3.1.1: exchange surfaces and breathing Flashcards
why is diffusion alone enough to supply the needs of single-celled organisms but not for multi-cellular organisms?
their metabolic activity is usually low and they have a large surface area to volume ratio. larger organisms have a smaller surface area to volume ratio
how does the surface area to volume ratio work?
as the size of an organisms increases, its surface area to volume ratio decreases
what features do effective exchange systems have?
- increased surface area: overcomes the limitations of the sa:v and gives a larger areas to exchange
- thin layers: decreases diffusion distance
- good blood supply: ensures a steep concentration gradient
- ventilation (for gases): maintains concentration gradient
what is the journey of air though the lungs?
nasal cavity > trachea > bronchus > bronchiole > alveoli
what controls the action of the intercostal muscles?
the diaphragm (a layer of muscle tissue beneath the lungs)
what protects the lungs and how are they held together?
the ribs held together by the intercostal muscles
what are the important features of the nasal cavity?
- large surface area with good blood supply
- a hairy lining which secretes mucus
- moist surfaces to increase the humidity of the incoming air
what is the role of cartilage in the trachea and why is it in incomplete rings?
- provides strength and support to keep the trachea open and prevent it from collapsing
- allows space for food to to move down the oesophagus
what is the trachea and its branches lined with?
- ciliated epithelium (cilia) that wafts the mucus upward to the back of the throat to be swallowed
- goblet cells which secretes mucus which traps microorganisms and dust from reaching the lungs
what does the smooth muscle in the walls of the trachea, bronchi and bronchioles do?
allows their diameter to be controlled. during exercise the smooth muscle relaxes, making the tube wider meaning their is less resistance to airflow
what do the elastic tissues in the alveoli do?
allow the alveoli to stretch as air is drawn in and when they return to their resting size, they help squeeze the air out, known as the elastic recoil of the lungs
how has the alveoli adapted for effective gas exchange?
- large surface area as there are many alveoli in the lungs
- thin layers as their cell walls are only on epithelial cell thick
- good blood supply as they are surrounded by a network of millions of capillaries
- good ventilation as breathing moves air in and out
what is the inner surface of the alveoli covered in and what is its role?
a solution of water, salt and lung surfactant, which makes it possible for the alveoli to remain inflated
what is inspiration/inhalation?
- external intercostal muscles and diaphragm contract
- ribcage moves upwards and outwards
- diaphragm flattens
= increasing the volume of the thorax
= decreasing the pressure to below the atmospheric pressure
= air is forced in
what is expiration/exhalation?
- external intercostal muscles and diaphragm relax
- ribcage moves downwards and inwards
- diaphragm becomes curved
= decreasing the volume of the thorax - increasing the pressure to above the atmospheric pressure
= air is forced out
how do you calculate the ventilation rate (volume of air someone takes in per minute)?
breathing rate (the amount of breaths per minute) x tidal volume (volume of air exchanged per minute)
what is a spirometer and how does it work?
a piece of equipment that can be used to investigate breathing
- a person breaths in and out through their mouth (holding their nose) via the mouthpiece
- air is trapped between the enclosed chamber between the float and water
- when breathing in, the volume in the air chamber decreases and the float drops
- when breathing out, the volume in the air chamber increases and the float rises
- the float is attached to a pen which writes on the paper, recording the breathing movements
safety precautions:
- make sure the soda-lime is being used so the person isn’t breathing in exhaled carbon dioxide
- that the person is healthy
- sterilise the mouthpiece between different users
how can the bell jar model demonstrate how the lung and diaphragm
1) as the rubber sheet is pulled down, the volume of the bell jar will increase
2) pressure will decrease to be less than the atmospheric pressure
3) air will be forced in through the glass tube and will fill the balloons
4) equilibrium pressure is reached
- glass tube = trachea and bronchi
- glass bell jar = ribcage
- balloons = lungs
- flexible, rubber sheet = diaphragm
why do fish need a specialised gas exchange system?
- 1000x denser than air
- 100x more viscous
- has a much lower oxygen content
how does the structure of the gills make them more efficient for gas exchange?
- water containing oxygen enters the fish through the mouth and passes through gills
- each gill is made from lots of tiny branches (gill filaments/primary lamellae) = large surface area
- gill filaments are covered in gill plates/secondary lamellae = increasing surface area
- each gill is supported by a gill arch
- gill plates have a lot of capillaries and a thin surface layer = efficient diffusion
- overlapping of gill filaments increases resistance to water flow and slows it down = more time for exchange to take place
what do some more primitive forms of fish use to ventilate their gills?
ram ventilation - continually move in water to pass it over the gills
how does counter-current flow helps with the fish exchange system?
- blood flows through gill plates in one direction, with water moving in the opposite direction
- maintains a large concentration gradient between the water and blood
- concentration of oxygen in water is higher than in blood = as much oxygen as possible diffuses from water into the blood
- across the whole length of the gill
how do the gills in bony fish stay ventilated?
1) fish opens mouth which lowers the floor of the buccal cavity
2) volume of buccal cavity increases = decreasing the pressure inside the cavity
3) water sucked into cavity
4) fish closes its mouth and the floor of the buccal cavity is raised
5) volume inside decreases = pressure increases and water us forced out of cavity and across the gill filaments
6) each gill is covered by a bony called the operculum (protects gill)
7) increase pressure causes the operculum on each side to open. allowing water to leave the gills
(some fish have an operculum that bulges out = increasing the volume of the cavity behind the operculum just after the buccal cavity lowers = contributes to the decrease in pressure that causes water to increase in the fish’s mouth)
how do you dissect a fish?
1) wear apron/lab coat and gloves as it can be messy
2) place the fish on a dissection tray of cutting board
3) push back the operculum and use scissors to carefully remove the gills
4) cut each gill arch through the bone at the top and bottom
5) if looked closely, should be able to see gill filaments (can be put in water for a better view)
6) draw and label what you see
