30.5 Transport of Water and Solutes in Plants
4 min read•june 14, 2024
Plants have a remarkable system for managing water and nutrients. drives water movement through plants, from roots to leaves, following a gradient. This process is influenced by factors like , stomatal regulation, and environmental conditions.
Sugar transport in plants occurs through the tissue. The explains how sugars move from source to sink areas. This process is crucial for distributing energy and resources throughout the plant, supporting growth and development.
Water Potential and Movement in Plants
Water potential in plants
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- () measures the potential energy of water in a system compared to pure water
- Pure water has a water potential of zero at standard temperature and pressure
- Water moves from areas of high water potential (less negative) to areas of low water potential (more negative)
- Components of water potential
- () positive pressure increases water potential
- in plant cells is an example of positive pressure potential that helps maintain cell shape and rigidity
- () dissolved solutes decrease water potential
- is another term for solute potential and is always negative due to the presence of dissolved solutes (sugars, ions)
- () gravity decreases water potential with height
- Water at higher elevations in a plant (top of a tall tree) has lower water potential due to the influence of gravity
- () positive pressure increases water potential
- The water potential equation:
- The sum of pressure potential, solute potential, and gravity potential determines the total water potential of a system
Movement of water through plants
- Water moves through plants from high water potential to low water potential following a water potential gradient
- Water enters the roots from the soil due to low water potential in root cells created by osmotic potential and transpiration pull
- Water moves up the due to the combined effects of transpiration pull, cohesion of water molecules, and adhesion of water to cell walls
- Transpiration is the loss of water vapor from leaves through
- Transpiration creates a pull that helps draw water up the xylem from the roots to the leaves
- Factors affecting transpiration rate
- Humidity low humidity increases transpiration rate by increasing the water vapor concentration gradient between the leaf and the atmosphere
- Temperature high temperatures increase transpiration rate by increasing the kinetic energy of water molecules and promoting evaporation
- Wind high wind speed increases transpiration rate by removing the boundary layer of humid air around the leaf surface
- is the combined water loss from transpiration and evaporation from soil and plant surfaces
- Evapotranspiration is an important factor in the water cycle and can influence local climate and water availability
- Stomata control gas exchange and water loss in leaves
- regulate stomatal opening and closing through changes in turgor pressure
- When guard cells are turgid (high turgor pressure), stomata open; when flaccid (low turgor pressure), stomata close
- Factors affecting stomatal opening and closing
- Light stomata typically open during the day to facilitate gas exchange for photosynthesis and close at night to conserve water
- Carbon dioxide concentration low CO2 levels in the leaf promote stomatal opening to allow more CO2 uptake for photosynthesis
- Water availability drought stress triggers stomatal closure to conserve water and prevent excessive water loss
- regulate stomatal opening and closing through changes in turgor pressure
Water and solute transport pathways
- pathway: water and solutes move through cell walls and intercellular spaces without crossing cell membranes
- pathway: water and solutes move through the cytoplasm of cells, connected by (channels between adjacent cells)
- Transmembrane pathway: water moves across cell membranes, facilitated by (specialized water channel proteins)
- (xylem and ) provides long-distance transport of water and solutes throughout the plant
Transport of Sugars and Photosynthetic Products
Transport of photosynthetic products
- Sugars and photosynthetic products are transported through the phloem tissue
- Phloem is composed of and
- Sieve elements are living cells that lack a nucleus and other organelles, allowing for efficient transport of sugars and other solutes
- support the function of sieve elements by providing energy and maintaining cellular functions
- Phloem is composed of and
- The pressure flow hypothesis explains the movement of sugars in the phloem
- Sugars are actively loaded into the phloem at the source (leaves) using energy from ATP
- Active loading creates high sugar concentration and high osmotic pressure in the phloem
- Water enters the phloem by due to the high osmotic pressure, increasing the turgor pressure
- The high turgor pressure drives the bulk flow of sugars and water from the source to the sink
- are areas of sugar unloading and utilization (roots, fruits, growing tissues, storage organs)
- At the sink, sugars are actively unloaded or used in metabolism, decreasing the osmotic pressure
- Water exits the phloem by osmosis, maintaining the pressure gradient and allowing for continuous flow
- Sugars and other photosynthetic products transported by the phloem
- Sucrose is the primary sugar transported in most plants due to its non-reducing properties and stability
- Other transported compounds include amino acids (products of nitrogen metabolism), hormones (growth regulators), and some minerals (phloem sap composition)
- influence the direction and rate of sugar transport in the
Key Terms to Review (40)
Abscisic acid: Abscisic acid is a plant hormone that plays a crucial role in regulating various physiological processes, particularly in response to stress conditions such as drought and salinity. This hormone helps plants conserve water by promoting stomatal closure, thus reducing transpiration and aiding in the transport of water and solutes during challenging environmental conditions.
