Botany – Water in Plants & Plant Nutrients

I. Molecular movement in cells

A. _______________________________- spontaneous, random

movement from high to low concentration

1. Requires no energy input by cell

2. Remember that cell membranes are ____________________.

a. The cell membrane is only permeable to

_______________________________ molecules and a

few other __________________________ molecules like

oxygen (O₂) and carbon dioxide (CO₂).

b. These diffuse freely in and out of the cell.

B. What are cell membranes not permeable to?

1. Charged molecules known as __________________________

There are 2 classes of ions…

a. __________________________ have a positive charge.

This includes _______________________________

b. __________________________ have a negative charge.

This includes _______________________________

2. Small hydrophilic (water soluble) molecules like ____________.

3. Macromolecules like proteins and RNA

C. So, how do these particles get past the cell membrane barrier?

1. Facilitated Diffusion-

a. Transmembrane proteins create a water-filled pore

through which ions and some small hydrophilic molecules

can pass by diffusion.

b. The channels can be opened (or closed) according to the

needs of the cell.

c. Because we are moving along a concentration gradient,

this costs the cell ______________________________.

d. ____________________________ enters cells through

facilitated diffusion.

2. Active Transport-

a. Involves special transmembrane proteins called

transporters.

b. __________________________ enter and leave cells

through active transport.

D. The diffusion of water across a selectively permeable membrane is so

crucial & vital that it is given a special name, ______________________.

II. Why is water such a special molecule?

A. The chemical formula for water is ___________________________.

Water is a ______________________.

that is made up of two atoms of hydrogen and one atom of oxygen.

1. Atoms have a nucleus where you find __________________.

a. Each proton has a positive charge.

2. Circling around the nucleus are ______________________.

a. Each electron has a negative charge.

b. The electrons occupy electron shells.

c. The innermost electron shell can hold 2 electrons.

d. The next electron shell can hold 8 electrons.

3. Atoms and molecules try to be as electrically stable as

possible. Two ways they can achieve this stability include…

a. Remaining electrically neutral (i.e. the number of

electrons must equal the number of neutrons)

1) If an atom or molecule has more electrons

than protons, it will become negative.

2) If an atom or molecule has more protons

than electrons, it will become positive.

b. Filling their outermost electron shells.

B. Water is a _____________________________________ molecule.

1. The atomic number of ____________________ is 1. That

means that it has one proton in its nucleus and 1 electron in its

electron shell.

a. To fill that electron shell, it would have to gain an

electron.

b. That would make it less stable because it would have a -1

charge.

2. The atomic number of ______________________ is 8. Oxygen

has 8 protons in its nucleus. It has 2 electrons in its innermost

electron shell and 6 electrons in the next electron shell.

a. To fill its outermost electron shell, it would have to gain 2

electrons.

b. That would give it a -2 charge, which is less stable.

3. _____________________________________ are formed by

covalent bonds. Two hydrogens and one oxygen share their

electrons.

a. This allows the atoms to have their outermost shells filled

at least part of the time, increasing ___________________.

b. By sharing their electrons, they avoid gaining negative

charges.

C. Water is a ______________________ molecule.

1. Oxygen has a +8 charge in its nucleus. The two hydrogen

atoms have only a +1 charge in their nuclei.

a. Because Oxygen has a greater positive charge, it attracts

the electrons more strongly.

1) Think about a big kid on a playground by the

swings. The big kid will get to swing more often and

longer.

b. Thus, oxygen develops a partial __________________

charge (δ^- ).

c. The hydrogen develops a partial __________________

charge (δ⁺ ).

Electronic Distribution in H₂O

2. Because it is both partially positive and partially negative, it is

attracted to & dissolves anything that has a charge.

a. Water is referred to as the ______________________.

b. Because it is both partially positive and partially negative,

it is attracted to & dissolves anything that has a charge.

Table Salt Dissolving in Water

3. Water molecules are also attracted to each other, forming

hydrogen bonds, resulting in ______________________________.

Hydrogen Bonding between Water Molecules

4. As a general rule, ____________________________________

____________________________________________________.

Important topic: Why water moves in & out of cells

III. ______________________ – the diffusion of water from an area of high

concentration, across a semi-permeable membrane, to an area of low

concentration.

