NCERT Class-9 Science Solutions: Chapter 6 – Tissues Part 10

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Question 52:

Give reasons for

  1. Meristematic cells have a prominent nucleus and dense cytoplasm but they lack vacuole.

  2. Intercellular spaces are absent in sclerenchymatous tissues.

  3. We get a crunchy and granular feeling, when we chew pear fruit.

  4. Branches of a tree move and bend freely in high wind velocity.

  5. It is difficult to pull out the husk of a coconut tree.

Answer:

(a) Meristematic cells are the continuously dividing cells of the plant body i.e., they remain metabolically active and as we know that vacuoles serve the purpose of storage in plant cells. Therefore meristematic cells do not require vacuole.

(b) Sclerenchyma tissue are dead simple permanent tissue of the plant. The cells of sclerenchyma are closely packed without intercellular spaces, like tiles in mosaic floor so that, it can provide the strength, rigidity, flexibility and elasticity to the plant to withstand various strains.

(c) The get a crunchy and granular feeling when we chew pear fruit due to the presence of sclerenchyma tissue. The cell walls of sclerenchyma are greatly thickened due to the presence of lignin. Lignin is a complex polymer with high tensile strength i.e., it does not breaks easily on stretching and a high compressional strength, it does not buckle easily.

(d) Collenchyma cells are characterized by the deposition of extra cellulose at corners of the cell. In collenchyma intercellular spaces are absent and cells are elongated. It is a mechanical tissue which provides support and elasticity to the branches of a tree so that, they move and bend freely in high wind velocity.

(e) It is difficult to pull out the husk of a coconut tree due to the presence of sclerenchyma tissue. The cells of sclerenchyma tissue are closely packed without intercellular spaces, a middle lamella exists between them. Middle lamella is a thin layer of connecting substance containing pectin, lignin and protein.

Question 53:

List the characteristics of cork. How are they formed? Mention their role.

Answer:

Characteristics:

    • Cells of cork are dead at maturity

    • These cells are compactly arranged

    • Cells do not possess intercellular spaces.

    • Cells possess a chemical substances Suberin in their walls

    • They are several layers thick.

  1. As plants grow older, a strip of secondary meristem replaces the epidermis of the stem. Cells cut on the outer side by this meristem are called cork.

  2. They are protective in function for older stem/twigs/branches. They are impervious to gases and water.

Question 54:

Why xylem and phloem are called complex tissues? How are they different from one other?

Answer:

Xylem and Phloem
xylem and phloem

Xylem

Phloem

Consists of tracheids, vessels, xylem, parenchyma and xylem fibers

Consist of sieve tubes, companion cell, and phloem parenchyma and phloem fibers.

They transport water and minerals vertically from soil to aerial parts of the plant.

They transport food from leaves to other parts of the plant.

Most of the cells except xylem parenchyma are dead cells

Most of the cells except phloem fibers are living cells.

Image Xylem

Image Xylem

Image Xylem

Image Phloem

Image Phloem

Image Phloem

Question 55:

  1. Differentiate between meristematic and permanent tissues in plants

  2. Define the process of differentiation

  3. Name any two simple and two complex permanent tissues in plants.

Answer:

  1. The basic differences between meristematic and permanent tissues of plants are tabulated below

    Differences between Meristematic and Permanent Tissues of Plants
    differences between meristematic and permanent tissues of plants

    Meristematic tissue

    Permanent tissue

    Its component cells are living, small, spherical or polygonal and un-differentiated

    Its components cells may be living or dead. They are large, differentiated with different shapes.

    Cytoplasm is dense and vacuoles are nearly absent as they are metabolically active.

    Large central vacuole occurs in living permanent cells as, they are less metabolically active.

    Intercellular spaces are absent.

    Intercellular spaces are often present.

    Cell wall of its cells is thin and elastic.

    Cell wall of its cells may either thin or thick.

    Nucleus of each cell of this tissue is large and prominent.

    Nucleus of each cell of this tissue is less conspicuous.

    Its cells grow and divide regularly

    Its cells do not normally divide.

    It is a simple tissue.

    It can be simple, complex or specialized,

    Cell organelles of its cells are simple

    Cell organelles of its cells are well developed.

    Cell of this tissue do not contain crystals and other inclusions

    Cells of this tissue possess crystals and other inclusions

    It provides growth to the plant.

    It provides protection. Support, conduction photosynthesis, storage, etc.

    Image Meristematic tissue

    Image Meristematic Tissue

    Image Meristematic tissue

    Image Permanent tissue

    Image Permanent Tissue

    Image Permanent tissue

  2. Cells derived from the division of meristematic tissues take up specific roles and gradually lose their ability to divide. Thus, they form permanent tissue. The process by which the cells divide meristematically to take a permanent shape, size and function is called differentiation.

  3. Two simple permanent tissue in plants are parenchyma and collenchymas while two complex permanent tissue in plants are xylem and phloem.