferate and differentiate.
- Once cambial continuity is established, new xylem and phloem develop, rest...