PLANT CELL

A plant cell may be defined as a unit of life or a mass of protoplasm covered with a cell membrane and the cell wall.

COMPONENTS OF A CELL 1. Living components

Two components2. Non-living components

Cytoplasm and Organelles

Living component – ProtoplasmNucleus

a. Cell wall

Non-living components b. Vacuole

c. Cell Inclusions

LIVING COMPONENTS Protoplasm - It is the physical basis of life. Function - Metabolism, nutrition, growth, movement. Physical Nature of Protoplasm 1. Colloidal state 2. Semitransparent3. Foamy or granular 4. Semifluid substance, somewhat like the white of an

egg. 5. Semipermeable i.e it allows only certain substances

and not others to enter its body.

Colloidal State

Semitransparent

Chemical Nature of Protoplasm Active protoplasm contains - water 90 %

- protein 40 % - 60 % - fatty substances

( true fats and lipids ) 12 % - 14 %- carbohydrates 12% - 14 % - inorganic salts 5 % - 7 %

oxygen, carbon, hydrogen, nitrogen, are present in large quantities. Chlorine, sulphur, phosphorus, silicon, calcium, magnesium, potassium, copper, boron and molybdenum are present in trace.

Biological Properties of Protoplasm - Metabolism , Irritability , Growth , Reproduction ,

Movement

Metabolism1. Anabolism2. Catabolism

Irritability

E.g. Sundew

E.g. Venus flytrap

E.g. Picture plant

Growth

MovementE.g. Chlamydomonas and Euglena

Reproduction

PlantAsexual or Sexual

Animal

THE PLASMA MEMBRANE - The plasma membrane or cell membrane is the

outer boundary of the living part of the cell. Function:

(i) selective permeability, i.e. it allows certain molecules to pass through, while preventingothers from entering or leaving the cell;

(ii) to receive signals from the outside environment.

CYTOPLASM- The cytoplasm is composed of several types of

organelles and a fluid matrix, the cytosol in which the organelles are distributed.

- The cytosol is an aqueous solution of salts, sugars, amino acids, fatty acids, nucleotides andother materials

MITOCHONDRIA

Organelles Mitochondria (Gk, mitos = thread, chondrios = granule) - They are the powerhouses of the cell and maternal

inheritance organelles. - It appears as short rods or filamentous or sausage

shaped bodies. - Mitochondria have a double membrane around them. - The outer membrane is fairly smooth. - The inner membrane is highly folded to form structures called

cristae.- The cristae greatly increase the inner membrane's surface area. - Both respiratory electron transport chain and ATP synthetase are

located in inner membrane.- Enzymes connected to the cristae control the chemical reactions

that form ATP.- Function - Production of energy during cellular respiration

RIBOSOMES

Ribosomes - Rhizomes are not membrane bound. - They are very tiny granules and packets of RNA,

nucleoproteins and enzymes.- They are found both in prokaryotes and eukaryotes. - They are very abundant in embryonic cells. - Each ribosome comprises two parts, a large subunit

and a small subunit. - These subunits are synthesized in nucleolus.- Multiple ribosomes on a single mRNA strand form a

polyribosome or polysome. - Functions - to synthesize proteins, including

enzymes.

Golgi Apparatus

Golgi Apparatus

Golgi Apparatus (Named for Camillo Golgi in 1898) - It is a stack of membrane-bound vesicles. - It is likely an outgrowth of the ER system.- It associates with the ER, involved with packaging

of materials for transport in the cells. - The Golgi apparatus occupies a central portion in the

secretory pathway, receiving newly synthesized proteins and lipids from the ER and directing them to either the cell membrane or the vacuoles (tonoplast).

- During mitosis, Golgi stacks provide the membrane and cell wall molecules needed for cell plate formation in plant cells.

- The new Golgi stacks arise by fission. - Functions : Production of cellular secretion.

Centrosomes

Centrosomes (Gk. centrum = center and soma = body)- It may occasionally be present in some cells of

lower plants.- It lies near the exterior surface of the nucleus. - It is nonmembranous mass of two rod-like centrioles.- Each centriole contains 9 triplet microtubules that

radiate from the center like the spokes of a wheel. - The 2 centrioles lie at right angles to each other.- They are duplicated when the cell undergoes cell

division. - Functions : to take part in cell division.

Endoplasmic Reticulum

Endoplasmic Reticulum Gk = endo = within,plasma = something - molded L. reticulum = net.

- It appears to be a fine network, extending throughout the ground substance of the cytoplasm.

- It is found to be continuous with the nuclear membrane and the plasma membrane and also from cell to cell.

- Linked to it are the nucleus, the mitochondria, the ribosomes and all the cytoplasmic inclusions.

- When cytoplasm as a whole streams or moves, the endoplasmic reticulum streams and moves too and the formed inclusions are carried along.

- Function : intracellular transport.

Peroxisomes

Peroxisomes- Peroxisome is a specialized metabolic

compartment bounded by a single membrane.- Function : consume oxygen in various metabolic

functions.

Microtubules

Microtubules- Microtubules are unbranched, thin, hollow, tube-

like structures.- They are composed of proteins and vary in length. - Most are between 15 and 25 nanometers in diameter

and are commonly found just inside the plasma membrane.

- Function : (1) Addition of cellulose to the cell wall (2) Movement of cilia and flagella. (3) Tracks along which vesicles shuttled around the

cell. •

Microfilaments

Microfilaments - Microfilaments are long protein filaments,

with an average diameter of 6 nanometers often occurring in bundles.

- Function : - Cytoplasmic streaming, contraction and

movement of cells. - Microtubules and microfilaments form a

fiexible framework, within the cytoplasm called the cytoskeleton.

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