Q20 of 386 Page 155

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

Xylem and phloem both are conducting or vascular tissues of the plants. They are called as complex tissues because each of them is made of more than one type of cells.

Differences between xylem and phloem:




























Xylem



Phloem



It is composed of four types of elements: xylem vessels, tracheids, xylem parenchyma and xylem fibres.



It is composed of four types of elements: sieve tubes, companion cells, phloem parenchyma and phloem fibres.



It consists of mainly dead cells.



It consists of mainly living cells.



It conducts water and minerals.



It conducts food.



Conduction is mostly unidirectional, i.e., from roots to apical parts of the plant.



conduction may be bidirectional, i.e. from leaves to storage organs or growing parts or from storage organs or growing plants.



It provides mechanical strength to the plant.



It does not provide mechanical strength to the plant.



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18

Give reasons for

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


(b) Intercellular spaces are absent in sclerencytmatous tissue


(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 coconut.

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List the characteristics of cork. How is it formed? Mention its role.

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(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.

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Name the plant tissue found in the husk of coconut and also identify the chemical which is responsible for its stiffness.