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Questions and Answers
What is the primary mechanism by which ions are absorbed by plant roots?
What is the primary mechanism by which ions are absorbed by plant roots?
Which structural feature of xylem vessels primarily facilitates water transport?
Which structural feature of xylem vessels primarily facilitates water transport?
In phloem loading, how do sugars move against a concentration gradient?
In phloem loading, how do sugars move against a concentration gradient?
Which factor has the least effect on the rate of transpiration in plants?
Which factor has the least effect on the rate of transpiration in plants?
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What role does the endodermis play in nutrient uptake in roots?
What role does the endodermis play in nutrient uptake in roots?
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Which of the following is NOT a factor involved in the ascent of water in plants?
Which of the following is NOT a factor involved in the ascent of water in plants?
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Why do aquatic plants source carbon dioxide from their surrounding water?
Why do aquatic plants source carbon dioxide from their surrounding water?
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Which characteristic is unique to companion cells in the phloem?
Which characteristic is unique to companion cells in the phloem?
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Which process is used when the concentration of a specific ion in the soil is higher than that inside the root hair cell?
Which process is used when the concentration of a specific ion in the soil is higher than that inside the root hair cell?
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What aids in the passive movement of water from the root hairs to the xylem?
What aids in the passive movement of water from the root hairs to the xylem?
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Which part of the plant primarily absorbs inorganic ions from the soil?
Which part of the plant primarily absorbs inorganic ions from the soil?
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What is the role of the specific transporter proteins in the uptake of ions?
What is the role of the specific transporter proteins in the uptake of ions?
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What describes the structure surrounding all plant cells, including those in the cortex?
What describes the structure surrounding all plant cells, including those in the cortex?
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How does water travel across the cortex and into the xylem?
How does water travel across the cortex and into the xylem?
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What occurs when water moves through the symplast pathway?
What occurs when water moves through the symplast pathway?
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Why is water important for plant cells that do not photosynthesize?
Why is water important for plant cells that do not photosynthesize?
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What is the primary function of xylem tissue in plants?
What is the primary function of xylem tissue in plants?
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What factor is NOT listed as affecting transpiration rates?
What factor is NOT listed as affecting transpiration rates?
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Which characteristic of xylem vessels allows water to move easily from roots to leaves?
Which characteristic of xylem vessels allows water to move easily from roots to leaves?
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What is the role of lignin in the structure of xylem vessels?
What is the role of lignin in the structure of xylem vessels?
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What happens to the end walls of xylem elements as they develop?
What happens to the end walls of xylem elements as they develop?
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Why is measuring the rate of transpiration challenging?
Why is measuring the rate of transpiration challenging?
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Where does most transpiration occur within the plant?
Where does most transpiration occur within the plant?
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How do xylem vessels contribute to water movement in plants?
How do xylem vessels contribute to water movement in plants?
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What process allows sucrose to move from the companion cell to the sieve tube?
What process allows sucrose to move from the companion cell to the sieve tube?
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What happens to sucrose once it is unloaded into tissues?
What happens to sucrose once it is unloaded into tissues?
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Why was there debate about the mechanism of phloem transport until the late 20th century?
Why was there debate about the mechanism of phloem transport until the late 20th century?
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What is the comparative speed of phloem transport relative to diffusion?
What is the comparative speed of phloem transport relative to diffusion?
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How does the removal of forests to create agricultural land affect local climate?
How does the removal of forests to create agricultural land affect local climate?
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What effect does replacing grassland with agricultural land have on average temperatures in the Midwest?
What effect does replacing grassland with agricultural land have on average temperatures in the Midwest?
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What role do phloem proteins play in the mechanism of phloem transport?
What role do phloem proteins play in the mechanism of phloem transport?
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What is the primary factor affecting transpiration rates between crops and forest trees?
What is the primary factor affecting transpiration rates between crops and forest trees?
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What is the function of a potometer in plant physiology?
What is the function of a potometer in plant physiology?
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Which organic substance is primarily transported in phloem?
Which organic substance is primarily transported in phloem?
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What is a unique feature of sieve elements in phloem?
What is a unique feature of sieve elements in phloem?
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What happens to the pores in sieve plates during the preparation of specimens for microscopic viewing?
What happens to the pores in sieve plates during the preparation of specimens for microscopic viewing?
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Why do companion cells have a larger number of mitochondria and ribosomes compared to typical plant cells?
Why do companion cells have a larger number of mitochondria and ribosomes compared to typical plant cells?
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Which of the following statements about the structure of sieve elements is false?
Which of the following statements about the structure of sieve elements is false?
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What is one characteristic that distinguishes companion cells from sieve elements?
