Plant Transport: Xylem, Stems & Transpiration
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Questions and Answers

If a plant's shoot tip is removed, which of the following hormonal effects would most likely be diminished?

  • Promotion of root growth due to the unrestricted flow of hormones to the roots.
  • Increased ethylene production leading to accelerated fruit ripening.
  • Stimulation of lateral bud growth due to decreased apical dominance.
  • Inhibition of lateral bud growth due to apical dominance. (correct)

A plant physiologist applies a high concentration of auxin to a stem. Which of the following responses is least likely to occur?

  • Decreased stem elongation. (correct)
  • Inhibition of lateral bud growth.
  • Formation of adventitious roots at the application site.
  • Increased ethylene production.

A researcher discovers a mutant plant that exhibits excessive lateral bud growth, even when the shoot apex is intact. Which hormone is most likely deficient in this mutant?

  • Ethylene
  • Gibberellin
  • Auxin (correct)
  • Cytokinin

How would applying carbon dioxide to fruits during shipping affect their ripening process, and why?

<p>It would delay ripening by inhibiting ethylene action. (C)</p> Signup and view all the answers

A farmer wants to increase the yield of their sugarcane crop. Based on the information, which hormone would be most effective to apply?

<p>Gibberellin (A)</p> Signup and view all the answers

A seed company aims to produce seeds that germinate more rapidly. Which hormonal treatment would likely be most effective in achieving this goal?

<p>An application of gibberellin to break seed dormancy and stimulate enzyme production. (A)</p> Signup and view all the answers

A horticulturist notices that a particular plant species exhibits reduced fruit formation even after successful pollination. Which hormone application might best address this issue?

<p>Auxin, to stimulate fruit formation directly. (D)</p> Signup and view all the answers

During the transportation of phloem sap, what primarily drives the movement of substances from source to sink?

<p>Positive pressure generated by the loading of sugars at the source (A)</p> Signup and view all the answers

What is the significance of companion cells in relation to the function of phloem?

<p>They assist in the loading and unloading of sugars into the sieve tube elements. (B)</p> Signup and view all the answers

If a plant is genetically modified to produce excessive amounts of cytokinin in its root apical meristems, what is the most likely outcome?

<p>Inhibited root growth and promoted lateral bud formation. (A)</p> Signup and view all the answers

In the pressure flow model, what is the primary mechanism that drives the movement of phloem sap from source to sink?

<p>A high-pressure potential in the phloem, resulting from a high concentration of sugar at the source drawing water from the xylem. (D)</p> Signup and view all the answers

Which of the following accurately describes the role of companion cells in phloem tissue?

<p>They modulate flows in sieve tube elements, load food into and out of sieve tube elements, and provide energy. (C)</p> Signup and view all the answers

How does the movement of sugars in phloem differ fundamentally from the movement of water in xylem?

<p>Phloem transports sugars bidirectionally, supporting the growth of roots and fruits, whereas xylem primarily transports water upward from the roots. (D)</p> Signup and view all the answers

Considering the source-sink relationship in plants, which of the following scenarios accurately describes a shift in these roles?

<p>During the early stages of development, young leaves act as sinks, but transition to sources as they mature and begin photosynthesizing. (A)</p> Signup and view all the answers

In the context of translocation, what would happen if the active transport of sugars into the phloem at a source location were inhibited?

<p>Water would still enter the phloem due to osmosis, but the reduced sugar concentration would lead to a lower pressure potential and slower translocation. (B)</p> Signup and view all the answers

Within the pressure flow model, what is the immediate consequence of the rapid removal of sugars from the phloem at a sink?

<p>A decrease in pressure potential, facilitating the continuous flow of phloem sap from source to sink. (B)</p> Signup and view all the answers

Which of the following is the most accurate comparison of the driving forces behind fluid movement in xylem versus phloem?

<p>Xylem depends on transpiration pull and cohesion-tension, while phloem relies on active transport of solutes and resulting pressure gradients. (D)</p> Signup and view all the answers

How do the structural characteristics of xylem vessel elements and sieve tube elements reflect their respective functions in transport?

<p>Xylem's rigid walls withstand negative pressure, whereas phloem's sieve plates allow controlled bidirectional flow. (D)</p> Signup and view all the answers

Why is the active transport of sugars into sieve tube elements essential for the pressure flow mechanism?

<p>It decreases the water potential within sieve tubes, causing water to enter by osmosis and increases the pressure potential. (C)</p> Signup and view all the answers

If a plant is experiencing water stress, how might this impact the translocation of sugars, and why?

<p>Sugar translocation would decrease because reduced water availability would limit the ability to generate the pressure gradients needed for bulk flow. (A)</p> Signup and view all the answers

If a plant's transpiration rate significantly decreases due to a prolonged drought, which of the following is the most likely direct consequence within the xylem?

