20 Which of the following do not have spongy stem with air cavities ? *
1/1
Answers
Answer:
Aerenchyma cells are present in the aquatic plant. Such cells have large air cavities, which enable the plant to float in water.
Collenchyma cells are living, elongated and irregularly thickened at corners with less intercellular space. They do not have air cavities to provide buoyancy in water. Therefore, option B is incorrect.
Sclerenchyma is dead, long, thin, narrow cells with thickened walls without any internal space. These cells have a narrow lumen. Hence cannot have a large air cavity for buoyancy. Therefore, option C is incorrect.
Xylem is a vascular or conductive tissue of the plant. Their main function is to carry out the conduction of water and minerals in the plant.
Parenchyma cells are thin-walled, flexible and loosely packed cells. They have large central vacuole. They carry out many functions in plants. They are often alive at maturity. Their shape changes as per function. Such parenchyma cells have large air cavities to give buoyancy to the plant and enable them to float in water. These cells are called aerenchyma. Hence, option A is correct.
Therefore, option D is incorrect.
Aerenchyma is a spongy tissue that forms spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and the root. The channels of air-filled cavities (see image to right) provide a low-resistance internal pathway for the exchange of gases such as oxygen and ethylene between the plant above the water and the submerged tissues. Aerenchyma is also widespread in aquatic and wetland plants which must grow in hypoxic soils. The large air-filled cavities provide a low-resistance internal pathway for the exchange of gases between the plant organs above the water and the submerged tissues. This allows plants to grow without incurring the metabolic costs of anaerobic respiration. Some of the oxygen transported through the aerenchyma leaks through root pores into the surrounding soil. The resulting small rhizosphere of oxygenated soil around individual roots support microorganisms that prevent the influx of potentially toxic soil components such as sulfide, iron, and manganese.
So the correct answer is 'aerenchyma
#ITZ ATTITUDE QUEEN ❤