Plant cell (additional components which are not present in animal cells)

Cell structure and function

Cell is the structural functional unit of life. And these are the building blocks of living organisms. Here there is a misconception between the basic unit of matter and living organism’si.e atom and cell. Cell is the simplest unit of life and atom is the smallest unit.

Within cells there is an intricate network of organelles that all have unique functions. These organelles allow the cell to function properly.

Cell structure:According to cell theory of cell, cell basically consist of three basic parts

1­-Cell membrane

2-Cytoplasm

3- Nucleus

Cell function: Cell consist of many different types of organelles, which performs different functions and these functions are collectively consider as the functions of the cells.

Different organelles of cell are described below structurally as well as functionally:

→Cell wall:

The cell wall is the tough, flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, in addition to acting as a filtering mechanism. A major function of the cell wall is to act as a pressure vessel, preventing over-expansion when water enters the cell. Cell walls are found in plants, bacteria, fungi, algae, and some archaea. Animals and protozoa do not have cell walls.

The material in the cell wall varies between species, and can also differ depending on cell type and developmental stage. In bacteria, peptidoglycan forms the cell wall.Archaean cell walls have various compositions, and may be formed of glycoproteinS-layers, pseudopeptidoglycan, or polysaccharides. Fungi possess cell walls made of the glucosamine polymer chitin, and algae typically possess walls made of glycoproteins and polysaccharides. Unusually, diatoms have a cell wall composed of biogenic silica. Often, other accessory molecules are found anchored to the cell wall.

Structurelly cell wall consist of three layers

1-Primary wall

2-Midlle lamella

3-Secondry wall

→Primary cell wall:

Primary wall is made up of cellulose in plant cells and present inside of middle lamella.

→Middle lamella:The middlelamella first to be formed in between primary walls of neighbouring cells.

→Secondary wall:The secondary wall is formed on its inner surface and is comparatively thick and rigid.It is composed of inorganic salt ,silica, waxes, cutin and lignin. Prokaryotic cell wall lacks cellulose; its strengthening material is peptidoglycan or murein. Fungal cell wall contain chitin.

Function: Cell wall is very important. It provides a definite shape to the cell and keep rigid. It does not act as a barrier to the material passing through it.

2-Endoplasmic reticulum

→Production and transport: The endoplasmic reticulum are complex membrane-bound flattendsheets ,sacs, and tubules, that branches and spread throughout the cytoplasm. The ER are continuous from nuclear membrane to plasma membrane and contains various channels that circulate material throughout the cytoplasm.

The three dimensional structure of Endoplasmic reticulum is given below

It is also a point for enzymes storage and other proteins. And provide surface for attachment of ribosomes. On the basis of presence or absence of ribosomes, ER are of two types.

1-Rough Endoplasmic reticulum:

Endoplasmic reticulum with attached ribosomes are rough ER.

2-Smooth Endoplasmic reticulum:

ER without attached ribosomes is smooth endoplasmic reticulum.

Functions:

Smooth ER is the site for lipid production , detoxification of a wide variety of organic molecules and storage of calcium ions in muscles cells. Most cells have both types ER, Although the relative proportion varies among cells.

3-Mitocondria:

Mitochondria  are double membrane bound organelles that are spherical to elongate in shape. A small space separates the outer membrane from the inner membrane. The inner membrane folds and double in on itself to form incomplete partition called cristae. The cristae increase the surface area available for chemical reactions that trap useable energy for cell. The space between the cristae is known as Matrix. The matrix contains ribosomes ,circular DNA and other materials. Because they convert energy to usable form, mitochondria are frequently called “power generation”of the cell. Mitochondria usually multiply  whenacell need to produce more energy.

4-Plastids:Membrane bounded mostly pigment containing bodies present in the cell are called plastids. Plastids are are present inplant cells only. There are three types of plastids

→Chloroplast

→Chromoplasts

→Leucoplasts

1-Chloroplasts:  In photosynthetic plant cells there are membrane bound structure containing a green pigment , called chloroplasts. The green pigment is an organic molecule. Chlorophyll , which helps the cell to absorb light energy and utilize it to manufacture food. Chlorophyll molecule resembles to haem  group of haemoglobin , a protein used to transport oxygen. The main difference between these two molecules is that the chlorophyll has Mg++ while haem has Fe++ as the central atom.

2-Chromoplasts :They impart colours to the plant other than green. They are present in the petals of the flower and in the ripened fruit. They help in pollination and dispersal of seeds.

3-Leucoplasts : They are colourless. They are triangular , tubular  or some of other shape. They are found in the under ground parts of plants and store food.

Referances:

1-8^th edition of ZOOLOGY Miller and Harley, topic cell biology  , chapter No. 2 and page no. 19.

2- Punjab text book of Lahore for Fsc , chapter no. for 4 and page no. 60

3- Star and Tagart International edition of biology page no. 57