<p>A reduction in the negative water pressure, hindering the upward movement of water. (A)</p> Signup and view all the answers

Consider a plant with a mutation that impairs the function of aquaporins in root cells. How would this mutation most likely affect water uptake via the apoplast pathway?

<p>Water uptake via the apoplast pathway may be reduced but not eliminated, as water can still move through cell walls and intercellular spaces. (B)</p> Signup and view all the answers

A researcher discovers a new plant species in a desert environment. The plant exhibits an extremely high rate of transpiration, even under drought conditions. Which of the following adaptations would most likely be present in this plant to prevent fatal dehydration?

<p>Highly efficient mechanisms for water storage in specialized stem tissues, coupled with rapid stomatal closure during peak sunlight hours (C)</p> Signup and view all the answers

Suppose a plant is exposed to a toxin that specifically inhibits the activity of companion cells in the phloem. What would be the most likely direct consequence of this exposure?

<p>Inhibition of the loading and unloading of sugars into and out of the sieve tube elements, disrupting translocation (D)</p> Signup and view all the answers

In a plant with a fully functional vascular system, what mechanism primarily prevents the backflow of water in the xylem, especially during periods of low transpiration at night?

<p>The inherent tensile strength and cohesive properties of the water column, combined with adhesion to xylem walls (B)</p> Signup and view all the answers

A plant physiologist is studying a mutant plant with abnormally high levels of abscisic acid (ABA) in its leaves. How could this affect the plant's response to drought conditions?

<p>The plant would exhibit enhanced stomatal closure, reducing water loss but also potentially limiting photosynthesis. (D)</p> Signup and view all the answers

During the growing season, a herbaceous plant invests heavily in the growth of its above-ground parts (stems, leaves, and flowers). Which of the following correctly describes the relationship between source and sink tissues within this plant?

<p>Mature leaves are the primary sources, while developing leaves, stems, roots, and flowers are the primary sinks. (B)</p> Signup and view all the answers

A scientist is comparing the xylem of a young, rapidly growing tree with that of an old, mature tree. Which of the following differences would they expect to find?

<p>The xylem of the young tree would have wider vessel diameters, facilitating greater water flow compared to the mature tree. (B)</p> Signup and view all the answers

A plant is genetically engineered to produce a modified form of cellulose that is more rigid and less flexible than normal cellulose. How would this likely affect the plant's physical properties and response to environmental stimuli?

<p>The stems would be more rigid and less able to bend in the wind, potentially increasing the risk of breakage. Root growth may be stunted. (B)</p> Signup and view all the answers

A researcher is studying the long-distance transport of a newly discovered signaling molecule in plants. They find that the molecule is primarily transported in the phloem but its movement doesn't correlate with the source-to-sink pathway. What could they hypothesize?

<p>The molecule is actively loaded and unloaded into sieve elements along its path, creating local concentration gradients that drive its movement independently of the main source-to-sink flow. (D)</p> Signup and view all the answers

Flashcards

Transport in Plants

The movement of substances from one place to another within a plant.

Vascular System

Plant tissue forming a network of tubes to transport water, minerals, and sugars.

Stem

The plant organ that connects roots to leaves, providing support and a pathway for transport.

Xylem

Vascular tissue that transports water and minerals from the roots to the rest of the plant.

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Transpiration

The process of water movement through a plant and its evaporation from aerial parts, such as leaves.

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Water Movement in Xylem

Water movement in the xylem is unidirectional: from soil, to root, to stem, to the leaves and then to air.

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Cohesion

Water molecules stick to each other

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Adhesion

Water molecules stick to other surfaces.

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Negative Water Pressure

The force that enhances the flow of water molecules from soil to leaves.

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Apoplast Route

A pathway where water moves through the cell walls and intercellular spaces of the root cortex.

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Symplast Route

Water moves through the cytoplasm of root cortex cells.

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Cohesion (in water transport)

The attraction between water molecules due to hydrogen bonds.

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Adhesion (in water transport)

The attraction of water molecules to other surfaces.

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Osmosis (in roots)

Water movement from high to low concentration across a membrane, through root hairs.

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Phloem

Moves sugars both up and down a plant to roots and fruits.

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Sources (in plants)

Locations that produce or release sugars for the growing plants

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Sinks (in plants)

The points of sugar delivery, such as roots, young shoots and developing seeds.

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Translocation

The transport of sugars from source to sink in plants.

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Pressure Flow Model

High sugar at source draws in water, creating high pressure, driving movement of phloem sap to the sink.

