Component 3 (Adaptations for gas exchange) Flashcards
How does an organism’s size relate to its
surface area to volume ratio?
The larger the organism, the lower the
surface area to volume ratio.
How does surface area to volume (SA/V)
ratio affect transport of molecules?
The lower the SA/V ratio, the further the
distance molecules must travel to reach all
parts of the organism. Diffusion alone is not
sufficient in organisms with small SA/V ratios.
Why do larger organisms require mass
transport and specialised gas exchange
surfaces?
● Small SA/V ratio
● Diffusion insufficient to provide all cells with the
required oxygen and to remove all carbon dioxide
● Large organisms more active than smaller organisms
Name four features of an efficient gas
exchange surface.
● Large surface area
● Short diffusion distance
● Steep diffusion gradient
● Moist and permeable for gases
Describe the gas exchange mechanism
in the Amoeba.
● Unicellular organism with a large SA/V ratio
● Thin cell membrane provides short diffusion distance
● Simple diffusion across the cell surface membrane is
sufficient to meet the demands of respiratory processes
Describe the gas exchange mechanism
in flatworms.
● Multicellular organisms with a relatively small SA/V ratio (in
comparison to the Amoeba)
● However, flat structure provides a large surface area and
reduces the diffusion distance
● Simple diffusion is sufficient to meet the demands of
respiratory processes
Describe the gas exchange mechanism
in earthworms.
● Cylindrical, multicellular organisms with a relatively small SA/V ratio
(in comparison to the flatworm)
● Slow moving and low metabolic rate ∴ require little oxygen
● Rely on external surface for gas exchange
● Circulatory system transports oxygen to the tissues and removes
carbon dioxide, maintaining a steep diffusion gradient
Define ventilation.
The movement of fresh air into a space and
stale air out of a space to maintain a steep
concentration gradient of oxygen and
carbon dioxide.
Name the organ of gaseous exchange
in fish.
Gills
What are gill filaments?
● Main site of gaseous exchange in fish, over which water
flows
● They overlap to increase resistance to flowing water -
slowing it down and maximising gaseous exchange.
● Found in large stacks, known as gill plates, and have
gill lamellae which provide a large surface area and
good blood supply for exchange
Explain the process of ventilation in
bony fish.
● Buccal cavity volume increases and pressure decreases to
enable water to flow in
● Contraction of the buccal cavity forces water across the gills
● Pressure in the gill cavity rises, opening the operculum.
Water leaves
How is a steep diffusion gradient
maintained across the entire gas
exchange surface in bony fish?
Due to counter current flow.
How is a steep diffusion gradient
maintained across the entire gas
exchange surface in bony fish?
Due to counter current flow.
Define counter current flow.
Blood and water flow in opposite
directions across the gill plate.
How does counter current flow maintain
a steep diffusion gradient? What is the
advantage of this?
● Water is always next to blood of a lower oxygen
concentration
● Keeps rate of diffusion constant and enables 80%
of available oxygen to be absorbed
What type of flow is exhibited in
cartilaginous fish?
Parallel flow
Define parallel flow.
Water and blood flow in the same
direction across the gill plate.
Compare counter current and
parallel flow.
Counter current flow
* Blood and water flow in opposite directions across
the gill plate
* Steep diffusion gradient maintained, allowing
diffusion of oxygen across the whole gill plate
* High rate of diffusion
* More efficient - more oxygen absorbed into the
blood
* Found in bony fish
Parallel flow
* Water and blood flow in the same direction across
the gill plate
* Diffusion gradient not maintained ∴ diffusion of
oxygen does not occur across the whole plate
* Lower rate of diffusion
* Less efficient - less oxygen absorbed into the
blood
* Found in cartilaginous fish, e.g. sharks
Name and describe the main features of
an insect’s gas transport system.
● Spiracles - small, external openings along the thorax and abdomen
through which air enters, and air and water leave the gas exchange
system
● Tracheae - large tubes extending through all body tissues, supported by
rings of chitin to prevent collapse
● Tracheoles - smaller branches dividing off the tracheae
What is the main site of gas exchange in
insects?
Tracheoles
Describe the adaptations of the insect
tracheal system to a terrestrial
environment.
● Spiracles can be opened or closed to regulate diffusion
● Bodily contractions speed up the movement of air through the
spiracles
● Highly branched tracheoles provide a large surface area
● Impermeable cuticle reduces water loss by evaporation
Describe the ventilation of the tracheal
system in insects.
