1. Botany: Part III
Plant Nutrition

2. Water and minerals in the soil are absorbed by the roots.
Figure
Plant Nutrition and
Transport
H2O
Water and minerals in the soil are absorbed by the roots.
Transpiration, the loss of water from leaves (mostly through stomata), creates a force within leaves that pulls xylem sap upward.
What force is “pushing” water up the plant against gravity? (root pressure)
However, transpirational “pull” is the most important factor in moving water through plants, as discussed in the following slides.
Water moves from areas of high water potential to low water potential. Water potential includes the combined effects of solute concentration and physical pressure.
Roots absorb water and minerals from the soil. Most water absorption occurs near the root tips through the root hairs. The roots of many types of plants have symbiotic relationships with fungi. This mutualistic relationship is called mycorrhizae, and leads to the absorption and transport of water and certain minerals into the plant. Once in the root xylem, water and minerals are transported long distances – to the rest of the plant– by bulk flow. Transpiration is the loss of water vapor from the leaves and other parts of the plant that are in contact with air and plays a key role in the movement of water up from the roots via water’s cohesive forces.
H2O and minerals

3. Getting Water Into The Xylem Of The Root
Emphasize that water enters the xylem through different pathways, as shown in the image above. The details of these pathways nor their names (Symplast and Apoplast) are on the AP exam, so cover these in general terms. Emphasize that water moves up the plant via the xylem.
Important: All of the water movement is due to gradients in water potential. The water potential inside the root hair should have a more negative number (such as −0.6 mPa in the root and −0.3 mPa) Note that water potential is measured in MPa, megapascals.
If you wish to cover the pathways in a little more detail:
Symplastic movement- water movement simply through the cytosol or cytoplasm.
Apoplastic movement-water movement around the cell walls.
The Casparian strip is a band of cell wall material deposited on the radial and transverse walls of the endodermis, which is chemically different from the rest of the cell wall. It is used to block the passive flow of materials, such as water and solutes into the stele of a plant.
Endodermis means “inner skin” that regulates what enters the xylem and phloem or stele. The stele is the column of cells found inside the endodermis.

4. Generation of Transpirational Pull
In addition to apoplastic and symplastic movement, there are newly discovered channels called aquaporins that allow only water to move across the membrane. Water movement through aquaporins is quicker since no lipids are involved.
Aquaporins were discovered by Peter Agre in 1992 as he was  studying the Rh blood group antigen. He won the Nobel prize for its discovery in Aquaporins are found in plant and animals cells such as the collecting ducts of the kidney.

5. Movement of Minerals Into The Root
Plants need minerals to synthesize organic compounds such as amino acids, proteins and lipids.
Plants obtain these minerals from the soil and are transported by various transport proteins.
Explain the three types of transport proteins. Point out that plants require large amounts of nitrogen, potassium and phosphate and that these minerals are contained in fertilizers. Most minerals combine with water to form xylem sap.

6. Macro- and Micro- Nutrients
Macronutrients are required by plants in relatively large amounts and compose much of the plant’s structure. (C, N, O, P, S, H, K, Ca, Mg, Si, etc. ) Micronutrients are needed in very small quantities. Typically function as cofactors.
These nutrients are essential for proper growth and function of plants. Ask students which macronutrients are obtained from the air. (C, H, and O). There are about eleven nutrients essential to plant growth and health that are only needed in very small quantities. The micronutrients are manganese, boron, copper, iron, chlorine, sodium, molybdenum, nickel, cobalt, aluminum and zinc. Though these are present in only small quantities, they are all indeed necessary.

7. Mycorrhizae: A Mutualistic Relationship
Roots
Ask the students what “mutual” means. (Both parties benefit from the relationship.) The fungus benefits from a steady supply of sugar donated by the host plant. In return, the fungus benefits the plant by increasing the amount surface area for water uptake, selectively absorbs minerals that are taken up by the plant, and secreting substances that stimulate root growth and provides antibiotics that protect the plant from invading bacteria.
Fungus

8. Gas exchange occurs through the stomata.
Figure
CO2 O2
H2O
Gas exchange occurs through the stomata.
CO2 is required for photosynthesis and O2 is released into the atmosphere.
Roots exchange gases with the air spaces in the soil, taking in O2 and releasing CO2.
Through stomata, leaves take in CO2 and release O2.
Roots exchange gases with the air spaces of soil, taking in O2 and releasing CO2.
H2O and minerals O2
CO2

