Tissues-2

Exercises (pg 79)
1. Define the term “tissue”.
Tissue is a group of cells which have common origin and structure and perform similar functions.

2. How many types of elements together make up xylem tissue? Name them.
The elements which make up xylem tissue are:
(i) Vessels: They are narrow tube-like structures having annular and spiral thickenings in
proto-xylem. They are dead.
(ii) Tracheids: They are elongated tube like structures. They do not have perforations or
openings at their end. They are also dead.
(iii) Xylem parenchyma: They are the only living elements in xylem and are also called
wood parenchyma.
(iv) Xylem fibres: They are long, slender and pointed dead sclerenchymatous cells. They are called wood fibres. They have small pits and thickened walls.

3. How are simple tissues different from complex tissues in plants?

Simple	Complex
1. They are made up of one type of cells with uniform mass.	These are composed of more than one type of cells.
2. Their cells are similar in structure and function,	Their cells are different in structure and function.
3. eg – Parenchyma, Collenchyma, Sclerenchyma	eg – Xylem, Phloem

4. Differentiate between Parenchyma, Collenchyma and Sclerenchyma.

Nature	Parenchyma	Collenchyma	Sclerenchyma
1. Shape	Isodiamtetric, oval or spherical.	Elongated.	Angluar.
2. Cell wall	Thin and cellulosic.	Unevenly thickened with cellulose at corners with lignin.	Evenly thickened with pectin.
3. Vacuole	Single large.	Small.	Does not have any.
4. Nucleus	Present (living cells).	Present (living cells).	Absent (dead cells).
5. Intercellular spaces	Found.	Mostly absent.	Absent.
6. Occurence	Cortex of roots, ground tissue in stems, mesophyll of leaves.	Below epidermis in stems. However, genrally absent in roots and leaves.	Stems, veins of leaves and hard covering of seeds.
7. Functions	Stores food, provides support, food manufacture by photosynthesis (only if chloroplast is present)	Gives mechanical support, makes food (only if chloroplast are present)	Provides mechanical strength, helps in conduction, protective in function.

5. What are the functions of stomata?
The functions of stomata are:
(i) The exchange of gases (oxygen and carbon dioxide).
(ii) Transpiration takes place by means of stomata found in leaves.

7. What is the specific function of cardiac muscle?
The main function of the cardiac muscle is rhythmic contraction and relaxation of heart wall throughout life withut fatigue under the normal coditions.