Plant Transport

NT: 190 – 199

Bill Indge: 166-168

Structure of the Root

root meristem

root cap

root hairs

region of cell division (mitosis)

lengthening cells in this region pushes the root tip through the soil

zone of differentiation (maturation)

Root structure

Structure of a Plant Root

The passage of water through a plant (missing answers HB p11):

Root Xylem Stem Leaves Stomata pores Transpiration

See next slide to help you add water potential values to the diagram

What is the function of root hairs?

To absorb water and mineral ions.

How are root hairs adapted for their function?

Have a large Surface Area to Volume ratio, so more water and mineral ions can be absorbed at the same time.

Root hairs have a thinner cellulose cell wall which reduces the diffusion pathway.

Now do the following annotations 1-7 for the diag at top of p12 handbook :

Entry of water into the roots, up a plant and out of the leaves. 1. Water enters root hairs by osmosis as

the water potential of the cells in the root hairs is _______ negative than that of the soil.

more

Structure of a RootShowing one of the routes by which water and mineral salts may be drawn from the soil into the vascular tissue.

root hair

air space

soil particle

endodermis

xylem vessel

cortex (parenchyma)

2 possible pathways through which water may pass

i) Apoplast pathway through all cell walls

ii) Symplast pathway through cytoplasm and plasodesmata

plasmodesmata

There are 2 possible pathways through which water may pass:

(A) Symplast pathway: Water passes through cytoplasm and plasodesmata

(B) Apoplast pathway: Water passes through the cellulose cell walls

2. The passage of water through the cytoplasm is called the symplast pathway.

As water enters the cell it _______ the water potential of that cell so it becomes _____ negative than that of the next cell, so water passes from cell to cell down the water potential gradient into the root.

Water moves through the cytoplasm by ________

raises

less

osmosis

APOPLAST PATHWAY SYMPLAST PATHWAY

3. The passage of water through the cellulose cell walls of adjacent cells is called the apoplast pathway.

This occurs due to cohesion (attraction) forces between water molecules due to hydrogen bonding.

How does the water then enter the xylem vessels?

At the endodermis the casparian strip, a layer made of impermeable suberin molecules halts the apoplast pathway forcing water into the cytoplasm and thus the symplast route.

Mineral salts are actively transported by the Endodermal cells into the xylem vessels. This then encourages the entry of water into the xylem by osmosis.

4. Cohesion maintains a ‘chain’ of water molecules that moves up the xylem vessels of the root and stem (due to hydrogen bonding).

5. Water moves across leaf cells by osmosis and cohesion.

6. Heat energy causes water to evaporate from leaf cells into the air spaces of the leaf

7. Water moves out of the leaf by diffusion through the stomata. (transpiration)

See good transpiration animation link

http://www.biologymad.com/resources/transpiration.swf

 

Biology TestFirst lesson back after half term break

The Blood Circulatory System (mass flow) Blood Vessels Blood, Plasma, Tissue Fluid & Lymph. Plant Transport of Water Leaf Structure and Xerophytic Adaptations.

Check HW answers from p189 on p252 and check answers from p195 using pp252-253

Capillary Action

Some water can move up a short distance of a very narrow tube by capillary action. To explain this, learn notes about hydrogen bonding and cohesion tension forces, and also the forces of adhesion (ref HB p13)

Structure of a Plant Root

Xylem Vessels

Now complete the 2 paragraphs in your handbook p13 using the words below:

Root pressure:

Symplast, more, actively transported endodermal, xylem, osmosis, Casparian

Cohesion – tension :

Osmosis, evaporated, strong cohesion forces, more negative, inwards, hydrogen bonds, narrower, lignin, impermeable, mesophyll, more, strong

Missing words from middle of HB p13 in the correct order: Casparian Symplast Actively transported Endodermal Xylem More Osmosis

Missing words from the bottom of HB p13 in the correct order: Evaporated More Osmosis Osmosis More negative Strong cohesion forces Lignin Strong and impermeable Inwards Narrower

Loss of water from the leaf.

What is transpiration?

What is the Transpiration stream ?

Loss of water vapour by diffusion/evaporation from the open stomata pores of leaves.

The movement of water going into, up and through a whole plant, including the loss of water vapour by evaporation from the leaves of a plant.

StomataOpen

In the daylight-

There is the highest rate of transpiration

The guard cells swell up and bend, opening the stomata pore and water evaporates out, down the water potential gradient.

Do the tasks from the middle of HB p14, using AS Textbook p195 to help you.

Now complete the Application exercise on page 195 of your text book.

END.