transport of materials in flowering plants + trans location

Transport of Materials in Flowering Plants

Chapter 9

Please read pg 170 - 175

Learning Objectives

(a) Identify& explain functions of xylem & phloem vessels

(b) Relate the structure to functions of root hairs

(c) Explain movement of water between plant cells, and between plant and the environment (water potential)

(d) Outline the water transport pathway

(e) Define transpiration & explain how it occurs as a consequence of gaseous exchange

(f) Describe effects of varying air movement, temperature, humidity and light intensity on transpiration rate

(g) Describe how wilting occurs

(h) Define translocation as the transport of food in the phloem tissue and illustrate the process through translocation studies

(i) Apply the knowledge gained in this session.

INTRODUCTIONChapter 9

Q1.1 Why do plants need a transport system?

• To transport – Water and mineral salts from the

roots to the leaves– Dissolved food substances (sucrose,

amino acids) from leaves to other parts of the plant

Q1.2 How do plants transport food and water?

• System of vessels called transport tissue / vascular tissue

• Types of tissues in T/V tissue xylem and phloem

• Found in the roots, stem and leaves

A) WHERE ARE THE XYLEM & PHLOEM VESSELS LOCATED?

Chapter 9

HTTP://ACADEMIC.KELLOGG.EDU/HERBRANDSONC/BIO111/ANIMATIONS/0032.SWF

Xylem and Phloem

Q2. Where are the xylem and phloem located in a dicotyledonous plant stem? pg174

1) Epidermis

5) Cambium

3) Phloem

4) Xylem

2) Cortex

6) Pith

7) Vascular Bundle

Q3. Where are the xylem and phloem located in a dicotyledonous plant root?

6) Root hairs1)Epidermis

2) Cortex

3) Phloem

4) Xylem

5) Cambium

A) HOW DO XYLEM & PHLOEM VESSELS LOOK LIKE?

Chapter 9

collenchyma

phloemxylemvascular bundle

pith

cortex

epidermis Cambium

Q4. What is the xylem made up of?

• Consists of dead, long, hollow fine tube-like vessels

• Thick lignified cellulose walls

Q5. What is the phloem made up of?

• Made up of living cells

• Consists of sieve tubes and companion cells

Q6. Where are the xylem and phloem located in a dicotyledonous plant leaf?

1) Phloem 2) Leaf blade

4) Xylem

3) Midrib

A) WHAT ARE THE FUNCTIONS OF THE XYLEM & PHLOEM VESSELS?

Chapter 9

Q7. What are the 2 functions of the xylem?

• Transports water and dissolved mineral salts

• From roots, through the stem and to the leaves

• Unidirectional flow of substances

• Provides mechanical support for plants

Q8. What is the function of the phloem?

• Conducts manufactured food (sucrose and amino acids)

• From leaves to all parts of plant

• Two-directional flow of substances

Sieve plate

Companion cell

Sieve plate

sieve tube

Q9. What is the purpose of the companion cell?

Companion cells contain mitochondria which provides energy for loading sugar from mesophyll to sieve tubes by active transport.

Sieve plates with holes for rapid flow of substances

Q10. What are the adaptations of the various plant structures?

Structure Features Function

Xylem -Empty lumen

-thickened with lignin

•Reduce water flow resistance•Mechanical support

Phloem -Companion cells-Sieve plates

•Active transport of sugars•Rapid flow of substances

Q. WHAT ARE THE FUNCTIONS OF THE THE OTHER REGIONS

Chapter 9

Q11. What is the function of the …..?

• Epidermis– Maintains the shape and protects

against bacterial or fungal infection

• Cambium– Cambium cells undergo mitotic

divisions to produce new cells for growth

TRANSPORT MECHANISMS IN FLOWERING PLANTS

Chapter 9

Q12. What are the mechanisms involved in the movement of water and mineral salts in a plant?

