Tag: structural organization in living organisms

Histogen theory was proposed by Hanstein in 1870. According to this theory,  shoot apical meristem consists three distinct zones namely, dermatogen (external layer) which form outer covering of all organ of plant. Periblem (middle layer) which gives rise to cortex and endodermis. Plerome (central layer) which forms pith and primary vascular bundle. 
Thus, the correct answer is option C.

• A meristem is a tissue which is composed of undifferentiated cells found in the regions of the plant where growth takes place.
  
• The various organs of a plant are derived from a meristem.
• The word meristem is derived from a Greek word 'merizein' which means 'to divide'.
• Another Greek term used in relation to meristem is 'meristos' which means 'divisible'.
• Thus, meristematic cells are those cells which have the power to divide continuously. So, the correct answer is 'Divided'.
  

The term meristem was first used in 1858 by Carl Wilhelm von Nägeli in his book Beiträge zur Wissenschaftlichen Botanik. So, the correct answer is " C. Nageli".

Meristematic tissues are the undifferentiated cells that are found in the growth zones. It gives rise to various organs. They have plastids that are not differentiated and present in the form of proplastid. The cell wall of the meristematic cell is made up of cellulose, the cell wall is thin and flexible while the secondary wall is absent. Cells lack intercellular spaces and also lack reserve food as it is highly active and does not require any reserve food for energy.

A.Meristem – actively dividing cells – true

B.Xylem – Transport of food – false, because it transport water.

C.Phleom – Transport of water – false, because it transport food.

D.Sclerenchyma – Storage of starch – false, because it is dead mechanical tissue.

So, the correct option is ‘Meristem – Actively dividing cells’.

Simple permanent tissues are simple as they are made up of only one type of cell. They are known as permanent tissue because they have lost the power of division and are specialized. They are classified into three main types parenchyma, sclerenchyma, and collenchyma.

Cambium is a kind of meristem which is most active in woody plants and it lies between the bark and wood of the stem. The vascular cambium forms tissues that carry water and nutrients throughout the plant. On the outer surface, the vascular cambium forms new layers of phloem, and on the inner surface, new layers of xylem. The cork cambium creates cells that eventually become bark on the outside and cells that add to the cortex on the inside. In woody plants, the cork cambium is part of the periderm. So, the correct answer is "both vascular and cork cambium".

Meristematic activity is seen the maximum in the shoot of a plant. The meristematic tissue contains undifferentiated cells found in the zone of the plant where growth can take place.