Apoplast: The apoplast refers to the network of cell walls and intercellular spaces in plants through which water and solutes can move freely without crossing any cell membranes. This pathway is crucial for the transport of water and nutrients, as it allows substances to bypass the living protoplasts and move through a passive route, contributing to the overall transport mechanisms within plant tissues.
Apoplastic Transport: Apoplastic transport refers to the movement of water and solutes through the apoplast, which is the network of cell walls and intercellular spaces in plants. This pathway allows substances to move freely without crossing cell membranes, enabling efficient transport of water and nutrients from roots to other parts of the plant.
Aquaporins: Aquaporins are specialized membrane proteins that facilitate the transport of water molecules across cell membranes. These channels are crucial for regulating water balance in various biological systems, allowing cells to efficiently manage water flow, which is essential for maintaining homeostasis in both plants and animals.
Auxin: Auxin is a plant hormone that plays a crucial role in regulating growth and responses to environmental stimuli. It influences various physiological processes, including cell elongation, root formation, and tropisms, allowing plants to adapt to their surroundings and optimize resource use. By promoting growth on the side of the plant that is away from light, auxin helps direct growth towards favorable conditions.
Auxins: Auxins are a class of plant hormones that play a crucial role in the regulation of plant growth and development. They are primarily responsible for cell elongation, root formation, and responses to light and gravity.
Cohesion-tension theory: Cohesion-tension theory explains how water moves through plants, particularly in the xylem, by utilizing the properties of cohesion and tension. This theory highlights that water molecules stick to each other (cohesion) and also adhere to the walls of xylem vessels (adhesion), which creates a continuous column of water that can be pulled upward from roots to leaves due to transpiration. The loss of water vapor from leaf surfaces generates a negative pressure (tension) that aids in drawing more water up from the roots, allowing for efficient transport of nutrients and maintaining plant hydration.
Companion cells: Companion cells are specialized parenchyma cells found in the phloem of flowering plants. They play a crucial role in the transport of photosynthates (sugars) from source tissues to sink tissues.
Companion cells: Companion cells are specialized plant cells that play a crucial role in the transport of nutrients, particularly sugars, within the phloem tissue. These cells are closely associated with sieve tube elements and support their function by providing the necessary energy and resources for the active transport of substances. The relationship between companion cells and sieve tube elements is vital for efficient communication and nutrient distribution throughout the plant.
Evapotranspiration: Evapotranspiration is the process by which water is transferred from the land to the atmosphere through evaporation from soil and water surfaces, as well as transpiration from plants. This process is crucial for the water cycle and has significant impacts on plant physiology, soil moisture levels, and climate patterns. Understanding evapotranspiration helps in recognizing how plants regulate their internal water balance and how ecosystems respond to changes in climate.
Gravity potential: Gravity potential refers to the potential energy stored in an object due to its position in a gravitational field, often represented in terms of height above a reference point. In the context of water and solute transport in plants, gravity potential plays a significant role in influencing how water moves through plant tissues and contributes to the overall water potential, impacting processes like osmosis and transpiration.
