Give reasons:
(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.
Answers
Answer:
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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
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Answer:
(a) Answer: Meristematic cells are continuously dividing cells so they have a prominent nucleus and dense cytoplasm.
- But since these cells do not store food material or waste materials, they lack vacuole. Sclerenchyma cells have lignified cell walls which makes them compact and leaves no intercellular spaces.
(b)Intercellular spaces are absent in sclerenchymatous tissues because they have a cementing substance (known as lignin) around their cell membrane which makes them stiff and hard. ... The sclereids give a crunchy feeling to the pear fruit because it provides support and hardens the tissue.
(c) In a pear fruit, cells of sclerenhyma are small, rounded and called stone cells. They are hard with highly thickened cell wall. These cells give the crunchy and granular feeling when we chew pear fruit.
(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.
Explanation: