Plant and Animal Cells

Cell – The Basic Unit of Life

The cell is the most basic unit of life. All living things – all plants and all animals – are made up of many cells.

Most cells are extremely small and can only be viewed under a microscope. Some living things, such as bacteria, yeasts, amebae and algae, simply consist of one single cell (Unicellular) which is capable of carrying out all the functions of the living being. Plants and animals are made of millions and millions of cells (Multicellular), each set of cells specialized for a particular function. For example, the human body has muscle cells, nerve cells, cells that make up the heart, lungs, and other organs, and so on.

Cells come in all kinds of shapes and sizes. They typically have a Cell Membrane or Cell Wall around the outside which holds all the contents of the cell together.

Unicellular Organisms

Most unicellular organisms simply look like tiny balls. Other unicellular organisms, such as bacteria, resemble balls, rods and coils. Some may be shaped like boxes – square, round, oblong, triangular. The ameba has no particular shape at all!

Animal Cells

Animal cells are generally smaller than plant cells. Multicellular animal cells have the greatest variety in shapes – they may be round, egg-shaped, square, or rectangular. Some muscle cells are long and thin, pointed at the ends. Some nerve cells are branched like trees.

The shape of a cell is related to the function that the cell needs to carry out. Long muscle cells can expand and contract to do work. Branched nerve cells can relay messages to all parts of the body.

The size of any multicellular plant or animal is determined by the total number of cells it has, and not the size of the cells. An elephant or a giant Sequoia tree has trillions of more cells than a mouse or a small bush, not because the cells are larger or smaller in size.

Check Point

1. Which of these is multicellular?
   1. Bacteria
   2. Algae
   3. Giraffe
   4. Ameba
2. Which of these is unicellular?
   1. Rose Plant
   2. Bacteria
   3. Cat
   4. Sequoia tree
3. Plant cells are made up of structures known as ______ which contain ______ which is essential for the process of ______.
4. Plant cells walls contain ______ to provide stiffness to stems.
5. ______ cells are branched so that they can relay messages to all parts of the body.

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