Guard cells: Guard cells are specialized cells located on the surface of plant leaves that control the opening and closing of stomata, which are tiny pores that facilitate gas exchange. By regulating the size of these pores, guard cells play a crucial role in the transport of water and solutes, balancing the plant's need for carbon dioxide for photosynthesis with the loss of water through transpiration.
Megapascals: Megapascals (MPa) are a unit of pressure or stress, commonly used to measure water potential in plants. One MPa is equal to one million pascals or approximately 10 atmospheres of pressure.
Osmosis: Osmosis is the movement of water molecules through a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration, aiming to balance solute concentrations on both sides of the membrane. This process is vital for maintaining cellular homeostasis and plays a crucial role in various biological systems, including plant hydration and nutrient transport.
Osmotic potential: Osmotic potential is a measure of the tendency of water to move into or out of a solution through osmosis, which is the diffusion of water across a semipermeable membrane. It plays a crucial role in the movement of water and solutes within plant cells, influencing their turgor pressure and overall health. Understanding osmotic potential is essential for grasping how plants absorb water from the soil and transport nutrients throughout their tissues.
Phloem: Phloem is the vascular tissue responsible for the transport of sugars and other metabolic products downward from the leaves. It plays a crucial role in the distribution of nutrients throughout seedless vascular plants.
Phloem: Phloem is a type of vascular tissue in plants responsible for the transport of organic nutrients, particularly sucrose, from the leaves where photosynthesis occurs to other parts of the plant. This tissue plays a critical role in the overall growth and energy distribution of plants, connecting various parts and facilitating nutrient flow.
Plasmodesmata: Plasmodesmata are microscopic channels that traverse the cell walls of plant cells, facilitating communication and transport between them. These channels allow the movement of substances such as nutrients, signaling molecules, and genetic material.
Plasmodesmata: Plasmodesmata are microscopic channels that traverse the cell walls of plant cells, allowing for communication and transport of materials between adjacent cells. These structures play a crucial role in maintaining cellular activities by enabling the exchange of ions, nutrients, and signaling molecules, thereby facilitating the coordination of physiological processes across plant tissues.
Pressure flow hypothesis: The pressure flow hypothesis explains how sugars and other organic compounds are transported in plants through the phloem. This process relies on the differences in pressure created by the loading of sugars into the phloem at the source and their unloading at the sink, leading to a flow that moves the nutrients efficiently throughout the plant.
Pressure Potential: Pressure potential is the component of water potential that represents the physical pressure exerted by water within plant cells. This pressure, which can be positive or negative, plays a crucial role in maintaining turgor pressure and facilitating the transport of water and solutes in plants, especially in relation to cell walls and osmotic balance.
Root pressure: Root pressure is the positive pressure generated in the roots of plants, primarily due to the accumulation of solutes and water in the root xylem. This pressure plays a crucial role in the upward movement of water and nutrients from the roots to other parts of the plant, especially during periods when transpiration rates are low, such as at night.
Sieve elements: Sieve elements are specialized cells in the phloem of vascular plants that are responsible for the transport of sugars and other organic nutrients throughout the plant. These cells are characterized by their elongated shape and perforated end walls, allowing for efficient movement of materials between cells. Sieve elements work closely with companion cells, which provide metabolic support and regulate the flow of nutrients.
Sinks: Sinks are plant tissues or organs that consume or store carbohydrates and other solutes transported from sources. They are crucial for the distribution of nutrients within the plant, supporting growth and development.
Solute potential: Solute potential, also known as osmotic potential, is a measure of the tendency of water to move into a solution due to the presence of solutes. It is an essential concept in understanding how water and solutes are transported within plants, influencing processes such as osmosis and plant turgor pressure. The solute potential is always a negative value, reflecting the effect of solutes on reducing the water potential of a solution.