9. Sugars are produced by photosynthesis in the leaves.
Figure
CO2 O2
Light
Sugar
H2O
Sugars are produced by photosynthesis in the leaves.
Phloem sap(green arrows) can flow both ways.
Xylem sap(blue arrows) transport water and minerals upward from roots to shoots.
This comprehensive diagram gives an overview of plant nutrient acquisition and transport. O2
H2O and minerals
CO2

10. Water Is In The Root, So Now What?
Root pressure is caused by active distribution of mineral nutrient ions into the root xylem.
Without transpiration to carry the ions up the stem, they accumulate in the root xylem and lower the water potential.
At night in some plants, root pressure causes guttation or exudation of drops of xylem sap from the tips or edges of leaves as pictured here.
Root pressure is osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves.
Root pressure occurs in the xylem of some vascular plants when the soil moisture level is high either at night or when transpiration is low during the day. When transpiration is high, xylem sap is usually under tension, rather than under pressure, due to transpirational pull.

11. Water Is In The Root, So Now What?
Water then diffuses from the soil into the root xylem due to osmosis.
Root pressure is caused by this accumulation of water in the xylem pushing on the rigid cells.
Root pressure provides a force, which pushes water up the stem, but it is not enough to account for the movement of water to leaves at the top of the tallest trees.

12. Let’s Apply Some TACT To The Situation!
A more likely scenario involves the Cohesion-Tension Theory (also known as Tension-Adhesion-Cohesion-Transpiration or TACT Theory)
Tension: Water is a polar molecule.
When two water molecules approach one another they form an intermolecular attraction called a hydrogen bond.
This attractive force, along with other intermolecular forces, is one of the principal factors responsible for the occurrence of surface tension in liquid water.
It also allows plants to draw water from the root through the xylem to the leaf.
It is essential that students do a transpiration lab. The cohesion-tension theory is a theory of intermolecular attraction commonly observed in the process of water traveling upwards (against the force of gravity) through the xylem of plants which was put forward by John Joly and Henry Horatio Dixon.
Make the distinction between the intermolecular force known as a “hydrogen bond” (occurs between neighboring water molecules) and a “bonded hydrogen” (occurs within a single water molecule as a result of sharing a pair of electrons) .

13. Let’s Apply Some TACT To The Situation!
Adhesion occurs when water forms hydrogen bonds with xylem cell walls.
Cohesion occurs when water molecules hydrogen bond with each other.

14. Let’s Apply Some TACT To The Situation!
Transpiration: Water is constantly lost by transpiration in the leaf.
When one water molecule is lost another is pulled along by the processes of cohesion and adhesion.
Transpiration pull, utilizing capillary action and the inherent surface tension of water, is the primary mechanism of water movement in plants.
Emphasize that transpiration is not the only mechanism involved. Any use of water in leaves forces water to move into them. Transpiration in leaves creates tension (differential pressure) in the mesophyll cells. Because of this tension, water is literally being pulled up from the roots into the leaves, helped by cohesion (the pull between individual water molecules, due to hydrogen bonds) and adhesion (the stickiness between water molecules and the hydrophilic cell walls of plants, again by hydrogen bonds). This mechanism of water flow works because of water potential (water flows from high to low potential), and the rules of simple diffusion.

15. Generation of Transpiration Pull
Negative pressure (tension) at the air-water interface in the leaf is the basis of transpiration pull, which draws water out of the xylem.
Explain the diagram using the following key:
In transpiration, water vapor (shown as blue dots) diffuses from the moist air spaces of the leaf to the drier air outside via stomata.
At first, the water vapor lost by transpiration is replaced by evaporation from the water film that coats mesophyll cells.
The evaporation of the water film causes the air-water interface to retreat farther into the cell wall and to become more curved. This curvature increases the surface tension and the rate of transpiration.
The increased surface tension shown in step 3 pulls water from the surrounding cells and air spaces.
Water from the xylem is pulled into the surrounding cells and air spaces to replace the water that was lost.

16. Ode To The Hydrogen Bond
This may be an oversimplification, but this graphic does a nice job of summarizing the process in simple terms while emphasizing the importance of the intermolecular force we call hydrogen bonding and the properties of water.

