|
Breathing
and the structures
Monacia
Williams, Contributor
Last
week, we looked at breathing and the
structures associated with breathing
in humans. I cannot over-emphasise
that you need to read and reread this
material until you become comfortable
with it so that your knowledge can
be used to answer any question that
you might be given on the topic.
This
week, we will look at gaseous exchange
surfaces in humans, fish and plants.
Before we do so, let us take a look
at the differences between the air
that is exchanged across these surfaces.
|
Inspired
air |
Expired
air |
Reason
for difference |
Oxygen
|
21%
|
16%
|
Some
of the oxygen is used int he cells
for respiration. |
Carbon
dioxide
|
0.03%
|
4%
|
Carbon
dioxide is released as a result
of respiration in the cells. |
Nitrogen
|
78%
|
78%
|
This
gas is not used in respiration |
Water
|
Percentage
varies
|
This
is always higher than the inspired
air
|
Some
of the moisture on the surface
of the alveoli evaporates with
each breath. |
Temperature
|
Degree
varies
|
Expired
air always has a higher temperature
than inspired air. |
Air
is warmed by the heat of the body
|
Gaseous
exchange surfaces
Gaseous
exchange is defined as the exchange
of gases across a respiratory surface.
A gaseous exchange surface is any
surface across which the exchange
of gases takes place.
Regardless
of the organism in which they are
found, these surfaces have certain
characteristics in common. These are:
Large
surface area
| Man |
Fish |
Leaf |
The
lungs are made up of thousands
of alveoli - these tiny sacs that
are found at the end of the bronchioles,
the total surface area of the
alveoli is about 100m2
|
There
are thousands of finely divided
gill lamellae in each gill. These
together create a very large surface
area. The fish has several gills
on either side of its head.
|
Leaves
are thin, broad and flat. They
have ont heir underside hundreds
of tiny pores, the stomata, through
which gaseous exchange takes place.
All the leaves together on a tree
create a very large surface area
for gaseous exchange. |
| Man |
Fish |
Leaf |
The
walls of the alveoli are only
one cell thick. This puts the
air in them into close contact
with the blood in the capillary
which surrounds it. Special cells
in the alveoli secrete a watery
liquid in which the oxygen dissolves.
|
The
gill lamellae are one cell thick
and are also surrounded by blood
capillaries.
|
The
leaves are thin and have in the
spongy mesophyll layer lots of
ir spaces to which the cells are
exposed. Water vapour from the
xylem keeps the intercellular
air spaces moist.
|
-
Gaseous exchange takes place by
diffusion. For this to take place
quickly, the gaseous exchange surface
must be thin and moist.
- A
transport system - This is required
to move the gases as they come to
the respiratory surface. Remember
that the gases move by diffusion
and for diffusion to occur, a diffusion
gradient must be maintained. As
the oxygen diffuses across the membranes
it must be transported away from
the membrane.
| Man |
Fish |
Leaf |
The
alveoli are surrounded by capillaries
which are connected to the pulmonary
artery and the pulmonary vein.
The pulmonary artery supplies
the carbon dioxide-rich blood
to the alveoli and the pulmonary
vein removes the xygen-rich blood
from the alveoli.
|
The
gill lamellae are surrounded by
capillaries which take the gases
that diffuse from and into the
water across the membrane.
|
Air
movements ensure that gases do
not remain in place and disrupt
the diffusion gradient.
|
See
you all next week, as we continue
our journey!
|
|
|
Tina
Myers-Matalon (second left),
marketing manager for KFC, cuts
the ribbon to mark the official
opening of the JLS/KFC Chicky
Homework Centre and Reading
Room at Westmoreland Parish
Library. Observing the procedure
(from left) are Karen Barton,
senior director at the Jamaica
Library Service (JLS); Cecil
Graham, senior librarian Westmoreland
Parish Library, and some students.
- Photo by Dalton Laing
|
Monacia
Williams teaches at Glenmuir High
School.
|