Source-sink relationships: Source-sink relationships refer to the dynamic interactions between areas of a plant that produce and store resources, such as photosynthates, and those that require these resources for growth and development. Sources are typically mature leaves or stems that synthesize nutrients, while sinks are young tissues, fruits, or roots that depend on these nutrients. Understanding these relationships is crucial for comprehending how plants allocate resources to optimize their growth and reproduction.
Sources: Sources are the parts of a plant where photosynthesis occurs, producing sugars and other organic molecules. Common sources include leaves and green stems.
Stomata: Stomata are small openings found on the surfaces of leaves and stems that allow for gas exchange between the plant and its environment. They play a crucial role in regulating photosynthesis, respiration, and transpiration, influencing how plants interact with their surroundings and manage water loss.
Symplast: Symplast refers to the continuous network of cytoplasm interconnected by plasmodesmata, allowing for the transport of water, nutrients, and other solutes within plant cells. This pathway is crucial for maintaining cellular communication and nutrient distribution in plants, connecting living parts of the plant and facilitating the movement of substances from cell to cell.
Symplastic transport: Symplastic transport refers to the movement of water and solutes through the cytoplasm of plant cells, interconnected by plasmodesmata, which are microscopic channels that allow for direct communication and exchange between adjacent cells. This pathway is crucial for maintaining cellular homeostasis and facilitating nutrient transport within plants, contributing to overall plant growth and function.
Translocation: Translocation is the movement of materials from one part of an organism to another. In biology, it often refers to either the transfer of chromosomes or segments between non-homologous chromosomes or the transport of nutrients and water within plants.
Translocation: Translocation refers to the process of moving substances from one part of an organism to another, which can occur at both the genetic and physiological levels. In genetics, translocation describes the rearrangement of chromosomal segments that can lead to inherited disorders, while in plants, it involves the transport of water and nutrients through specialized tissues. Understanding translocation is crucial for exploring how genetic mutations can affect health and how plants manage resources essential for their growth.
Translocation stream: Translocation stream refers to the process by which water, nutrients, and organic compounds are transported within a plant from one part to another, primarily through specialized tissues like phloem. This process is essential for the distribution of resources that support growth and development, as it allows plants to move products of photosynthesis and other vital substances throughout their structures.
Transpiration: Transpiration is the process by which plants lose water vapor from their aerial parts, mainly through small openings called stomata. This water loss is crucial for maintaining plant health as it helps in nutrient uptake, temperature regulation, and overall physiological balance.
Turgor pressure: Turgor pressure is the pressure exerted by the fluid (usually water) inside the central vacuole of a plant cell against the cell wall. This pressure helps maintain the cell's shape, supports the plant structure, and regulates growth. It is vital for maintaining cellular functions and is influenced by factors such as water availability and solute concentration.
Vascular tissue: Vascular tissue is specialized plant tissue responsible for the transport of water, nutrients, and food throughout the plant. It consists primarily of xylem and phloem, which play critical roles in supporting plant structure and facilitating growth. The presence of vascular tissue marks a significant evolutionary advancement in plants, allowing them to grow larger and thrive in a variety of environments.
Water potential: Water potential is a measure of the potential energy in water and drives the movement of water through plants. It is influenced by factors like solute concentration and pressure.
Water potential: Water potential is a measure of the potential energy of water in a system, influencing the direction and movement of water across membranes. It combines both osmotic potential and pressure potential, determining how water moves through plants and organisms. Understanding water potential is crucial for grasping how water is transported in plant cells, affects passive transport, and plays a role in maintaining osmotic balance within cells.
Xylem: Xylem is a type of vascular tissue in plants responsible for the transport of water and nutrients from the roots to other parts of the plant. It also provides structural support.
Xylem: Xylem is a type of tissue in vascular plants responsible for the transport of water and dissolved minerals from the roots to the rest of the plant. This tissue plays a crucial role in supporting plant structure and facilitating photosynthesis by ensuring that leaves receive the necessary water for transpiration and nutrient uptake.