17. Water Potential
Water potential quantifies the tendency of free (not bound to solutes) water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects such as surface tension.
Water potential has proved especially useful in understanding water movement within plants, animals, and soil.
Water potential is typically expressed in potential energy per unit volume and very often is represented by the Greek letter psi,  . (pronounced as “sigh” )
Water potential is the physical property that predicts the direction in which water will flow. The unit for water potential is the megapascal (MPa). By definition the  of pure water in a container open to the atmosphere under standard conditions (25C and 1 atm pressure) is 0 MPa.
One MPa is equal to about 10 times atmospheric pressure at sea level. The internal pressure of a living plant cell due to the osmotic uptake of water is about 0.5 MPa or about twice the air pressure inside an inflated car tire.

18. Water Potential
The addition of solutes to water lowers the water's potential (makes it more negative), just as the increase in pressure increases its potential (makes it more positive).
Pure water is usually defined as having an osmotic potential () of zero, and in this case, solute potential can never be positive.
Free water moves from regions of higher water potential to regions of lower water potential if there is no barrier to its flow.
Emphasize that the word “potential” refers to water’s potential energy which is water’s capacity to perform work when it moves from a region of higher water potential to a region of lower water potential.  = S + P where  is the water potential, S is the solute potential (directly proportional to its molarity and sometimes called the osmotic potential and the S of pure water is zero) and P is the pressure potential.
So, why do we have this annoying negative sign convention in the first place? Because adding a solute to water interferes with the intermolecular forces water molecules have for each other (hydrogen bonding being the most famous). If something dissolves in water, it is because water is more attracted to the solute particle than to neighboring water molecules, so the water molecules are less likely to “move”, thus their potential to do work is decreased hence the negative sign slapped upon the numbers!

19. Water Potential
The word “potential” refers to water’s potential energy which is water’s capacity to perform work when it moves from a region of higher water potential to a region of lower water potential.
The water potential equation is  = S + P where  is the water potential, S is the solute potential (directly proportional to its molarity and sometimes called the osmotic potential and the S of pure water is zero) and P is the pressure potential.
Emphasize that the cell contents press against the cell wall producing turgor pressure. Ask students what happens if a plant loses turgor pressure. (It wilts)

20. Water Potential P is the physical pressure exerted on a solution.
It can be either positive or negative relative to the atmospheric pressure.
Water in a nonliving hollow xylem cells is under a negative potential (tension) of less than −2 MPa.
BUT the water in a living cell is usually under positive pressure due to the osmotic uptake of water.
Emphasize that the word “potential” refers to water’s potential energy which is water’s capacity to perform work when it moves from a region of higher water potential to a region of lower water potential.  = S + P where  is the water potential, S is the solute potential (directly proportional to its molarity and sometimes called the osmotic potential and the S of pure water is zero) and P is the pressure potential.

21.  Solutes have a negative effect on  by binding water molecules.
Pure water at equilibrium
H2O
Adding solutes to the right arm makes  lower there, resulting in net movement of water to the right arm:
Pure water
Membrane
Solutes
Positive pressure has a positive effect on  by pushing water.
Positive pressure
Applying positive pressure to the right arm makes  higher there, resulting in net movement of water to the left arm:
Solutes and positive pressure have opposing effects on water movement.
In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water:
Negative pressure (tension) has a negative effect on  by pulling water.
Negative pressure
Applying negative pressure to the right arm makes  lower there, resulting in net movement of water to the right arm: 
Water moves from regions of high water pressure to regions of low water pressure! We’ll take these scenarios one at a time
If a solute dissolves in water it is because it is either ionic or polar in nature. Either way the solute particles find water very attractive and set up intermolecular attractive forces which result in less “free” water which reduces the capacity for water to “move, flow or do work”. This is a negative effect, hence the negative sign convention on the number. A 0.1 M sugar solution has a S of −0.23 MPa. So, as the solute concentration or molarity increases, so does the negative value of S. Why does the water move to the right side of the U-tube? Osmosis!
Campbell Figure 36.8 Effects of solutes and pressure on water potential () and water movement.

