Page 47 - PRE-U STPM BIOLOGY TERM 1

Biology Term 1 STPM Chapter 2 Structure of Cells and Organelles

• There are no capillaries in the cells as the cell layers are
too thin for capillaries to enter.
• Mitosis can take place to replace dead or worn out cells
of the skin epidermis.
(iii) Their functions are as follows:
• The epithelia help to protect tissues or organs below
2 them.
• They help to absorb substances and allow substances to
cross them.
• Some of the epithelial cells are modified to form special
receptors for stimuli.
(iv) They are classified based on their cell arrangement or the
shape of the cells.
• Based on the arrangement of cells, they are classified
into three groups:
Simple epithelium – The cells are arranged in one layer.
Stratified epithelium – The cells are arranged in more
than one layer.
Pseudo-stratified epithelium – The cells seemed to be
arranged in layers but each is attached to the basement
membrane.
• Based on their cell shapes, they are classified into four
groups:
Squamous epithelium – The cells are flattened like scales
or tiles.
Cuboidal epithelium – The cells are more or less shaped
like cubes.
Columnar epithelium – The cells look like pillars, their
height is longer than their base width.
Transitional epithelium – The cells can change shape
when stretched.
(v) There are eight types of covering epithelia and the examples
are as follows:
• Simple squamous epithelium. This is found in the outer
layer of Bowman capsule, endothelium of blood vessels
and alveolar walls.
Top view
• Bowman capsule channels filtrate into proximal
convoluted tubule. Endothelium allow exchange of gases
and small molecule within the blood capillaries and
Vertical section
body fluid. Alveolar walls allow gaseous exchange in the
Figure 2.37 Simple squamous
epithelium capillaries and the lungs.
• Simple cuboidal epithelium. This epithelium is found in
the collecting ducts and tubules of the nephron.

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