A. Why does water move into and out of cells?

1. It depends upon the type of solution the cell is in.

a. Water is a __________________. Anything dissolved in

water is a ______________________.

c. As the solute concentration in a solution _____________,

the water concentration ______________________ &

vice versa.

2. We are going to look at an imaginary plant cell.

a. Our cell will be 75% water (we will use X’s to represent

water).

b. Our cell will be 25% solutes (we will use O’s to represent

the solutes).

3. First, let’s put our cell into a ____________________ solution –

one that has a lower water concentration than the cell.

a. We will put the cell into a solution that is 50% solutes and

50% water.

1) Water moves from higher to lower concentration.

2) The cell is 75% water, the solution is 50% water.

3) There will be a net movement of water out of the

cell into the solution.

Hypertonic Solution	The Results for the Cell
	The cell died! Then the plant wilted and died! YIKES! Why didn’t someone water this plant?

b. In hypertonic solutions, water will exit the cell.

1) The cell’s plasma membrane will shrink away from

the cell wall.

2) This is known as ______________________. The

cell will die.

c. Plant cells that become dehydrated lose their shape.

This results in the plant ______________________.

4. Next, let’s put our cell into an ______________________

solution – one that has the same concentration of water as the

cell.

a. We will put the cell into a solution that is 25% solutes and

75% water (just like the cell).

1) Water moves from higher to lower concentration.

2) However, the cell is 75% water and the solution is

75% water. Therefore, there is no area of higher or

lower water concentration.

3) There will NOT be a net movement of water.

Isotonic Solution	The Results for the Cell
	This solution is perfect for both plant and animal cells.

b. In this solution, the plasma membrane of the plant cell will

be pushed up against the cell wall.

1) This is actually due to water entering the central

vacuole of the cell, pushing against the cytoplasm.

2) If the plant loses any water, it will wilt.

5. Finally, let’s put our cell in a ______________________ solution

– one that has a higher water concentration than the cell.

a. We will put the cell into a solution that is 0% solutes and

100% water.

1) Water moves from higher to lower concentration.

2) The cell is 75% water, the solution is 100% water.

3) There will be a net movement of water into the

cell from the solution.

Hypotonic Solution	The Results for the Cell
	The cell wall (through turgor pressure) saved the cell! Hooray! (An animal cell will swell & burst.)

b. In these solutions, animals cells swell & burst.

c. However, plant cells have a rigid cell wall that prevents

this.

d. These cells are said to be ______________________.

They are filled with water. This plant will not wilt. ***This

is the normal condition of plant cells.***

IV. Osmosis in Plants

A. Recall that osmosis moves water from an area of high water

concentration to an area of low water concentration. It requires

______________________.

1. Plants have to constantly cope with changing osmotic pressures

due to changes in water availability and transpiration rates.

B. Unlike animal cells, plant cells don’t explode in hypotonic solutions

due to turgor pressure.

1. Turgor pressure –

2. Plant cells store ions, sugars, organic and amino acids and

other substances in considerable concentrations in their

_______________________________.

a. Remember that wherever a charged particle is or goes,

____________________________ is bound to follow.

b. Therefore, the solutes in the central vacuole cause water

to rush into and fill the vacuole with water.

c. As the vacuole fills with water, it presses against the

cell’s cytoplasm, which causes the plasma membrane to

press against the ____________________________.

d. This pressure prevents more water from moving in by

osmosis.

3. This causes plant cells to build up a large positive internal

pressure (pushing against the cell wall), the __________________.

4. Turgor pressure has a decisive influence on the maintenance of

the rigidity and stability of plant tissues.

a. Plants that lose water ____________________________

because their turgor pressure decreases.

C. In plants, we talk about the potential water molecules have to move.

This is the ____________________________. (Think of this as the

concentration of water.)

1. Distilled water has the greatest osmotic potential of any

solution.

2. Adding anything to the water (sugar, salt, etc.) lowers the

solution’s osmotic potential.

3. Water molecules always move from greater to lesser osmotic

potential.

