1. Transport and Nutrition in Plants
Chapter 25.
Transport and Nutrition in Plants
AP Biology

2. inorganic compounds as raw materials
Nutritional needs
Autotrophic does not mean autonomous
plants need…
sun as an energy source
inorganic compounds as raw materials

3. Macronutrients
Plants require these nutrients in relatively large amounts
C, O, H, N, P, K, Ca, Mg, S

4. Nutrient deficiencies
Hydroponics
Lack of essential nutrients
exhibit specific symptoms
dependent on function of nutrient
dependent on solubility of nutrient

5. Transport and Nutrition
H2O & minerals
Sugars
Gas exchange

6. Transport in plants H2O & minerals Sugars Gas exchange
transport in xylem
transpiration
evaporation, adhesion & cohesion
negative pressure
Sugars
Gas exchange

7. Transport in plants H2O & minerals Sugars Gas exchange
transport in xylem
transpiration
evaporation, adhesion & cohesion
negative pressure
Sugars
transport in phloem
bulk flow
Calvin cycle in leaves loads sucrose into phloem
positive pressure
Gas exchange

8. Transport in plants H2O & minerals Sugars Gas exchange
transport in xylem
transpiration
Sugars
transport in phloem
bulk flow
Gas exchange
photosynthesis
CO2 in; O2 out
stomates
respiration
O2 in; CO2 out
roots exchange gases within air spaces in soil
Why does over-watering kill a plant?

9. Transport in Plants Water Transport Active transport and root pressure
Cause water to move from soil to roots
Capillary action
Combined with active transport and root pressure, moves materials throughout the plant 10

10. Ascent of xylem “sap”: is it pushed up or pulled up? BOTH!
Pushing (positive pressure…..increases water potential): Due to Root Pressure
night = low transpiration
constant intake of ions/minerals
root pressure at night causes guttation
Pulling (negative pressure…lowers water potential): Due to transpiration

11. PUSHY ROOTS! Root Pressure - low transpiration at night
Root cells still pumping ions in
Increase ions decreases water potential
By osmosis, water follows ions
Creates high pressure in roots
Naturally xylem sap moves up
Over the night, this continues, causing guttation
Endodermis keeps the ions that are pumped inside
Casparian strip is like a one way for water, so it doesn’t flow back out
If the process continues throughout the night, and transpiration is low, the high amount of water causes the leaves to be bloated allowing water drops to be pushed out of leaves (guttation)….not dew on the leaves always in the morning

12. Cellular transport Active transport
solutes are moved into plant cells via active transport
central role of proton pumps
chemiosmosis – the definition is…. the topic you thought you wouldn’t see again until the AP exam
The most important active transport protein in the plasma membranes of plant cells is the proton pump , which uses energy from ATP to pump hydrogen ions (H+) out of the cell. This results in a proton gradient with a higher H+ concentration outside the cell than inside. Proton pumps provide energy for solute transport. By pumping H+ out of the cell, proton pumps produce an H+ gradient and a charge separation called a membrane potential. These two forms of potential energy can be used to drive the transport of solutes.
Plant cells use energy stored in the proton gradient and membrane potential to drive the transport of many different solutes. For example, the membrane potential generated by proton pumps contributes to the uptake of K+ by root cells.
In the mechanism called cotransport, a transport protein couples the downhill passage of one solute (H+) to the uphill passage of another (ex. NO3−). The “coattail” effect of cotransport is also responsible for the uptake of the sugar sucrose by plant cells. A membrane protein cotransports sucrose with the H+ that is moving down its gradient through the protein.
The role of proton pumps in transport is an application of chemiosmosis.

13. STOP PULLING! Transpiration Main cause of water movement up a plant
Leaves = Water evaporates through stomata causing a pulling (tension) to replace the lost water
Stem = cohesion and adhesion properties of water (capillary action)
Roots = osmosis from ground to roots, then roots to xylem
Osmosis into the roots because high water potential in the ground. Osmosis into the xylem because the xylem sap has high ion concentration

14. Transport in Plants Capillary action (cohesion and adhesion)
Capillary transport results from both cohesive and adhesive forces
Water molecules attracted to one another
Water is also attracted to the xylem tubes in the plant
Causes water to move from roots to the stem and upward 12

15. Regulation of stomates
light trigger
temperatures
depletion of CO2
K ion concentration
Natural circadian rhythm
Stomata open when the potassium ions enter the guard cells, and water follows allowing for high turgor pressure. Like limp vs blown up balloon demo. Potassium enters by active transport. As K starts to go into guard cells, H ions naturally flow out proton pump and generates ATP. So, light acts as a trigger for guard cells to accumulate K ions (causing water to go in) causing the stomata to be open during the day (which allows for CO2 to come in). At night stomata close to reduce water loss, but still can go through the Calvin cycle to make glucose

16. Long distance transport
Bulk flow
movement driven by pressure
flow in xylem tracheids & vessels
negative pressure
transpiration creates negative pressure pulling (mainly) xylem sap upwards from roots
flow in phloem sieve tubes
positive pressure
loading of sugar from photosynthetic leaf cells generates high positive pressure pushing phloem sap through tube
Diffusion in a solution is fairly efficient for transport over distances of cellular dimensions (less than 100 μm), but it is much too slow to function in long– distance transport within a plant. For example, diffusion from one end of a cell to the other takes seconds, but diffusion from the roots to the top of a giant redwood would take decades or more. Long–distance transport occurs through bulk flow, the movement of a fluid driven by pressure. In bulk flow, water and solutes move through the tracheids and vessels of the xylem and through the sieve tubes of the phloem.
In the phloem, for example, the loading of sugar generates a high positive pressure at one end of a sieve tube, forcing sap to the opposite end of the tube.
In xylem, it is actually tension (negative pressure) that drives long–distance transport. Transpiration, the evaporation of water from a leaf, reduces pressure in the leaf xylem. This creates a tension that pulls xylem sap upward from the roots.

17. Pressure flow in sieve tubes
Water potential gradient
“source to sink” flow
direction of transport in phloem is variable
sucrose flows into phloem sieve tube decreasing H2O potential
water flows in from xylem vessels
increase in pressure due to increase in H2O causes flow
can flow 1m/hr
In contrast to the unidirectional transport of xylem sap from roots to leaves, the direction that phloem sap travels is variable. However, sieve tubes always carry sugars from a sugar source to a sugar sink. A sugar source is a plant organ that is a net producer of sugar, by photosynthesis or by breakdown of starch. Mature leaves are the primary sugar sources. A sugar sink is an organ that is a net consumer or storer of sugar. Growing roots, buds, stems, and fruits are sugar sinks. A storage organ, such as a tuber or a bulb, may be a source or a sink, depending on the season. When stockpiling carbohydrates in the summer, it is a sugar sink. After breaking dormancy in the spring, it is a source as its starch is broken down to sugar, which is carried to the growing tips of the plant.
A sugar sink usually receives sugar from the nearest sources. Upper leaves on a branch may send sugar to the growing shoot tip, whereas lower leaves export sugar to roots. A growing fruit may monopolize sugar sources around it. For each sieve tube, the direction of transport depends on the locations of the source and sink connected by that tube. Therefore, neighboring tubes may carry sap in opposite directions. Direction of flow may also vary by season or developmental stage of the plant.
What plant structures are sources & sinks?

18. Nutrient Transport Source to Sink
Most nutrients are pushed through plant
Nutrient movement takes place in phloem
Source to Sink
Source – any cell that produces sugars
Sink – any cell where sugars are used
Pressure-flow Hypothesis 20