transport in plants

What is xylem

Xylem are dead tissues containing tubes called vessels and are primarily used for transportation of water and provision of mechanical support to the plants. Moves in one direction (down to up)

What is phloem

Phloem are alive tissues containing tubes called sieve tubes. They’re mainly responsible for transport of sucrose (glucose created by the pant) and they deliver it from the source t the sinks located throughout the plants. Phloem moved in multi direction

Explain process of sucrose loading into phloem from source and getting unloaded in the sink

The loading of sucrose into the sieve tube lowers the water potential of the phloem sap, making it more negative. As a result, water enters the sieve tube by osmosis down the water potential gradient from surrounding xylem, increasing the volume of fluid inside the sieve tube. This rise in volume increases the hydrostatic (turgor) pressure at the source end. At the sink, sucrose is removed, which raises the water potential so water leaves, creating a lower hydrostatic pressure there. The difference in hydrostatic pressure between the high-pressure source and the low-pressure sink causes phloem sap to move along the sieve tube down the pressure gradient, resulting in mass flow of sucrose from source to sink.

Explain how xylem transports water from the roots to the leaf

The root hairs absorb water and minerals from the soil thru osmosis. The substances diffuse into the context and move toward the endodermis randomly by apo plastic and sympoas pathway. Once the substance enters the endodermis, apo plastic pathway is stopped by a suberin containing band called casparuan strip. Since the sell membersnes are partially pemewble, only some parts of the substances move into the endodermis and continues moving to the xylem vessel. From the xylem vessels, water being a polar molecule, bonds to other water molecule and minerskas thru cohesion and adhesion. Thus creates more pressure in the bottom of the xylem tube, therefore crrating tension. So water can move through a pressure gradient. As transpiration occurs in the leaf, the chain of water molecules get pulled upward and moves into the leaf.

Elements present in sieve tubes

Sieve plate, sieve pore, mitochondria, cell wall, cell surface memebrsne, thin cytoplasm, ER and a large vacuole

Schlerenchyma

Type of tissues that are dead and are kignified, mainly provides support and structure to the xylem tubes.

Collenchyma

A type of parenchyma tissues that are dead and have extra deposits of cellulose, providing extra support and thickens cells in certain areas of the plant (like in midrib)

Parenchyma

A basic plant tissue used as a packing tissue between specialised structures. it acts as a storage, and accommodates metabolic activities in the plant.

Adaptations of xerophyes

Hinge cells that cause leaves to roll up/shrink to expose thick cuticle, preventing rate of water loss

Hair/needle like leaf structure to trap moisture closer to leaves, reducing steepness of wp gradient, reducing surface area and protects plant from predator.

Sunken stomata to lower transpiration rate

Succulent leaves to store water and assimilateS

What are pits and their usefulness

Pits are gaps in xylem tube that allows water to move from one vessel to a neighbouring vessel.

When air bubbles form, water cannot pass thru it and so water moves into a neighbouring vessel thru the pits

Elements present in companion cell

Cell wall, mitochondria, RER, cell membrane, plasmodesmata, vacuole, tomolast, nucleus, cytoplasm

Y r companion cells required

Phloem tubes have a larger air space to accommodate transportation of assimilates, and loading of sucrose requires energy, companion cells complete the sieve tube element and keeps it alive and provides atp.

Y is diffusion alone not sufficient for large plants

Diffusion is too slow to meet the metabolic needs of large plants because the distances between the external environment and inner tissues are very great. As plants increase in size, their surface area to volume ratio becomes very small, meaning there is not enough surface area for diffusion to supply all internal cells with water, minerals, and sugars quickly enough. Inner cells are located far from the leaf surface or root surface, so diffusion over long distances would take far too long to sustain life.

Transpiration

The loss of water in the form of water vapou from the leaves due to evaporation.