Chapter 6 Anatomy of Flowering Plants Solutions
Question - 11 : - What is periderm? How does periderm formation take place in dicot stem?
Answer - 11 : -
Periderm is composed of the phellogen, phellem, and phelloderm.
During secondary growth, the outer epidermal layer and the cortical layer are broken because of the cambium. To replace them, the cells of the cortex turn meristematic, giving rise to cork cambium or phellogen. It is composed of thin-walled, narrow and rectangular cells.
Phellogen cuts off cells on its either side. The cells cut off toward the outside give rise to the phellem or cork. The suberin deposits in its cell wall make it impervious to water. The inner cells give rise to the secondary cortex or phelloderm. The secondary cortex is parenchymatous.
Question - 12 : - Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.
Answer - 12 : -
Dorsiventral leaves are found in dicots. The vertical section of a dorsiventral leaf contains three distinct parts.
[1] Epidermis:
Epidermis is present on both the upper surface (adaxial epidermis) and the lower surface (abaxial epidermis). The epidermis on the outside is covered with a thick cuticle. Abaxial epidermis bears more stomata than the adaxial epidermis.
[2] Mesophyll:
Mesophyll is a tissue of the leaf present between the adaxial and abaxial epidermises. It is differentiated into the palisade parenchyma (composed of tall, compactly-placed cells) and the spongy parenchyma (comprising oval or round, loosely-arranged cells with inter cellular spaces). Mesophyll contains the chloroplasts which perform the function of photosynthesis.
[3] Vascular system:
The vascular bundles present in leaves are conjoint and closed. They are surrounded by thick layers of bundle-sheath cells.