Evolution - Specialised Cells

1. Red Blood Cells (erythrocytes)

·        It is flat and has a biconcave shape which increases the surface area to volume ratio, resulting in an increase in the diffusion of oxygen in and out of the cell. 

·        Has no nucleus so as to store more Haemoglobin, a red pigment that combines with oxygen to form oxyhaemoglobin. This also allows the Red Blood Cell to transport more oxygen.

·        Has a greater surface area for gas exchange, thus increasing the surface area to volume ratio for diffusion.

·        Red Blood Cell can change shape to a great extent, without breaking, as it squeezes single file through the capillaries.

Function: Transports oxygen from lungs to other parts of the body.  

 (image taken from: http://www.rkm.com.au/cell/red-blood-cells.html)

2. Xylem Cells   

·        Cells are arranged end to end.

·        Long narrow tubes with a continuous space (lumen).

·        Consists of dead cells with no protoplasm and cross walls. This enables water and dissolved mineral salts to move more easily.

·        They have lignified cell wall and the secondary walls of vessels are filled with lignin, a kind of hard glue. The lignin is deposited on the cell walls to strengthen them and provide mechanical support.

·        Three different types of cells: Xylem parenchyma cells and xylem fiber cells, which simply provide structural support for the most important xylem cells, the tracheary elements (TE). The TE are completely dead at maturity and act like popes to allow water and dissolved minerals to flow through them.

·        A key feature of their structure are secondary cell wall thickenings. These thickenings form in distinctive patterns, frequently rings, to provide maximum structural support. 

Function: 1) To transport water and mineral salts from the roots to the other parts of the plant. 2) To support the plant.

 

(image taken from: http://pharamcytimes.wordpress.com/tag/plants-tissues/)

3. Root Hair Cells

·      The Root Hair Cells have a long and narrow protruding end which increases the surface area to volume ratio, enabling the root hair cells to absorb more water and mineral salts from the soil. 

Function: Absorb water and mineral salts from the surrounding soil. 

(taken from: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/cells/cells2.shtml)

4. Intestinal cells (Epithelial cells)

·      Epithelial cells in the small intestine are a type of brush border cell (covered in microvilli)

·      These cells are covered in microvilli to increase their absorptive surface area.