Composition of cell wall, Biology

Assignment Help:

COMPOSITION OF CELL WALL

Cell wall composed of cellulose, hemicellulose, pectin, lignin, cutin & chitin.

Cell wall consists of 3 parts -

1. Matrix

  • Highly cross-linked amorphous gel-like ground substances.
  • Water = 30-60%, forms dispersion medium, hydration.
  • Pectin = 2-8%, heteropolysaccaride, helps in cross-linking, determines hydration of cell wall, elasticity, growth.
  • Hemicellulose = 5-15%,     Lipid = 0.5-3%, Protein = 1-2%

2. Microfibrils

  • Structural elements of cell wall. Provide rigidity of cell wall.
  • In plants microfibrils are formed of cellulose.
  • They are 10-25 mm in thickness, 0.5-0.7 mm in length.
  • Cellulose forms the backbone of the plant cell.
  • Cellulose polymer of b-D-glucose.
  • A cellulose microfibril consists of about 3000 glucose molecules.
  • Many chains of cellulose molecules lie parallel to each other to form the bundles.
  • A bundles of 100 molecules of cellulose forms the one elementary fibril known as the micelle.
  • The 20 micelle when get arraged parallely, form the fibrils of 250Å thick, known as microfibrils.
  • Microfibril forms large size bundle of cellulose fibres to form the macrofibrils. (macrofibril form skeletal of cell wall).
  • Microfibrils are loose & wavy in primary wall.
  • Microfibrils are close & parallel arrangement in secondary wall.
  • The hemicellulose is composed of monosaccharide units like arabinose, xylose, mammose & galactose.
  • The pectin chemically composed of glucuronic and galacturonic acid.
  • The lignin chemically composed of confieryl alcohol.
  • The cutin composed of many fatty acids.
  • In fugal cell wall formed of chitin material.
  • The chitin is a polymer of b (1® 4) acetyl glucosamine.
  • Chitin also occurs in Exoskeleton of Arthropods (insects + crustaceans)
  • Chitin is second most abundant organic material.
  • In bacterial cell wall made up of peptidoglycan mucopeptide (murein).
  • Murein is made of N-acetyl glucosamine, acetyl muramic acid and small peptide chains.
  • i.e. Murein is polymer of NAG and NAM

3. Deposition on the cell wall

(a) Lignin

  • Deposition of lignin on cell wall is called lignification.
  • After lignification cell becomes dead & impermeable to water.
  • It provides hardness to the wall.
  • Lignification commonly occur in seconday cell wall.
  • Lignin is the derivative of cellulose.
  • Lignification developed with evolution of land plants.

(b) Cutin

  • Depostion of cutin is called cutinization.
  • Cutin derivative of lipid. Polymer of Hydroxy fatty acids.
  • Deposition on epidermal cells of leaf.
  • Epidermal layer form a layer "cuticle" outside the cell wall.
  • Formation of cuticle layer is called "Cuticularisation".
  • Cutin reduces the rate of transpiration. (Loss of water in vapour form)

(c) Suberin

  • Deposition of suberin is called Suberization.
  • Suberin derivative of fatty acids. Consists of Phellonic acid and Glycerol.
  • After suberization cell becomes dead and impermeable to water.
  • It occurs in cork cells and endodermal cells.
  • Commercial cork is obtained from Quercus suber (Spanish oak)

(d) Silica

  • Deposition occur in Atropa, Grasses, Equisetum, Diatoms.
  • It provides stiffness to wall. Protects the plants from fungal attack. Irritation to grazing animals.

(e) Nonsiliceous Minerals

  • Deposition of Fe and Cu occurs in aquatic habitat plants, e.g. Chara

(f) Wax

  • Polymer of fatty acid and alcohol.
  • Wax occurs as component of cuticle and surface bloom.
  • Water repellent and control transpiration.

Related Discussions:- Composition of cell wall

Assignment, Structure and development of leaf

Structure and development of leaf

For the biological diversity is mitosis or meiosis, For the biological dive...

For the biological diversity is mitosis or meiosis the more important process? Meiosis is the cell division process that permits the formation of gametes to sexual reproduction

Why the av node of a mammalian heart is destroyed, The AV node of a mammali...

The AV node of a mammalian heart is destroyed. A. A depolarization in a cell in the left atrium will cause a depolarization of a cell in the left ventricle. B. The contracti

Which are the eukaryotic, Which of the following are eukaryotic? Bacteria p...

Which of the following are eukaryotic? Bacteria protists fungi animals' archaea plants and animals only all of the choices are eukaryotic.

Fusion of sperm and egg, Fusion of Sperm and the Egg After the penetr...

Fusion of Sperm and the Egg After the penetration of the extracellular layers by sperm there occurs the fusion of the - sperm plasma membrane with that of the egg. In mammals

Role of mesoderm and ectoderm in limb morphogenesis, Role of Mesoderm and E...

Role of Mesoderm and Ectoderm in Limb Morphogenesis A series of very interesting experiments on wing and leg buds of chick embryos have clarified the respective roles of meso

What is allantois, What is Allantois One of the extraembryonic eggs foun...

What is Allantois One of the extraembryonic eggs found in the amniote animals. The allantois contains the metabolic wastes created by the developing embryo. May also be involved

Climax forest - xerarch, Climax Forest - Xerarch First, some xerophyti...

Climax Forest - Xerarch First, some xerophytic species of trees, establish in this area. They are sparsely distributed and are stunted because the conditions are still not ver

Fallopian tube, Fallopian tube: There are two fallopian tubes connec...

Fallopian tube: There are two fallopian tubes connected to the uterus one on each side of it. The ovum released from the ovarian follicle enters the fallopian tube. Th

Free-hand sectioning of plant tissue (stem), What are the processes involve...

What are the processes involved in the preparation of plant tissue for free hand sectioning?

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd