Question

3)   Draw a diagram which shows a cross-section of a stem after one year of secondary growth and label all the tissues that are found in the stem at this stage, including the 2 meristems associated with secondary growth.

Answer 1

Question 3

Ans :

Cross-section of a stem after one year of secondary growth

Note : Cork cambium and Vascular cambium are the two meristems associated with secondary growth.

Explanation of labelled parts :

Epidermis : It is the outermost layer of cells covering the stem, a protective barrier against mechanical injury, water loss, and infection.

Periderm : A group of secondary tissues forming a protective layer which replaces the epidermis. It is composed of cork cambium, phelloderm, and cork.

Cork : It is a tissue formed on the outer side of phellogen or cork cambium. It is composed of dead cells and is used for protection.

Cork cambium : It is the meristematic cell layer that creates the periderm. Cells that grow inwards from there are termed phelloderm, and cells that develop outwards are termed phellem or cork.

Phelloderm (Secondary cortex) : The layer of tissue produced on the inside of the cork cambium in woody plants. It forms a secondary cortex.

Primary phloem : The primary phloem is a type of phloem that forms from the procambium during the primary growth.

Secondary phloem : It is a type of phloem that formed from the vascular cambium during the secondary growth. The secondary growth is responsible for the growth in diameter in plants.

Bark : It refers to all the tissues outside the vascular cambium. It overlays the wood and consists of the inner bark and the outer bark.

Vascular cambium : It is the meristematic tissue in between the xylem and phloem that creates new xylem and phloem cells for secondary growth in the stems and roots.

Primary xylem : Primary xylem is the xylem that is formed during the primary growth from procambium of apical meristems.

Secondary xylem : It is created during secondary growth and is for an increase in width of the stem. The secondary xylem is differentiated into sapwood and heartwood.

Sapwood : It is the soft outer layers of secondary wood of trees recently formed between the heartwood and the bark, containing the functioning vascular tissue.

Pith : It is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant. It is  located in the center of the stem.

Heartwood : It is located at the inner part (center) of the wood. It is the passive, non-functional component of the xylem.