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PLANT TISSUES
(pp 261-268)

HOW ARE CELLS ORGANIZED IN PLANTS?

I.MERISTEMATIC TISSUES

A.APICAL MERISTEMS Primary Growth

1.Initials

a.Occur near tips of roots and shoots

b.Cells have thin walls, prominent nuclei, and small vacuoles

c.Functions

1)Establish patterns of growth.

Leaf pattern.

2)Produce new, genetically healthy cells

3)Produce derivatives which in turn account for primary growth i.e. elongation.

2.Derivatives

a.Protoderm - becomes the epidermis

b.Procambium - becomes the vascular tissue (xylem and phloem)

c.Ground Meristem - becomes the cortex and pith

B.LATERAL MERISTEMS - Secondary Growth

1.Vascular Cambium

a.Secondary Xylem
b.Secondary Phloem

2.Cork Cambium

a.Periderm (bark)

C.INTERCALARY MERISTEMS

1.Most common in grasses
2.Occur at base of nodes

II.NON-MERISTEMATIC TISSUES

A.PRIMARY TISSUES

1.GROUND TISSUES

a.General

1)Differentiates from ground meristem

2)Constitutes most of primary plant body

3)Found as part of other tissues (e.g. vascular)

4)Functions

Storage

Basic metabolism

Support

b.Parenchyma

1)Cortex of stems & leaves, pith of stems, leaf mesophyll, flesh of fruits.

2)Capable of cell division

3)Role in regeneration and wound response.

4)Adventitious roots on stem cuttings

5)Secretion

6)Storage

7)Photosynthesis

c.Collenchyma

1)Living at maturity

2)Associated with epidermis of stems and petioles and bordering veins in dicot leaves (strings on celery)

3)Typically elongated cells with unevenly thickened cell walls.

4)Function in support.

d.Sclerenchyma

1)Fibers are long slender non living support cells occurring in strands or bundles. Hemp, jute and flax.

2)Sclereids are short non living cells at maturity; dispersed throughout ground tissues.

They are the seed coats, shells of nuts, the stone of stone fruits and the gritty texture in pears.

2.DERMAL TISSUES

a.The epidermis is usually one cell layer thick made up of flat tile-like cells.

b.Cells lack chlorophyll, tend to be transparent.

c.Have vacuoles which may contain pigment (e.g. anthocyanins)

d.Function is related to features of the epidermis.

1)Cuticle protects plant from desiccation (Thick cuticle = dry environment; thin cuticle = wet environments).

Fatty material called cutin
Epicuticular wax makes lvs look whitish (carnauba wax comes from lvs of wax palm

2)Guard cells - Two bean-shaped (dicots) or dumbbell-shaped (monocots) cells that control a hole (stoma) on leaf surface.

Regulate gas exchange by controlling size of stomatal opening.

Regulation is environmentally induced.

3)Trichomes are single-celled or multicellular outgrowths of epidermal cells.

Nutrition and absorption
sundew & butterwort
root hairs

Protection
deter herbivores
release sticky substances
release irritating chemicals (nettle)

Economic importance
cotton
menthol oil from peppermint
THC from Cannabis

3.VASCULAR TISSUE

a.Xylem: principal water conducting tissue but also transports minerals, stores food and provides support.

1)Tracheids

More primitive than vessel

Vessel evolved independently in a variety of plants including monocots, dicots, ferns, Selaginella, and Equisetum. CONVERGENT EVOLUTION

Similar as above but no perforation plate.

Pits concentrated in overlapping tapered ends of cells.

Water must pass through the membrane of pit pair.

Present in all tracheophytes.

2)Vessels

Elongated cells with secondary walls, no protoplast at maturity. •Pits in side walls, perforations in end walls (perforation plate)

More efficient water conductor than tracheids.

Found in angiosperms.

3)Fibers

4)Ray cells

5)Parenchyma

b.Phloem: principal food conducting tissue, may be of primary or...
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