Leaf Modifications and Transport

Question 1

Specialized Leaves

Answer 1

• Tendrils
• Spines
• Water storage
• Bracts
• Insect trapping
• Flower pot leaves
• Reproductive Leaves

Question 2

Tendrils

Answer 2

Modified leaves for climbing or support
e.g. Pea

Question 3

Spines

Answer 3

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

Question 4

An Aside:

Answer 4

Thorns, Spines, Prickles

Question 5

Thorns are modified

Answer 5

stems (arise in leaf axils)

Question 6

Spines are modified

Answer 6

leaves (have buds at base)

Question 7

Prickles are

Answer 7

outgrowths of epidermis or cortex

Question 8

Water storage:

Answer 8

Have parenchyma cells with large vacuoles
e.g. Succulent Leaves of Jade Plant

Question 9

4. Bract:

Answer 9

A modified leaf at the base of a flower or flowers

Question 10

5. Insect Trapping Leaves e.g.

Answer 10

-Venus Fly Traps
-Pitcher Plant with downward
sloping hairs
-Sundew with sticky
glandular trichomes

Question 11

6. Flower-Pot Leaves

Answer 11

• 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

Question 12

8. Reproductive Leaves e.g.

Answer 12

e.g. Mother of Thousands

Question 13

Water moves
– through and around

Answer 13

the
cell walls of the epidermis,
root hairs, and cortex, until
it reaches the endodermis.

Question 14

Water moves across the

Answer 14

cell membranes
of the endodermal cells to
reach the xylem.

Question 15

Water moves upwards through

Answer 15

the plant
via the xylem and diffuses
out through stomates

Question 16

Cohesion Tension Theory of Water
and Mineral Transport in the Xylem

No

Answer 16

energy is required from the plant. The
driving force is the evaporation of water
through the stomates. Water is pulled out
through the stomates.

Question 17

Pulling force =

Answer 17

evapotranspiration

Question 18

Cohesion Tension Theory of Water
and Mineral Transport in the Xylem

Water molecules are very

Answer 18

cohesive (hard to
pull apart).

Question 19

Cohesion

Answer 19

attraction between
like molecules. Water is very cohesive due to
hydrogen bonds.

Question 20

Water is polar because

Answer 20

– Electrons more attracted to
the electronegative oxygen
– Partial positive charge
associated with hydrogens
– Partial negative charge
associated with the oxygen

Question 21

bonds formed between water molceules

Answer 21

hydrogen bonds

Question 22

Cohesion Tension Theory of Water
and Mineral Transport in the
Xylem

C. Water tends to

Answer 22

adhere to the walls in a capillary
tube

e.g. vessels and tracheids

Question 23

capillarity

Answer 23

Water tends to adhere to the walls in a capillary
tube

Question 24

vessels and tracheids =

Answer 24

capillary tubes

Question 25

Attraction between unlike things

Answer 25

adhesion

Question 26

Water Movement Through the Plant

Answer 26

-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.

Question 27

Transpiration

Answer 27

Water
vapor loss from the leaf

Question 28

Regulation of Transpiration

Answer 28

• Stomates regulate transpiration and gas exchange.
  – Stomate = 2 guard cells + stoma (opening).
  – Transpiration rates influenced by humidity, light,
  temperature, and carbon dioxide concentration.

Question 29

2. Flow in the Phloem

Answer 29

• 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

Question 30

Use of Aphids to

Answer 30

Study What is
Transported in the Phloem

Question 31

how using aphids can help find out what is transported in the phloem

Answer 31

• 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