TRANSPORT OF TRANSPORT OF SUBSTANCES IN PLANTSSUBSTANCES IN PLANTS

Necessity for transport in Necessity for transport in plantsplants

• Transport water and mineralsTransport water and minerals

• Water needed as an important Water needed as an important component of cellscomponent of cells

• Mineral ions needed for chlorophyll Mineral ions needed for chlorophyll synthesis, growth and developmentsynthesis, growth and development

• Plants have less elaborate and slower Plants have less elaborate and slower transport system than animalstransport system than animals

Vascular TissueVascular Tissue

• Xylem and phloem form vascular tissueXylem and phloem form vascular tissue• Xylem: gives support and transport Xylem: gives support and transport

water and mineral ions from root to water and mineral ions from root to upper parts of plants. Movement of upper parts of plants. Movement of substances against gravitational forcesubstances against gravitational force

• Phloem: transport organic food Phloem: transport organic food substances synthesised by leaves substances synthesised by leaves during photosynthesisduring photosynthesis

Structure of XylemStructure of Xylem

Structure of XylemStructure of Xylem

• In flowering plants: xylem mainly In flowering plants: xylem mainly consists of vessel, tracheids and consists of vessel, tracheids and parenchymaparenchyma

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

Structure of XylemStructure of Xylem

• Conifers and ferns do not have xylem Conifers and ferns do not have xylem vessels yet tracheidsvessels yet tracheids

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

Structure of PhloemStructure of Phloem

• Transports organic food substances (sucrose and Transports organic food substances (sucrose and amino acids from leaves to other part of the plants)amino acids from leaves to other part of the plants)

• Phloem tissue: consists mainly of sieve tubes and Phloem tissue: consists mainly of sieve tubes and companion cellscompanion cells

• Sieve tubes: cylindrical tube consists of living sieve Sieve tubes: cylindrical tube consists of living sieve tube cells. The cross-walls separated the sieve cells tube cells. The cross-walls separated the sieve cells are perforated by small pores. This walls are called are perforated by small pores. This walls are called sieve platessieve plates

• No nucleus exists in mature sieve tubesNo nucleus exists in mature sieve tubes• Companion cells: found only in flowering plants, Companion cells: found only in flowering plants,

adjacent to sieve tubes, has a nucleus, dense adjacent to sieve tubes, has a nucleus, dense cytoplasm and many mitochondria, helps to transport cytoplasm and many mitochondria, helps to transport manufactured food from leaf cells to the sieve tubes.manufactured food from leaf cells to the sieve tubes.

Transport of Substances in Transport of Substances in PlantsPlants

• Translocation: two-directional transport Translocation: two-directional transport of soluble organic food materialsof soluble organic food materials

• Transpiration: Loss of water in the form Transpiration: Loss of water in the form of water vapour from the plants to the of water vapour from the plants to the atmosphereatmosphere

• Transpiration creates a transpirational Transpiration creates a transpirational pull, water creates turgidity to the pull, water creates turgidity to the leaves cells and stems.leaves cells and stems.

Pathway of Water from Soils to Pathway of Water from Soils to the Leavesthe Leaves

Cell sap in root Xylem Vessel

Osmosis

Water

Osmosis

Root pressureCapillary action

Transpirational pull

Root pressureCapillary action

Transpirational pull

Find out what is guttation?

Factors Affecting Rate of Factors Affecting Rate of TranspirationTranspiration

• Air movement: rate of transpiration Air movement: rate of transpiration increases in windy conditionincreases in windy condition

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

Factors Affecting Rate of Factors Affecting Rate of TranspirationTranspiration

• Light Intensity: Higher light intensity Light Intensity: Higher light intensity stimulates opening of stomata. Sunlight stimulates opening of stomata. Sunlight provides heat energy as so increases rate of provides heat energy as so increases rate of evaporationevaporation

• Relative humidity: High relative humidity, low Relative humidity: High relative humidity, low transpiration rate, low relative humidity, high transpiration rate, low relative humidity, high transpiration ratetranspiration rate

• Find out how the process of opening and Find out how the process of opening and closing of stomata that may influence rate of closing of stomata that may influence rate of transpirationtranspiration