State what is meant by the term ‘plant tissue’.
PLANT TISSUES are GROUPS OF
DIFFERENTIATED CELLS forming LAYERS WITH SPECIALISED FUNCTIONS
- Can be formed from ONE OR MORE TYPES OF CELL
PRIMARY TISSUEresults from growth at the
APICAL MERISTEMS(stems and roots)
SECONDARY TISSUEresult form growth at the
CAMBIUMin stems and roots) * Results in
SECONDARY THICKENINGin WOODY
PLANTS* Secondary growth also occurs in many nonwoody plants, e.g. tomato, 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 (
- Single layer of living cells
- No air spaces between
- Waxy cuticle
- Can form
Outer protective/enclosing tissues.
Produces root hairs for water uptake. Provides protection from pests and diseases, but does not prevent water-loss in roots.
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.
Hairs on EPIDERMIS
Hard, waxy layer of PROTECTIVE 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.
Downward translocation of organic materials, sugars and minerals.
Combination of two cell sieve element with a companion cell.
Upward movement of water/minerals.
Long tubular cells.
Secondary cell walls.
Becoming lignified at maturity/dead/wood.
Cell division/responsible for secondary thickening, producing new xylem and phloem.
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.
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.
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