Transcript Document

Leaf structure
By Martin Samaj
Leaf basics
• Above ground plant organ
specialized for
• Leaves are the site where
transpiration and guttation
takes place
• Leaves can store food and
water, in other plants they
can serve different
Leaf anatomy
• Leaf of an angiosperm consists of:
 Petiole (leaf stem)
 Lamina (leaf blade)
 Stipules
• Leaf consists of the following tissues:
 Epidermis
 Mesophyll
 Arrangement of veins
Leaf anatomy
• Outer layer of cells covering the leaf,
covered by a thick waxy cuticle
• It isolates the plant’s inner parts from the
• Serves several functions: regulation of
gas exchange, secretion of metabolic
compounds, prevents water loss from
the upper surface
• Palisade mesophyll consists of densely
packed cylindrical cells with many
• Palisade mesophyll is the main
photosynthetic tissue and is positioned
where the light intensity is the highest
• Spongy mesophyll consists of loosely
packed cells with few chloroplast
• This tissue provides the main gas
exchange surface
Leaves and transpiration
• Photosynthesis depends on gas exchange
over a moist surface.
• Spongy mesophyll cells provide this
• Water often evaporates from the surface
and is lost and this process is called
• Transpiration is the loss of water vapor
from the leaves and stems of plants
Factors affecting transpiration
• The rate of water loss through
transpiration depends on internal and
external conditions
• Abiotic factors that have effect on the rate
of transpiration
• There are 4 main factors: Light,
Temperature, Humidity and Wind
The 4 abiotic factors
• Light - gurad cells close the stomata in the night = greater
rate of transpiration
• Temperature - as the temperature rises the rate of
transpiration increases
• Humidity - The lower the humidity outside the leaf the faster
the rate of transpiration
• Wind - Wind blows the saturated air away and so increases
the rate of transpiration