Elementor #32034

Photosynthesis and Transport in Plants

Key Concepts:

• Photosynthesis: Process by which cells in a plant leaf produce glucose using sunlight, carbon dioxide, and water.
• Transport in Plants: Glucose produced in the leaves must be transported to other parts of the plant for use and storage.

Xylem and Phloem:

• Xylem:
  • Function:
    • Transports water and mineral ions from the roots to the rest of the plant.
    • Provides structural support to the plant.
  • Location: Found in roots, stems, and leaves.
• Phloem:
  • Function:
    • Transports sucrose and amino acids from the leaves to other parts of the plant.
  • Location: Found in roots, stems, and leaves.

Identification in Plant Sections:

• Roots:
  • Xylem and phloem are centrally located, with xylem forming a star-shaped structure and phloem surrounding it.
• Stems:
  • Xylem forms a ring on the inside, while phloem forms a ring on the outside of the vascular bundles.
• Leaves:
  • Xylem is located on the upper side, and phloem is on the lower side of the vascular bundles.

Root Hair Cells:

• Function:
  • Increase the surface area for water and mineral ion uptake.
  • Absorb water and mineral ions from the soil.
• Structure: Long and thin extensions of root epidermal cells, providing a large surface area.

Pathway of Water in Plants:

1. Root Hair Cells: Absorb water and mineral ions from the soil.
2. Root Cortex Cells: Water moves through the cortex towards the xylem.
3. Xylem Vessels: Transport water and dissolved minerals from the roots to the leaves.
4. Mesophyll Cells: Water moves from xylem to mesophyll cells where it can be used for photosynthesis or evaporated during transpiration.

Transpiration:

• Definition: The process of water vapour loss from the aerial parts of the plant, mainly through the stomata in the leaves.
• Mechanism: Water evaporates from the mesophyll cells and diffuses out of the stomata. This creates a negative pressure that pulls more water up through the xylem from the roots.

Factors Affecting Transpiration Rate:

• Temperature:
  • Higher temperatures increase the rate of evaporation and transpiration.
• Wind Speed:
  • Higher wind speeds remove the humid air around the leaf surface, increasing transpiration.

Diagrams for Reference:

Root Structure:

• Xylem and Phloem Arrangement:
  • Xylem is central and star-shaped.
  • Phloem surrounds the xylem.

Stem Structure:

• Vascular Bundles Arrangement:
  • Xylem on the inner side.
  • Phloem on the outer side.

Leaf Structure:

• Vascular Bundles in Leaves:
  • Xylem on the upper side.
  • Phloem on the lower side.

Summary

Understanding the roles and positions of xylem and phloem, as well as the process of transpiration and factors affecting it, are crucial for mastering plant transport mechanisms in the IGCSE Combined Science curriculum.