CELL ORGANISATION IN PLANTS

Nur Sabrina binti Nasron1K2

Plant tissues

Meristematic tissues

Apical meristems

Lateral meristems

Consist of small cells which have thin walls, large nuclei, dense cytoplasm and no vacuoles.

Consist of young and actively dividing cells which have not undergone differentiation.

Meristematic tissue

Apical meristems are located at the tips of roots and the buds of shoots. The tissues undergo mitosis to increase the number of cells for plant growth.

Lateral meristems or cambia (singular, cambium) are found in the peripheral areas of stems and roots. They are responsible for secondary growth which makes it wider for support and strength in plants.

Meristematic tissue

Consist of more nature cells that either underoing differentiation or have already undergone differentiation.

There are three types of permanent tissues;a. epidermal tissueb. ground tissuec. vascular tissue

Permanent tissues

Tissue Characteristics FunctionEpidermal tissue

Root hair

Guard cells and stomata

Forms tissue the epidermis, the outermost layer that covers the stems, leaves and roots of young plants. This tissue also covers the flowers, fruits and seeds.

• The walls of epidermal cells which are exposed to air are normally covered by a waxy, waterproof coating called cuticle.

• Most epidermal cells are flat and have large vacuoles.

• The cuticle on the epidermal tissuea. prevents the loss

of excessive water through evaporation

b. protects the plant from mechanical injury

c. prevents invasion by disease-causing microorganisms

• Root hair in roots increase the surface area for absorption of water and minerals.• Guard cells surround the stomata control the opening and closing of stomata.

Tissue Characteristics FunctionsGround tissueForms the bulk of a plant. There are three types of ground tissue.

a. Parenchyma tissue

• Consists of thin-walled cells which are loosely arranged with spaces between them.• These cells are generally round and have large vacuoles.• They are the least specialised cells and can be found in all the organs of a plant.

• Products of photosynthesis such as sugar and starch. • The palisade mesophyll cells and spongy mesophyll cells in leaves are specialised parenchyma cells which contain chloroplasts and carry out photosynthesis.• Gives support and shape to plants.

Tissue Characteristics Functions

b. Collenchyma tissue• Consists of elongated, polygonal cells with unevenly thickened cell walls.• The cell walls are thickened by cellulose and pectin. They are strong and flexible.

• An important source of support in herbaceous plants, young stems, leaf stalks and petioles.

Tissue Characteristics Functions

c. Sclerenchyma tissue

• Sclerenchyma cells are much are rigid than collenchyma cells because they have cell walls which are uniformly thickened by lignin.• Most of the cells are dead at maturity.

• Supports and strengthens the plant body and provides protection to the plant.

Tissue Characteristics FunctionsVascular tissueVascular tissues, which are continuous throughout the plant, are involved in the transport of substances between the roots and the shoots. There are two types.

a. Xylem tissue

• Consists of tracheids and xylem vessels. These are long tubes joined together end to end, from the roots right up of the shoots.• The cell walls of the xylem are thickened with lignin which prevents food substances from entering the cells. Consequently, the xylem tissue dies upon reaching maturity.

• Conducts water and minerals from the roots to the leaves.• Provides support and mechanical strength to the plant.

Tissue Characteristics Functions

b. Phloem tissue• Consists of parenchyma cells, sclereids, sieve tubes and companion cells.• The conducting cells of phloem are the sieve tubes which have pores at both ends, called sieve plates.• Sieve tubes obtain nutrients and energy from the adjacent companion cells.

• Transports organic substances such as carbohydrates and amino acids from the leaves to storage organs and to growing parts of plants.

Cell Specialisation in Plants

Main organs are the stems,leaves, buds, flowers and fruits.

Stems and branches act as support system, holding the leaves in a position that facilitate maximum absorption of sunlight and position flower for pollination

Leaves are main photosynthesis system, the product transported via phloem to other parts of plants

Flowers are the reproductive system of the plant which produce fruits and seeds

Shoot system

Main organs are the roots Absorptive system Highly branched to absorb water and

minerals from the soil & transport them to the main vascular system (xylem)

Anchor the plant to the ground

Root system