12 Transpiration and Nutrient Acquisition

Transpiration provides the driving force for the movement of water from the soil to the highest leaves of plants. Transpiration is also linked to other processes in plants, including photosynthesis and the transport of mineral nutrients. Which of the following statements correctly describe(s) a relationship between transpiration and other processes in plants? Select all that apply.

- Transpiration is important in cooling leaves on warm, sunny days. - In most plants, the highest rate of transpiration occurs when the rate of photosynthesis is also highest. - Open stomata provide a low -resistance pathway for CO2 to enter and for water to exit the leaf. - To minimize water loss during dry conditions, most plants must also restrict their ability to carry out photosynthesis.

Which of these events would not cause transpiration rates to decrease in a large tree?

A day with low relative humidity

A plant leaf is constructed from a variety of cell types with specialized structures and functions. Many of the properties of leaf cells facilitate some aspect of water transport.The diagram below shows a cross section through a leaf.Drag the labels to the appropriate targets to match the function with the structure indicated in the diagram. Labels may be used once, more than once, or not at all.

A. cells that transport water from the roots to the leaves B. a group of different cell types involved in long-distance transport of water and nutrients C. cells with a coating that prevents evaporation of water D. cells with a coating that prevents evaporation of water E. cells where most evaporation of water in the leaf occurs F. cells that control the rate of water loss from the leaf

The apoplast and symplast are two regions of the plant that serve as pathways for water and solute transport over both short and long distances. These pathways are represented by the arrows in the diagram below, which shows three adjacent cells in a leaf or root.

Apoplastic Pathway: - is depicted by the red arrow in the diagram - involves water transport outside the protoplast - consists of a porous matrix of hydrophilic monomers Symplastic Pathway: - is depicted by the blue arrow in the diagram - involves water moving via plasmodesmata- can involve water entering vacuoles Neither Pathway: - requires water to cross multiple plasma membranes

What characterizes the rates of photosynthesis and transport in a plant on a dry cloudy day?

Both the photosynthesis and transpiration rates are low

In roots the _____ forces water and solutes to pass through the plasma membranes of _____ cells before entering the _____.

Casparian strip ... endodermis ... xylem

What is the force behind the process of transpiration?

Cohesion-tension

Some plants growing in arid climates have small leaves and thick waxy cuticles on the upper epidermis. This is an adaptation for

Decreasing water loss from leaves

Which tissue acts as a filter on the water absorbed by root hairs?

Endodermis

True or false? Root pressure can move water a long distance up the xylem because of the higher water potential of the xylem in comparison to the water potential in the surrounding cells.

False

True or false? The rate of sugar transport in a plant depends on the rate of photosynthesis, the rate of transpiration, and the difference in turgor pressure between the source and the sink.

False

Why is the presence of clay particles important in soil?

The negative charges on clay bind to positively charged ions and prevent them from being leached out of the soil

What determines soil texture?

The proportions of gravel, sand, silt, and clay in soil

What is the role of companion cells in the movement of sugars through plants?

They accumulate sucrose, which is then transferred to adjacent sieve-tube elements.

Which of the following is true regarding sieve-tube elements?

They lack a nucleus and rely on companion cells to regulate their metabolic activity.

_____ provide(s) the major force for the movement of water and solutes from roots to leaves.

Transpiration

Phloem cells located in "source" regions can have relatively high pressure. How is that pressure generated?

Water enters the phloem by osmosis, thereby increasing pressure within the phloem.

A cell is placed in a solution that is hypotonic to the cell. Which of the following best describes movement of water in this situation?

Water will flow into and out of the cell, but the overall net movement will be into the cell.

Mycorrhizae enhance plant nutrition mainly by

absorbing water and minerals through the fungal hyphae

Which of these are symbiotic associations?

mycorrhizae

You go out into a field early in the morning and notice small droplets of water along the edges of the leaves. It did not rain overnight−−what caused these droplets?

