Leaf Modifications and Transport Flashcards
Specialized Leaves
- Tendrils
- Spines
- Water storage
- Bracts
- Insect trapping
- Flower pot leaves
- Reproductive Leaves
Tendrils
Modified leaves for climbing or support
e.g. Pea
Spines
Modified leaves that reduce water loss, and
protect from herbivory.
e.g Cacti: Leaves replaced with sclerenchyma containing
spines (Cacti can have irritating hairs as well).
e.g. Barberry Spines
An Aside:
Thorns, Spines, Prickles
Thorns are modified
stems (arise in leaf axils)
Spines are modified
leaves (have buds at base)
Prickles are
outgrowths of epidermis or cortex
Water storage:
Have parenchyma cells with large vacuoles
e.g. Succulent Leaves of Jade Plant
- Bract:
A modified leaf at the base of a flower or flowers
- Insect Trapping Leaves e.g.
-Venus Fly Traps
-Pitcher Plant with downward
sloping hairs
-Sundew with sticky
glandular trichomes
- Flower-Pot Leaves
- Leaves develop into urn-like
pouches that become homes for
ant colonies. - Ants carry in soil and add
nitrogenous wastes that provide
a good growing medium for the
plant’s own roots, and the ants
also protect the plants
– Dischidia rafflesiana, an
epiphyte found in Australia
- Reproductive Leaves e.g.
e.g. Mother of Thousands
Water moves
– through and around
the
cell walls of the epidermis,
root hairs, and cortex, until
it reaches the endodermis.
Water moves across the
cell membranes
of the endodermal cells to
reach the xylem.
Water moves upwards through
the plant
via the xylem and diffuses
out through stomates
Cohesion Tension Theory of Water
and Mineral Transport in the Xylem
No
energy is required from the plant. The
driving force is the evaporation of water
through the stomates. Water is pulled out
through the stomates.
Pulling force =
evapotranspiration
Cohesion Tension Theory of Water
and Mineral Transport in the Xylem
Water molecules are very
cohesive (hard to
pull apart).
Cohesion
attraction between
like molecules. Water is very cohesive due to
hydrogen bonds.
Water is polar because
– Electrons more attracted to
the electronegative oxygen
– Partial positive charge
associated with hydrogens
– Partial negative charge
associated with the oxygen
bonds formed between water molceules
hydrogen bonds
Cohesion Tension Theory of Water
and Mineral Transport in the
Xylem
C. Water tends to
adhere to the walls in a capillary
tube
e.g. vessels and tracheids
capillarity
Water tends to adhere to the walls in a capillary
tube
vessels and tracheids =
capillary tubes
Attraction between unlike things
adhesion
Water Movement Through the Plant
-transperation
– More than 90% of
the water entering a
plant is transpired.
– Can be demonstrated
by covering the soil
of a potted plant,
then covering the
plant with a bell jar.
Transpiration
Water
vapor loss from the leaf
Regulation of Transpiration
- Stomates regulate transpiration and gas exchange.
– Stomate = 2 guard cells + stoma (opening).
– Transpiration rates influenced by humidity, light,
temperature, and carbon dioxide concentration.
- Flow in the Phloem
- Pressure-Flow Hypothesis or Mass-Flow Hypothesis
- Transport up and down
- Transport through sieve tube elements
- Transport within the phloem requires energy (ATP)
- Transport is from a source of carbohydrate to a
sink for carbohydrate.
– Source-sink relationships determine the direction of
transport - Sucrose is the transport form of carbohydrate
- Sucrose is loaded into the phloem at the source
– Special carriers are involved - Sucrose is unloaded at the sink
Use of Aphids to
Study What is
Transported in the Phloem
how using aphids can help find out what is transported in the phloem
- Contents of phloem
studied by using aphids
that insert stylets
(mouthparts) directly
into phloem - Remove the body of
the aphid and leave the
stylet that acts like a
straw
