Question

2. Why the cell is called the structural and functional unit of life? Give reasons for

(a) Meristematic cells have a prominent nucleus and dense cytoplasm but they

lack vacuole.

(b) Intercellular spaces are absent in sclerenchymatous tissues.

(c) We get a crunchy and granular feeling, when we chew pear fruit.

(d) Branches of a tree move and bend freely in high wind velocity.

(e) It is difficult to pull out the husk of a coconut tree.

3. (a) Differentiate between meristematic and permanent tissues in plants

(b) Define the process of differentiation

(c) Name any two simple and two complex permanent tissues in plants.

4. Differentiate between a) parenchyma and sclerenchyma

b) sclerenchyma and collenchymas

5. Find out incorrect sentence.

(a) Parenchymatous tissues have intercellular spaces.

(b) Collenchymatous tissues are irregularly thickened at corners.

(c) Apical and intercalary meristems are permanent tissues.

(d) Meristematic tissues, in its early stage, lack vacuoles.

6. A nail is inserted in the trunk of a tree at a height of 1 metre from the ground level. After 3

years the nail will

(a) move downwards

(b) move upwards

(c) remain at the same position

(d) move sideways

7. Parenchyma cells are

(a) relatively unspecified and thin-walled

(b) thick walled and specialised

(c) lignified

(d) none of these​

Answer 1

Answer:

(d) Meristematic tissues, in its early stage, lack vacuoles.

6. A nail

Answer 2

Answer:

Answer is in thefollowing

Explanation:

2.The cell is known as the structural and functional unit of life because all living beings are formed of cells. Cells are very important for performing various life processes which are required for sustaining life on earth. Moreover, cells give form and structure, process nutrients and make it into usable energy.

(a) Meristematic cells are the continously 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, flexibilty and elasticity to the plant to withstand various strains.

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

(d) Collenchyma cells are characterised by the deposition of extra cellulose at corners of the cell. In collenchyma intercellular spaces are absent and ceils 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.

3.(a) The basic differences between meristematic and permanent tissues of plants are tabulated below

Meristematic tissue

• Its component cells are living, small, spherical or polygonal and un-differentiated  
• Cytoplasm is dense and vacuoles are nearly absent as they are metabolically active.  
• Intercellular spaces are absent.  
• Cell wall of its cells is thin and elastic.
• Nucleus of each cell of this tissue is large and prominent.
• Its cells grow and divide regularly.
• It is a simple tissue.
• Cell organelles of its cells are simple
• Cell of this tissue do not contain crystals and other inclusions.
• It provides growth to the plant.

Permanent tissue

• Its components cells may be living or dead. They are large, differentiated with different shapes.
• Large central vacuole occurs in living permanent cells as, they are less metabolically active.
• Intercellular spaces are often present.
• Cell wall of its cells may either thin or thick.
• Nucleus of each cell of this tissue is less conspicuous.
• Its cells do not normally divide.
• It can be simple, complex or specialized
• Cell organelles of its cells are well developed.
• Cells of this tissue possess crystals and other inclusions.

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

(b) 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.

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