Aim: -To study structure and distribution of stomata in upper and lower epidermis of leaf.

 

XII   BIOLOGY PRACTICAL-3

Que. 1-………………………………….4 Marks

Make a temporary potato osmoscope to study osmosis. Sketch & label the diagram showing the change in the water level.

OR

Make a temporary slide to study plasmolysis. Sketch & label the diagram.

OR

Make a temporary mount of leaf epidermis to study the structure & distribution of stomata. Sketch & label the structure of stomatal apparatus.

OR

Find out the adulteration of the given milk sample, for water and starch.

OR

Perform the experiment to isolate DNA from given sample. Show your result to the examiner.

Q. 1 Make a temporary mount of leaf epidermis to study the structure & distribution of stomata. Sketch & label the structure of stomatal apparatus.

•        Preparation of slide……………… 2Marks

•        Observation / Conclusion……….1 Mark

•        Diagram of stomata…..………..1 Mark

•        Total-4 Marks

Aim: -To study structure and distribution of stomata in upper and lower epidermis of leaf.

Requirements: Fresh leaf of Hibiscus/ Maize, slides, cover slips, watch glass, blades, glycerine, etc.

Theory-    

1. Stomata are tiny openings that are located in the young shoots of plants and epidermis of the leaves.
2. They govern the gas exchange process in plants.
3. The structure of the stomata includes a pair of specialized cells that are found girdling around the opening.
4.  These cells are termed as guard cells and are responsible to check and regulate the size of the closing and opening of the stomata.
5. Through the process of transpiration, water escapes from the stomata into the atmosphere in the form of water vapor.
6. Along with this, carbon dioxide and oxygen too are exchanged in the leaf through these openings.
7. Stomata are distributed differently between dicots and monocots, between the top side and underside of leaves, between different plant species, etc.
8. Mostly, stomata are found on surfaces of plants that flourish under greater availability of light, lesser carbon dioxide levels in the atmosphere and also in moist environments.
9. In a dicot leaf, in comparison with the upper surface, the lower surface has a higher distribution of stomata .
10. whereas in a monocot leaf, usually, the upper and the lower surfaces usually see an equal distribution of stomata.

Procedure

1. One fresh leaf from a four-o’clock plant is used in this experiment
2. On two watch glasses, add some distilled water
3. Slit the leaf in an oblique manner
4. With the help of forceps, peel a section from the upper surface of the leaf
5. Set this section into one of the watch glass holding water
6. With the help of forceps, peel another section from the lower surface of the leaf
7. Set this section on another watch glass which is also holding water
8. With the help of a dropper, add few drops of safranin solution into both the watch glasses
9. Now place cleared glass slides on each of the peels one at a time with the help of a brush
10. From each of the peels, cut a square or a rectangular piece with the help of a blade
11. With the help of a dropper, add one drop of glycerine on each of the slides
12. With the help of a needle, gently place a cover slip on the peel
13. Examine each of the glass slides under the microscope
14. Notice and count the occurrence of stomata in each of the peels of both the lower and upper epidermis of the four-o’clock leaf.

Observation:(If Hibiscusleaf provided)

The peel of Hibiscus leaf shows presence of kidney shaped guard cells surrounded by subsidiary cells.

(If Maize leaf provided)-The peel of Maize leaf shows presence of dumb-bell shaped guard cells surrounded by two subsidiary cells.

Conclusion:

(If Hibiscus leaf provided)The number of stomata on upper epidermis is less than on lower epidermis.

(If Maize leaf provided)The number of stomata on upper epidermis and lower epidermis is generally equal.

Inferences- The section  of leaf plucked from the four-o’clock plant shows that the number of stomata is much more in the lower epidermis while a few are found in the upper epidermis of the lea.

  

 Conclusion-

The section of leaf plucked from the four-o’clock plant shows that the number of stomata is much more in the lower epidermis while a few are found in the upper epidermis of the leaf.        

Q 1. Make a temporary mounting of leaf epidermis tonstudy structure of stomata. 

Slide preparation 2 Marks,      labelled diagram 2 Marks. 

Q.1.Which type of leaf you will use to study comparative rates of transpiration? Why? It is advised to use dicot leaves for studying the rates of transpiration in leaves. 

Ans=Dicot leaves have an unequal number of stomata present on both their surfaces. 

The upper part has very few stomata as compared to the lower part. 

Whereas monocot leaves have an equal number of stomata on both sides.

Difference between the number of stomata on each side gives a better range of observations as to how the position and number of stomata influence the rate of transpiration. 

Leaves tilt in different manners and to different extents upon blocking each side of stomata in a dicot leaf. 

The basic rule of thumb is that the more the number of stomata blocked, the lesser it will transpire. Hence, upon blocking the lower surface of the dicot leaf with petroleum jelly, it will lose less water as compared to upper leaf blockage.

·        Q.2.what are stomata ?

Ans- There are small openings on the lower surface of the leaves. These pores are called stomata. These openings are surrounded by guard cells. 

Q.3.What  are the  functionof stomata ?

• Ans= Functions of stomata:-
• 1. It helps in the transpiration of water, i.e., the loss of excess water from the plant.
• 2. Loss of water from the stomata creates an upward pull, i.e., suction pull which helps in the absorption of water from the roots.
• 3. They help in the exchange of gases.

Q.4.What is guttation?

Ans- Guttation is the process of secretion of water droplets from the pores of plants Effects of root pressure is observed at night and early morning when evaporation is low, excess water collects in the form of droplets around special openings of veins near the tip of grass blades, and leaves of many herbaceous plants. Such water loss in its liquid phase is known as guttation

Q.5. Which structures are known as 'water stomata' and where are they located?

Water stomata are the pores of the hydathode which facilitate guttation.  

They are usually located on the leaf margins

Q.6. Why is that there is differential number of stomata on the leaf surfaces in betel leaf?

Ans=All surfaces of the leaf have some amount of stomata for regulating gas exchange for photosynthesis. However, the lower epidermis (the underside of the leaf) has more, because it is more often in the shade and so it is cooler, which means evaporation won't take place as much.