Mastering Biology Chapter 35 and 36

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.

- In most plants, the highest rate of transpiration occurs when the rate of photosynthesis is also highest. - Transpiration is important in cooling leaves on warm, sunny days. - 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.

Drag a label to each target in the table to indicate the role that surface tension, adhesion, and cohesion play in the transport of water in the xylem. Labels may be used more than once. (Hint: The label "generates pull" belongs in only one target in the table.)

- Surface tension in leaves generates the force that pulls water through the xylem. - Cohesion between water molecules in leaves, stems, and roots transmits that force. - Adhesion of water to plant cell walls in leaves and stems opposes the force of gravity, which tends to pull water downward in the xylem.

Explain whether negatively charged chloride ions or positively charged calcium ions are more readily absorbed by root hairs in soil with a neutral pH.

Because anions such as Cl- are less likely to bind to soil particles in neutral soil, they are more available and more readily absorbed by root hairs than cations such as Ca2+. Explanation: However, rain may leach the anions away before they can be absorbed by the roots.

Water follows a specific path as it moves from the xylem in the vein of a leaf to the air outside the leaf.

Because xylem cells lack cytoplasm, the xylem is part of the apoplast. Water moves via the apoplastic pathway from the xylem through the bundle sheath to all of the mesophyll cells of the leaf. From the mesophyll cell walls, water evaporates into the interior air spaces of the leaf. Finally, it exits the leaf as water vapor through the stomata.

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

Both the photosynthesis and transpiration rates are low. Explanation: On a cloudy day with low soil moisture, the photosynthesis rate is low and stomata are closed, so the transpiration rate is low.

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

Casparian strip ... endodermis ... xylem Explanation: The Casparian strip is a waterproof barrier that forces water and solutes to pass through the plasma membranes of endodermis cells.

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

Endodermis Explanation: Endodermal cells filter solutes from water and allow them to pass through to the vascular tissue.

True or false? Plants use both active and passive transport processes to transport ions against their concentration gradients.

False Explanation: Plants use passive transport, which requires no energy expenditure, to transport ions down their concentration gradients, but they can only use active transport, which requires energy in the form of ATP, to transport ions against their concentration gradients.

True or false? Soil texture affects the amount of water available to plants; water is held best by clay and sand particles.

False Explanation: Soil texture does indeed affect the amount of water available to plants, but water is held best by the smallest soil particles, clay and silt.

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 Explanation: Root pressure can move water a short distance up the xylem because of the lower water potential of the xylem in comparison to the water potential in the surrounding cells.

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 Explanation: While the rate of photosynthesis and the difference in turgor pressure between the source and the sink do influence the rate of sugar transport in the phloem, the rate of transpiration does not; transpiration mainly influences the rate of water transport through the xylem.

What are the largest particles formed from the breakdown of rock?

Gravel Explanation: Gravel particles are the largest particles formed from the breakdown of rock.

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

Guard Explanation: Guard cells regulate the opening and closing of stomata.

Most of the dry mass of a plant is derived from ________.

H2O and CO2

_____ bonds are responsible for the cohesion of water molecules.

Hydrogen Explanation: Hydrogen bonds among water molecules are responsible for the tendency of those molecules to stick together.

What defines a micronutrient?

It is needed in very minute quantities. Explanation: The prefix micro- refers to the amount that is required.

What defines an essential nutrient for plants?

It is required for normal growth and reproduction. Explanation: If an essential nutrient is lacking, a plant cannot complete its life cycle.

Which of the following is an elemental ion?

K+

Which of the following statements about nutrient uptake by plants is true?

Plants require other elements besides carbon, hydrogen, and oxygen to grow, and they can obtain these in soil. Explanation: This statement is true; plants also require elements such as phosphorus, sulfur, and magnesium.

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

Sink Explanation: A sink is an area where sugars are used or stored; typically, these are the roots and fruits of a plant.

The Pressure-Flow Hypothesis

Sugars are able to move into and out of companion cells. - True The pressure in "sink" phloem cells is higher than the pressure in "source" phloem cells. - False Water is pulled through xylem under negative pressure, but sugars move through phloem under positive pressure. - True A leaf is an example of a "source," and a fruit is an example of a "sink." - True Sugars move from companion cells to "source" cells and from "sink" cells to companion cells. - False

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. Explanation: Companion cells play an important role in moving sugars 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 is the decomposition of dead organisms important for soil formation?

The process adds organic matter to the soil, which is necessary to support the growth of larger plants. Explanation: Decomposition of dead organisms adds organic matter, or humus, to the soil; humus is necessary to support plant growth.

