Describe the characteristics and state the function of plant tissues.

State what is meant by the term ‘plant tissue’.

PLANT TISSUES

PLANT TISSUES are GROUPS OF DIFFERENTIATED CELLS forming LAYERS WITH SPECIALISED FUNCTIONS

• Can be formed from ONE OR MORE TYPES OF CELL
• PRIMARY TISSUE results from growth at the APICAL MERISTEMS (stems and roots)
• SECONDARY TISSUE result form growth at the LATERAL MERISTEMS (CAMBIUM in stems and roots) * Results in SECONDARY THICKENING in WOODY PLANTS * Secondary growth also occurs in many nonwoody plants, e.g. tomato,[1] potato tuber, carrot taproot and sweet potato tuberous root. * A few long-lived leaves also have secondary growth * Credit: de:Benutzer:Griensteidl - Cehagenmerak [Public domain], via Wikimedia Commons (to be relabelled)

Credit: Berkshire Community College Bioscience Image Library [CC0], via Wikimedia Commons

Credit: Brer Lappin [Public domain], from Wikimedia Commons

Describe the characteristics and function of: protective (epidermis), meristematic (cambium), transport (phloem, xylem) and packing (parenchyma) plant tissues.

PROTECTIVE-TISSUE SEE EPIDERMIS

EPIDERMIS

PROTECTIVE TISSUE (EPIDERMIS)

• Single layer of living cells
• Flattened
• No air spaces between
• Waterproof
• Airtight
• Waxy cuticle
• Can form EPIDERMAL HAIRS

In ROOTs:

Outer protective/enclosing tissues.

Produces root hairs for water uptake. Provides protection from pests and diseases, but does not prevent water-loss in roots.

IN STEMS

Epidermis – single layer of living, tightly packed cells with thickened walls and a waterproof layer called a cuticle. May have stomata. Can produce hair-like growths. Function: protection of under-laying tissues, prevention of water loss, stomata gaseous exchange.

EPIDERMAL HAIRS

Hairs on EPIDERMIS

CUTICLE

Hard, waxy layer of PROTECTIVE TISSUE

TRANSPORT TISSUE

Transport (phloem & xylem) in vascular bundles/veins each side of the cambium: Phloem responsible for the translocation of soluble organic materials in the plant (down) – starches and sucrose away from the leaves/auxin from the apical meristems of shoots (translocation). Xylem responsible for the translocation of materials in the plant (up) – water (transpiration) and minerals.

PHLOEM Downward translocation of organic materials, sugars and minerals. Phloem: Combination of two cell sieve element with a companion cell.

XYLEM Upward movement of water/minerals. Transpiration. Xylem: Long tubular cells. Secondary cell walls. Becoming lignified at maturity/dead/wood.

CAMBIUM Cell division/responsible for secondary thickening, producing new xylem and phloem.

PACKING TISSUE

Usually larger, quite basic cells that fill up spaces. Can be involved in starch storage. As they can be meristematic they can be involved in wound healing. Cortex and pith in young stems/mesophyll in leaves.

PARENCHYMA

PACKING TISSUE

MERISTEMATIC TISSUE

Meristematic (cambium) layers of cells with the power of division lying between the phloem and xylem in vascular bundles/veins. Give rise to secondary thickening in dicot stems. In horticulture allows for cuttings to root or grafts to join: Living cells. Incompletely or not at all differentiated. Capable of continuous cellular division. Small cells. Protoplasm fills cell completely. Extremely small vacuole. Packed closely together without intercellular cavities. Cell walls very thin – primary cell walls.