transport in plants

• Plants require a transport system to ensure all plant cells receive sufficient nutrients
• Xylem tissue enables water and dissolved minerals to travel up the plant in the passive process of transpiration
• Phloem tissue enables sugars to reach all parts of the plant in the active process of translocation
• Vascular bundle in the roots:
• Xylem and phloem are components of the vascular bundle for transport of substances and structural support
• Xylem vessels are arranged in an X shape in the centre of the vascular bundle for mechanical support
• Endodermis surrounds the X shape arrangement of xylem vessels to supply them with water
• Pericycle, an inner layer of meristem cells, is present in the vascular bundle
• Vascular bundle in the stem:
• Xylem is inside in non-wooded plants for support and flexibility
• Phloem is found on the outside of the vascular bundle
• Cambium layer between xylem and phloem consists of meristem cells for new tissue production
• Vascular bundle in the leaf:
• Vascular bundles form midrib and veins of a leaf
• Dicotyledonous leaves have a network of veins for transport and support
• Xylem vessels:
• Transport water and minerals, provide structural support
• Long cylinders made of dead tissue with open ends, can form a continuous column
• Contain pits for water to move sideways, thickened with lignin for flexibility
• Water flows only upwards
• Phloem vessels:
• Tubes made of living cells, involved in translocation of nutrients
• Consist of sieve tube elements and companion cells
• Sieve tube elements transport sugars like sucrose in sap, can move upwards or downwards
• Companion cells aid in ATP production for loading sucrose into sieve tubes
• Cytoplasm of sieve tube elements and companion cells linked through plasmodesmata for communication and substance flow
• Transpiration:
• Process where plants absorb water through roots, move it up the plant, and release it as water vapor through leaves
• Transpiration stream supplies water for photosynthesis, growth, and elongation
• Involves osmosis, evaporation, and diffusion of water vapor
• Rate can be measured with a potometer
• Xerophytes:
• Plants adapted to dry conditions with adaptations to minimize water loss
• Adaptations include smaller leaves, densely packed mesophyll, thick waxy cuticles, closed stomata, hairs, and pits to trap moist air
• Hydrophytes:
• Plants living in water with adaptations like thin waxy cuticles, many open stomata, wide flat leaves, air sacs, and large air spaces for buoyancy
• Movement of water in the root:
• Water enters through root hair cells and moves into xylem tissue due to a water potential gradient
• Root hair cells provide a large surface area for water movement, minerals absorbed by active transport
• Water can move via symplast or apoplast pathways, encountering Casparian strip in the endodermis