6) Transpiration pull 5) Root pressure 4) Capillary action

7) Transpiration

1) Osmosis 2) Active transport 3) Diffusion

C. MOVEMENT OF WATERChapter 9

C) Movement of water and mineral salts from soil into root hair cell

Q13. How is the root hair cell adapted for uptake of water?

• Long and narrow projections– Increase surface area for water

uptake

• Cell surface membrane– Prevents cell sap from leaking out

• Cell sap in vacuole

B) What are the adaptations of the root hair cell? Pg 180

Structure Features Function

Root hair cells(which makes up the piliferous layer)

-tubular-elongated & narrow(Increase surface area: volume ratio) -cell surface membrane

Maximum absorption of water and mineral salts

Q14. How do plants overcome gravity in the transport of materials up the stem?

• Root pressure / Guttation

• Capillary action / Capillarity

• Transpiration pull / stream

Learning Objectives










D. DETAILS OF WATER TRANSPORT PATHWAY

Chapter 9

D. Q15. What is root pressure?

• Pressure of water exerted in the xylem vessel

Q 16. What causes root pressure?

• Mineral ions are actively transported to the xylem

• Decrease in water potential in the xylem vessel

• Thus more water is drawn into the xylem vessel

• Water pressure in the root rises

• Root pressure pushes water and dissolved mineral ions up the xylem

Properties of water

Adhesion of the water for the glass allows the water to move up the wall of the cylinder just a little above the level of the water in the center of the cylinder

Cohesion of water molecules cause the gradual curve observed

• The water is adhering to the beads, but cohesion keeps a strand of water between the beads. As the gap widens, the strand of water gets narrower until it eventually breaks because cohesion of the water is not strong enough to pull the water together over wide distances

• This is essentially why water moves up farther into smaller capillary tubes. There is less mass of water in a small capillary and the cohesion of water can hold a longer water column

Q 17. What is capillary action?

• Strong cohesive force between water molecules in a fine xylem vessel

• Strong adhesion of water to the xylem vessel walls

• Allows a thin column of water to be pulled up without breaking

H

O Column of water molecules H

H H

H H O O

Q 18. What is transpiration pull?

• A suction force exerted as a result of transpiration

• Causes a long, thin and continuous column of water to be pulled from the roots to the top of a tallest tree

Learning Objectives










E. TRANSPIRATIONChapter 9

Q 19. What is transpiration?

• Loss of water vapour from the aerial parts of a plant, especially through the stomata of the leaves

Q 20. Why is transpiration important?

Facilitates the lifting of water and mineral salts from roots to leaves

Cool the plant; prevent scorching

How do leaves control the rate of transpiration?– Cuticle – Stomata

F. FACTORS AFFECTING TRANSPIRATION

Chapter 9

Q 21. What is a potometer?

• An instrument used to measure the rate of transpiration under different experimental conditions

Assumption

Rate of water lost to surroundings = Rate of water absorbed

Air bubble

Q 22. Think about this

• Which condition would result in the higher rate of transpiration: light or dark?


• Which condition would result in the higher rate of transpiration: humid environment or dry environment?


• Which condition would result in the higher rate of transpiration: breezy conditions or still air?


• Which condition would result in the higher rate of transpiration:hot environment or warm environment?


• How do plants that live in very dry and hot habitats minimise water loss?

Q 27. What are the factors that affect transpiration?

• Temperature

• Humidity

• Light intensity

• Wind

• Structure and surface area of leaf

• Size of stomata pore

G. HOW DOES WILTING OCCUR?Chapter 9

Q 28. What do you think has happened to the plants below?

Q 29. What is wilting?

• When rate of water loss from the leaves exceeds the rate of water replacement, leaf cells lose turgor

• Cells become flaccid and plant wilts

Transpiration Definition

Importance

Factors that affect transpiration

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Transpiration

Importance

has

Factors

affected by

Light

Humidity of air

Wind or air movement

Temperatu-re of air

Wilting

in excess causes

Advantages

• When the leaf folds up, the surface area that is exposed to sunlight is reduced, causing the guard cells to become flaccid.

