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General Biology lab
Lab 14
The Leaves
• The Leaves
– are lateral outgrowth of the stem which develop from the
meristematic tissues .
• Functions of Plant Leaves
– Photosynthesis
– Transpiration
• The exit of water is through the stomata
– Food Storage
Dicotolydonous leaf (dicot.leaf)
• Epidermis:- there are some differences between upper and
lower epidermis.
– Stomata are more distribution in the lower epidermis than the upper
epidermis.
– Stomata are kidney shape.
– Have not bulliform cells.
• Mesophyll:– Palisade parenchymal cell are elongated cells located in many
leaves just below the epidermal tissue.
– Spongy parenchymal cells occur below the one or tow layers of
palisade cells.
• Vascular bundles:– large bundles enclosed in ground parenchyma of the thickened
vein ribs.
– Have not bundle sheath.
– Xylem in vascular bundles has arm shape.
• Venation in the leaf blade: net venation, meaning they
have one or a few prominent mid veins, form which
smaller minor veins branch into a meshed network.
Typical Dicot Leaf Cross-Section
Cuticle
Palisade
Parenchyma
Epidermis
Vascular
bundles
Guard
Cells
Spongy
Parenchyma
Stoma
Monocotyledonous leaves (monocot leaves)
• Epidermis: This typical of grasses.
– Stomata are equally distributed in upper and lower epidermis.
– Stomata are damples shape.
– Have buliform cells.
• Mesophyll: is homogenous and there are some difficult to
distinguished between palisade and spongy parenchyma.
• Vascular bundles:– there are more than one vascular bundles.
– Have bundle sheath.
• Venation in the leaf blade: parallel venation, meaning
several prominent and parallel veins interconnect with
smaller, inconspicuous veins.
Typical Monocot Leaf Cross-Section
Midvein
Vein
Bundle
sheath cell
Epidermis
Phloem
Xylem
Bulliform
Cells
Stoma
Leaves and Habitats
• Leaves vary much in both form and internal structure.
• They variations in plant structure that are commonly
related to the habitat and habit are particularly strongly
expressed in the structure of leaves.
• Therefore, the leaves in particular may be used to
characterize the (ecologic types) of plant, the mesophytes,
hydrophytes, and xerophytes.
• Hydrophytes
– Hydrophytes are plant that live in an abundance of water and thus
display few adaptations to reduce water loss in the leaves.
– These leaves display aerenchyma, a loosely- organized
parenchymatous tissue with wide intercellular spaces containing
air.
– The submerged aquatics are exemplified by the leaf of Elodea
• Xerophytes
– Zerophytc leaves are adapted to arid condition.
– Note the thick cuticle, epidermis and hypodermis on the upper and
lower surface of the leaf.
– Stoma are recessed deeply into the lower surface of the leaf with
numerous dermal hairs in the cavity surrounding the stomata.
• This reduces air flow across the stoma surface thus reducing water loose
from the leaf.
• Mesophytes
– Mesophytes represent the remainder of the plants, which
typically are found in areas in which water is available in the
soil most of the time and droughts are short in duration.
Photosynthesis
• Photosynthesis is one of the most fundamentally important
biological processes.
• All green plant can produce their own food simply by
using the energy in sunlight to convert carbon dioxide
(present in the surrounding air) into a carbohydrate.
6 CO2 + 6 H2O
Carbon dioxide
Water
C6H12O6 + 6 O2
Carbohydrate
Oxygen