Transport in flowering plants

Transport in flowering plants

7.1 Uptake and transport of water and ions

1. Relate the structure of root hair cells to their function of water and ion uptake?

Root hair cells are specialized cells on the surface of plant roots that play a crucial role in water and ion uptake. Their unique structure allows them to perform this function efficiently.

 Here’s how their structure relates to their function:

1. Large surface area:

  Root hair cells have a large surface area due to their long, thin shape and numerous hair-like projections. This increases their exposure to the surrounding soil, allowing for greater absorption of water and ions.

2. Thin cell walls:

  The cell walls of root hair cells are thin and permeable, enabling easy entry of water and ions into the cell.

3. High concentration of transport proteins:

Root hair cells have a high concentration of transport proteins in their cell membranes, which facilitate the uptake of specific ions and water.

4. Vacuoles:

Root hair cells contain large vacuoles that help store water and ions, allowing the cell to regulate its internal environment and maintain turgor pressure.

5. Close proximity to xylem:

Root hair cells are located near the xylem, the vascular tissue responsible for water and ion transport. This proximity enables efficient transfer of absorbed water and ions into the plant’s vascular system.

The structure of root hair cells allows them to:

• Increase the surface area for absorption
• Facilitate easy entry of water and ions
• Transport specific ions and water into the cell
• Regulate internal environment and turgor pressure
• Efficiently transfer absorbed water and ions into the plant’s vascular system

2. Outline the pathway taken by water through the root, stem and leaf, limited to: root hair cells, root cortex cells, xylem and mesophyll cells?

The pathway taken by water through the root, stem, and leaf, including the specified cells:

1. Root Hair Cells:

Water enters the plant through root hair cells, which are specialized cells on the surface of the root that increase surface area for absorption.

2. Root Cortex Cells:

Water moves through the root cortex cells, which are the layers of cells inside the root that help filter and regulate the movement of water and minerals.

3. Xylem:

Water enters the xylem, a type of vascular tissue that transports water and minerals from the root to the stem and leaves.

4. Stem Xylem:

Water moves up the stem through the xylem, which forms a continuous tube from root to leaf.

5. Leaf Xylem:

Water reaches the leaf xylem, which branches into smaller veins that distribute water throughout the leaf.

6. Mesophyll Cells:

Water enters the mesophyll cells, which are the cells inside the leaf where photosynthesis occurs. Water is used for photosynthesis and other cellular processes

Root Hair Cells → Root Cortex Cells → Xylem → Stem Xylem → Leaf Xylem → Mesophyll Cells

Key points:

• Osmosis: The primary driving force for water movement is osmosis, the movement of water from a high concentration to a low concentration.
• Apoplastic and symplastic pathways: Water can move through the cell walls (apoplastic) or from cell to cell (symplastic).
• Xylem: The xylem is the main transport vessel for water in plants.
• Transpiration: The loss of water from the leaves through stomata pulls water up the xylem from the roots.

3. Investigate, using a suitable stain, the pathway of water in a cut stem

Experiment:

Materials:

• A fresh, leafy stem (e.g., celery)
• Red food coloring
• Water
• A clear glass or beaker
• A scalpel or sharp knife

Procedure:

1. Prepare the stem: Cut the stem at an angle to expose the vascular tissue.
2. Add the stain: Place the cut end of the stem in a glass or beaker filled with water. Add a few drops of red food coloring to the water.
3. Observe: Allow the stem to sit for several hours or overnight.
4. Examine the stem: Carefully cut a cross-section of the stem and observe the distribution of the red stain.

Expected Results:

The red food coloring will be visible in the xylem tissue, which is responsible for transporting water and minerals up the stem. The xylem cells will appear stained red, while the other tissues (phloem, cortex, pith) will remain unstained or only slightly stained.

Explanation:

• Water uptake: The red food coloring, dissolved in the water, will be absorbed by the root hairs and transported through the root cortex to the xylem.
• Xylem transport: The xylem vessels, which are dead cells, form a continuous tube that transports water and minerals up the stem. The red dye will be carried along with the water.
• Transpiration: The transpiration pull, caused by the evaporation of water from the leaves, will draw the water and dye up the xylem.
• Observation: The stained xylem tissue will be visible in the cross-section of the stem, indicating the pathway of water movement.

Additional Considerations:

• Stem type: The choice of stem can affect the rate of water uptake and the visibility of the stain. Woody stems may take longer to show results.
• Stain concentration: The concentration of the red food coloring can be adjusted to improve visibility.
• Observation time: The time required for the stain to travel up the stem can vary depending on factors such as temperature and the size of the stem.

By following this procedure, you can effectively investigate the pathway of water in a cut stem and visualize the role of the xylem in transporting water and minerals throughout the plant.

