Cell specialisation (or modification or differentiation) is actually a process that occurs after cell division where the newly formed cells are structurally modified so that they can perform their function efficiently and effectively.
Examples of specialised cells
1. Red Blood Cell (ERYTHROCYTE)
A red blood cell is a tiny, disc-like cell (biconcave shape) which has no nucleus. In the cytoplasm of a red blood cell, there is a red pigment called haemoglobin. Each red blood cell lives for about four months, after which it breaks down. The red haemoglobin changes to a yellow pigment, which is excreted in the bile. The iron from the haemoglobin is stored in the liver. Red blood cells are made by the bone marrow of certain bones in the skeleton.
Functions of red blood cells
It contains haemoglobin that can combine with oxygen to form oxyhaemoglobin.
It has no nucleus so that more haemoglobin can be accommodated (hence more oxygen can be transported). By having no nucleus, enable a red blood cell to squeeze through small blood capillaries.
It has biconcave shape for increasing its surface area thus diffusion of oxygen in and out of the red blood cell becomes easy.
2. Root hair cell
Root hair cells are actually modified epidermal cells of the roots. A root hair cell has a long and narrow protrusion. A root hair cell has a large vacuole with lots of mitochondria in the cytoplasm. Now, unlike any typical plant cells, root hair cells have no chloroplasts.
Function of root hair cell: To absorb water and mineral salts by osmosis and active transport respectively.
Adaptations to function:
The hair-like structure helps to increase the surface area of the root hair cell, thus helps the root hair cell to absorb more water and mineral salts.
The hair-like structure which is long and narrow helps the root hair cell to penetrate in between soil particles in search of water and mineral salts.
The presence of mitochondria in large number in the cytoplasm of the root hair cell helps for more absorption of mineral salts by active transport (Remember, active transport will only occur in the presence of energy provided by the mitochondria).
The large vacuole enables more water and mineral salts to be stored after being absorbed.
3 .The xylem vessels
A xylem vessel is made up of long cells joined end to end. Once a region of the plant has ceased growing, the end walls of these cells are digested away to form a continuous fine tube. At the same time, the cell walls are thickened and impregnated with a substance called lignin which makes the cell wall very strong and impermeable. Since these lignified cell walls prevent free passage of water and nutrients, the cytoplasm dies. So a xylem is just like a water pipe which is hollow with no living materials in it.
Function of xylem vessel: To transport water and minerals from the roots to other parts of a plant as well as to provide support to the whole plant hence enable a plant to stand erect.
Adaptations to functions:
The cell walls of the xylem vessel being lignified adds or provides strength. This in turn provides support to the whole plant. The xylem in the leaf for example, helps the leaf to be positioned horizontally on the plant towards the sun. This helps the leaf to absorb as much light energy as possible to be used for photosynthesis.
The absence of protoplasm and cross-wall in the xylem vessel provides no obstacle for water to flow up the xylem vessel.
Being very narrow helps water to move up the xylem vessel by means of capillary action.
Other examples of specialised cells
4. Guard cells
Guard cells are cells in between a stoma. They are specialised in such a way that the cell wall in the inner side of the guard cells is thicker than the outer side.
This feature helps the guard cells to bend outward when they become turgid. This results in the opening of the stoma. If the guard cells become flaccid, the guard cells will bend inward resulting in the closing of the stoma.
5. Muscle cell
A muscle cell is generally elongated and elastic containing mitochondria in large number. The elongated and elastic feature helps muscle tissues to contract and relax. Contraction and relaxation of muscle tissues help in movement. The large number of mitochondria is very important in tissue respiration in the muscle cells (Remember, energy is required for muscle to contract)
You may think that all the cells in your body and the cells in a plant are all alike. Well, that is not the case. A large organism like you may contain many millions of cells which are totally different structurally and functionally. Almost all of these cells can perform the activities which are characteristics of living things, but many of them specialise in doing some of these better than other cells do.
Let’s see how cells are specialised to form tissues, organs and organ systems.
A tissue is a group of specialised cells having the same structures, which perform a particular function for example, the layer of cells lining your stomach. The function of this tissue is to make digestive enzymes which helps digestion of protein in the stomach.
An organ is a group of tissues working together to perform a particular function. Examples: Stomach, heart, kidney, leaf. Consider a leaf, it consists of the epidermal layers: palisade mesophyll layer, spongy mesophyll layer and the vascular tissues. Each of these tissues has its own function but they work together to make food in photosynthesis.