Lab 10 Plant tissues Plant tissues Tissues can

Lab 10 : Plant tissues

Plant tissues Ø Tissues can be classified into : § Meristematic tissues § Permanent tissues

Ø Meristematic tissue characteristics: - Small , thin – walled cells. No central vacuole. No specialized features. Ability to divide. Found in young tissues of embryo. o Types of meristematic tissues: - Primary meristems : apical meristems ( near tips of root and stems). - Secondary meristems : vascular cambium & cork cambium.

Meristematic tissues

Ø Permanent tissue characteristics: - Derived from meristems. - Mature , differentiated tissue.

1. Epidermis : Location : outermost layer , covering plant parts. Function : desiccation resistance , gas exchange, protection against herbivores and pathogens. Cell types of the epidermis: • Pavement cells : secrete a water-repellent cuticle that reduces water loss and pathogen invasion. • Guard cells : form (stomata )ﺛﻐﻮﺭ for gas change.

Epidermis

Pavement cells CUTICLE

Guard cells stomata

2. Ground tissue: Ø Parenchyma: is the main ground substance of the plant body in which other important tissues are present. Types : - Aerenchyma : parenchyma with air spaces. - Chlorenchyma : parenchyma full of chloroplasts. Locations : - cortex of roots and stems. - pith of roots and stems. - mesophyll of leaf. Function : - storage , respiration, photosynthesis

Characteristics: - Mature , living cells. May become active to divide. Polyhedral in shape. It has spaces between cells

Ø Collenchyma: Characteristics: - living at maturity. - they have much thicker cell walls. - the thickening of the walls may be in the angle or on the tangential. Function: - provide support. Location : - the outer part of cortex

Ø Sclerenchyma: It form of : - Fibers : long slender cells occur in vascular bundle ( xylem fibers , phloem fibers, bundle sheath) - Sclereids : have variable shapes , found in seed coats. Characteristic: - thick-walled lignified , non-living and lack protoplast. Function : - support and protection

Ground tissues SCLERENCHYMA (FIBERS) SCLEREIDS 14

Ground tissues PARENCHYMA COLLENCHYMA

3. Vascular tissues : include xylem ﺍﻟﺨﺸﺐ and phloem ﺍﻟﻠﺤﺎﺀ 1. xylem : - is the principle of water conducting tissues in vascular plants. - It may also act as a mechanical support to different plant organs. Primary xylem: is the xylem formed during primary growth from procambium. It includes Protoxylem and Metaxylem. Secondary xylem: is the xylem formed during secondary growth from vascular cambium. Xylem is a complex tissue formed from of: 1. vascular elements : - vessels - Tracheid ﺍﻟﻘﺼﻴﺒﺎﺕ ﺍﻟﻮﻋﺎﺋﻴﺔ 2. xylem fibers 3. xylem parenchyma

2. Phloem- is the principle food conducting tissue of the vascular plants. It is a complex tissues formed of: 1. Sieve elements 2. Phloem fibers. 3. Parenchyma cells

VASCULAR TISSUES

Monocot Stem

Dicot leaf Monocot leaf