Question

Distinguish between primary growth and secondary growth, and describe the cell types involved in each.

Short answer

Primary growth is the elongation of plant shoots and roots, occurring at apical meristems and involving cell types such as apical meristem cells, protoderm, ground meristem, and procambium. Secondary growth increases plant thickness and forms wood and bark, occurring at vascular cambium and cork cambium and involving cell types such as vascular cambium and cork cambium. Primary growth results in elongation, while secondary growth results in increased thickness.

Step-by-step solution

1. Primary Growth

Primary growth in plants is the elongation of the plant shoots and roots, which enables them to grow taller and deeper into the soil. This type of growth occurs at the apical meristems, which are located at the tips of shoots and roots. Cell division in the apical meristems produces new cells that lengthen the plant. The key cell types involved in primary growth are: 1. Apical meristem cells: These undifferentiated cells actively divide and give rise to new cells that will make up the primary tissues. 2. Protoderm: This group of cells differentiates into the epidermis, which is the outermost layer of cells in primary plant tissues. 3. Ground meristem: These cells differentiate into ground tissue, which includes parenchyma, collenchyma, and sclerenchyma cells. These tissues have various functions, such as photosynthesis, storage, and support. 4. Procambium: These cells differentiate into primary vascular tissues, such as the xylem and the phloem, which facilitate water and nutrient transport.

2. Secondary Growth

Secondary growth is the process by which plants increase in thickness or girth by adding new layers of cells to their existing tissues. This type of growth occurs in the vascular cambium and the cork cambium (phellogen). In woody plants, secondary growth results in the formation of wood and bark. The key cell types involved in secondary growth are: 1. Vascular cambium: This lateral meristem consists of a thin layer of cells that continuously divide to produce secondary xylem (wood) on the inner side and secondary phloem (inner bark) on the outer side. The secondary xylem and phloem both function in the transport of water, nutrients, and sugars. 2. Cork cambium (phellogen): This lateral meristem is responsible for producing the outer layers of bark, which consist of cork cells (phellem) and cork parenchyma cells (phelloderm). These cells provide protection and insulation for the underlying tissues. To summarize:

Primary Growth:

- Occurs at apical meristems in shoots and roots - Involves cell types such as apical meristem cells, protoderm, ground meristem, and procambium - Results in the elongation of shoots and roots

Secondary Growth:

- Occurs at vascular cambium and cork cambium in woody plants - Involves cell types such as vascular cambium and cork cambium - Results in an increase in plant thickness and the formation of wood and bark