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Auxin (IAA)

Plant hormone that promotes stem elongation, root formation, inhibits leaf loss, promotes cell division, increases ethylene production, stimulates fruit formation and inhibits lateral bud growth.

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Phototropism and Auxin

The growing tips of plants sense light and auxin is then transported to the shaded side of the shoot.

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Apical Dominance

Production of auxin by the shoot apex inhibits the growth of lateral buds.

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Cytokinin

Plant hormone produced in root apical meristems and fruits, stimulating cell division, promoting chloroplast formation, delaying leaf aging, promoting lateral bud formation and inhibiting root growth.

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Gibberellin

Plant hormone that promotes stem elongation, stimulates enzyme production in germinating seeds and breaks seed dormancy.

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Ethylene

Plant hormone that controls shedding of leaves, flowers, fruits and promotes fruit ripening.

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Ethylene's Commercial Use

Ethylene is used to ripen green fruits commercially. Carbon dioxide has the opposite effect.

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Pressure potential

A phenomenon where positive pressure pushes from the source.

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Sieve tube elements

A sugar-conducting cells in the pholem. They are supported by companion cells.

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Pressure potential

Negative pressure due to pull from the top (transpiration, tension).

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Study Notes

  • Transport facilitates the movement of substances from one location to another
  • Plant transport involves vascular tissues

Xylem

  • Xylem transports water via transpiration
  • Xylem consists of cells stacked to create a tube

Stem

  • Stems connect leaves to roots
  • Stems provide structural support for upward growth
  • Stems are flexible to bend without snapping
  • Some cactus' stems are swollen with water storage
  • Some stems twist with tendrils
  • Some stems are covered in thorns

Stem Visualisation

  • The stem is analogous to chopsticks and straws
  • The rubber band symbolizes the dermal tissue which covers the plant and protects it
  • The chopsticks represent the ground tissue to provide structural support
  • The drinking straws represent the vascular tissue which transports water, nutrients, and sugars

Transpiration

  • Transpiration is the driving force that enables movement

Water Transportation

  • Water moves in the xylem, acting as a one-way street
  • The route that water molecules take is soil to roots to stem to leave, then air
  • Water molecules in xylem move with cohesion and adhesion properties
  • Transpiration creates negative water pressure for water molecules to flow from soil to leaves

Water Entering the Root Hair Xylem

  • In the Apoplast route, water moves through cell walls and intracellular spaces
  • In the Symplast route, water runs through the cytoplasm of the root cortex

Forces for Water Transportation

  • Osmosis happens in the root hair
  • Cohesion
  • Transpiration happens in the stomata
  • Adhesion

Phloem

  • Phloem transports sugars via translocation
  • The movement of sugars in plants differs greatly from water movement
  • Phloem moves substances both up and down the plant
  • This action allows roots to extend and fruits to grow

Source vs. Sink

  • These are two terms associated with pholem
  • The source is where sugars are produced or released
  • This includes leaves and some roots
  • The sink is where sugars are delivered
  • This includes developing seeds, young shoots, and roots

Phloem Tissue

  • The tissue consists of two types of cells that are less rigid
  • Sieve tube elements are cells separated by perforated plates
  • Companion cells modulate flows in sieve tube elements, load/unload food, and provide energy

Translocation

  • Translocation is the process by which sugars move from a source to a sink
  • The pressure flow model explains it
  • A source with high sugar concentration causes low solute potential
  • Water is drawn into the phloem near the xylem
  • This creates high pressure potential, driving pholem sap movement
  • Sugars are then removed from the phloem at the sink

Xylem vs. Phloem

Xylem Pholem
Driving Force Transpiration from leaves Active transport of sugar
Cells Faciltating Non-living Living cells
Pressure Potential Negative Positive

Plant Hormones

  • Auxin (indole acetic acid/IAA) causes stem elongation and growth and promotes cell division
  • Auxin also creates formation of roots, increased ethylene, and formation of fruits
  • High levels of Auxin can inhibit the growth of lateral buds and cause leaf loss
  • Cytokinin hormones stimulate cell division and promote chloroplast formation
  • Cytokinin delays leaf aging and promotes the formation of lateral buds.
  • Gibberellin promotes stem elongation, stimulates enzyme production in germinating seeds, stimulate elongation and breaks seed dormancy
  • Ehylene controls shedding of leaves, flowers, and fruits. It also promotes fruit ripening
  • Ethylene is produced by apical meristems, leaf nodes, aging flowers, and ripening fruits

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Plant Anatomy and Physiology: Transport and Hormones - PDF

Description

Explore plant transport focusing on xylem, stems, and transpiration. Xylem facilitates water transport through transpiration, while stems connect leaves to roots, offering structural support. Transpiration is the primary force driving substance movement in plants.

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