Transport Of Substances In Plants

TRANSPORT OF SUBSTANCES IN PLANTS

Necessity for transport in plants • Transport water and minerals • Water needed as an important

component of cells • Mineral ions needed for chlorophyll synthesis, growth and development • Plants have less elaborate and slower transport system than animals

Vascular Tissue • Xylem and phloem form vascular

tissue • Xylem: gives support and transport water and mineral ions from root to upper parts of plants. Movement of substances against gravitational force • Phloem: transport organic food substances synthesised by leaves during photosynthesis

Structure of Xylem

Structure of Xylem • In flowering plants: xylem mainly

consists of vessel, tracheids and parenchyma • Xylem vessels: long, hollow, continuous tubes. The cell wall is strengthened by lignin (provide mechanical support). Vessel consists of dead cells. No protoplasm in the vessels

Structure of Xylem • Conifers and ferns do not have xylem

vessels yet tracheids • Tracheids: less efficient in conducting water, do not have open ends. Water pass from cell to cell through openings called pits.

Structure of Phloem • Transports organic food substances (sucrose and • • • •

amino acids from leaves to other part of the plants) Phloem tissue: consists mainly of sieve tubes and companion cells Sieve tubes: cylindrical tube consists of living sieve tube cells. The cross-walls separated the sieve cells are perforated by small pores. This walls are called sieve plates No nucleus exists in mature sieve tubes Companion cells: found only in flowering plants, adjacent to sieve tubes, has a nucleus, dense cytoplasm and many mitochondria, helps to transport manufactured food from leaf cells to the sieve tubes.

Transport of Substances in Plants • Translocation: two-directional

transport of soluble organic food materials • Transpiration: Loss of water in the form of water vapour from the plants to the atmosphere • Transpiration creates a transpirational pull, water creates turgidity to the leaves cells and stems.

Pathway of Water from Soils to the Leaves Root pressure Capillary action Transpirational pull

Water

Root pressure Capillary action Transpirational pull

Cell sap in root

Osmosis

Find out what is guttation?

Xylem Vessel

Osmosis

Factors Affecting Rate of Transpiration • Air movement: rate of transpiration

increases in windy condition • Temperature: rate of transpiration increases with temperature. Increase temperature increase kinetic energy of water molecules, water move faster through stomata

Factors Affecting Rate of Transpiration • Light Intensity: Higher light intensity

stimulates opening of stomata. Sunlight provides heat energy as so increases rate of evaporation • Relative humidity: High relative humidity, low transpiration rate, low relative humidity, high transpiration rate • Find out how the process of opening and closing of stomata that may influence rate of transpiration