4. Describe transpiration as the loss of water vapour from leaves?

Transpiration is the process by which plants lose water vapor through tiny pores called stomata on the underside of their leaves. This evaporation of water from the leaves creates a pulling force that draws water up from the roots through the plant’s vascular system.

Key factors influencing transpiration:

• Stomatal opening: The size of the stomata openings directly affects the rate of transpiration. When stomata are open, water vapor can easily escape.
• Temperature: Higher temperatures increase the rate of evaporation, leading to increased transpiration.
• Humidity: Lower humidity increases the difference in water vapor concentration between the inside and outside of the leaf, promoting transpiration.
• Wind: Wind can help to remove water vapor from the leaf surface, increasing transpiration.
• Light: Light stimulates the opening of stomata, increasing transpiration during the day.

Benefits of transpiration:

• Water movement: Transpiration is essential for pulling water and minerals up from the roots to the rest of the plant.
• Cooling: As water evaporates, it takes heat with it, helping to cool the plant.
• Mineral transport: Transpiration also helps to transport minerals from the soil to the leaves.

Adaptations to reduce transpiration:

• Stomatal closure: Plants can close their stomata to reduce water loss, especially during dry conditions.
• Waxy cuticle: Some plants have a waxy cuticle on their leaves to help prevent water loss.
• Reduced leaf surface area: Plants in arid environments may have smaller leaves or spines to reduce the surface area exposed to the sun and wind.

5. Understand that water evaporates from the surfaces of the mesophyll cells into air spaces and then diffuses out of the leaves through the stomata as water vapour?

Break down the process of water transpiration step by step:

1. Evaporation from Mesophyll Cells:
   • Water Loss: Mesophyll cells, the photosynthetic cells within leaves, contain a high concentration of water. This water evaporates from the surfaces of these cells into the air spaces within the leaf.
2. Diffusion into Air Spaces:
   • Concentration Gradient: The air spaces within the leaf have a lower concentration of water vapor than the mesophyll cells. This creates a concentration gradient, driving the diffusion of water vapor from the cells into these spaces.
3. Diffusion through Stomata:
   • Stomatal Openings: Stomata are tiny pores on the underside of leaves. When these pores are open, water vapor can diffuse out of the leaf into the surrounding atmosphere.
   • Concentration Gradient: The concentration of water vapor in the atmosphere is generally lower than that within the leaf’s air spaces, further facilitating diffusion.

The process of transpiration involves the evaporation of water from mesophyll cells, its diffusion into the leaf’s air spaces, and finally, its diffusion out of the leaf through the stomata as water vapor. This process is essential for plants as it helps to transport water and minerals throughout the plant and also plays a role in cooling the plant.

6. Effects of Environmental Factors on Transpiration Rate
7. a) Effects of Wind Speed, Temperature, Humidity, and Light Intensity:

• Wind Speed:
  • Increased Transpiration: Higher wind speeds can increase transpiration by removing water vapor from the leaf surface more quickly. This creates a steeper concentration gradient between the leaf and the surrounding atmosphere, promoting further evaporation.
  • Boundary Layer: Wind can disrupt the boundary layer, a thin layer of still air that surrounds the leaf. By breaking up this layer, wind can improve the exchange of water vapor between the leaf and the atmosphere.
• Temperature:
  • Increased Transpiration: Higher temperatures increase the kinetic energy of water molecules, making them more likely to evaporate. This leads to a higher rate of transpiration.
  • Stomatal Opening: Warmer temperatures can also cause stomata to open wider, increasing the area available for water vapor to escape.
• Humidity:
  • Decreased Transpiration: Higher humidity reduces the difference in water vapor concentration between the leaf and the surrounding atmosphere, slowing down the rate of transpiration.
  • Concentration Gradient: A smaller concentration gradient means less driving force for water vapor to diffuse out of the leaf.
• Light Intensity:
  • Increased Transpiration: Light stimulates the opening of stomata, increasing the area available for water vapor to escape.
  • Photosynthesis: Light is also necessary for photosynthesis, which indirectly affects transpiration. Photosynthesis requires water, and as plants use water for photosynthesis, more water is pulled up from the roots, increasing transpiration.

1. b) How Wilting Occurs:

Wilting occurs when a plant loses water at a faster rate than it can absorb it from the soil. This can happen due to a variety of factors, including:

• Insufficient Water: If the soil is dry or the plant’s roots are unable to absorb enough water, the plant may wilt.
• High Transpiration Rates: High temperatures, low humidity, or strong winds can increase transpiration rates, leading to excessive water loss.
• Root Damage: If the plant’s roots are damaged, it may be unable to absorb water efficiently.
• Diseases or Pests: Some diseases and pests can affect a plant’s ability to absorb or retain water.

