CELL- STRUCTURE AND FUNCTIONS

MADE BY: ANAMCLASS:VIII-A

Discovery of the cell The andy was first discovered by Robert Hooke in 1665,

which can be found to be described in his book Micrographia. In this book, he gave 60 ‘observations’ in detail of various objects under a coarse, compound microscope .One observation was from very thin slices of bottle cork. Hooke discovered a multitude of tiny pores that he named "andys". This came from the Latin word Cella, meaning ‘a small room’ like monks lived in and also Cellulae, which meant the six sided cell of a honey comb. However, Hooke did not know their real structure or function. Before, it had been thought that cells shared walls and the fluid passed between them this way.

Cell theory In biology, cell theory is a scientific theory which describes the

properties of cells. These cells are the basic unit of structure of all organisms and also the basic unit of reproduction. With continual improvements made to microscopes over time, magnification technology advanced enough to discover cell in the 17th century. This discovery is largely attributed to Robert Hooke, and began the scientific study of cell, also known as cell biology. Cell theory has become the foundation of biology and is the most widely accepted explanation of the function of cells.

The three tenets to the cell theory are as described below: All living organisms are composed of one or more cells The cell is the most basic unit of life. All cells arise from pre-existing, living cells.

Parts of a cell

All cells, whether they are prokaryotic or eukaryotic, have some common features.

The common features of prokaryotic and eukaryotic cells are: 1. DNA, the genetic material contained in one or more

chromosomes and located in a nonmembrane bound nucleoid region in prokaryotes and a membrane-bound nucleus in eukaryotes

2. Plasma membrane, a phospholipid bilayer with proteins that separates the cell from the surrounding environment and functions as a selective barrier for the import and export of materials

3. Cytoplasm, the rest of the material of the cell within the plasma membrane, excluding the nucleoid region or nucleus, that consists of a fluid portion called the cytosol and the organelles and other particulates suspended in it

4. Ribosomes, the organelles on which protein synthesis takes place

Cell diversity

Living organisms include unicellular organisms living as only one cell, and multicellular organisms whose bodies are made of many cells. Various kinds of unicellular organisms exist, from bacteria such as the 1-2-μm-long Escherichia coli (E. coli) to protists such as the 200-μm-long paramecia Multicellular organisms, e.g., humans, are made of a great variety of cells. Cells have various shapes, including flat cells (e.g., skin epithelial cells), disc-shaped cells (e.g., red blood cells), and long, narrow, extended cells (e.g., nerve cells). Cell sizes vary from a diameter of about 7 am in red blood cells to a dendrite length of up to 1 m in nerve cells. Plant cells also have a variety of shapes and sizes, including rectangular compartmentalized cells (e.g., cork cells), cells resembling jigsaw puzzle pieces (e.g., spongy cells), and cells elongated from a few millimeters to several dozen centimeters in length (e.g., pollen tube cells).

Cell division Cell division is the process by which a parent cell divides into

two or more daughter cells.Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct type of cell division: a vegetative division, whereby each daughter cell is genetically identical to the parent cell (mitosis), and a reductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half, to produce haploid gametes (meiosis). Meiosis results in four haploid daughter cells by undergoing one round of DNA replication followed by two divisions: homologous chromosomes are separated in the first division, and sister chromatids are separated in the second division. Both of these cell division cycles are in sexually reproducing organisms at some point in their life cycle, and both are believed to be present in the last eukaryotic common ancestor Prokaryotes also undergo a vegetative cell division known as binary fission, where their genetic material is segregated equally into two daughter cells. All cell divisions, regardless of organism, are preceded by a single round of DNA replication.

Animal cell

Plant cell

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