• The stomata close and the rate of transpiration is decreased.

Disadvantages

•Amount of carbon dioxide entering is reduced. Carbon dioxide becomes a limiting factor, rate of photosynthesis.

•The rate of photosynthesis is also reduced because water becomes a limiting factor.

• Transpiration pull draws water & mineral salts from roots to the stems & leaves.

• Evaporation of water from the cells in the leaves removes latent heat of vaporization and cools the plant.

•Water transported to the leaves can be used to:

- in the photosynthesis; - to keep cells turgid- to replace water lost by the cellTurgid cells keep the leaves spread out widely to trap sunlight for photosynthesis.

H. TRANSLOCATION & INVESTIGATION STUDIES

Chapter 9

Q30. What is Translocation?

• The transport of manufactured food substances such as sugar and amino acids in plants.

Aphids ‘Ringing’ Isotopes

• Aphids feed on plant juices

• Proboscis (long mouth par) of aphid penetrated leaf or stem.

• Aphid is anaesthetised while feeding, body cut off leaving the proboscis in plant tissues.

• Liquid exuded from the cut end of proboscis is then analyzed.

• 3 twigs are used.

• Complete ring of bark is removed (phloem and cambium parts) from main stem of 2 twigs only leaving the xylem exposed at different position of the stem.

• The exposed region of the first twig is submerged in water while the other is above the water level.

• The third twig which is unringed acts as a control.

• The setup is then observed daily for occurrences of roots/swellings for the next few days.

• Carbon-14 (14C) radio active isotope can be detected by X-ray.

• A leaf is provided with radioactive carbon dioxide (14CO2)

• The plant is allowed to photosynthesize. The Carbon-14 isotope would be incorporated in the sugars formed.

• After a few days, the stem/leaf is cut and a section of it exposed onto an X-ray photographic film to observe for presence of radioactive substances.

Translocation Studies:

Learning Objectives










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64

3. Water flows across cortex down a water potential gradient across root section.

1. Phloem translocates sucrose and amino acids from leaves to other parts of the plant, including the roots.

2. The sap in the root hair cell has lower water potential than the soil solution.Water enters the root hair by osmosis and dissolved mineral salts by active transport.

4. Xylem conducts water and mineral salts upwards, from roots to leaves.

Thick lignified walls prevent collapse of xylem vessels.

5. In the leaves, Water movement by osmosis to the cells adjacent to air spaces.

Water evaporates from surface of mesophyll cells into the intercellular air space.

3

6. Water vapour diffuses out of leaf through stomata i.e.

Transpiration

Key:

path of

water

path of

water vapour

Transport of Materials in Flowering Plants

April 10, 2023Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 65

Section of Leaf

Section of Root

phloem

Phloem translocates sucrose and amino acids from leaves to other parts of the plant, including the roots.


Section of Leaf

Section of Root

Key:

path of water

The sap in the root hair cell has lower water potential than the soil solution. Water enters the root hair by osmosis and dissolved mineral salts by active transport.

phloem



Section of Leaf

Section of Root

Water flows across cortex down a water potential gradient.

Key:

path of water


phloem



Section of Leaf

Section of Root

Xylem conducts water and mineral salts upwards, from roots to leaves.


xylem vessels


Key:

path of water


phloem



Section of Leaf

Section of Root

water movement by osmosis

intercellular air space

Water evaporates from surface of mesophyll cells into the intercellular air space.Xylem conducts

water and mineral salts upwards, from roots to leaves.


xylem vessels


Key:

path of water


phloem



Section of Leaf

Section of Root






xylem vessels


Key:

path of water


phloem


Water vapour diffuses out of leaf through stomata

stoma


Section of Leaf

Section of Root






xylem vessels


Key:

path of water


phloem


Water vapour diffuses out of leaf through stomata

stoma

Transpiration

cools the plant

creates transpirational pull

excessive transpiration causes wilting

transport of materials in flowering plants + trans location

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