MBC BIOLOGY

Schematic diagram of primary and secondary growth in dicot stem  Image source: https://commons.m.wikimedia.org/wiki/File:Crescita_primaria_e_secondaria_del_fusto.png#file Q.N. 1. Define secondary growth in plants. Describe the secondary growth due to the activity of vascular cambium. The process of formation of extra layers or secondary tissues due to activity of vascular cambium and cork cambium for increasing girth or thickness or diameter of plant is called secondary growth. It takes place in stellar regions due to the activity of vascular cambium (see Figure 1 ) and in extra-stellar regions due to the activity of cork cambium (see Figure 5 ). Secondary growth in stellar regions due to the activity of cork cambium Secondary growth due to activity of vascular cambium takes place by the formation of a cambium ring , formation of secondary tissues , formation of annual rings or growth rings , and formation of heartwood and sapwood . Formation of cambium ring The dicot stem has a...

Isobilateral leaves of Paddy ( Oryza sativa ) Image source: MB Chand

Flat beans Image source:Sengai Podhuvan, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons Anatomy of Dicot and Monocot Stem Q.N. 1. Describe the anatomy or internal structure of the dicot stem.  Primary dicot stem consists of epidermis , hypodermis , cortex , endodermis , pericycle , vascular bundles , medullary rays or pith rays , and pith or medulla (see Figure 3 ). 1. Epidermis Epidermis is the outermost layer of the stem. It is composed of elongated, barrel-shaped parenchymatous cells without intercellular spaces . It is covered externally by a cuticle . Stomata and several unbranched multicellular hairs or trichomes are also present . Each stoma has a pai r of specialized kidney-shaped cells, guard cells . Epidermis helps in protection of internal tissues, exchange of gases through stomata, reduces the rate of surface transpiration by cuticle, prevents the entry of harmful organisms and heat insulation by epidermal hairs. 2. Hypodermi...

Prop Roots of Maize License: Jamain, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons Anatomy of Dicot and Monocot Root Q. N. 1. Describe the anatomy or internal structure of the dicot root. A young dicot root possesses epiblema, cortex, endodermis, pericycle, vascular bundles, conjunctive tissues, and pith (see Figure 12 ).  1. Epiblema Epiblema is the outermost part of root. It is made of a single layer of thin-walled, radially elongated parenchymatous cells without intercellular spaces . It lacks cuticles and stomata . Some of its elongated cells form root hairs, which are unicellular tubular outgrowths. Due to the presence of root hairs, epiblema is also known as piliferous layer. It is also called rhizodermis. Root hairs help in absorption of water and mineral salts from soil.   2. Cortex Cortex is a zone below the epiblema of roots. It is made of a few layers of thin-walled, oval, rounded or angular parenchyma with i...

Magnolia flower Photo by Paul Brennan via PublicDomainPicture.net . CC0 License     Q.N. 1. Define tissue. Give a brief account on the classification of plant tissues.  Tissue is defined as a group of cells having a common origin and co-operating with one-another to perform a similar function.  Based on their capacity to divide, tissues can be classified as meristematic tissues or meristems and permanent tissues, in plants.  1. Meristems  Meristems are groups of young cells which retain the   capacity of cell division. They occur in the growing regions of plants.  Meristems are categorised as promeristems, primary meristems, and secondary meristems on the basis of origin and development; as apical meristems, intercalary meristems, and lateral meristems based on position; protoderm, procambium, and ground meristems on the basis of functions.  2. Permanent tissues Permanent tissues are the tissues that have their growt...