Gas Exchange in Animals Flashcards
1
Q
The Importance of Gas Exchange in Animals
A
- allowing animals to obtain oxygen and eliminate carbon dioxide
- facilitates the delivery of oxygen to tissues and ensures the removal of metabolic waste products
- present in a wide range of animals, from simple unicellular organisms to complex multicellular organisms.
2
Q
How do gases cross the plasma membrane?
A
- gases move into and out of a cell across the plasma membrane via diffusion along a concentration gradient.
- Carbon dioxide and oxygen molecules are small enough to move straight through the membrane.
3
Q
Conditions for Efficient Gas Exchange
A
- The environment be moist.
- The membrane must be thin and
permeable. - There must be a large surface area in relation to
the volume of the organism - There must be a greater concentration of required
gas on one side of the membrane than the other.
4
Q
Exchanging with Air or Water
A
- Organisms will exchange gases with the environment they live in: air or water.
- Some organisms can exchange gases with both e.g. frogs
- Water holds a lot less dissolved oxygen than air and warm water is able to hold even less
dissolved oxygen than cold water.
5
Q
Gas Exchange in Multi-cellular
Organisms
A
- Challenge of multi-cellular organisms on gas exchange: some cells are just too far away
from the external environment to obtain gases by diffusion. - To over-come, surface area available increased for gas exchange and linking this to
a transport system that connects with every cell. - Animals have specialised structures that allow
for efficient gas exchange - The complexity of these structures depends on the
size, behaviors and activity levels of the organism. In small organisms these structure can be very simple.
6
Q
Gas Exchange in Multi-cellular
Organisms: Air Breathers
A
- Air breathers have the advantage that oxygen is
much more readily available in air - As gas exchange occurs across a moist surface air breathers will continually loose water to their environment. Respiratory surfaces are a major site for water loss.
- larger animals have developed internal respiratory organs.
7
Q
The Human Respiratory System
A
- Air is drawn through
the nose and enters the
pharynx (throat) - Air then passes into the
trachea and the paired bronchi. Here the dust and bacteria are
trapped by mucus and
swept up to the throat
by cilia. The trachea is
supported by cartilage
rings that prevent its
collapse. - Air passes into the
bronchioles and from
here into the alveolus.
It is here that gas
exchange takes place.
7
Q
Gas Exchange in Multi-cellular
Organisms: Invertebrate Air Breathers
A
- Many invertebrates have small holes in their
abdomen known as spiracles. - Some invertebrates also have air sacs that can be pumped to move air through the system.
- Many vertebrates have internal respiratory organs
known as lungs.
– Air is forced into the lungs under pressure
– Air is drawn into the lungs under negative pressure (suction) - Frogs are an example of an animal that ventilates
their lungs under pressure. - In air breathers, oxygen is readily available.
- Air breathers therefore are more sensitive to changes in carbon dioxide concentration and this drives ventilation.
- Receptors that are sensitive to carbon dioxide and blood pH will indicate when ventilation needs
to be modified.
8
Q
The Human Respiratory System
A
- The alveoli are designed for extremely efficient gas exchange
- The alveoli provide a large area for gas exchange (equivalent to the size of a tennis
court) - They are lined with a very thin layer of flat cells that is in direct contact with a network of capillaries
- These cells are also lined with a surfactant, a lipoprotein, that prevents the alveoli from
collapsing.
9
Q
The Human Respiratory System: Lung Ventilation
A
- The lungs are kept expanded due to pressure differences in the thorax (chest cavity)
- This negative pressure keeps the lungs inflated
- At the base of the lungs is a diaphragm- the largest
muscle in the body. - When the diaphragm contracts (active process) it pulls downward expanding the chest cavity and the ribs and causing the lungs expand.
- This expansion draws air into the lungs.
- When the diaphragm relaxes (passive process) the thorax returns to its resting position forcing air
out of the lungs.
10
Q
This represents the amount of air that is moved in and out during each breath. IT varies according to oxygen
demand.
A
Tidal volume
11
Q
This represents the maximum amount of air that we can move into and out of the
lungs in one breath.
A
Vital capacity
12
Q
Lung Ventilation: Residual Volume
A
- One-way ventilation (in and back out the same
pathway) is not the most efficient way to exchange
gas. - We can never exhale all of the air from our lungs
and so “stale air” is drawn back into the lungs in
the next breath. - The volume of air left in the lungs after exhalation is
referred to as the residual volume. - Residual volume has a benefit as this air prevents
the lungs from collapsing.
13
Q
Transporting Gases: Haemoglobin
A
- Oxygen is transported around the body in the blood
by respiratory pigments such as haemoglobin that
combine reversibly with oxygen and increase the
oxygen carry capacity of blood. - Haemoglobin is found in red blood cells. Four
oxygen molecules can bind with one haemoglobin
molecule. - When oxygen is bound to haemoglobin they form
a complex known as oxyhaemoglobin. In this state
the haemoglobin turns red.
14
Q
Transporting Gases: Carbon
Dioxide
A
- Carbon dioxide forms an acid when it combines
with water the therefore only a limited amount can
be carried in the blood (7%) - Some carbon dioxide combines with haemoglobin
to form carbaminohaemoglobin (23%). - The rest (70%) is converted by red blood cells into
hydrogen carbonate ions. As soon as the hydrogen
carbonate reaches the lungs it returns to the red blood
cells and is turned back into carbon dioxide for
release.