● Expansion of the abdomen opens the thorax spiracles
(through which air enters) and closes the abdominal
spiracles
● Compression of the abdomen closes the thorax spiracles
and opens the abdominal spiracles (through which air is
expelled)
Compare the gas exchange surface of
an active and inactive amphibian.
● Active amphibian has simple lungs
● Inactive amphibian relies on its moist
external surface for gas exchange
How are mammals adapted for gas
exchange?
Alveoli provide a large surface area and thin
diffusion pathway, maximising the volume of
oxygen absorbed from one breath. They also
have a plentiful supply of deoxygenated blood,
maintaining a steep concentration gradient.
Describe the structure and function of
the larynx.
A hollow, tubular structure located at the
top of the trachea involved in breathing
and phonation.
Describe the trachea and its function in
the mammalian gaseous exchange
system.
● Primary airway, carries air from the nasal cavity down into the chest
● Wide tube supported by C-shaped cartilage to keep the air passage
open during pressure changes
● Lined by ciliated epithelial cells which move mucus, produced by
goblet cells, towards the back of the throat to be swallowed. This
prevents lung infections
Describe the structure of the bronchi.
● Divisions of the trachea that lead into the lungs
● Narrower than the trachea
● Supported by rings of cartilage and lined by
ciliated epithelial cells and goblet cells
Describe the structure and function of
the bronchioles.
● Many small divisions of the bronchi that allow the passage
of air into the alveoli
● Contain smooth muscle to restrict airflow to the lungs but
do not have cartilage
● Lined with a thin layer of ciliated epithelial cells
What is the primary gaseous exchange
surface in humans?
Alveoli
Describe the alveoli in the mammalian
gaseous exchange system.
● Mini air sacs, lined with epithelial cells
● Walls one cell thick
● Good blood supply to maintain a steep diffusion gradient
● 300 million in each lung
What are the pleural membranes?
Thin, moist layers of tissue surrounding
the pleural cavity that reduce friction
between the lungs and the inner chest
wall.
Define pleural cavity.
The space between the pleural
membranes of the lungs and the inner
chest wall.
Describe ventilation in humans.
● The movement of fresh air into the lungs
and stale air out of the lungs via
inspiration and expiration
● Via negative pressure breathing
What are internal intercostal muscles?
A set of muscles found between the ribs
on the inside that are involved in forced
exhalation.
What are external intercostal muscles?
A set of muscles found between the ribs
on the outside that are involved in forced
and quiet inhalation.
Explain the process of inspiration and
the changes that occur throughout the
thorax.
● External intercostal muscles contract (while internal relax), raising the ribcage
● Diaphragm contracts and flattens
● Outer pleural membrane moves out, reducing pleural cavity pressure and
pulling the inner membrane out
● The alveoli expand. Alveolar pressure falls below air pressure so air moves
into the trachea
What is surfactant?
A fluid lining the surface of the alveoli that
reduces surface tension and prevents
collapse of the alveoli during exhalation.
Describe the function of the waxy cuticle.
Reduces water loss from the leaf
surface.
Describe how the upper epidermis is
adapted for photosynthesis.
● Layer of transparent cells allow light to
strike the mesophyll tissue
● Epidermal cells also synthesise the waxy
cuticle, reducing water loss
Where is the palisade mesophyll layer
located?
Directly below the upper epidermis.
How is the palisade mesophyll layer
adapted for photosynthesis?
It receives the most light so contains the
greatest concentration of chloroplasts.
How is the spongy mesophyll layer
adapted for photosynthesis?
● Contains air spaces that reduce the diffusion
distance for carbon dioxide to reach the
chloroplasts in the palisade layer
● Contains some chloroplasts
What is a vascular bundle?
The vascular system in dicotyledonous
plants. It consists of two transport
vessels, the xylem and the phloem.
Why are vascular bundles important in
photosynthesis?
They form a large network to deliver
water and nutrients to photosynthetic
tissues and remove glucose.
Describe how the lower epidermis is
adapted for photosynthesis.
It contains many stomata which enable
the evaporation of water and inward
diffusion of CO2
.
What are stomata?
Small holes found on leaves that can be
opened or closed by guard cells to
control gas exchange and water loss.
Summarise the ‘malate’ theory.
The ‘malate’ theory states that the
accumulation or loss of malate and K+
ions
by guard cells results in changes in turgor
pressure that open or close the stomata.
By what mechanism do K+
ions enter
guard cells?
Active transport
How does the accumulation of K+
and
malate ions affect guard cells?
● Lowers the water potential of guard cells
● Water moves in by osmosis
● Guard cells becomes turgid, opening the
stomata
Why is starch important for stomatal
opening?
Starch is converted to malate ions.