22.  Solutes have a negative effect on  by binding water molecules.
Pure water at equilibrium
H2O
Adding solutes to the right arm makes  lower there, resulting in net movement of water to the right arm:
Pure water
Membrane
Solutes
Positive pressure has a positive effect on  by pushing water.
Positive pressure
Applying positive pressure to the right arm makes  higher there, resulting in net movement of water to the left arm:
Solutes and positive pressure have opposing effects on water movement.
In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water:
Negative pressure (tension) has a negative effect on  by pulling water.
Negative pressure
Applying negative pressure to the right arm makes  lower there, resulting in net movement of water to the right arm: 
 If we apply a mechanical pressure to the right side of the U tube (in the absence of solutes), then the water is mechanically forced to the left side of the U-tube.
Campbell Figure 36.8 Effects of solutes and pressure on water potential () and water movement.

23.  Solutes have a negative effect on  by binding water molecules.
Pure water at equilibrium
H2O
Adding solutes to the right arm makes  lower there, resulting in net movement of water to the right arm:
Pure water
Membrane
Solutes
Positive pressure has a positive effect on  by pushing water.
Positive pressure
Applying positive pressure to the right arm makes  higher there, resulting in net movement of water to the left arm:
Solutes and positive pressure have opposing effects on water movement.
In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water:
Negative pressure (tension) has a negative effect on  by pulling water.
Negative pressure
Applying negative pressure to the right arm makes  lower there, resulting in net movement of water to the right arm: 
 Adding solute to the right side of the U-tube AND applying a positive mechanical pressure to the right side as well (like the one the cell wall applies to the plant cell) can balance the pressure since they have opposing effects on the pressure.
Campbell Figure 36.8 Effects of solutes and pressure on water potential () and water movement.

24.  Solutes have a negative effect on  by binding water molecules.
Pure water at equilibrium
H2O
Adding solutes to the right arm makes  lower there, resulting in net movement of water to the right arm:
Pure water
Membrane
Solutes
Positive pressure has a positive effect on  by pushing water.
Positive pressure
Applying positive pressure to the right arm makes  higher there, resulting in net movement of water to the left arm:
Solutes and positive pressure have opposing effects on water movement.
In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water:
Negative pressure (tension) has a negative effect on  by pulling water.
Negative pressure
Applying negative pressure to the right arm makes  lower there, resulting in net movement of water to the right arm: 
 Negative pressure (tension) as occurs during transpiration, causes a negative pressure. It is important to note that the water potential of air is EXTREMELY negative (about −65 MPa) and since water moves toward the more negative potential, transpiration is favored!
Campbell Figure 36.8 Effects of solutes and pressure on water potential () and water movement.

25. Water Potential vs. Tonicity
Connect this new concept of water potential to the more familiar concept of tonicity (which should be prior knowledge). Ask students leading questions to see what they know about the movement of water across the cell membrane AND how the resulting size and shape of animal vs. plant cells change.
Next, ask them to compare the water potential of the solutions depicted in the bottom 3 graphics.
Figure (c) has an intermediate amount of solute particles pictured in the solution surrounding the cell AND there appears to be an equivalent amount of solute particles within the cell so the water potentials for both have reached equilibrium (isotonic; water potential for both environments is negative but nearly equal in magnitude thus the net rate of water movement is about equal).
Figure (d) has more solute particles within the cell (thus lower potential) compared to fewer solute particles (thus higher potential) in the solution surrounding the cell. Therefore, water moves in through the semipermeable membrane and bursts the cell wall if it is damaged or weakened. (hypotonic; a lower water potential inside the cell since more solute particles are present than outside the cell. Water moves from higher potential to lower potential.)
Figure (e) has far more solute particles in the surroundings (thus much lower potential) than present within the cell. Water moves out of the cell, it shrivels (leaving the cell wall intact). Emphasize that figure (e) represents plasmolysis when this occurs in plant cells. (hypertonic; higher water potential outside the cell than inside the cell. Water moves from higher potential to lower potential.)

26. Water Potential and Plant Vocabulary
Finally, connect the words plasmolyzed, to flaccid, to turgid with respect to all three concepts. Phew!
The green arrows indicate water moving OUT of the cell.
The yellow arrows indicate water moving INTO the cell.