D. ____________________________– the osmotic potential of a cell.

1. For animal cells, the water potential is the osmotic potential of

the cytoplasm.

2. In plant cells this is different.

3. Plant cells have a cell wall, which exerts an inward pressure

when the cell is turgid.

a. This is known as the pressure potential (pressure

b. potential = turgor pressure).

4. The water potential of a plant cell is equal to the osmotic

potential of the cytoplasm plus the cell wall pressure, OR…

W.P. = O.P. + P.P.

E. THIS IS THE RULE OF WATER MOVEMENT IN PLANTS:

1. Water always moves from an area of high water potential to an

area of low water potential.

Important topic: Why water moves in plants

V. Molecular Movement In Plants- So, water and solutes (anything dissolved in

water to make a solution) are moving around in plants. What types of

movements do we see & why?

A. _______________________________- attraction (adhesion) of water

molecules to colloidal substances –

1. Water molecules are attracted to any charged particle

(_______________________________).

2. The water molecules attract more water molecules

(_______________________________).

3. Works in a manner similar to osmosis.

4. This is how seeds expand when soaked in water.

B. Transpiration-

1. Approximately _________________________ of the water that

a plant absorbs is lost by transpiration!

2. Transpiration is also partially responsible for water movement

through the xylem, and the prevention of heat damage to plant

cells.

3. Typical transpiration rates (L/day):

a. Mature corn plant- 15

b. Acre of corn- 13, 250

c. Birch tree- 200-1000

C & D: Why water moves up the xylem

C. _______________________________________ – first discovered

& measured by Stephen Hales.

***Botany’s first attempt to explain why water moves from the ground up a

plant.***

1. The force that drives the water through the root is based on

differences in the water potential of the root's surrounding

(usually soil) and its xylem sap.

a. The _________________ that have passed through the

__________________ are usually trapped and cannot leave

the ________________________ any more.

b. The built-up ions attract water by __________________.

c. Thus, root pressure develops. The build-up of water

presses the water in the xylem (with its dissolved ions, called

the __________________________________________)

upward.

2. When a tomato plant is carefully severed close to the base of

the stem, sap oozes from the stump. The fluid comes out under

pressure due to root pressure.

3. Although root pressure plays a role in the transport of water in

the xylem in some plants and in some seasons, it does not

account for most water transport.

a. Root pressure is always small, and doesn’t even develop

in some plants.

b. The highest root pressures occur in the ___________

when the xylem sap is highly ___________________ to

soil water, but the rate of transpiration is low.

c. In the summer, when transpiration is high and water is

moving rapidly through the xylem, often no root pressure

can be detected.

D. _______________________________- Water rises in small tubes

(tracheids and vessels) to some extent because of adhesion to the

tube walls (capillarity) and cohesion between water molecules.

***Botany’s BEST explanation for why water moves up through

xylem.***

1. ___________________ - Spontaneous movement of liquids up

or down narrow tubes, or capillaries.

a. The height that water will rise in a tube is ____________

proportional to the diameter of the tube.

b. The larger the diameter of the tube, the smaller the

percentage of water molecules in direct contact with the

glass and, correspondingly, the __________________

the rise in the water in the tube.

2. Water in the xylem can be thought of as columns of water

molecules held together by cohesion.

3. As water transpires from the leaves of a tree, it results in a lower

water potential in the leaves.

4. More water enters the roots by osmosis due to the subsequent

decrease in water potential in the xylem.

5. Rapid transpiration can cause the roots to grow rapidly towards

the nearest source of water.

6. During rapid transpiration, water may move through the roots by

_____________________________—simple movement from high

water potential to low water potential—with little osmosis taking

place.

E & F: Why water moves down the phloem (with food)

E. _______________________________________________________-

Organic solutes move from an area of high concentration

(_______________________________) to an area of low concentration

(_______________________________) by diffusion.

1. For example, glucose (sugar) is produced in the leaves & then

stored in the roots of some plants. In this case…

a. The leaves are the source (there is a greater

concentration of sugar in the leaves where it is being

produced).

b. The roots are the sink

F. _______________________________

***Botany’s BEST explanation for why water moves down through

phloem.***

1. At the source (the photosynthesizing cells in the leaves), sugar

is actively transported into phloem cells.

