Plant Physiological Adaptations Quiz
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Questions and Answers

Which tissue types serve as major sinks for carbohydrate import and development?

  • Roots, tubers, developing fruits, and immature leaves (correct)
  • Mature stems and leaves
  • Upper mature leaves and mature fruits
  • Flowers and seeds

What factor significantly influences the source-to-sink transport in plants?

  • Size of the root system
  • Age of the plant leaves
  • Proximity of the source to the sink (correct)
  • Number of photosynthetic cells

During the reproductive development of a plant, which sinks typically become dominant?

  • Mature foliage
  • Young immature leaves
  • Fruits (correct)
  • Root apices

What is an orthostichy in relation to plant vascular systems?

<p>A pattern describing leaf arrangement on a stem (A)</p> Signup and view all the answers

What can alter established translocation patterns in plants?

<p>Interference through wounding or pruning (C)</p> Signup and view all the answers

How do source leaves preferentially supply sinks in the shoot system?

<p>By direct vascular connections (C)</p> Signup and view all the answers

What is the role of anastomoses in translocation pathways?

<p>To serve as alternative pathways in the absence of direct connections (D)</p> Signup and view all the answers

Which statement about leaves and their relation to sinks is true?

<p>Upper mature leaves primarily provide to growing shoots and immature leaves (D)</p> Signup and view all the answers

What is the primary function of xylem parenchyma cells modified as transfer cells?

<p>To retrieve and reroute solutes moving in the xylem (A)</p> Signup and view all the answers

Why are plasmodesmata significant in companion and transfer cells?

<p>They serve as pathways that can carry viruses systemically (D)</p> Signup and view all the answers

What characteristic most distinguishes intermediary cells in plants?

<p>Numerous plasmodesmata connecting them to surrounding cells (B)</p> Signup and view all the answers

What term describes the areas where sap is produced in plants?

<p>Sources (C)</p> Signup and view all the answers

During which phase does the storage root of Beta maritima serve as a sink?

<p>In the first growing season (C)</p> Signup and view all the answers

Which of the following statements about phloem translocation is correct?

<p>Translocation occurs from sources to sinks regardless of gravity. (A)</p> Signup and view all the answers

Which type of cell lacks developed thylakoids and starch grains in their chloroplasts?

<p>Intermediary cells (B)</p> Signup and view all the answers

What is the role of sinks in plant physiology?

<p>To store or metabolize nutrients that are transported from sources (A)</p> Signup and view all the answers

What is the preferred unit for measuring mass transfer rate in sieve elements?

<p>grams per hour per square centimeter (g h–1 cm–2) (B)</p> Signup and view all the answers

Which mechanism of phloem translocation accounts for most of the available experimental and structural data?

<p>Pressure-flow model (D)</p> Signup and view all the answers

What is the range of observed rapid rates of translocation in phloem?

<p>50 to 250 cm hr–1 (D)</p> Signup and view all the answers

In the context of phloem function, what does phloem loading refer to?

<p>Initial transfer of assimilate from leaf mesophyll cells into sieve elements (B)</p> Signup and view all the answers

Which of the following is NOT a factor that a comprehensive theory of phloem translocation must account for?

<p>The role of root hairs in nutrient uptake (C)</p> Signup and view all the answers

Which of the following best describes the role of energy in either sources or sinks during phloem translocation?

<p>Energy is necessary to move photosynthate into the sieve elements in sources. (D)</p> Signup and view all the answers

What type of cytoplasm is present in sieve elements that is important for phloem function?

<p>Active cytoplasm (C)</p> Signup and view all the answers

How do current preferred SI units differ from earlier publications regarding phloem movement?

<p>They use meters or millimeters instead of centimeters. (C)</p> Signup and view all the answers

What effect do sieve plates have on the pressure gradient in sieve elements?

<p>They increase resistance and create a pressure gradient. (C)</p> Signup and view all the answers

Which of the following must be true for effective translocation through sieve elements?

<p>Pores must be clear to prevent high resistance. (A)</p> Signup and view all the answers

What is the effect of low temperature on phloem translocation?

<p>It has no effect on translocation. (C)</p> Signup and view all the answers

What must be true regarding the turgor pressure in sources compared to sinks?

<p>Turgor pressure in sources must be higher. (C)</p> Signup and view all the answers

Which component is primarily involved in phloem loading?

<p>Cytosol converting triose phosphate to sucrose. (A)</p> Signup and view all the answers

What role does P-protein play in sieve elements?

<p>It blocks sieve plate pores if abundant. (D)</p> Signup and view all the answers

What happens to stored starch during phloem loading at night?

<p>It exits the chloroplast as glucose before being converted to sucrose. (C)</p> Signup and view all the answers

What is a key prediction of the pressure-flow model?

<p>Turgor pressure must be higher in source sieve elements. (D)</p> Signup and view all the answers

What is the primary process by which sugars are transported into the sieve elements and companion cells?

<p>Sieve element loading (B)</p> Signup and view all the answers

What is meant by the term 'sieve element–companion cell complex'?

