Notes for topic 2 - genes and health for A-Level Biology. not just copied from the textbook, dyslexic friendly lots of pictures all well explained, no waffle just covers exactly what you need to know. Grade A student.
, Cystic fibrosis
● Thick sticky mucus in tubes and ducts of the respiratory,
digestive and reproductive systems.
● Caused by a faulty gene on chromosome 7 which codes for
CFTR (cystic fibrosis transmembrane regulator) protein.
● CFTR protein is embedded in the membrane of epithelial cells
that line the tubes and ducts.
● It is involved in transport of chloride ions out of the cell,
which in turn regulates osmosis of water out of the cells and
thinks of the mucus.
● The faulty gene leads to a faulty protein which cannot regulate
the osmosis of water. This results in the thick sticky mucus.
● CF is caused by a recessive gene.
Gas exchange
Gas exchange is the transfer of gases between the organism and the
environment.
● It takes place by diffusion
● It occurs at gas exchange surfaces
Factors influencing gas exchange
● The quantity of oxygen required by an organism which is
determined by:
○ The number of living cells (volume of the organism)
○ The rate at which the cells are
respiring (metabolic rate)
● The rate at which oxygen can diffuse into
cells which partly depends on:
○ The surface area of gas exchange
(surface area:volume ratio)
As an organism gets bigger the surface area for
gas exchange decreases.
, Surface area:volume ratio can be increased by changing
shape.
Specialised gas exchange structures have:
● Large surface area
● Short diffusion distances
● Mechanisms to maintain a diffusion gradient
● Moist
The respiratory system
➔ When you breath in the diaphragm moves
down and the ribs and intercostal muscles,
pressure in the lungs decreases and air is
drawn in.
➔ When you breath out the diaphragm moves up
and the ribs and intercostal muscles push
inwards, the pressure in the lungs increases
and air is pushed out.
➔ The trachea, bronchi and bronchioles are
lined with epithelial cells and covered in a
layer of mucus. Mucus traps debris and
microorganisms. Hair like extensions (cilia)
on the epithelial cells move the mucus out of
the lungs (ciliated epithelial cells).
➔ Goblet cells produce mucus.
How are alveoli adapted?
● Have a folded surface area so the surface is very large
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