CHAPTER 4 : REPRODUCTION & GROWTH

4.8 – Primary & Secondary Growth

in Plants

LEARNING OUTCOMESState the types of growth in plants;State what primary growth &

secondary growth are;Name the tissues involved in

primary & secondary growth;State the location of the tissues

involved in primary & secondary growth;

LEARNING OUTCOMESExplain the importance of primary

growth;Explain the importance of secondary

growth;Compare & contrast plants that

undergo secondary growth with plants that do not undergo secondary growth;

State the economic importance of plants that undergo secondary growth.

THE TYPES OF GROWTH IN PLANTS

Two types of growth : primary growth & secondary growth.

Primary growth = occurs after germination, shown in all plants.

Secondary growth = the growth in diameter of the stem, root & trunk of plants. (perennial plants)

Refers to elongation of its shoot & root enables a plant to increase in height.

Tissues involved – the apical meristem (shoot meristem & root meristem)

3 growth zone : cell division, cell elongation & cell differentiation.

Result in an increase in length of the stem & root.

PRIMARY GROWTH

SECONDARY GROWTHRefers to an increase in the girth/

diameter of a plant.

Occurs in dicots but rarely in monocots.

Two types of lateral meristems : vascular cambium & cork cambium.

Vascular cambium is found in between phloem & xylem in the vascular bundle.

Cork cambium is found in the cortex beneath the epidermis.

SECONDARY GROWTHCells in vascular cambium divide

radially many cambial cells in between the vascular bundle. link together ring cambium

Cambium ring divide actively cells on the outside, inside the ring.

Outside differentiate secondary phloem primary phloem to be pushed outwards.

SECONDARY GROWTHInside differentiate secondary

xylem primary xylem pushed inwards.

Formation of more vascular tissues because the plant grow bigger need more food & water, support.

Cork cambium divide inside secondary cortex, outside become cork

Secondary

growth

COMPARISON BETWEEN PLANTS THAT UNDERGO SECONDARY GROWTH WITH

THOSE THAT DO NOT

UNDERGO DO NOT UNDERGOMostly dicots Mostly monocots

Vascular cambium present Vascular cambium absentCork, cork cambium &

secondary cortex presentCork, cork cambium &

secondary cortex absentGenerally bigger in size Generally smaller in size

Have woody stems Have non-woody stemsHave more vascular tissues (secondary phloem & xylem

present)

Have less vascular tissues (only primary phloem & xylem

present)Perennial plants Live for one season only

The Economic Importance of Plant that Undergo Secondary Growth

• Have woody stems great economic value.

• Firewood as a source of fuel.• Timber logs for construction,

building houses & bridges.• Making furniture & paper (pulps).• Production of resin & oils (meranti)• Ornamental/decorative pieces