Plant Tissues Different plant cells have specific functions

Plant Tissues Different plant cells have specific functions

Meristematic Tissues • Meristems – the growth regions where cells actively divide – Apical – Known as “primary” growth. Tips of roots & shoots, increase in length – Lateral – Secondary growth. Tissues that increase girth of roots & stems

Lateral Meristems • Cambium – – Inner – growth rings – Outer – Bark & cork; provides insulation, support, & protection – Vascular Conducting Tissue • Xylem – Water up • Phloem – Food away

Tissues produced by meristems • Parenchyma cells – The most abundant of all cell types, found in almost all major parts of plants – Thin, pliable walls can be up to 14 sided – Parenchyma cells with numerous chloroplasts are called chlorenchyma • Function in photosynthesis – Parenchyma cells without chloroplasts function mainly in food & water storage – Parenchymal cells play a vital role in tissue repair

Tissues produced by meristems • Collenchyma cells – Cell walls generally thicker than parenchymal cells. – Provide flexible support for both growing & mature organs (leaves, flower parts, etc…) – Generally occur just below the epidermis – Celery “strings” are an example of collenchyma

Tissues produced by meristems • Sclerenchyma cells – Thick, tough, secondary walls – Strengthened by “lignin” – Most sclerenchyma cells are dead at maturity, function in support and protection – “Sclereids” are related cells – hard cells found throughout all plant tissues; sometimes called “stone cells”

Complex Tissue – Epidermis • Epidermis – Outermost layer of cells in all young plants – Usually one cell thick – Most epidermal cells secrete a fatty substance called “cutin” – A layer of cutin is called the “cuticle” • Prevents H 2 O loss – “transpiration” • Exceptionally resistant to bacteria – Stomata – small “pores” in the epidermis • Guard cells – regulate transpiration rate

Complex Tissue – Epidermis • Trichomes – specialized epidermal cells – Epidermal hairs to reduce water loss – Glandular – oils, fragrance, enzymes – Stinging hairs – acids (nettles) – Trigger hairs – stimulate reaction in carnivorous plants (fly trap)

Complex Tissue – Epidermis • Cork – Formed when outer cambium produces enough girth to split epidermis – Secretes “suberin” • Fatty substance which blocks air & water movement • Makes cork cells waterproof; protects phloem & other tissue below bark

Other Complex Tissues • Tracheids – Dead vertical cells in xylem tissue – Aid in water conduction/transport – Provide support • Sieve cells – Nutrient transport in phloem tissue – Translocation of food/sugar through “sieve tubes”

Secretory Tissues • Secretory cells “secrete” – Trichomes (we talked about these 3 slides ago) – Nectaries – nectar – Hydathodes – water – Secretory – contains oils, resins – Laticifers – latex rubbers, alkaloids