A buildup of ions in the root xylem resulted in a positive pressure that pushed water up the xylem.

Why is nitrogen fixation an essential process?

Fixed nitrogen is often the limiting factor in plant growth.

Which of the following, if used as a fertilizer, would be most immediately available for plant uptake?

NO3-

Your friend claims that phloem always carries sugars down a plant. What, if anything, is wrong with that statement?

Phloem can carry sugars down a plant, but it can carry sugars up as well (e.g., if sugars are moving to flowers or fruits).

What nutrients are transferred into plant roots by mycorrhizal fungi?

Phosphate (H2PO4-) and ammonia (NH3)

Nitrogen fixation is a process that

converts nitrogen gas into ammonia

What drives the flow of water through the xylem?

the evaporation of water from the leaves

Which criteria allow biologists to divide chemicals into macronutrients and micronutrients?

the quantities of each required by plants

_____ cells are the cells that regulate the opening and closing of stomata, thus playing a role in regulating transpiration.

Guard

Which of the following would tend to increase transpiration?

Higher stomatal density

_____ bonds are responsible for the cohesion of water molecules.

Hydrogen

Explain how water absorption by grass roots might be affected when a lawn is overfertilized.

If the concentration of solutes in the soil water is greater than in the root cells (as a result of extra fertilizer), then water will tend to leave the roots and enter the soil by osmosis.

Root cells establish a net negative charge as a result of pumping protons out of the cells. This negative charge draws cations into the cells as long as the electrical gradient is strong enough to overcome the concentration gradient. What happens to cation and anion uptake if H+-ATPases fail?

If there is no voltage across the root-hair membrane, there is no electrical gradient favoring entry of cations through channel proteins. Similarly, without an electrical gradient, anions cannot enter the cells through cotransporters.

What defines a micronutrient?

It is needed in very minute quantities.

What defines an essential nutrient for plants?

It is required for normal growth and reproduction.

How do sieve-tube elements and companion cells differ?

Sieve-tube elements lack nuclei and most other organelles, while companion cells have nuclei and organelles

Which term describes an area where sugars are used or stored?

Sink

Which of the following correctly describes how sugars move from a photosynthetic leaf cell into phloem?

Sugars are first transported into companion cells and from there move into phloem.

Which of the following statements about the distribution of sap throughout a plant is true?

The mechanism that explains the movement of sugars throughout a plant is called the pressure-flow hypothesis.

Why are proton pumps in root-hair plasma membranes important?

They set up an electrochemical gradient that makes it possible for roots to absorb cations and anions.

Which of the following statements about xylem transport is true?

Water and minerals move through the root cortex into the xylem and upward through the stem and into leaves.

Water follows a specific path as it moves from the xylem in the vein of a leaf to the air outside the leaf.Drag the labels into the flowchart to show the sequence of events after water enters a leaf in the xylem. Not all labels will be used.

a) water exits the xylem and enters the walls of surrounding cells b) water spreads as a film in and on the surface of mesophyll cell walls c) water evaporates from the surface of mesophyll cells d) water vapors diffuses through the air spaces of the leaf e) water vapor exits the leaf through the stomata

A major function of magnesium in plants is to

be a component of chlorophyll

When water moves from soil into the vascular tissues inside the root, it can take three possible pathways. Of these, the apoplastic route is

between cells and through cell walls

In response to hot, dry conditions, well-adapted plants will often

close their stomata to prevent a loss of turgor pressure in leaf cells

The transport of a water column up a very tall tree can be explained by

cohesive and adhesive forces of the water column under evaporative tension

What important role does the Casparian strip play in the movement of water through plants?

forces water to move through the cytoplasm of living endodermal cells as it makes its way from the soil to the xylem

Root hairs are most important to a plant because they

increase the surface area for absorption

The NPK percentages on a package of fertilizer refer to the

percentages of three important mineral nutrients

Root hairs absorb some nutrients from soil against the nutrient concentration gradient. To achieve this, root hairs use

proton pumps