<p>A functional unit for loading sugars into phloem (B)</p> Signup and view all the answers

In the context of phloem transport, what is the main role of sink organs?

<p>To store or metabolize sugars (C)</p> Signup and view all the answers

What is the process by which sugars leave the sieve elements in sink tissues known as?

<p>Sieve element unloading (B)</p> Signup and view all the answers

Which of the following correctly describes the relationship between source and sink processes?

<p>Sink processes essentially reverse the events that took place at the source (D)</p> Signup and view all the answers

Which step follows sieve element unloading during the import of sugars into sink cells?

<p>Short-distance transport (D)</p> Signup and view all the answers

What process determines the total amount of fixed carbon available for translocation?

<p>Photosynthetic rate (C)</p> Signup and view all the answers

What is involved in the regulation of the diversion of fixed carbon into various metabolic pathways?

<p>Allocation of fixed carbon (D)</p> Signup and view all the answers

What primarily determines sink strength in a plant?

<p>Sink size and sink activity (B)</p> Signup and view all the answers

Which of the following activities can limit the rate of uptake by a sink?

<p>Unloading from sieve elements (D)</p> Signup and view all the answers

What does the term partitioning refer to in the context of plant vascular systems?

<p>Differential distribution of photosynthates within the plant (D)</p> Signup and view all the answers

How does cooling a sink tissue affect photosynthate transport?

<p>It decreases the speed of transport towards the sink (A)</p> Signup and view all the answers

Which enzyme is NOT mentioned as influencing sink strength?

<p>Starch phosphorylase (C)</p> Signup and view all the answers

What is an observed effect of a mutant corn plant with a defective enzyme for starch synthesis?

<p>It has reduced transport of material to the kernels (A)</p> Signup and view all the answers

Sink size is defined as which of the following?

<p>The total weight of the sink tissue (B)</p> Signup and view all the answers

What is NOT a factor affecting sink activity?

<p>Transpiration rate from source leaves (C)</p> Signup and view all the answers

Flashcards

Transfer Cells in Xylem

Specialized parenchyma cells in xylem that retrieve and reroute solutes, effectively acting as transport hubs within the xylem.

Apoplast

The interconnected system of cell walls and spaces outside of the plasma membrane in plants, facilitating movement of water and solutes.

Plasmodesmata in Companion and Transfer Cells

Companion cells and transfer cells are largely isolated from surrounding cells by plasmodesmata (tiny channels connecting cells), but they still have a few present and their function is unknown, despite the potential for viral transmission.

Intermediary Cells

Specialized cells with numerous plasmodesmata connecting them to surrounding cells, particularly bundle sheath cells. They are involved in solute uptake and have distinctive features like numerous small vacuoles and poorly developed thylakoids in chloroplasts.

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Sap

The fluid contents of plant cells found in the phloem, responsible for transporting sugars and other nutrients throughout the plant.

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Source (in Translocation)

Organs that produce photosynthetic products in excess of their own needs, acting as sources of sugars for the rest of the plant. Examples include mature leaves.

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Sink (in Translocation)

Organs that utilize or store photosynthetic products, receiving sugars from source organs. Examples include roots, fruits, and growing tissues.

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Photosynthate

Products of photosynthesis, including sugars, starches, and other organic molecules, transported through the phloem.

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Sink Tissues

Tissues that require carbohydrates for development, like roots, tubers, young fruits, and immature leaves.

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Source-to-Sink Translocation

The movement of sugars from source tissues (photosynthesis) to sink tissues (growth and storage).

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Proximity in Translocation

The closer a source is to a sink, the more likely it is to supply that sink with sugars.

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Development and Translocation

The importance of different sinks changes as a plant grows. Roots and shoots are important during vegetative growth, while fruits become dominant during reproduction.

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Vascular Connections and Translocation

A direct vascular connection increases the likelihood of a source supplying a particular sink.

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Orthostichy

A vertical row of leaves on a stem.

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Anastomoses

Alternative pathways for translocation when the main route is blocked or damaged.

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Modification of Translocation Pathways

The ability of a plant to redirect sugars to different sinks, especially when a source is removed.

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Mass Transfer Rate

The rate at which a substance travels through a specific area over time, quantified by the amount of material passing through a given cross-section of phloem per unit time.

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Velocity

The linear distance a substance travels per unit time. It's one way to describe phloem transport, but mass transfer rate offers a more accurate picture because it accounts for the cross-sectional area of the sieve elements.

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Pressure-Flow Model

The dominant theory explaining how sugars are translocated in angiosperms, relying on the pressure difference created by the loading of sugars at sources and the unloading of sugars at sinks.

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Phloem Loading

The process where sugars produced in source tissues are actively loaded into the sieve elements of phloem for transport.

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Phloem Unloading

The process where sugars unloaded from the sieve elements of phloem are taken into the sink cells for storage or utilization.

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Sieve Elements

Cells in the phloem that are responsible for transporting sugars and other nutrients throughout the plant. They have distinctive features like sieve plates and P-protein, which help facilitate the movement of sap.

