Tag: biology

Vascular rays, also known as medullary rays, consist of parenchymatous cells passing radially through the secondary xylem and phloem. Their primary role is the radial conduction of water and organic nutrients across the woody stem.

The primary function of the epidermis in plants is to provide a protective barrier against water loss, mechanical injury, and pathogen entry.

Ringing/Girdling experiments demonstrate that phloem is responsible for translocation of food because phloem is present outside to xylem so when a ring of bark is removed from a woody plant, the woody xylem part remains intact, water and nutrient reaches the leaves. After the preparation of the photosynthate, it is not transported to other parts below the girdle since the phloem part is removed. This experiment shows that the phloem tissue aids food transport.

Xylem flow is unidirectional and phloem flow is bidirectional because xylem transport water from soil to leaves and phloem transfers the food.

Starch and sucrose are more efficient forms in which the energy can be stored when compared to glucose. The starch is not soluble in water. Hence, the sucrose which is soluble in water is the form which is used for transport. This structural form increases the efficient energy transfer. Sucrose is not as reactive as glucose. This helps to prevent the chemical reactions which can convert the sucrose while transport. 

Spring is considered as the flowering season. This is the period when there is growth of the floral buds which are formed at the apex of the vegetative shoots. Generally, there is a flow of sugar from the source (leaves) to sink end (roots). Due to the increase in the activity in the apex regions of the plant, there is consumption of food in the leaves. Hence, the food to the flower buds is supplied by the roots. 

The parenchyma cells in the phloem tissue are known as phloem parenchyma. There are different types of phloem parenchyma cells, companion cells, albuminous and other parenchyma cells. The transfer cells are a type of companion cells. These are the cells which have folded cell wall surface. This helps to increase the transfer of the sugar in the lateral sides. They also help in scavenging the solutes which require ATP to move across the membranes. 

The sugar molecules are transported by the conducting cells in the phloem tissue in the form of sucrose. These sugar molecules are transported from the source end to the sink end. The source end is the region where the sugar is present in high concentrations. The sugar needs to be moved in the sieve elements in the source end by the process of sieve elements. Energy needs to be spent to move the sugar molecules in the form of ATP. The sugar molecules are transported through osmosis and removed from the sieve cells in the sink end by active transport.