What determines soil texture?

The proportions of gravel, sand, silt, and clay in soil Explanation: Soil texture affects the ability of roots to penetrate soil and the ability of soil to hold water.

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

They lack a nucleus and rely on companion cells to regulate their metabolic activity. Explanation: Sieve-tube elements are elongated sugar-conducting phloem cells that lack a nucleus and many other organelles.

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

Transpiration Explanation: Transpiration, the evaporation of water from leaves, exerts a pull that bears the primary responsibility for the movement of water and solutes from roots to leaves.

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. Explanation: Water and minerals that are taken up in the soil are transported from roots to leaves by the xylem.

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. Explanation: The pressure that is generated helps drive the movement of phloem sap.

Which of the following steps occurs first during soil formation?

Weathering of solid rock occurs. Explanation: Weathering is the process by which solid rock is broken down into smaller pieces and is the first step in soil formation.

Which of these factors does not help enhance the availability of magnesium and calcium ions in the soil for uptake by plant roots?

When soil becomes acidified, it is easier for the plant roots to absorb cations like magnesium and calcium. Explanation: When soil becomes acidified, the increased number of protons present in the soil water may help displace cations bound to the soil particles. However, rain is likely to leach the cations away before they can be absorbed by the roots.

If a plant grows on another plant, obtaining nutrients from and harming the other plant, it is most specifically described as _____.

a parasitic plant Explanation: A parasite lives in close physical contact with its host, obtaining resources from and reducing the fitness of the host.

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 - involves water transportoutside the protoplast consists of a porous matrixof hydrophilic polymers - is depicted by thered arrow in the diagram symplastic pathway - involves water movingvia plasmodesmata - can involve waterentering vacuoles - is depicted by theblue arrow in the diagram neither pathway - requires water to crossmultiple plasma membranes - The apoplastic pathway is a continuous route formed by cell walls, extracellular spaces, and the interior of dead xylem cells. - The symplastic pathway is made up of the cytoplasm of cells. It is also continuous because plasmodesmata connect the cytoplasm of adjacent cells. - These two pathways are separated by plasma membranes. Each pathway can transport water and solutes over both short and long distances.

What name is given to the process seen in this animation?

cation exchange Explanation: Cations, positively charged ions, in the soil solution are displacing cations on soil particles.

Which of these ions is most likely to be leached from the soil?

chlorine ions Explanation: Chlorine ions are negatively charged and are therefore not likely to be bound to negatively charged soil particles.

Acid precipitation _____.

decreases soil fertility Explanation: Acid precipitation promotes cation exchange. However, the precipitation then washes the ions away before they can diffuse into root hairs.

How do cations enter root hairs?

diffusion. Explanation: Cations diffuse into root hairs.

The binding of H+ ions to soil particles _____.

displaces mineral cations Explanation: Positively charged hydrogen ions displace positively charged mineral ions on soil particles.

The release of CO2 into the soil results in the formation of _____.

hydrogen ions and carbonate ions Explanation: When carbon dioxide combines with water hydrogen in the soil, cations and carbonate anions are released.

Sort each statement into the appropriate bin to indicate if the change described in the statement would increase, decrease, or not affect the pull that transpiration generates in the xylem of a tree.

increase transpirational pull - larger diameter of stomatal pores decrease transpirational pull - less curvature of water surface on mesophyll cell walls - higher relative humidity in air around leaf - lower rate of water evaporation from surface of mesophyll cells - thicker film of water on surface of mesophyll cells would not affect transpirational pull - larger air space in leaf interior

Which of these arrows is least like the others in its purpose in the model?

leaf Explain: The purpose of the leaf arrow is different from all other arrows. This arrow is identifying which structure is a leaf rather than showing the input or output of molecules or light from the plant.

Which of these are symbiotic associations?

mycorrhizae Explanation: Mycorrhizae are mutualistic associations of roots and fungi.

Carnivorous plants trap and digest insects to obtain _____.

nitrogen deficiency in low-nitrogen soils Explanation: Due to low decomposition rates, nitrogen is in short supply in the wet environments where most carnivorous plants are found.

Water potential (the potential energy of water in a particular environment) is determined by _____.

physical pressure on water and the concentration of solutes dissolved in it Explanation: Water potential is the combination of pressure potential and solute potential.

The channels indicated by the pointer, are _____.

plasmodesmata Explanation: Water and ions can pass from cell to cell via these channels. Also, recall that plasmodesmata are a type of cell junction.

What process is the source of the CO2 that root hairs release into the soil?

respiration Explanation: CO2 is a by-product of respiration.