Leaves are responsible for photosynthesis and making food for plants. They have a layered structure including epidermis, mesophyll, and veins. The epidermis protects the leaf and regulates gas exchange through stomata. The mesophyll, divided into palisade and spongy layers, is where photosynthesis occurs. Veins transport water and nutrients throughout the leaf. Leaves come in different shapes, sizes, arrangements on the stem, and venation patterns, and these characteristics are used to identify plant species.

1. LEAVES
Leaves are the above organ of the plant responsible for making
their own food by the process called photosynthesis.
Leaves are the power house of the plant.
Photosynthesis Is the process of making food in plants by using
the sunlight.
Structures within the leaves convert the energy from the sun
into the chemical energy that the plant can use as food,
chlorophyll is the molecules in leaves that uses the energy from
the sunlight and carbon dioxide gas(CO2 ) into food.
 This process is called photosynthesis.

2. Leaf anatomy (Structure of the leaf)
A leaf is made of layers sandwiched between
the layers of epidermis.
This layer protects the leaf from insect,
bacteria and other pastes.
A complete leaf of angiosperm consist of
 Petiole (Leaf stem)
 Lamina (leaf blade)
 Stipules.

3.  The petiole attaches to the stem at a point called leaf axil.
 Not all leaves contains the above mentioned structures.
 The following are the layers of the leaf;
 An epidermis
 Mesophyll
 Vascular tissue (veins)
 Epidermis;
 Epidermis covers the upper and lower surfaces of the leaf.
 Epidermis is said to have a wax cuticle layer made by epidermis
itself (epidermal cells that lack chloroplast).
 It helps the leaf from drying out
 It protect the leaf from invading bacteria, insects and fungi.

4.  Epidermis is usually transparent and consists cuticle layer that
prevent water loss.
 The cuticle is thinner on the lower epidermis (abaxil) and
thicker on the upper epidermis (adaxial)
 The epidermis is covered with pores called stomata,a part of a
stoma complex consisting or a pore surrounded on each side
by chloroplast- containing guard cell.
 Guard cell are pair of sausage shaped that surround the
stoma, guard cell change shape making the stomata to open
(absorption of water) and close (water loss), and two to four
subsidiary cells that lack chloroplast.
 Stomata are more numerous on the lower part than of the
upper part.
 Stomata are used for gaseous Exchange.

5. The epidermis consist the following:-
• Epidermal cell
• Guard cell
• Subsidiary cell and
• Epidermal hairs ( trichomes)
Function of Epidermis
- Protection against water loss
- Regulation of gas exchange
- Secretion of metabolic compound.
- Absorption of water

6. Mesophyll layer (chlorenchyma)
 Is the layer found between the epidermis.
 Photosynthesis takes place on the mesophyll layer.
 The mesophyll is divided into two layers in fens and
flowering plant;
 The palisade layer,
 Spongy layer.
 The upper palisade layer consist of tightly packed vertically
elongated cells, one to two cells thick directly beneath the
adaxial epidermis
 These long cylindrical cells are regularly arranged in one to
five rows.
 Cylindrical cells, with the chloroplasts close to the walls of the
cell, can take optimal advantage of light.

7.  The slight separation of this cells provides maximum
absorption of carbon dioxide.
 This separation must be minimal to afford capillary action for
water distribution.
 Sun- Leaves have a multi- layered palisade layer, while shade
leaves or older leaves closer to the soil are single- layered.
 Spongy Layer
 It is found below the palisade layer
 The cells of the spongy layer are more rounded and not so
tightly packed.
 There are large intercellular air spaces.
 These cells contain fewer chloroplasts than those of the
palisade layers.

8. • The pores or stomata of the epidermis open into substomatal
chambers, connecting to air spaces between the spongy layer
cells.
• These two different layers of the mesophyll are absent in
many aquatic and marsh plants.
• The equation of photosynthesis as follows:
Chlorophyll + CO2U.V Light O2+ glucose (assimilate.)
Note: The mechanism of a tree shedding leaves is called
abscission
Veins (vascular tissue)
• The veins are the vascular tissue of the leaf and are located in
the spongy layer of the mesophyll.
The veins are made up of:-
• Xylem
• Phloem
Xylem: brings water and minerals from the roots to the leaf.