27. Once More With Feeling!
Initial conditions: cellular  greater than environmental 
0.4 M sucrose solution:
Initial flaccid cell:
Plasmolyzed cell
at osmotic equilibrium
with its surroundings
P = 0
 S = −0.7
 P = 0
 S = − 0.9
 = − 0.9 MPa
 = − 0.7 MPa
 = − 0.9 MPa
Ask students to explain this diagram. Don’t settle for just the “what” answers, draw the “why” answers out of them!
Start easy…examine the initial conditions. Which water potential is higher? The INITIAL cell at -0.7 MPa or the 0.4 M sucrose solution at -0.9 MPa? The cellular potential is higher. Uh, oh! This is where the trouble starts! Negative numbers, ugh! Ask students to think about the number line with zero in the middle. The “higher or greater” potential is the one closest to zero on the number line.
Typical student response: The cell loses water and plasmolyzes. (not good enough)
Ask the student “WHY?” Because, water moves from high potential to low potential. (still not good enough)
Ask the student “What data are you basing that answer upon?” The fact that the water potential for the cell is MPa vs. the surrounding solution with a cell potential of -0.9 MPa, water moves out of cell. (almost good enough, answer is quantified)
Ask the student “So…what does that mean?” Water moves from an area of high water potential (−0.7 MPa) to an area of low water potential (−0.9 MPa), therefore water moves out of the cell into the surroundings and plasmolyzes. (much better when put all together!)
After plasmolysis is complete, the water potentials of the cell and its surroundings are the same.

28. Last Time, I Promise!
Initial conditions: cellular  less than environmental 
Distilled water:
Initial flaccid cell:
Turgid cell
at osmotic equilibrium
with its surroundings
 P = 0
 S = − 0.7
 S = 0
 P =
 = − 0.7 MPa
 = 0 MPa
 = − 0 MPa
Round 2, ask students to explain this diagram as well. Again, don’t settle for just the “what” answers, draw the “why” answers out of them!
Typical student response: The cell gains water and becomes turgid. (not good enough)
Why? The cell gains water and becomes turgid because the surrounding water potential is higher (0 MPa) than the cellular water potential (−0.07 MPa) and water moves from an area of high potential (surroundings) to low potential (cell), thus water moves into the cell making it turgid. (Better answer!)

29. Wilting Turgor loss in plants causes wilting
Which can be reversed when the plant is watered
Images from Campbell

30. Ascent of Xylem Sap
Again, note that water potential is measured in MPa, megapascals. There are 101 KPa per 1 atm of pressure. So, one megapascal is equivalent to about 10 times atmospheric pressure at sea level. Other pressure units they may be familiar with include bars, mmHg, torr (all the same with 760 of them per atmosphere)
Explain the ascent of xylem sap. Hydrogen bonding allows water molecules to form an unbroken chain extending from the leaves down to the soil. The force driving the ascent of xylem sap is a gradient of water potential (Ψ). For bulk flow over long distance, the Ψ gradient is due mainly to the gradient of the pressure potential (ΨP). Transpiration results in the ΨP at the leaf end of the xylem being lower that the ΨP at the root end. The Ψ values shown at the left are a “snapshot.” They may vary during daylight, but the direction of the Ψ remains the same.
Check for understanding: What would cause the Ψ to decrease in the soil, go below −0.3MPa? (a loss of water or drought would make the water potential more negative) What effect would this change in water potential of the soil have on transpiration? (It would decrease the amount of transpiration.)
Ask students to explain the roles of both adhesion and cohesion in transpiration.

31. Stomata Regulate Transpiration Rate
When water moves into guard cells from neighboring cells by osmosis, they become more turgid.
The structure of the guard cells’ wall causes them to bow outward in response to the incoming water.
This bowing increases the size of the pore (stomata) between the guard cells allowing for an increase in gas exchange.
Ask students the following questions:
Why is it important for guard cells to open? (to allow for gas exchange)
What is a consequence of guard cells staying open? (dehydration)
What reactant for photosynthesis is gaseous? (Carbon dioxide)
What product is gaseous? (Oxygen gas is the waste product being released.)
Can you say “form fits function”? (F3)
The intake of carbon dioxide is the gaseous reactant coming into the leaf.   
That comment by Jackie “Form fits function” may have to do with the kidney shape of the guard cells with one side thicker (concave side) so that when the cells become turgid it forms the stoma.

32. Homeostasis and Water Regulation
By contrast, when the guard cells lose water and become flaccid, they become less bowed , and the pore (stomata) closes.
This limits gas exchange.

