1.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.
2. List the characteristics of cork. How are they formed? Mention their role.
3.. Why are xylem and phloem called complex tissue?
Answers
Answer:
(a) 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. ... The branches of a tree have collenchyma cells which provide tensile strength to plant parts.
(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.
(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) 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 because it is made up of sclerenchyma tissues which are dead cells. This gives rigidity and stiffness.
2. List the characteristics of cork. How are they formed?
Cells of cork are dead at maturity.
These cells are compactly arranged.
Cells do not posses intercellular spaces.
Cells possess a chemical substance 'suberin' in their walls.
There are several thick layers. As plants grow older, a strip of secondary meristem replaces the epidermis of the stem.
3. Xylem and phloem are known as complex tissues as they are made up of more than one type of cells. These cells work in a coordinated manner, as a unit, to perform the various functions of the xylem and phloem. Tracheids are elongated, thick-walled dead cells with tapering ends.