BIO(Plant tissues)

              Plant Tissues

         Plants that we observe around us are

usually multi-cellular. They perform

several life processes such as growth,

respiration, excretion, etc, similar to those

performed by animals. In addition to these

they can perform photosynthesis and

prepare food not only for themselves but

also for all the other living organisms dependent on them, either directly or indirectly. Let us recall the information about different parts of the plants and the functions they are associated with.

Activity-1:

Parts of the plant and their

functions.

We have studied about the functions of

the parts of the plant in the earlier classes.

Read the functions given below and write

the names of the parts involved in

performing the respective function.

    Function Name of the parts:

1. Absorption of water from soil

2. Exchange of gases (air)

3. Photosynthesis

4. Transpiration

5. Reproduction

Activity-2:

Cells in onion peel

- Take a piece of an onion peel.

- Now place it on the slide.

- Put a drop of water and then a drop of

glycerine on it.

- Gently cover it with a cover -slip.

- Observe it under the microscope.

- Draw and label the diagram that you

have observed under the microscope.

Compare your drawing with figure-1 to

find out labelled parts.

Are all the cells similar?

How are the cells arranged?

Activity-3:

Cells in a leaf peel.

- Take a betel leaf or Tradescantia or

Rheo leaf.

- Tear it with a single stroke. So that a

thin edge be seen at the torn end.

- Observe the thin edge where the leaf

has been torn under the microscope

in the same manner as you had

observed the onion peel.

Draw a diagram of what you have

observed and compare it with figure-2.

Are all the cells similar?

Is there any difference in their

arrangement?

What can we infer from the above

activities?

Have you noticed that the cells are in

groups in both the activities?

Compare and write a note on the

arrangements of the cells that you have

observed in both of the activities.

You may have observed that the cells are

present in groups with certain

arrangement. With the help of the

following activities we shall try to find out

whether these arrangements have special

roles to play in the plant body.

Activity-4:

(a) Cells in root tip

- Are the cells in the root similar to that

of a leaf. Let us find out how the cells

are arranged in the root. For this we

need onion root tips.

- Take a transparent (plastic/glass) bottle

filled with water. Take an onion bulb

slightly larger than the mouth of the

bottle.

- Put the onion bulb on the mouth of the

bottle.

- Observe the growth of roots for a few

days till they grow to nearly an inch.

- Take the onion out and cut some of the

root tips.

- Take an onion root tip.

- Place it on the slide.

- Put a drop of water and then a drop of

glycerine on it.

- Cover it with a cover-slip.

- Remove excess water with the help of

blotting paper.

- Tap the cover-slip gently and press with

the blunt end of the needle or brush to

spread the material.

- Observe the structure and arrangement

of the cells.

- Draw the diagram of that you have

observed under the microscope.

· Are all the cells similar?

· How is the arrangement of cells?

       Cells in Onion roots tip:

Activity-5:

(b) Growing roots

- Take the onion used in the previous

activity and mark the cut end of the

roots with a permanent marker.

- Put the onion bulb on the mouth of the

bottle in the same way as you did in the

previous activity.

- Leave the set up aside for at least four

to five days. Take care that there is

enough water in the glass so that the

roots are submerged.

Did all the roots grow in a same manner?

What happened to the roots which had

been cut off?

Write down your findings, regarding the

cut roots and those that were not?

We observe that by removing the tip of

the onion root, having a particular

arrangement of cells, the growth of the root

in length is stopped.

You have observed that cells are present

in groups. Cells in groups which are nearly

similar in structure perform similar

functions. Such groups of cells are called tissues.

      Growth on roots in onion bulb

Types of plant tissues:

There are four basic types of tissues in

the plants. They are

Tissues that bring about overall growth

and repair are called Meristematic

tissues.

Tissues that form outer coverings are

called as Dermal tissues.

Tissues that form the bulk of the plant

body, helping in packing other tissues

are called as Ground tissues.

 Tissues that help in transport of

materials are called as Vascular tissues.

You have already observed some types

of tissues. To observe various types of plant

tissues we need to know some techniques

for preparing slides and cutting sections.

See annexure for the same.

1. Meristematic tissues:

Observe the given figure of a stained

section of a shoot tip

From the above figure you can infer

that meristematic tissues are present on

the tip, sides and in between layers of other

tissues. Meristematic tissues at the

growing tip that bring about growth in

length are called as apical meristematic

tissues.

Tissues present around the edges in a

lateral manner and giving rise to growth in

the girth of stem are called lateral

meristematic tissues.

Areas from which branching takes place

or a leaf or a flower stalk grows, we find

a kind of meristematic tissue called

intercalary meristematic (also called

Cambium) tissue.

Activity-6:

Dicot Stem tissues

Prepare a temporary mount of the TS

of a dicot stem.

Observe it under the microscope.

Draw and label the diagram.

Compare it with figure given below

       Dicot stem (TS) - Tissues

What are the similarities between the

tissues in root and in shoot as shown

in the above figure?

Are all the cells similar in shape and

structure?

Activity-7:

Rheo leaf - Dermal tissue. 

- Take a fresh leaf of Rheo or Betel plant

- Tear it in a single stroke, so that a thin whitish edge can be seen at the torn end.

Slowly remove it and observe that peel

under the microscope (by preparing a

temporary mount).

See the arrangement of cells .Are all

cells similar? Are there any spaces

between the cells?

This activity shows a part of the dermal

tissue of the plants.

Dermal tissue (Dermis) usually consists

of a single layer of cells showing variations

in the types of cells on the basis of their

functions and location. These tissues are

divided into three different types. They are

epidermis (outer most layer), mesodermis

(The middle layer) and endodermis (the

innermost layer).

The walls of the cells of dermal tissue

are comparatively thicker than the cells of

meristematic tissues. In desert plants it may

be even more thick and waxy. Small pores

are seen in the epidermis of the leaf, called

stomata. They are enclosed by two kidney

shaped cells, called guard cells. Cells of

the roots have long-hair like parts, called

root hair.

        Parenchyma:

The cells of the parenchyma are soft,

thin walled and loosely packed. The

Parenchyma which contains chloroplasts is

called “Chlorenchyma”. The Parenchyma

which contains large air cavities or spaces

is called “Aerenchyma”. The Parenchyma

which stores water or food or waste

products is called “Storage Tissue”.

Collenchyma tissues have thick walled,

longer cells when compared with parenchyma. In the sclerenchyma the cells are thick walled and tightly packed without spaces. So when compared with dermal tissue, the ground tissue is of various types. And some of the ground tissues help in photosynthesis. Let us observe the ground tissue of some other stems.

Activity-8:

Take permanent slides of Chlorenchyma, Arenchyma, Storage Tissue from your laboratory and observe them under the microscope. Find out the characteristics differences and record them in your notebook.

       Chlorenchyma

             Arenchyma

          Storage Tissue

      Vascular Tissue:

We know that roots can absorb water

from the soil and send it to other parts of

the plant. The leaves and other green parts

prepare food and supply it to all the parts

of the plant.

Let us study the tissues involved in

transportation.

We have done an experiment on

transportation in class VII, in the chapter

on plant nutrition. We have observed that

when a plant is kept in red coloured water,

Some of the parts of the plant turned red.

Do the same experiment again by keeping

a small plant (with roots) in red coloured

water. Leave it for two hours. Now cut a

T.S. of the stem and observe it under the

microscope.

Which part of the plant is responsible

for this transport?

Draw a rough sketch of that part and

mark the part that appears red.

What do you conclude from your observation?

The tissues involved in transportation are vascular tissues. They are composed of different

types of cells which show specific arrangements.