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Morphology of Flowering Plants Class 11 Science Notes Download in PDF-3(THE LEAF),CBSE

Morphology of Flowering Plants Class 11 Science Notes Download in PDF-3(THE LEAF),CBSE

 THE LEAF

 THE LEAF IS A LATERAL, GENERALLY FLATTENED STRUCTURE BORNE ON THE STEM.

IT DEVELOPS AT THE NODE AND BEARS A BUD IN ITS AXIL.

LEAF ORIGINATE FROM THE SHOOT APICAL MERISTEM.

LEAVES ARE ARRANGED IN AN ACROPETAL ORDER ON THE STEM.

THEY ARE THE MOST IMPORTANT VEGETATIVE ORGAN FOR PHOTOSYNTHESIS.

PARTS OF A LEAF

A TYPICAL LEAF CONSISTS OF THREE MAIN PARTS:

1) LEAF BASE
2) PETIOLE
3) LAMINA

LEAF BASE
THE LEAF IS ATTACHED TO THE STEM WITH HELP OF LEAF BASE. THE LEAF BASE BEARS TWO SMALL LEAF LIKE STRUCTURES CALLED STIPULES.

IN MONOCOTYLEDONS, THE LEAF BASE EXPANDS INTO A SHEATH TO COVER THE STEM THE PARTIALLY OR WHOLLY.

SWOLLEN LEAF BASE CALLED PULVINUS IS FOUND IN LEGUMINOUS PLANTS.

PETIOLE
IT HELPS IN HOLDING THE LEAF BLADE, FACING TOWARDS LIGHT. LONG FLEXIBLE PETIOLE HELPS THE LEAF BLADE TO FLUTTER IN WIND. THUS COOLING THE LEAF AND BRINGING FRESH AIR TO THE LEAF SURFACE. 

 LAMINA OR LEAF BLADE

 IT IS THE EXPANDED PART OF THE LEAF HAVING VEINS AND VEINLETS. IN LAMINA, USUALLY A MIDDLE PROMINENT RIB CALLED MIDRIB IS PRESENT. VEINS HELPS IN PROVIDING RIGIDITY TO THE LEAF. THEY ALSO ACTS AS CHANNELS OF TRANSPORT OF WATER, FOOD MATERIALS AND MINERALS.

NOTE- ON THE BASIS OF MARGIN, SHAPE, APEX, SURFACE AND EXTENT OF INCISION, THE LAMINA OF LEAF VARIES IN DIFFERENT PLANTS.

PARTS OF LEAF

                         PARTS OF A LEAF

VENATION
The arrangement of veins and veinlets in the lamina of leaf is termed as venation.
Venation is of two types –
Reticulate venation
Parallel venation
What is reticulate venation?
When the veins form the network, then the venation is known as reticulate venation.

LEAF VENATION (RETICULATE)

                           RETICULATE VENATION
What is parallel venation?
When the veins run parallel to each other, then the venation is known as parallel venation.
Note – in dicots reticulate venation is found and in monocots parallel venation is found.

LEAF VENATION (PARALLEL)

                           PARALLEL VENATION


TYPES OF LEAVES
A LEAF IS SAID TO BE SIMPLE WHEN THE LAMINA IS ENTIRE OR INCISED PROVIDED THE INCISION DO NOT TOUCH THE MIDRIB.
WHEN THE INCISION REACHES THE MIDRIB, THE LAMINA BREAKS UP INTO NUMBER OF LEAFLETS AND SUCH TYPE OF IS KNOWN AS COMPUND LEAF.
THE COMPUND LEAF ARE OF TWO TYPES
PINNATELY COMPOUND
PALMATELY COMPOUND


PINNATELY COMPOUND – IN THIS TYPE OF LEAF, NUMBER OF LEAFLETS ARE PRESENT ON THE COMMON AXIS CALLED RACHIS. e.g., neem.

PINNATELY COMPOUND LEAF

                         PINNATELY COMPOUND

PALMATELY COMPOUND – IN THIS TYPE OF LEAF, A NUMBER OF LEAFLETS ARE ATTACHED TO A COMMON POINT. i.e., at the tip of petiole. e.g., silk cotton.

PALMATELY COMPONUD LEAF

                         PALMATELY COMPOUND


PHYLLOTAXY
THE PATTERN OR ARRANGEMENT OF LEAVES ON THE BRANCHES OR STEM IS TERMED AS PHYLLOTAXY.

PHYLLOTAXY IS OF THREE TYPES-

ALTERNATE PHYLLOTAXY- IN THIS OF ARRANGEMENT, SINGLE LEAF ARISES FROM EACH NODE AND IN ALTERNATE FASHION. FOR EXAMPLE, CHINA ROSE, MUSTARD AND SUN FLOWER PLANTS.

ALTERNATE PHYLLOTAXY

                       ALTERNATE PHYLLOTAXY


OPPOSITE PHYLLOTAXY – IN OPPOSITE TYPE OF PHYLLOTAXY, A PAIR OF LEAVES ARISES FROM EACH NODE AND BOTH OF THEM ARE OPPOSITE TO EACH OTHER. FOR EXAMPLE, Calotropis and Guava plants.

OPPOSITE PHYLLOTAXY
OPPOSITE PHYLLOTAXY


WHORLED PHYLLOTAXY- IN THIS TYPE OF ARRANGEMENT, MORE THAN TWO LEAVES ARISES FROM EACH NODE IN A WHORL TYPE FASHION. FOR EXAMPLE, Alstonia.

WHORLED PHYLLOTAXY
WHORLED PHYLLOTAXY



MODIFICATION OF LEAVES
LEAVES OFTEN MODIFY THEMSELVES TO PERFORM FUNCTIONS OTHER THAN PHOTOSYNTHESIS.


TENDRILS- THEY BECOME TENDRILS TO PROVIDE SUPPORT TO THE WEAK PLANT. FOR EXAMPLE, PEAS.

LEAF TENDRILS, LEAF MODIFICATION
LEAF TENDRILS 


SPINES- IN SOME PLANTS LEAF REDUCES TO SPINES IN ORDER TO PROVIDE PROTECTION FROM BROWSING ANIMALS OR TO PROVIDE DEFENCE. FOR EXAMPLE, CACTUS.

LEAF SPINES , MODIFICATION OF LEAF
LEAF SPINES


STORAGE – LEAVES ALSO HELPS IN STORAGE OF FOODS AS IN ONION AND GARLIC.

FLESHY LEAVES , MODIFICATION OF LEAF

                       FLESHY LEAVES OF ONION

NOTE – 1. IN PLANTS LIKE Australian acacia, THE LEAVES ARE SMALL AND SHORT LIVED. IN THIS CASE THE PETIOLE EXPANDS, BECOMES GREEN AND PERFORM PHOTOSYNTHESIS.
2. THE LEAVES OF INSECTIVOROUS PLANTS LIKE PITCHER PLANT AND VENUS FLY TRAP ARE ALSO EXAMPLES OF MODIFIED LEAVES. LEAVES IN THEM TAKE THE FORM OF PITCHER IN ORDER TO TRAP INSECTS IN THEM.

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