2. Sugar is a solute. Because the sugar (or solute) load in the

phloem cells has increased, the concentration of water in these

cells decreases.

3. Water flows by osmosis from an area of higher concentration

into these phloem cells.

a. This osmosis creates ____________________________

________________________________________________

which drives the fluid through the sieve-tube cells.

4. At the sink (any cell that needs sugar to carry out its functions),

sugar is actively transported out of the phloem

a. Again, water again follows by osmosis, decreasing the

turgor pressure near the sink.

5. Phloem fluid moves by mass flow from high turgor pressure (the

leaves or source) to low turgor pressure (any cell needing sugar

or sink).

6. As sugar is used up by the cells, its concentration decreases.

a. As the solute (sugar) concentration decreases, the water

concentration increases.

b. Again, water moves from high to low concentration, so it

now leaves the cells.

c. This water moves into the ________________________

where it is recirculated or transpired.

III. Regulation of Transpiration- a plant MUST maintain a balance between

_______________________________ (necessary to make sugar) and

_______________________________ (through transpiration) by opening and

closing its __________________________. (Think about the dangers of the hot

summer sun – plant wilting! YUCK!)

A. Stomata- openings in the epidermis formed by two guard cells.

1. They are responsible for the regulation of transpiration and gas

exchange.

2. The inside wall of each guard cell is thicker than the outside

wall.

3. When turgor pressure increases (due to water entering the cell’s

vacuole), the outside wall expands more than the inside wall.

4. This causes the inside wall to bow out and open the stoma.

5. Stomata open when the guard cells actively transport

_______________________________ into their cytoplasm.

a. Water follows by osmosis and turgor pressure increases.

6. Under water stress, the water potential outside the cell becomes

lower than inside the cell.

a. Water leaves the cell by osmosis and the stomata close.

7. The hormone _______________________________may be

produced during water stress and cause the guard cell membranes

to leak potassium, thus decreasing the turgor pressure.

A. _______________________________- most plants have their stomata

open during the day so that CO₂ can enter for photosynthesis. Some

plants (CAM) found in arid regions only open their stomata at night in

order to decrease water loss. They have a specialized form of

photosynthesis.

C. Transpiration Rate Factors:

1. Light- due to photosynthesis. __________________________

2. CO₂ concentration- due to photosynthesis

3. Air Currents- cause gradients in water vapor over the stomata.

_______________________________

4. Humidity- inversely correlated with transpiration rate.

_______________________________

5. Temperature- positively correlated with transpiration rate.

_______________________________

D. _______________________________- production of water droplets

on leaves of some plants by structures called ___________________.

1. Usually occurs when a cool night follows a humid day.

2. As the water evaporates during the day, solutes are left behind.

3. At night, these solutes attract water, which beads up on the

leaves’ margins.

VII. Plant nutritional requirements- most plants get their mineral from the soil

and soil water.

A. Minerals are non-organic nutrients that are necessary for proper plant

metabolism.

1. Organic elements- constitute most of the dry weight of the plant.

a. Includes C, H, & O

2. Macronutrients- used in large amounts by plants, and constitute

0.5-3% of dry their weight.

a. Includes N, K, Ca, Mg, & S

3. Micronutrients- needed in small amounts, and constitute only a

few ppm of plant dry weight.

b. Includes P, Fe, Na, Cl, Cu, Mn, Co, Zn, Mo, & B

4. When necessary, elements are deficient in the soil, the plant

will not grow normally.

a. Fertilizers are used to replace or increase nutrients in the

soil.

B. Uses of key elements in plants:

1. N- proteins, nucleic acids, chlorophyll

2. K- activates enzymes, concentrates in meristems, controls guard

cells

3. Ca- middle lamella, membrane transport

4. P- nucleic acids, coenzymes, activates enzymes, cell division

5. Mg- activates enzymes, chlorophyll

6. S- some amino acids

7. Fe- chlorophyll, respiration

8. Mn- activates enzymes

9. B- influences use of Ca, but overall function unknown