exchange surfaces and breathing

how does a high SA:V ratio affect the rate of diffusion

diffusion of substances if fast

why do multicellular organisms require specialised surfaces rather than substances diffusing directly across the membrane

• cells are not in direct contact with the external environment

• diffusion distances between cells and their environment are large

• larger organisms have higher metabolic rates, so they need more oxygen and glucose

what are the four features of a specialised exchange surface

1. a large surface area- this provides a larger area across which substances can be exchanged

2. thin walls- these minimise the diffusion distance

3. an extensive blood supply and/or ventilation- this maintains steep concentration gradients

4. being surrounded by selectively permeable plasma membranes- this controls which substances are exchanged

describe the pathway of air through the body

1. air first enters the trachea

2. it travels into the two bronchi, with one bronchus going to each lung

3. air travels into smaller airways called bronchioles

4. air travels into clusters of air sacs called alveoli at the end of the bronchioles

what specialised tissue is located throughout most of the airways

ciliated epithelium

what is the role of goblet cells in the ciliated epithelium

secrete mucus that traps dust and pathogens

what is the function of the cilia on ciliated epithelial tissue

they waft the mucuc upward to the mouth so it can be swallowed

what are the structural adaptations of the trachea

• rings of cartilage keep the airway open

• smooth muscle can contract or relax to constrict or dilate the airway and change airflow

• elastic tissue contains elastic fibres with elastin that allows stretching and recoiling

• lined with ciliated epithelial cells and goblet cells

what are the structural adaptations of the bronchi

• reinforced with cartilage to keep the airway open

• smooth muscle can contract or relax to constrict or dilate the airway and change airflow

• elastic tissue contains elastic fibres with elastin that allows stretching and recoiling

• lined with ciliated epithelial cells and goblet cells

what are the structural adaptations of the bronchioles

• no cartilage, can change shape

• smooth muscle can contract or relax to constrict or dilate the airway and change airflow

• elastic tissue contains elastic fibres with elastin that allows stretching and recoiling

• simple squamos epithelium (only larger bronchioles have a ciliated epithelium)

what are adaptations of the pulmonary capillaries for gas exchange

1. thin walls (one endothelial cell thick)- maintains short dffusion distance

2. red blood cells pressed against capillary walls- reduces diffusion distance

3. large surface area- increases diffusion speed

4. movement of blood- maintains steep diffusion gradient

5. slow blood movement- allows more time for diffusion

what is ventilation

the constant movement of air into and out of the lungs, consisting of inspiration and expiration (breathing)

what three sets of muscles are involved in ventilation

1. diaphragm

2. external intercostal muscles

3. internal intercostal muscles

what are the steps for inspiration

1. the external intercostal muscles contract while the internal intercostal muscles relax, moving the ribcage up and out

2. the volume of the cavity increases

3. the diaphragm contracts and flattens, further increasing the volume of the cavity

4. the lung pressure decreases below atmospheric pressure

5. air flows into the lungs down the pressure gradient

what are the stages during expiration

1. the external intercostal muscles relax, moving the ribcage down and in

2. the volume of the cavity decreases

3. the diaphragm relaxes and unflattens, further decreasing the volume of the cavity

4. the lung pressure increases above atmospheric pressure

5. air is forced out of the lungs down the pressure gradient

what does a spirometer do

is calculates different lung volumes using a chamber containing a known volume of gas connected to a mouthpiece and recorder.

define breathing rate

the number of breaths taken per minute, measured by counting the number of peaks in a graph in a minute

define tidal volume

the volume of air breathed in or out in an average breath during rest, measured from the height of each peak at rest.

define vital capacity

the maximum volume of air that can be inhlaed or exhaled in one deep breath, measured from the maximum peak height

define oxygen consumption

the volume of oxygen used per minute

how could oygen consumption be measured

by measuring the slope of a spirometer trace

define ventilation rate

the volume of oxygen inhaled per minute

what prevents direct gas exchange in insects

their tough chitinous exoskeleton prevent direct gas exchange

what are adaptations of an insects trachea

reinforced with spirals of chitin- this prevents collapsing

multiple tachaea- increases surface area

what are the adaptations of the tracheoles in insects

• penetrate directly into tissues- reduces gas diffusion distance

• thin walls- reduces gas diffusion distance

• highly branched- maximises surface area

• not reinforced with chitin- allows gas exchange to occur

• tracheal fluid- allows oxygen to dissolve to aid diffusion and reduce water loss

what are adaptarions of spiracles within insects

they open and close, allowing them to control gas exchange with the atmosphere and minimise water loss

what are the stages of gas exchange in insects

1. air enters the tracheal system through open spiracles

2. air moves into larger tracheae and diffuses into smaller tracheoles

3. tracheoles brach throughout the body, transporting air directly to cells

4. oxygen dissolves in water in tracheal fluid and diffuses down its concentration gradient from tracheoles into body cells

5. carbon dioxide diffuses down its concentration gradient out of body cells into the tracheoles

6. air is then carried back to the spiracles via the tracheae and released from the body

why may some insects need additional ventillation systems

because they are particularly active

list some potential extra ventillation systems in insects

• more spiracles open

• movement of tracheal fluid out into tissues- this increases the diffusion rate and surface area for gas exchange

• movement of wing muscles connected to sacs- these pump air to ventilate the tracheal system

• vibration of thoracic muscles- this pumps air to ventilate the tracheal system

how does lactic acid accumulation affect the rate of gas exchange

1. it reduces the water potential in tracheal fluid at the end of tracheoles

2. water leaves the tracheoles via osmosis

3. a higher surface area is exposed for gas exchange

briefly describe the structure of the gills

• gills are covered by an operculum flap

• gills consist of stacked filaments containing gill lamellae

• gill lamellae are surrounded by extensive blood vessels

list the adaptations of the gills for efficient gas exchange

1. the llamellae provide a large surface area

2. the llamelae membranes are thin to minimise diffusion distance

3. the gills have a rich blood supply to maintain steep diffusion gradient

4. the countercurrent flow of blood and water creates even steeper concentration gradients

5. overlapping filament tips increase resistance, slowing water flow over gills and allowing more time for gas exchange

during the countercurrent flow system, does oxygen-rich blood meet water that is at its most oxygen rich or that is as its least oxygen rich

most oxygen rich, so that oxygen diffuses from the water into the blood

what are the steps in ventilation via the buccal cavity

1. when a fish opens its mouth, the volume of the buccal cavity increases

2. this decreases pressure, pulling water into the buccal cavity

3. water flows over the gills

4. water flows out through the operculum