leaf and its morphology ppt class 11 biology NCERT

2. 5.3 THE LEAF (vegetative organ)
•The leaf is a lateral ,generally flattened structure borne on
the stem.
•It consists of three parts leaf base, petiole and lamina .
• leaf base :-the attachment of leaf to its base .
•It has two lateral small leaf like structures called stipules.
•In leguminous plants leaf base becomes swollen and is
called pulvins.
•Petiole :-hold the blade to exposed light .
•Lamina:-green expanded part of leaf with veins and
veinlets.
• Veins:- provide rigidity to leaf blade and act as a channel
for transport of food and water
•Midrib:-middle prominent vein

3. 5.3.1 VENATION
• Venation:-The arrangement of veinlets in lamina of
leaf
• Reticulate:- veins forming a network.
• Parallel venation:-when veins run parallel to each
other within lamina
• Monocotyledonous plants show parallel venation
• Dicotyledonous plants show reticulate venation.

5. 5.3.2 TYPES OF LEAVES
• simple leaf:-when lamina of leaf is entire and
incision does not touch the midrib
• Pinnately compound leaf:-leaflet are present
on common axis rachis.
• Palmately compound leaf:-leaflet are attached
at tip of petiole .e.g. silk cotton.
• Compound leaf:- when incision of lamina
reach up to midrib breaking it into number of
leaflets.

7. 5.3.3 PHYLLOTAXY
• Phyllotaxy:-pattern of arrangements of leaf on
stem or branch.
• 3 types of phyllotaxy are:-
• Alternate:-single leaf arises at each node. single
leaf arises at alternate node .e.g. china rose.
• Opposite:- a pair of leaf arises at each node ad
lie opposite to each other. E.g.Calotropis.
• Whorled:-more than two leaf arises at each
node . E.g.Alstonia.

9. 5.3.4 MODIFICATION OF LEAVES
• Leaf are modified to perform function other than
photosynthesis.
• They are used for climbing and for defence .
• They are converted into tendrils for climbing e.g. pea.
• They are converted into spines for defence .e.g. Cacti
• The fleshy leaf of garlic store food.
• For those plant who bear shot leaf such as Australian
acacia the petiole in these plant expand and synthesise
food .
• Leaves of certain insectivorous plants such as pitcher
plant are modified leaves
• Venus fly trap are used as modified leaf.

10. Summing up
• Leaf:-lateral flattened surface
3 parts are:-leaf base ,petiole , lamina.
• Venation:- arrangement of veins and veinlets on lamina
of leaf
2 type are parallel, reticulate venation
• Types of leaf:-simple ,compound , pinnately compound
leaf, palmately compound leaf.
• Phyllotaxy:-arrangements of leaf on stem or branch.
3 types are opposite ,alternate ,whorled respectively.
• Flowers or their leaf are modified for :-
1.Sythesising food
2.Defence
3.Climbing
4.Pitcher plant and venus-fly trap are modified leaf