The Cell, Its General Structure and Activities

Introduction

In Unit 1, you learnt that every living organism carries out activities to show that they are alive. In this unit, you will learn that every organism is made up of cells. There are some organisms that are single celled. The cell is very tiny, you will need a microscope to view it. Even though it is tiny and not visible to the naked eyes, it carries out the processes that make the organism a living thing.

The Cell Concept

The cell is the basic unit of structure and function in living organisms. Two scientists, Schlieden and Schwann proposed what is commonly known as cell theory in 1838 and 1839 respectively. In 1855, another idea that new cells can only come from pre-existing cells was proposed. Study table 2.0 for historical developments in the area of cell biology.

An easy way of looking at cells is to consider them as a bag of chemicals that is capable of surviving and multiplying itself. The chemical constituent of each bag is such that it is different in many ways from those outside it. If this difference cannot be maintained, life could not exist. The barrier is a very thin membrane called the cell surface membrane. It serves as a border control point regulating the
movement of molecules in and out of the cell.

 Differences Between An Anim al Cell And A Plant Cell

Animal cells have adrenaline, thyroxine and the organelle centriole which are not found in plant cells. Plant cells have chlorophyll, cellulose and starch which are not found in animal cells. Plants have more elaborate structures. Other differences are:

1.  "a relatively rigid cell wall outside the cell surface membrane; pores containing fine threads known as plasmosdesmata link the cytoplasm of neighbouring cells through the cell walls. 
2. Chloroplasts in photosynthetic plant cells; 
3. A large central vacuole: animal cells may have small vacuoles such as phygocytic vacuoles." 

Tr y to look at the slides of a plant cell and animal cell under a microscope. Try to locate some of the structures you find on the diagrams. You can compare what you see in the slide under the microscope with the diagram of the structures.

N.B. Your tutor will help you in this task.

Diversity of Cells

Cells are of different kinds, different sizes shapes and form. But there is one thing common among them, they all possess nucleus and cytoplasm with other organelles structure of kinds of cells

1.  Epithelial cell 
2. White blood cell 
3. Nerve cell 
4. Smooth muscle fibre
5. Spermatozoon cell 
6. Parenchyma cells of plant 
7. Amoeba 

The cell is a unit of living organisms. Some organisms are made of just a single cell, some others are made of many cells (collectively they make up organism). An easy way of looking at cells is to consider them as a bag of the chemicals that is capable of surviving and multiplying itself. Plant cells are different from animal cells in many ways. Cells divide thereby increasing.