3.1 Exchange Surfaces Flashcards
single-celled organisms SA:V ratio
High SA:V ratio
The large surface area allows for maximum absorption of nutrients and gases and secretion of waste products
The small volume means the diffusion distance to all organelles is short
What happens as organism increase in size
their SA:V ratio decreases
There is less surface area for the absorption of nutrients and gases and secretion of waste products
The greater volume results in a longer diffusion distance to the cells and tissues of the organism
The need for specialised system of gas exchange
Supply of oxygen
Removal of carbon dioxide
Why do we need a supply of oxygen
Organisms require ATP in order to carry out the biochemical processes required for survival. The majority of ATP is produced through aerobic respiration which requires oxygen
Removal of carbon dioxide
Carbon dioxide is a toxic waste product of aerobic respiration
If it accumulates in cells/tissues it alters the pH
Why is diffusion not a viable transport mechanism for multicellular organisms
The time taken for oxygen to diffuse from the cell-surface membrane to the tissues would be too long
Metabolic rate of an organism
the amount of energy expended by that organism within a given period of time
Basal metabolic rate
the metabolic rate of an organism when at rest. The BMR is significantly lower than when an organism is actively moving
Different ways of measuring metabolic rate of oxygen
Oxygen consumption (respirometers)
Carbon dioxide production (carbon dioxide probe)
Heat production (calorimeter)
How does mass affect metabolic rate
the greater the mass of an organism, the higher the metabolic rate
What do effective exchange surfaces in organisms have
Large surface area
Short diffusion distance (thin)
Good blood supply
Ventilation mechanism
What does a larger surface area provide
A larger surface area provides more space over which the exchange of substances with the environment can occur
Root hair cells
Root hair cells have a root hair that increases the surface area (SA) so the rate of water uptake by osmosis is greater (can absorb more water and ions than if SA were lower)
Alveoli
The exchange of oxygen and carbon dioxide occurs between the alveoli and the capillaries in the lungs
How dos alveoli do gas exchange
The air in the alveoli contains a high concentration of oxygen. The oxygen diffuses from the alveoli and into the blood capillaries, before being carried away to the rest of the body for aerobic respiration
The blood in the capillaries has a relatively low concentration of oxygen and a high concentration of carbon dioxide. The carbon dioxide diffuses from the blood and into the alveoli and is then exhaled
Why do alveoli lead to a more efficient exchange surface
The walls of the alveoli are only one cell thick and these cells are flattened
This means that gases have a very short diffusion distance so gas exchange is quick and efficient
The large number of alveoli increases the surface area available for oxygen and carbon dioxide to diffuse across
Good blood supply in fish gills features
The extensive capillary system that covers the gills ensures that the blood flow is in the opposite direction to the flow of water - it is a counter-current system
The counter-current system ensures the concentration gradient is maintained along the whole length of the capillary
Water with the highest oxygen content is found next to blood that is oxygenated
There is still a difference in concentration so diffusion of oxygen into the blood still occurs
Ventilation mechanism in mammalian lungs
A ventilation mechanism also helps to maintain a concentration gradient across an exchange surface
Ventilation (mass flow of gases) in the lungs helps to ensure that there is always a higher concentration of oxygen in the alveoli than in the blood
What play vital roles in maintaining the health of the gas exchange system
Ciliated epithelial cells, goblet cells and mucous glands
What plays important structural roles in maintaining the gas exchange system
Cartilage, smooth muscle, elastic fibres and squamous epithelial tissue
Cartilage
strong and flexible tissue found in various places around the body
One place is in rings along the trachea, called Tracheal rings
These rings help to support the trachea and ensure it stays open while allowing it to move and flex while we breathe
Ciliated epithelium
a specialised tissue found along the trachea down to the bronchi
Each cell has small projections of cilia which sweep mucus, dust and bacteria upwards and away from the lungs and the epithelium itself
Goblet cells
They are mucus-producing cells that secrete viscous mucus which traps dust, bacteria and other microorganisms and prevents them from reaching the lungs
The mucus is then swept along by the cilia of the ciliated epithelium upwards and is swallowed
The mucus and any microorganisms will then be destroyed by the acid in the stomach
Squamous epithelium
The alveoli have a lining of thin and squamous epithelium, that allows for gas exchange
The squamous epithelium forms the structure of the alveolar wall and so is very thin and permeable for the easy diffusion of gases
Smooth muscle
can be found throughout the walls of the bronchi and bronchioles
It helps to regulate the flow of air into the lungs by dilating when more air is needed and constricting when less air is needed
Elastic fibres
They are very important as they enable the lung to stretch and recoil. This ability to recoil is what makes expiration a passive process
Capillaries
Each alveolus is surrounded by an extensive network of capillaries
Carbon dioxide diffuses out of the capillaries and into the alveoli to be exhaled, while oxygen diffuses the other way from alveoli and into the capillaries to be carried around the body
Trachea
The trachea is the channel that allows air to travel to the lungs
How do rings of cartilage affect trachea
C-shaped rings of cartilage ensure that this air channel remains open at all times
They are C-shaped to prevent any friction from rubbing with the oesophagus located close behind
Why does mucus cover the trachea
The trachea is lined with ciliated epithelium
There is a substantial covering of mucus inside the trachea (produced by goblet cells and mucous glands) that helps to trap dust and bacteria to prevent them from entering the lungs
The wall of the trachea contains smooth muscle and elastic fibres
Bronchi
similar structure to the trachea but they have thinner walls and a smaller diameter
The cartilage in the bronchi does not form a c-shape, but can form full rings, and can also form irregular blocks
Bronchioles
Bronchioles are narrow self-supporting tubes with thin walls
They are not usually supported by cartilage