
Homework:
 Work on PS 11 (#1, 6, 7)

Do Now:
 Take out the Photosynthesis Reading Worksheet
 Get back and look over your quiz

Goals for Today:
 Describe a structural adaptation and a symbiosis that helps
plants’ roots execute their functions
 Explain how root anatomy enables plants to selectively
uptake water and nutrients

Agenda:
 Lecture: Plant Anatomy & Root Adaptations
MAJOR PARTS OF A PLANT:
Leaves:
• Make sugar through
photosynthesis
• Release water through
transpiration
Stem:
• Transports water upwards
• Transports sugars wherever
needed
• Supports/positions leaves
Roots:
• Absorb water and nutrients
(N, P, K)
• Store sugars
• Anchor the plant in the soil
How do roots absorb water & nutrients?
• Structural adaptations
– High surface area
• Branching structure
• Root hairs
– Symbioses
• Mycorrizal fungi – increase surface area for water and
mineral absorption
• Rhizobium bacteria – fix nitrogen (N2) and convert it
into a form that plants can use
Fungal root symbionts: Mycorrhizae
Mycorrhizae
Root nodules on legumes:
formed by Rhizobium bacteria
Example: clover roots
How do roots absorb water & nutrients?
• Structural adaptations
– High surface area
• Branching structure
• Root hairs
– Symbioses
• Mycorrizal fungi – increase surface area for water and
mineral absorption
• Rhizobium bacteria – fix nitrogen (N2) and convert it
into a form that plants can use
Cross section of a root:
How do water and nutrients
enter
roots?
(First, watch the animation…)
1. Water moves through the root via two routes:
• Symplastic route – Through the cytoplasm &
plasmodesmata, after diffusing across the plasma
membrane of epidermal cells
• Apoplastic route – Along cell walls without entering cells
How do water and nutrients
enter roots?
(First, watch the animation…)
1. Water moves through the root via two routes:
• Symplastic route – Through the cytoplasm & plasmodesmata,
after diffusing across the plasma membrane of epidermal cells
• Apoplastic route – Along cell walls without entering cells
2. At the endodermis, the Casparian strip (waxy belt
around endodermal cells) forces water and solutes
into the cell
• Endodermal plasma membrane selects which minerals/nutrients
enter
• Thereby controlling what enters the xylem
3. Once inside endodermal cells, water & select
solutes flow into xylem cells

Homework:
 Work on PS 11 (#2)

Do Now:
 Read the article about trees.
 On the back, respond to the following :
 Summarize the mechanism that pulls water up through plants
and trees
 What do you remember about water potential? How do you
think it relates to water transport in plants?

Goals for Today:
 Explain how plants rely on passive mechanisms to transport water
from roots to leaves
 Design an experiment to measure rates of transpiration in different
plants and conditions
Water Flow into Roots
•
•
•
Driven by osmosis (sometimes following active
transport of minerals into roots)
Due to differences in ψ (water potential)
Quick review: What’s water potential?
– Tendency of water to leave an area and go somewhere
else
– Determined by
•
•
•
•
Pressure
Solute Concentration
If soil is too dry (ψsoil lower than
ψroot cells), water won’t enter roots
Result: wilted plant
How do plants transport water up
through the xylem?
• Xylem structure
– Long cells (tracheids & vessel elements) are dead
and hollow – just cell walls
– Cells connected at ends by holes/perforations for
water flow
Low WP
1. Transpiration
creates low WP in
leaf air spaces
2. Water from
veins moves into
leaves
4. Water from soil
flows in to replace
water pulled
upwards by TACT
High WP
3. Water in
veins is
connected by
H-bonds all
the way
down
through the
xylem.
Adhesion &
cohesion
create a pull
on the water
below.
How do plants transport water up
through the xylem?
• Transpiration-Adhesion-Cohesion-Tension
Mechanism (TACT)
– Transpiration pulls water out of leaves
– Water molecules in leaves stick to water molecules all
the way down the xylem (cohesion)
• Adhesion to cell walls also helps
– This creates negative pressure (tension) on the water
column in the xylem
A completely passive way to transport water, driven
by solar energy (powers transpiration) and
hydrogen bonds!

Goals for Today:
 Explain how plants rely on passive mechanisms to
transport water from roots to leaves
 Design an experiment to measure rates of transpiration
in different plants and conditions
1.
2.
3.
4.
5.
6.
7.
Take the plant out of the pot with the roots
and some soil.
Cover the roots/soil with a bag and seal it at
the top with a twist-tie.
Measure the initial mass.
Put it in the conditions you’re testing.
Later, measure the mass again (record time
between masses).
Calculate % change.
Divide by leaf surface area.
Follow the directions on page 6.

Homework:
 PS 11 due Monday! You will need to research a few questions on your
own.

Do Now:
 Sit with your lab group
 Decide which experiment treatment you want to do!

Goals for Today:
 Set up an experiment to measure rates of transpiration
 Explain how plants transport sugars through xylem

Agenda:
 Lab groups set up experiments & record initial masses
 Lecture on sugar transport
 Record masses @ end of class
Sugar Transport
• Phloem
– Cells are alive at functional maturity
– Two cell types:
• Sieve tube elements
– Contain only cytoplasm (no nuclei or other organelles)
– Connected end to end with sieve holes
• Companion cells
– Contain the nucleus and organelles to support themselves
AND the sieve tube cells
How do plants transport sugar from
source to sink?
• Sugar source – makes or releases sugars
– Photosynthesizing leaves
– Storage organs that are breaking down/releasing
sugar
• Sugar sink – absorbs and uses or stores sugars
– Actively growing parts
– Storage organs that are storing sugar (roots, fruits)
Xylem
Phloem
H2O
Sucrose
H2O
Pulled up by TACT mechanism
Bulk flow due to positive pressure
H2 O
SOURCE:
1. Sucrose pumped into phloem by
active transport.
Water follows by osmosis.
2. Positive pressure builds up in phloem near
sugar source.
Forces sugar-water to flow away from
source, towards sink.
(Pressure-flow mechanism)
SINK:
3. Sucrose unloaded into sink by
active transport.
Water diffuses back into xylem to
Sucrose
be recycled.