Test: Secondary Growth - 1 - ACT MCQ

Periderm—the Outer Defense Layer. The first defense line in conifer stems is the outer surface of the bark, the periderm. Inside the periderm is the cork cambium (or phellogen), a secondary meristem that produces cork tissue (phellem) outwards and secondary cortex (phelloderm) inwards.so option B.

A bark is everything outside the vascular cambium including the secondary phloem. The tissues in a bark comprise of secondary phloem and peridermis (secondary cortex, cork cambium and cork).

In the area where the petiole of the leaf joins the twig, theres an abscission zone made up of two kinds of tissue the abscission layer and the protective layer. The protective layer is closest to the twig. The abscission layer is between the protective layer and the petiole. Both of these layers are only a few cells thick. During the growing season this layer of cells is healthy and keeps the leaves attached to the tree. But when the days become shorter, things begin to change in this zone. The protective layer begins a process called as suberization in which suberin, a waxy chemical found in cork, builds up in the cells. This provides an area of tissue thats impervious to the outside elements.The suberized protective layer prevents leaf fall from leaving open wounds on the twigs. While the protective layer is becoming filled with corky tissue, the abscission layer also transforms.

Trees have two types of growth: primary growth and secondary growth. ... Cambium lies between the old wood and the bark of the tree. The vascular cambium is a thin layer cells that produces conducting cells – xylem and phloem.

The fibres usually occur in clusters or as bands alternating with bands of sieve tubes and parenchyma cells. As the vascular cambium continues to produce more secondary xylem to the inside, the older (most exterior) portions of the secondary phloem are crushed, die, and are sloughed off as part of the bark.

Due to differential seasonal activity of cambium,alternate light & dense wood is cut off leading to formation of annual rings.

As we know that Intrafascicular/intrastelar cambium is present between xylem and phloem in dicot stem and roots. Pith rays, present between the edges of intrafascicular cambium, divide to form a new cambium strip between the two vascular bundle i.e. interfascicular cambium. Thus, inter and intra fascicular cambium together forms a complete cambium ring, called as vascular cambium, which forms secondary xylem on inner side and secondary phloem on outer side. Differential cambial activity during autumn and spring season result in narrow and wide secondary xylem rings respectively, which together forms the annual growth ring. Thus, annual growth ring is derived from vascular cambium, which is derived from inter and intrastelar cambium.

Complementary cells are a mass of cells in plants , formed from the cork cambium .... Cork cambium is also known as PHELLOGEN ... complementary cells are formed at the position of Lenticels ... it is a group of lossely arranged cell that .... aid in gaseous exchange throughout cork ... Hence , option C is correct ...

Respiration In Stems. In the plants having herbaceous stem exchange of gases takes place through stomata and the carbon dioxide produced during the process gets diffused into the air via stomata only. While in the plants having hard and woody stems the exchange of gases takes place through lenticels.

A leaf is an organ of a vascular plant and is the principal lateral appendage of the stem. The leaves and stem together form the shoot. Leaves are collectively referred to as foliage, as in "autumn foliage".In woody plants, lenticels commonly appear as rough, cork-like structures on young branches. Underneath them, porous tissue creates a number of large intercellular spaces between cells. ... Discoloration of lenticels may also occur, such as in mangoes, that may be due to the amount of lignin in cell walls.

Lenticels originate beneath stomata, simultaneous with the initiation of the first layer or periderm or just before the initiation of periderm, during first growing season. As the lenticels formation starts, the parenchyma cells found near substomatal cavity lose their chlorophyll content and irregularly divide in different plants giving rise to a mass of colourless, rounded, thin walled, loosely arranged cells called as complementary cells. 
Some times complementary cells produced by phellogen towards outside instead of producing cork cells. As the complementary cells increase in number, pressure is exerted against the epidermis and it ruptures. Outer most cells gradually become dead and may replaced by cork cells. Beneath the outer layer some mass of closely packed cells alternate to loosely arranged cells are formed called as closing layer. From inner side continuous production of complementary cells cause rupture of closing layer at intervals. So, lenticels and its complementary cells are developed through the activity of phellogen and not of steler cambium, dermatogen and intercalary meristem. 
 

Answer: As the plants grow older, the outer protective tissue (i.e., epidermis) undergoes certain changes. A strip of secondary moisten, called halogen or cork cambium replaces the epidermis of the stem.It's cells prevent desiccation (loss of water from plant body), infection and mechanical injury.

Girdling refers to a process in which the bark encircling the tree is removed completely. The phloem layer of tissue is present just beneath the bark, and it is responsible for the transportation of food prepared in the leaves of the plant through photosynthesis to the roots. Thus, phloem facilitates downward movement of food, and if the stem is girdled the roots of the plant will not able to capture food and die first.