When a plant wilts, its leaves become droopy or flaccid. This is due to a decrease in turgor pressure, the internal pressure within plant cells that helps to maintain their structure. If wilting is severe or prolonged, it can damage the plant or even lead to death.

7. Investigating the Effects of Environmental Factors on Transpiration Rate

Experiment Design

Materials:

• Two potted plants of the same species and size
• Transparent plastic bags
• A fan
• A light source (e.g., a lamp)
• A thermometer
• A hygrometer

Procedure:

1. Control Setup:
   • Place one potted plant in a shaded area with minimal wind.
   • Cover the plant with a transparent plastic bag to create a humid environment.
2. Experimental Setup:
   • Place the other potted plant in a sunny location.
   • Use the fan to create a breeze around the plant.
3. Measurements:
   • Record the initial temperature, humidity, and light intensity at both setups.
   • Measure the rate of water loss by observing how quickly the water level in the pot decreases over a set period (e.g., 30 minutes).
4. Variations:
   • Light Intensity: Adjust the distance between the light source and the experimental plant to vary light intensity.
   • Temperature: Place the experimental plant in a warmer or cooler environment to vary temperature.
5. Repeat:
   • Repeat the experiment multiple times to ensure accuracy and reliability of the results.

Expected Results

• Wind Speed: Higher wind speeds should increase transpiration rates, as wind can remove water vapor from the leaf surface more quickly.
• Light Intensity: Increased light intensity should lead to higher transpiration rates, as light stimulates the opening of stomata, allowing more water vapor to escape.
• Temperature: Higher temperatures should increase transpiration rates, as warmer temperatures increase the kinetic energy of water molecules, making them more likely to evaporate.

Data Analysis

• Graphing: Plot the transpiration rates (water loss over time) against the corresponding environmental factors (wind speed, light intensity, and temperature).
• Correlation: Analyze the correlation between the environmental factors and transpiration rates.
• Statistical Analysis: Use statistical tests (e.g., t-test, ANOVA) to determine if the differences in transpiration rates are statistically significant.

Conclusion

Based on the experimental data, you can draw conclusions about the effects of wind speed, light intensity, and temperature variation on transpiration rates. This information can be used to understand how plants adapt to different environmental conditions and to develop strategies for plant water conservation

8. Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull that draws up a column of water molecules, held together by forces of attraction between water molecules?

Transpiration Pull: The Mechanism of Water Movement in Xylem

Transpiration pull is the primary force driving the upward movement of water in the xylem of plants. It’s a phenomenon that relies on the cohesive properties of water molecules and the evaporative force of transpiration.

Key steps involved in transpiration pull:

1. Transpiration: Water evaporates from the mesophyll cells of leaves through tiny pores called stomata. This evaporation creates a water vapor deficit within the leaf.
2. Water Deficit: The water deficit in the leaf cells leads to a decrease in water potential. This lower water potential pulls water from neighboring cells, including those in the xylem.
3. Cohesion and Adhesion: Water molecules are held together by cohesive forces due to hydrogen bonding. These forces create a continuous column of water molecules in the xylem vessels. Additionally, water molecules are attracted to the walls of the xylem vessels, a phenomenon known as adhesion.
4. Capillary Action: The combined forces of cohesion and adhesion create a capillary action effect. This allows water to move upward in narrow xylem vessels, even against gravity.
5. Continuous Pull: As water is lost through transpiration, the transpiration pull continues to draw more water up from the roots through the xylem. This creates a continuous flow of water from the soil to the leaves.

In essence, transpiration pull is a chain reaction:

• Evaporation: Water evaporates from leaves.
• Water Deficit: This creates a water potential gradient.
• Cohesion and Adhesion: Water molecules are held together and attracted to the xylem walls.
• Capillary Action: Water moves upward in the xylem vessels.
• Continuous Pull: The process repeats, drawing more water from the roots.

This mechanism ensures that plants can efficiently transport water and essential minerals from the soil to their aerial parts, supporting their growth and survival.

9. Describe translocation as the movement of sucrose and amino acids in the phloem from parts of plants that produce or release them (sources) to parts of plants that use or store them (sinks)?

Translocation is the process by which organic molecules, such as sucrose and amino acids, are transported throughout a plant. These molecules are moved from areas where they are produced or released (sources) to areas where they are used or stored (sinks).

Sources of organic molecules typically include:

• Leaves: Photosynthesis produces sucrose and other organic compounds.
• Storage organs: Organs like roots, tubers, or bulbs can release stored sugars.

