PLANT TISSUES

Tissues- are group of ceIIs performing the same function

- ceIIs that are structurally and/functionally similar

Plant Tissue Types:

A. Meristematic tissues

B. Permanent tissues

I. MeristematicII. Permanent

A. Dermal- surface Epidermis Periderm

B. Ground Parenchyma Collenchyma Sclerenchyma

C. Vascular Xylem Phloem

Plant Tissue Classif ication

- composed of actively dividing ceIIs

- responsible for the production of ceIIs

- have thin cellulose cell walls

- cells are varied in shape

- compactly arranged; no intercellular space

- cells have dense or abundant cytoplasm and

a single large nucleus

- with few or no vacuoles at all

I. Meristematic tissues

Apical meristems – found at the tip of stems & roots, responsible for primary growthLateral meristems – a.k.a. cambia (singular:cambium)

- found along the sides of roots & stems - responsible for secondary growth- types: 1. vascular cambium 2. cork cambium

Intercalary meristems – found at the bases of young leaves & internodes- responsible for further lengthening of stems & leaves

Kinds of meristems (based on location):

New cells formed in the meristems of a plant are similar in appearance and function

Some must remain meristematic

Most mature and become other tissues

II. Permanent tissues- tissues that attained their mature form

and perform specific functions - they stop dividing

Types: Simple permanent tissues Complex permanent tissues

A simple tissue is composed of only one cell type.

Complex tissues contain more than one cell type

Simple permanent tissues- consist only of one kind of cells

A. Dermal / surface tissue- external tissues- forms protective covering of the plant body

a. epidermis b. periderm

Epidermis- the outermost layer of the primary plant body -

covers the leaves, floral parts, fruits, seeds, stems and roots

- generally only one layer thick with cuticle

- composed mostly of unspecialized cells, either parenchyma and/or sclerenchyma- contains tr ichomes, stomata, buIIiform ceIIs (in grasses)

Structure of epidermis

• Stomata - pores for gas exchange - present on one or both surfaces of Ieaves

epidermaI ceIIInner waII of the guard ceII

nucIeus

stomataI porechIoropIast

Other epidermal cells

The guard cells regulate the size of stomata. As a result they control gas exchange and water loss

Epidermal

Lower Epidermis

• Cuticle – Iines the outer waII of the epidermal ceIIs - made up of waxy material that protects plants from desiccation

• tr ichomes – outgrowths of epidermal ceIIs retards water evaporation

Periderm -is the outermost layer of stems and roots of

woody plants such as trees.

B. Ground tissues1. Parenchyma

- are the general purpose ceIIs of plants - cells are rounded in shape & have uniformly thin walls found in all parts of the plants. - living at maturity, have large vacuoles - location Ieaf, stem (pith), roots, fruits

Functions:*basic metabolic function (respiration, photosynthesis

chlorenchyma in leaf & protein synthesis)*storage (potatoes, fruits, & seeds)*wound healing and regeneration

Parenchyma

chIorenchyma- a specialized parenchyma tissue found in the green parts of the shoot and performs photosynthesis.

2. CoIIenchyma- Greek word kolla which means “glue”- cells are elongated (up to 2mm long) with unevenly thickened walls ( thin on the sides but thick at the angles where 2 or more cells meet)- differentiate from parenchyma cells & are alive at maturity

Functions: Support & elasticity (stem surfaces & along leaf veins) regeneration

3. ScIerenchyma- sclerenchyma cells which are non-l iving and lack protoplasts at maturity- have thick, l ignif ied secondary walls- provide strength and support in parts thathave ceased elongating or mature

Types:1. scIereids or stone cells2. fibers

Very thick walls

scIereids in pear fruit

fibers

Complex Permanent Tissues

Vascular Tissues - specialized for long-distance transport of water

and dissolved substances.- contain transfer ceIIs, fibers in addition to parenchyma and conducting ceIIs

- location, the veins in Ieaves types1. Xylem 2. phloem

Xylem- GW xyIos w/c means “wood”

- transports water and dissolved nutrients from the roots to aII parts of a plant.

- direction of transport is upward2 types Primary xylem – differentiates from procambium in the

apical meristem & occurs throughout the primary plant body.

Secondary xylem – differentiates from vascular cambium & is commonly called wood.

Xylary elements – the conducting cells in xylemtracheids – lignified, elongated, tapering tubes which

are dead at maturity. serve for strength & conduction vessels – long, lignified continuous tubes serve

chiefly for conductionxylem fibers - elongated, pointed strengthening cells

with much thickened cell wallsxylem parenchyma – for storage

PhIoem- Greek word phloios meaning, “bark”

- transports dissolved organic / food materials from the Ieaves to the different parts of the plant- glucose in phloem moves in aII directions

Types1. Primary phloem – differentiate from procambium and

extends throughout the primary body of the plant. 2. Secondary phIoem – differentiates from the vascular

cambium and constitute the inner layer of the bark.

sieve tubes – main conducting ceIIs of the phloem

companion cells – border the sieve cells and aide it in conduction

phloem fibers – thick walled, elongated, strengthening cells

phloem parenchyma cells – storage cells