Primary Growth

Primary growth is the first growth of a plant.  It is when the plant grows upwards/downwards to make the plant longer.  In contrast, secondary growth is the outwards growth of the plant to make it thicker/wider. 

There are three basic stages of primary growth: 

• Cell division - cells divide by mitosis to produce more cells 

• Cell enlargement - cells get bigger 

• Specialisation - cells differentiate (change to suit a particular job) 

Plants grow at the tips of their shoots and roots, so these are always the youngest parts of the plant.  The roots and shoots grow through cell division at areas called apical meristems.  The cells produced here then fill with water and grow longer.  They will eventually mature and differentiate to become particular types of cells (e.g. skin cells, leaf cells, root hair cells).  Because the cells in an apical meristem can become any type of cell, they are called stem cells. 

In a young stem, substances are transferred around the plant in vascular bundles.  These contain three types of cells: 

• Xylem - transports water from the roots to the rest of the plant. 

• Phloem - transports sugar from the leaves to the other parts of the plant which need glucose. 

• Vascular Cambium - stem cells which will produce secondary growth  

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