Sinks of organic molecules include:

• Roots: Growing roots require sucrose for energy and building materials.
• Developing fruits: Fruits often store sugars for energy and attract animals for seed dispersal.
• Meristems: These regions of active growth require nutrients for cell division and expansion.
• Storage organs: Some organs, like tubers or bulbs, store sugars for future use.

Phloem: The phloem is the vascular tissue responsible for translocation. It consists of sieve tube elements and companion cells. Sieve tube elements form long, tubular structures that transport organic molecules. Companion cells provide support and metabolic functions to sieve tube elements.

Translocation Mechanism:

• Loading: Organic molecules are loaded into the phloem at source tissues. This process often requires energy (ATP).
• Pressure Gradient: The loading of organic molecules creates a higher osmotic pressure within the phloem at the source. This pressure gradient drives the movement of water into the phloem, increasing turgor pressure.
• Bulk Flow: The increased turgor pressure forces the solution of organic molecules to move through the phloem from the source to the sink.
• Unloading: At the sink tissues, organic molecules are unloaded from the phloem and used or stored.

Factors Affecting Translocation:

• Source-Sink Relationships: The strength of the source-sink relationship (the difference in osmotic pressure between source and sink) influences the rate of translocation.
• Metabolic Activity: The metabolic needs of the sink tissue affect the rate of unloading.
• Environmental Factors: Factors like temperature, light intensity, and water availability can influence translocation rates.

translocation is a vital process for plant growth and development. It ensures that organic molecules produced in one part of the plant can be efficiently transported to where they are needed.

10. Identify the positions of tissues as seen in transverse sections of non-woody dicotyledonous roots and stems, limited to: xylem, phloem and cortex?

Transverse Section of a Non-Woody Dicotyledonous Root

• Xylem: Located in the center of the root, forming a star-shaped pattern.
• Phloem: Surrounds the xylem, forming a ring of vascular bundles.
• Cortex: The outer layer of the root, between the epidermis and the vascular bundle.

Transverse Section of a Non-Woody Dicotyledonous Stem

• Xylem: Located towards the inside of the stem, often forming a ring or a “V” shape.
• Phloem: Surrounds the xylem, forming a ring of vascular bundles.
• Cortex: The outer layer of the stem, between the epidermis and the vascular bundles.

11. Key differences between root and stem tissue distribution:

• Xylem and Phloem: In roots, the xylem is in the center, surrounded by the phloem. In stems, the xylem and phloem are arranged in vascular bundles.
• Cortex: The cortex in roots is generally larger than in stems.

The specific arrangement of tissues can vary slightly depending on the species and developmental stage of the plant. However, the general pattern described above is common in non-woody dicotyledonous roots and stems.

12. State the functions of xylem as transport of water and mineral ions, and support?

Xylem is a vascular tissue found in plants that has three primary functions:

1. Transport of Water and Mineral Ions:
   • Upward Movement: Xylem vessels transport water and dissolved mineral ions from the roots to the rest of the plant. This is essential for photosynthesis, plant growth, and overall plant health.
   • Transpiration Pull: The evaporation of water from leaves (transpiration) creates a tension that pulls water up through the xylem vessels.
2. Support:
   • Structural Strength: Xylem cells, particularly tracheids, have thick cell walls that provide structural support to the plant. This helps to prevent the plant from bending or breaking.
   • Rigid Framework: The interconnected network of xylem vessels forms a rigid framework that supports the plant’s aerial parts.
3. Relate the structure of xylem vessels to their function, limited to:

             (a) thick walls with lignin (details of lignification are not required)

             (b) no cell contents

           (c) cells joined end-to-end with no cross walls to form a long continuous tube

Structure and Function of Xylem Vessels

Xylem vessels are specialized cells that form part of the vascular tissue in plants. Their structure is uniquely adapted to their function of transporting water and minerals from the roots to the rest of the plant.

1. a) Thick Walls with Lignin:

• Structural Support: The thick walls, reinforced with lignin, provide structural support to the plant. This is particularly important in tall plants, which need a strong framework to withstand the forces of gravity and wind.
• Waterproofing: Lignin is a hydrophobic substance that helps to waterproof the xylem vessels. This prevents water loss and helps to maintain the water column within the vessels.

1. b) No Cell Contents:

• Efficient Water Transport: The absence of cell contents creates a hollow, open space within the xylem vessel. This allows water and minerals to flow freely through the vessel without obstruction.
• Reduced Resistance: The lack of cellular material reduces the resistance to water flow, allowing for efficient transport.

1. c) Cells Joined End-to-End with No Cross Walls:

• Continuous Tube: The end-to-end arrangement of xylem cells, without cross walls, forms a long, continuous tube. This allows water and minerals to move uninterrupted from the roots to the leaves.
• Efficient Transport: A continuous tube reduces the number of points where water flow could be impeded or slowed down.