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Companion Cells

Specialized cells in the phloem that are closely associated with sieve elements and play a vital role in phloem loading and unloading. They provide metabolic support to sieve elements, which lack nuclei and ribosomes.

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Translocation in Phloem

The movement of sugars within the phloem from the source (where they are produced) to the sink (where they are used or stored).

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Short-distance transport in Phloem

The process by which photosynthetic products move from the mesophyll cells to the sieve elements of the smallest veins in a leaf, covering a short distance of only a few cell diameters.

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Sieve Element Loading

The process by which sugars are loaded into the sieve elements and companion cells, often resulting in a higher concentration of sugars in these cells compared to the mesophyll.

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Phloem Export

The movement of sugars away from the source, primarily through the vascular system, to the sink.

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Sieve Element Unloading

The process by which sugars leave the sieve elements in sink tissues.

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Short-distance transport in Sink Tissues

After sieve element Unloading, sugars are transported to cells in the sink by a short-distance transport pathway.

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Allocation

The regulation of the diversion of fixed carbon into various metabolic pathways.

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Storage and Metabolism

The process by which sugars are either stored or metabolized in sink cells.

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What is the pressure-flow hypothesis?

The pressure-flow hypothesis describes the movement of sugars from source tissues (photosynthesis) to sink tissues (growth and storage) in the phloem.

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How do sieve plates contribute to sugar transport?

The sieve plates, the porous structures connecting sieve elements, create resistance in the phloem, leading to a pressure difference between sources and sinks.

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How does the pressure gradient drive sugar movement?

This pressure gradient, higher in sources and lower in sinks, drives the movement of sugar through the phloem, much like water flowing through a hose.

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What happens to the pressure-flow hypothesis if sieve plates are blocked?

The pressure-flow hypothesis predicts that the sieve plates must be unobstructed. Any blockage would significantly hinder the movement of sugar through the phloem.

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Can sugar flow in both directions in a single sieve element?

The pressure-flow model also predicts that simultaneous transport in both directions within a single sieve element is not possible.

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Is energy needed for sugar translocation through the phloem?

Sugar loading into the phloem requires energy to maintain the sieve element structure and to replace any leaks from the transport pathway.

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What is phloem loading?

Phloem loading is the process of moving photosynthates from the mesophyll chloroplasts to the sieve elements of mature leaves.

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How does sucrose get loaded into the phloem?

The triose phosphate formed during photosynthesis is converted to sucrose and transported from the chloroplasts to the sieve elements in the phloem.

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Sink Strength

The ability of a sink to attract and absorb photosynthates from the source.

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Sink Size

Represents the total weight of the sink tissue. A larger sink size means more potential for storage or utilization of photosynthates.

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Sink Activity

The rate at which a sink absorbs photosynthates per unit weight. A higher sink activity means the sink is more efficient at using the supplied sugars.

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Partitioning

The process of allocating photosynthates to different sinks throughout the plant. This determines how resources are distributed for growth and storage.

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Cooling's Impact on Sink Activity

Cooling a sink tissue can reduce the speed of photosynthate transport because it inhibits metabolic processes needed for uptake and storage.

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Defective Enzymes and Sink Strength

Defects in enzymes responsible for starch synthesis can reduce photosynthate transport to the sink because storage is impaired, affecting sink activity.

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Sucrose-Splitting Enzymes and Sink Strength

Acid invertase and sucrose synthase are key enzymes in sucrose utilization. Their activity can influence sink strength by determining how quickly sucrose is broken down and used.

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Uncertain Relationship: Enzymes and Sink Strength

The presence and activity of sucrose-splitting enzymes might be correlated with sink metabolism and growth, but their role in controlling sink strength is still being investigated.

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Study Notes

Translocation in Phloem

  • Phloem is the vascular tissue responsible for transporting sugars (assimilates) from source (e.g., leaves) to sink (e.g., roots, fruits)
  • The source is where sugars are produced (e.g., during photosynthesis)
  • The sink is where sugars are used or stored
  • Sucrose is the main transported sugar in phloem
  • Sieve elements are essential in phloem translocation
  • Companion cells are closely associated with sieve elements, and play a vital role in the transport process
  • Sieve tube elements and companion cells are together referred to as sieve element-companion cell complex
  • Sieve elements are highly specialized cells, losing many cellular components during differentiation
  • Companion cells are involved in metabolic and transport functions for sieve elements
  • Transfer cells have finger-like wall ingrowths to enhance solute exchange
  • Phloem loading is the active transport of sucrose into the sieve elements
  • Phloem unloading is the removal of sugars from the sieve elements into sink cells
  • The pressure-flow model describes translocation through pressure differences generated by sugar loading and unloading in the sieve elements
  • Water moving into sieve elements at the source creates pressure for mass flow from source to sink
  • The rate of translocation is influenced by both size and activity of the sink

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CRP 201 Lecture Note 7 Translocation in Phloem PDF

Description

Test your knowledge on plant physiology with this quiz focusing on carbohydrate import, transport mechanisms, and the development of sink tissues. Explore concepts like source-to-sink transport and the role of vascular systems in plants. Perfect for biology students and plant science enthusiasts!

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