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
Size of bronchioles
Bronchioles vary in size and structure, getting smaller as they get closer to the alveoli
The larger bronchioles possess elastic fibres and smooth muscle that adjust the size of the airway to increase or decrease airflow
The smallest bronchioles do not have any smooth muscle but they do have elastic fibres
What do bronchioles have and but not contain
Bronchioles are lined with ciliated epithelium in the same way as the trachea and bronchi, though the usually do not contain any goblet cells
Alveoli structure
Bronchioles are lined with ciliated epithelium in the same way as the trachea and bronchi, though the usually do not contain any goblet cells
Passage of air
- Nose/mouth
- Trachea
- Bronchi
- Bronchioles
- Alveoli
What happens when you breathe in
the volume in the chest to increase and the air pressure in the lungs to decrease until it is slightly lower than the atmospheric pressure
As a result, air moves down the pressure gradient and rushes into the lungs
Mechanism of breathing in at rest
The diaphragm contracts and flattens, increasing chest volume
Mechanism of breathing in when exercising
In addition to the flattening of the diaphragm the external intercostal muscles contract, causing the ribcage to move upwards and outwards
Intercostal muscles
Muscles that lie between the ribs
Two sets:
Internal- contraction leads to expiration, making rib cage smaller
External- contraction leads to inspiration, making rib cage bigger
Diaphragm
A sheet of muscle that separates the thorax from the abdomen
It contracts and flattens and the chest cavity enlarges. This contraction creates a vacuum, which pulls air into the lungs
Breathing out
When at rest breathing out occurs mostly due to the recoil of the lungs after they have been stretched
Volume in the chest decreases and pressure increases, causing air to be forced out
Mechanism of breathing out when at rest
External intercostal muscles relax
The recoil of elastic fibres surrounding alveoli causes the air to be forced out
Diaphragm becomes dome-shaped
Mechanism of breathing out when exercising
Internal intercostal muscles contract to pull the ribs down and back
Abdominal muscles contract to push organs upwards against the diaphragm, increasing the internal pressure
This causes forced exhalation
Vital capacity
this is the maximum volume of air that can be breathed in or out in one breath
Tidal volume
this is the volume of air that is breathed in or out during normal breathing (at rest)
Breathing rate
this is the number of breaths taken in one minute (one breath = taking air in and breathing it back out again)
Oxygen uptake
this is the volume of oxygen used up by someone in a given time
How do spirometers prevent respiratory distress
Carbon dioxide is absorbed from the exhaled air by soda lime in order to stop the concentration of carbon dioxide in the re-breathed air from getting too high, as this can cause respiratory distress
How to find out vital capacity, tidal volume, and breathing rate from spirometer
As the subject breathes through the spirometer, a trace is drawn on a rotating drum of paper or a graph is formed digitally, which can be viewed on a computer
How can oxygen uptake be calculated from spirometer
Carbon dioxide is removed from the exhaled air, meaning that the total volume of air available in the spirometer gradually decreases, as oxygen is extracted from it by the subject’s breathing
This change in volume is used as a measure of oxygen uptake
Tracheal system of an insect
All insects posses a rigid exoskeleton with a waxy coating that is impermeable to gases
What have insects evolved to do
Evolved a breathing system that delivers oxygen directly to all the organs and tissues of their bodies
Spiracle
An opening in the exoskeleton of an insect which has valves
Allows air to enter and leave the insect and flow into system of tracheae
Tracheae
Are tubes within the insect respiratory system which lead to tracheoles
What keeps the tracheae open
Rigid rings of chitin
The site of insect gas exchange
A large number of tracheoles run between cells and into the muscle fibres
What does the gas exchange system of insects allow
For smaller insects, this system provides sufficient oxygen via diffusion
How is tracheal fluid withdrawn during periods of high oxygen demand
High metabolic demand which leads to high oxygen demand
If oxygen demand not met respiration becomes anaerobic leading to building up of lactic acid
Water moves out of tracheoles by osmosis
What happens to spiracle when oxygen demands are low
Will be closed
What happens to spiracles when oxygen demands are raised or c02 levels build up
More of the spiracles open
Tough exoskeleton
Little or no gaseous exchange takes place
Tracheal fluid
Carry’s oxygen
Where fluid and gas interact
Found towards end of tracheoles
Limits the surface area for diffusion but can be withdrawn to increase surface area at times of high 02 demand
Tracheoles
Each tracheae is a single, greatly elongated cell with no Caitlin lining so they are freely permeable to gases
Deliver oxygen to the cells and tissues of the insect
Mechanical ventilation
Volume of thorax increases/decreases
Pressure increases/decreases above/ below atmospheric pressure
Air moves in/out through spiracles
Pathway of oxygen in tracheal system
- Air enters into the body of insects through spiracles
- Spiracles transfer air to thin tubes called the tracheae
- the tracheal system contains a special fluid for carrying oxygen
What happens when water builds up at the bottom of tracheoles
Causing slower diffusion, to remove this lactic acid begins to build up in the cells, decreasing their water potential, where water can move back into the cells
Structure of fish gills in bony fish
Series of gills on each side of the head
Each gill arch is attached to two stacks of filaments
On the surface of each filament, there are rows of lamellae
What does the lamellae surface consists of
a single layer of flattened cells that cover a vast network of capillaries (main site of gaseous exchange)
Counter-current system
Blood flow is in the opposite direction to the flow of water
What does counter-current system ensure
the concentration gradient is maintained along the whole length of the gill
The water with the lowest oxygen concentration is found adjacent to the most deoxygenated blood
Ventilation mechanism in a fish 1
The ventilation mechanism in fish constantly pushes water over the surface of the gills and ensures they are constantly supplied with water rich in oxygen (maintaining the concentration gradient)
Ventilation of a fish 2
What happens when fish open their mouth
When the fish open their mouth they lower the floor of the buccal cavity. This causes the volume inside the buccal cavity to increase, which causes a decrease in pressure within the cavity
Ventilation mechanism of a fish 3
The pressure is higher outside the mouth of the fish and so water flows into the buccal cavity
Ventilation mechanism of a fish 4
The fish then raises the floor of the buccal cavity to close its mouth, increasing the pressure within the buccal cavity
Ventilation mechanism of a fish 5
Water flows from the buccal cavity (high pressure) into the gill cavity (low pressure)
Ventilation mechanism of a fish 6
As water enters pressure begins to build up in the gill cavity and causes the operculum (a flap of tissue covering the gills) to be forced open and water to exit the fish
Ventilation mechanism of a fish 7
The operculum is pulled shut when the floor of the buccal cavity is lowered at the start of the next cycle
Ethical concerns surrounding dissections
People worry about how the animals for dissections are raised and killed
It goes against the religious beliefs of some individuals
Dissecting method
Place the specimen on the dissecting board
Use the tools to access the desired structure
When using the scalpel cut away from your body and keep your fingers far from the blade to reduce the chance of cutting yourself
Scissors can be used for cutting large sections of tissue (cuts do not need to be precise)
A scalpel enable finer, more precise cutting and needs to be sharp to ensure this
Use pins to move the other sections of the specimen aside to leave the desired structure exposed
What should be worn when dissection
A lab coat, gloves and eye protection should be worn
To avoid contamination with biological material (which could cause an allergic reaction)
