Plants
Form and Function
Parts of a Leaf
What do these parts do?

Cuticle (waxy layer) and Upper Epidermis


Palisade Mesophyll


Prevent Water Loss
Cells contain lots of chloroplasts: absorption of
light for photosynthesis
Vascular Bundles

Transport water to the leaf (xylem) and starch
away (phloem)
What leaf parts do, con’t
 Spongy

Loosely packed, surfaces for gas exchange
 Lower

Mesophyll
Epidermis and Guard Cells
Guard cells open and close, controlling
water loss by transpiration and allowing for
gas exchange
The Xylem
Phloem
Xylem
The Xylem
 Mainly
carry water and dissolved minerals
from roots to leaves
 Woody
plants- they provide support for
the plant
The Phloem
 Transports
the plant.
 Carries
organic nutrients throughout
starches away from plant.
Root Picture of Xylem and
Phloem
Phloem
Xylem
Transpiration

Transpiration is the loss of water from leaves
and stems of plants

This loss of water causes a “pull” on the rest of
the water in the plant, causing water from the
roots of the plant to continue moving upward.

This is caused by the cohesion between water
molecules
Transpiration Pull
 Upward
movement through xylem
generates a transpiration pull
 Cohesion
between water molecules
allows water to by ‘sucked up’
Transpiration flow is controlled
by the rate of water loss
through the stomata
Closed Stoma
 CO2
uptake is LOW
 Water
loss is LOW
Stomata closing caused by:
 Water
shortage: forced closure to prevent
dehydration
 Darkness
Open Stoma
 CO2
uptake is high
 Water
loss is high
Stomata opening caused by:
 Sunlight/high
 Reduced
photosynthesis
CO2 concentration
What affects rate of
transpiration?

Wind


Temperature


Increasing Temperature causes greater transpiration
because more water evaporates
Light


Increases the rate of transpiration because humid air
near the stomata is carried away
Speeds up transpiration by warming the leaf and
opening stomata
Humidity

Decreasing humidity increases transpiration because of
the greater difference in water concentration
Photosynthesis
 Generates
a chemical storage of energy
in the form of carbohydrates.
 Converts
light energy to chemical energy
 Photosynthetic
autotrophs.
organisms are examples of
Photosynthesis Equation