33. Role Of Potassium Ion In Stomatal Opening And Closing
The transport of K+ (potassium ions, symbolized
here as red dots) across the plasma membrane and
vacuolar membrane causes the turgor changes of
guard cells.
H2O K+
The changes in turgor pressure in guard cells is largely due to the reversible absorption and loss of K+. Stoma open when guard cells actively accumulate K+ from neighboring epidermal cells lowering their water potential.

34. Homeostasis and Water Balance
Trees that experience a prolonged drought may compensate by losing part of their crown as a consequence of leaves dying and being shed.
Resources may be reallocated so that more energy is expended for root growth in the “search” for additional water.
Ask students the following question: What evolutionary role do plants surviving drought conditions play?
(The surviving plants may have adaptations that contributed to their survival. These adaptations may be passed on to future generations allowing them to thrive in more arid environments.)

35. Natural Selection and Arid Environments
Ask students to come up with examples of plant adaptations to arid environments before moving on to the next slide.

36. Natural Selection and Arid Environments
Plants that have adapted to arid environments have the following leaf adaptations:
Leaves that are thick and hard with few stomata placed only on the underside of the leaf
Leaves covered with trichomes (hairs) which reflect more light thus reducing the rate of transpiration
Leaves with stomata located in surface pits which increases water tension and reduces the rate of transpiration
Leaves that are spine-like with stems that carry out photosynthesis (cacti) and store water.
Be sure to connect natural selection to being in arid environments and adaptations. Ask students to work in small groups and come up with these connections.

37. Natural Selection and Flooding
Plants that experience prolonged flooding will have problems.
Roots underwater cannot obtain the oxygen needed for cell respiration and ATP synthesis.
As a result, leaves may dry out causing the plant to die.
Additionally, production of hormones that promote root synthesis are suppressed.
Ask them to explain how occasional flooding might select for plants that can live in an area where there is standing water such as swampland.
(The plants that survive flooding may have some adaptations that have helped them survive. These adaptations are passed on to future generations so they are better adapted to life in a wetter environment.)

38. Adaptations to Water Environments
Again ask students to come up with adaptations before moving to the next slide.

39. Adaptations to Water Environments
Plants that have adapted to wet environments have the following adaptations:
Formation of large lenticels (pores) on the stem.
Formation of adventitious roots above the water that increase gas exchange.
Formation of stomata only on the surface of the leaf (water lilies).
Formation of a layer of air-filled channels called aerenchyma for gas exchange which moves gases between the plant above the water and the submerged tissues.
Connect the adaptations and wet environment to natural selection.

40. Bulk Flow of Photosynthetic Products
Vessel
(xylem)
H2O
Sieve tube
(phloem)
Source cell
(leaf)
Sucrose
Sink cell
(storage root) 1
Loading of sugar (green dots) into the sieve tube at the source reduces water potential inside the sieve-tube members. This causes the tube to take up water by osmosis. 2 4 3
This uptake of water generates a positive pressure that forces the sap to flow along the tube.
The pressure is relieved by the unloading of sugar and the consequent loss of water from the tube at the sink.
In the case of leaf-to-root translocation, xylem recycles water from sink to source.
Transpiration stream
Pressure flow
Explain this diagram in detail. Note this is also called Pressure Flow or Mass Flow depending on the text book.

41. Nutritional Adaptations in Plants
Epiphytes- grow on other plants, but do not harm their host
Parasitic Plants-absorb water, minerals, and sugars from their host
Carnivorous Plants-photosynthetic but supplement their mineral diet with insects and small animals; found in nitrogen poor soils

42. Halophytes
Plants adapted to salt water environments. “Halophyte” means “salt plant”
Ask how plants exposed to occasional salt water and survive might be involved in natural selection. (The plants that survive a saline environment may have some adaptations that have helped them survive. This may be passed on to future generations so that they may live in a more saline environment.)

43. Adaptations of Plants: Saline Environments
Soil salinity around the world is increasing.
Many plants are killed by too much salt in the soil.
Some plants are adapted to growing in saline conditions (halophytes)
Have spongy leaves with water stored that dilutes salt in the roots
Actively transport the salt out of the roots or block the salt so that it cannot enter the roots
Produce high concentrations of organic molecules in the roots to alter the water potential gradient of the roots

44. AP Biology Teacher and Instructional Facilitator, Belton ISD
Created by:
Jackie Snow
AP Biology Teacher and Instructional Facilitator, Belton ISD
Belton, TX