9. Phloem:
 This is the tube that usually moves sap with dissolved sucrose,
produced by photosynthesis in the leaf and out of the leaf.
Leaf morphology
 External leaf characteristics( such as shape, margins, hairs) are
important for identifying plants species than stem and roots
Function of the leaf
 A place where gas exchange takes place.
 Secretion of metabolic compound
 Some are closed as food by human and wild animals.
 Also some species of leaves are used as drug.
 Is responsible for photosynthesis
 Respiration and transpiration.

10. CLASSIFICATION OF LEAVES
 The types of leaves is usually a characteristics of a species,
although some species produce more than one type of leaf.
TYPES ACCORDING TO THE PETIOLE (Characteristics of petiole)
Petiolated leaves
 Are those that have a petiole. This can be different in length
from one plant to another.
Sessile leaves do not possess a petiole, the blade expands itself
directly from the stem

11. ACCORDING TO THE BLADE
• Simple leaves: show an undivided blade or in case it has divisions,
they do not reach the midrib
• Compound leaves: Have a fragmented blade, with divisions
reaching the midribs sometimes each one of these fragments is
similar to a single leaf they are called leaflets
THE MARGINS OF A LEAF( leaf shape)
Entire:It is 3 to 4 times longer
than width.
Sinuate:has carves on its margin

12. • Dentate- Have little teeth the margin.
• Serrate- Have little bent like those of a saw.
Lobed- Have divisions that do not arrive the center of half blade
LEAF BLADE( lamina)
Elliptic
Has a smooth lamina.

13. Lanceolate; spear like shape.
Ovate
-Egg- shaped wider at the base than apex.
Cordate
-Heart shaped, move extended at the base than the ovate type and
with a notch

14. Hastate,
Halberd- shaped
Wide at the base but with lobes ending shaply ( apex)
Linear leaves- strip- shaped; Several times longer than wide. Not
pointed at the apex like in the acicular type.
According to the veins
Parallel veined
- The veins run at same distance to each other like in canes.

15. Pinnate
- There is main nerve (midrib) from which the other nerves
derived.
- Palmate
- The nerves diverge from the main point such as the fingers do
in the palm of the hand.

16. ARANGEMENT OF LEAVES ON A STEM
Alternate
- Springing one per node at different of the stem.
- Opposite
- Two per node, facing opposite sides of the stem.

17. Whorled
- Several leaves disposed at the same level around the stem.
- Rosulate
- Forming a rosette, like a ring around the stem.

18. DIVISION OF THE LAMINA
- Palmately compound leaves- have the leaflefts radiating
from the end of the petiole, like fingers of the palm of a hand
e.g. cannabis( hemp)
- Pinnately compaund Leaves- have the leaflets arranged a
long the main or mid veins
- Bipinnately compound leaves- twice divided, the leaflets are
arranged along a secondary vein that is one of several
branching of the rachis. Each leaflet is called a (pinnule)
- The pinnules on one secondary vein are called “pinna”. Eg.
Albizia(silk tree).
- Trifoliate- a pinnate leaf with just three leaflets e.g Trifolium (
clover)

19. - Pinnatifid, pinately dissected to the midrib, but with the
leaflets not entirely separate e.g sorbus ( whitebeams)
- Imparipinnate with single top leaflet.
- Paripinnate with a pair of top leafflet
- Base of the leaf
Acuminate- coming to a sharp,narrow,prolonged point.
Acute- coming to a sharp, but not prolonged point.
Auriculate- ear-shaped.
Cuneate- wedge-shaped
Hastate- shaped like an halberd and with the basal lobes
pointing outward.
Oblique: slanting
Sagittate: shaped like an arrowhead and with the acute basal
lobes pointing downward.

20. Trincate- appearing to teminate abruptly asifby cutting off.
Tips of leaf
-Acute- ending in sharp but not prolonged points.
- Cuspidate- With a sharp , elongated, rigid tip, tipped with ascp.
- Emarginated: Indented, with a shallow notch at the tip.
-Mucroate: A bruptly tipped with a small short pint s a
continuation of the midrib By tipped with a mucro.
- Mucronulate: mucronate, but with a smaller spine.
- Obcordate: rounded or blunt.
- Truncate- ending abruptly with a flat end, that looks act off.