Transport in Organisms and Plants

Transport in Organisms

• Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration.
• Single-celled organisms rely on diffusion to transport molecules because their surface area-to-volume ratio is large enough.
• Multicellular organisms have a smaller surface area-to-volume ratio. Therefore, they use specialized transport systems.
• Examples of specialized transport systems in multicellular organisms include alveoli in the lungs, villi in the small intestines, and root hair cells in plants.

Transport in Plants

Phloem Adaptations

• Phloem transports sucrose and amino acids between leaves and other plant parts (translocation).
• Phloem cells are located in roots, stems, and leaves.
• Phloem cells are elongated with perforated end walls called sieve plates, facilitating the movement of substances.
• Companion cells in the phloem provide energy to transport sugars.
• Translocation can occur in both directions, carrying sugars from sources (where they are made) to sinks (where they are needed).

Xylem Adaptations

• Xylem transports water and mineral ions from the roots to the leaves (water transport).
• Xylem cells are dead, hollow, and strengthened by lignin to support and transport water.
• Lignin deposition causes cells to die, allowing them to form continuous tubes.
• These tubes enable the movement of water from the roots to the leaves.
• Water molecules adhere to each other through hydrogen bonding, creating a continuous water column.
• Water evaporates from the leaves, creating a transpiration stream to pull more water up the plant.
• Bordered pits in the lignin allow water and minerals to pass into the xylem.

Water Absorption

• Water is absorbed from the soil by root hair cells.
• Root hair cells have a large surface area for efficient water absorption through osmosis.
• Increased transpiration rate increases water uptake rate to replace the lost water.

Transpiration and Water Uptake

• Transpiration is the evaporation of water from the surface of a plant.
• Stomata are openings on leaves that allow gases to enter and leave.
• Water evaporates through the open stomata.
• Water molecules' attraction to each other creates a pull that draws water up the plant.
• Water is drawn up from the soil, creating a transpiration stream.

Factors Affecting Transpiration

• Increase in light intensity: More stomata open to allow gaseous exchange for photosynthesis. This leads to increased water evaporation, hence increased transpiration rate.
• Increase in temperature: Higher temperatures result in faster-moving water molecules, increased evaporation, and thus increased transpiration rate.