What is one characteristic that distinguishes companion cells from sieve elements?
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What is the primary function of sieve plates in phloem?
What is the primary function of sieve plates in phloem?
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What is a primary function of plasmodesmata in plant cells?
What is a primary function of plasmodesmata in plant cells?
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Which statement best describes the flow of phloem sap?
Which statement best describes the flow of phloem sap?
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How is sucrose loaded into companion cells within the phloem?
How is sucrose loaded into companion cells within the phloem?
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Why do plasmodesmata allow the movement of larger molecules between plant cells at times?
Why do plasmodesmata allow the movement of larger molecules between plant cells at times?
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What role do hydrogen ions play in the process of loading sucrose into companion cells?
What role do hydrogen ions play in the process of loading sucrose into companion cells?
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What defines an area in a plant as a 'source'?
What defines an area in a plant as a 'source'?
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In comparison with animal cells, how do plant cells utilize plasmodesmata?
In comparison with animal cells, how do plant cells utilize plasmodesmata?
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What distinguishes the mass flow movement of phloem sap from other types of movement in plants?
What distinguishes the mass flow movement of phloem sap from other types of movement in plants?
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Study Notes
Plant Transport Systems
- Plants, like animals, need a consistent supply of oxygen and nutrients. Large plants, require efficient transport systems.
- Plants need carbon dioxide for photosynthesis, which they acquire from the air or water.
- Plants require oxygen for respiration, though photosynthetic cells produce enough for their needs.
- Photosynthetic cells produce organic food materials (like glucose). Other cells depend on these materials from photosynthetic or storage cells.
- All plant cells rely on water and inorganic ions from soil.
- Plant transport systems are slower than animal systems, which is partly due to lower energy requirements.
- Plants have evolved different systems for carrying water/inorganic ions and photosynthetic products.
- Plant transport systems do not carry oxygen or carbon dioxide, these travel by diffusion.
Uptake of Ions
- Plants absorb inorganic ions from the soil around root hairs.
- Ions are moved across the root and into the xylem for transport throughout the plant.
- Ions are absorbed by facilitated diffusion if their concentration is higher outside the root hair than inside.
- Active transport moves ions if their concentration is higher inside the root hair than outside (requiring ATP).
Water Transport
- Water enters roots through root hairs by osmosis.
- Water potential in soil is usually higher than inside the root hairs, leading to passive water movement.
- Water moves across the root to the xylem tissue.
- The xylem transports water upwards through the plant to the leaves.
Root Hair Adaptations
- Root hairs have a large surface area for water and mineral ion absorption.
- Each root hair is roughly 200-250µm wide with thousands on each root branch to maximize surface area (allowing contact with large volumes of soil).
Water Movement in Roots (Apoplast and Symplast Pathways)
- Water can move through cell walls (apoplast pathway) or cells (symplast pathway).
- Water moves passively down the water potential gradient.
- The endodermis in roots has cells with a Casparian strip that blocks the apoplast pathway for ion control.
Transpiration
- Water evaporates from leaves through stomata in a process called transpiration.
- This creates a water potential gradient, pulling water upward through the xylem. This is called transpiration pull.
- Cohesion (attraction between water molecules) and adhesion (attraction to xylem walls) help maintain a continuous water column.
- Capillarity also plays a role in water transport.
- Roots also exert root pressure pushing water upwards.
Stomata
- Stomata are pores in leaves that allow gas exchange, including water vapor.
- Stomata open or close to regulate water loss and carbon dioxide intake.
- Guard cells control stomatal opening and closing.
Factors Affecting Transpiration
- Humidity, temperature, wind speed, light intensity, and stomatal aperture affect the rate of transpiration.
- Higher humidity reduces transpiration, while higher temperature and wind increase it.
- Light intensity often indirectly affects rate by influencing stomatal opening.
Comparing Rates of Transpiration
- Using a potometer measures water uptake, which closely correlates with transpiration rates.
Plant Structure and Transpiration
- Plant structure (leaf hairs, number and distribution of stomata) adapts to reduce water loss.
Transport in Phloem (Translocation)
- Translocation is the transport of organic compounds (like sucrose) throughout a plant.
- Sieve elements and companion cells work together.
- Sucrose loading into sieve elements creates a lower water potential, drawing water into them.
- Differences in water potential between sources and sinks drive mass flow of sap.
- Sources are areas producing sucrose (leaf during photosynthesis) and sinks are areas where sucrose is used.
Phloem Sap Composition
- Phloem sap has components like sucrose, amino acids, and ions.
Evidence for Phloem Transport Mechanisms
- Evidence supports that phloem transport is primarily by mass flow driven by a pressure difference between source and sink.
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