SUPPORT AND MOVEMENT IN PLANTS

Necessity for support and movement

• Movement is a characteristic of all living organisms.
• It enables animals and plants to adjust to their environment.
• Most animals move from place to place but some are sessile (i.e. fixed to the substratum).
• Majority of plants move only certain parts.
• However, though not easily observed all living protoplasm shows movement of one type or another.

 

Necessity for support and movement in plants

• They enable plants to be held upright to trap maximum light for photosynthesis and gaseous exchange.
• To hold flowers and fruits in appropriate position for pollination and dispersal respectively.
• To enable plants to grow to great heights and withstand forces of environment e.g. strong winds.
• Movement of male gametes to effect fertilization and ensure perpetuation of a species.
• Plant parts move in response to certain stimuli in the environment of tropisms.

 

Tissue distribution in Monocotyledonous and Dicotyledonous plants

• Vascular bundles are the main support tissues in plants.
• In monocotyledonous stem they are scattered all over the stem.
• While in dicotyledonous stem they are found in a ring or rings.
• In monocots the xylem and phloem alternate around with pith in the centre.
• In dicots of the xylem forms a star in the centre – there is no pith.
• Phloem is found in between the arms of xylem.
• Dicotyledonous plants have cambium which brings about secondary growth resulting in thickening of the stem and root hence providing support.
• Secondary xylem becomes wood, providing more support to the plant.

 

Role of support tissues in young and old plant

Plants are held upright by strengthening tissues;

• parenchyma,
• collenchyma,
• sclerenchyma
• xylem tissue.

 

Parenchyma and collenchyma are the main support tissues in young plants.

Parenchyma

• They are found below the epidermis.
• They form the bulk of packing tissue within the plant between other tissues .
• They are tightly packed and turgid they provide support.

Collenchyma

• Their cell walls have additional cellulose deposited in the corners.
• This provides them with extra mechanical strength.

Sclerenchyma

• Their cells are dead due to large deposits of lignin on the primary cell wall.
• The lignified wall is thick and inner lumen is small, hence provide support.
• Sclerenchyma fibres are arranged in elongated and in longitudinal sheets giving extra support.
• They are found in mature plants.

Xylem

• Has two types of specialised cells.
• Vessels and tracheids.
• Vessels are thick-walled tubes with lignin deposited in them.
• They give support and strength to the plant.
• Tracheids are spindle-shaped cells arranged with ends overlapping.
• Their walls are lignified.
• They help to support and strengthen the plant.

 

Plants with weak stems obtain their support in the following ways.

• Some use thorn or spines to adhere to other plants or objects.
• Some have twinning stems which grow around objects which they come into contact with.
• Others use tendrils for support.
• Tendrils are parts of a stem or leaf that have become modified for twinning around objects when they gain support.
• In passion fruit and pumpkin, parts of lateral branches are modified to form tendrils.
• In the morning glory, the leaf is modified into a tendril.

 

See also:

STRUCTURE AND FUNCTIONS OF PARTS OF HUMAN EAR

STRUCTURE AND FUNCTION OF PARTS OF THE HUMAN EYE

EFFECTS OF DRUGS ABUSE ON THE HUMAN HEALTH

THE ROLE OF ENDOCRINE SYSTEM IN HUMAN BEINGS

SPINAL CORD