3.1.1: exchange surfaces and breathing

Question 1

why is diffusion alone enough to supply the needs of single-celled organisms but not for multi-cellular organisms?

Answer 1

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

Question 2

how does the surface area to volume ratio work?

Answer 2

as the size of an organisms increases, its surface area to volume ratio decreases

Question 3

what features do effective exchange systems have?

Answer 3

• 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

Question 4

what is the journey of air though the lungs?

Answer 4

nasal cavity > trachea > bronchus > bronchiole > alveoli

Question 5

what controls the action of the intercostal muscles?

Answer 5

the diaphragm (a layer of muscle tissue beneath the lungs)

Question 6

what protects the lungs and how are they held together?

Answer 6

the ribs held together by the intercostal muscles

Question 7

what are the important features of the nasal cavity?

Answer 7

• large surface area with good blood supply
• a hairy lining which secretes mucus
• moist surfaces to increase the humidity of the incoming air

Question 8

what is the role of cartilage in the trachea and why is it in incomplete rings?

Answer 8

• provides strength and support to keep the trachea open and prevent it from collapsing
• allows space for food to to move down the oesophagus

Question 9

what is the trachea and its branches lined with?

Answer 9

• 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

Question 10

what does the smooth muscle in the walls of the trachea, bronchi and bronchioles do?

Answer 10

allows their diameter to be controlled. during exercise the smooth muscle relaxes, making the tube wider meaning their is less resistance to airflow

Question 11

what do the elastic tissues in the alveoli do?

Answer 11

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

Question 12

how has the alveoli adapted for effective gas exchange?

Answer 12

• 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

Question 13

what is the inner surface of the alveoli covered in and what is its role?

Answer 13

a solution of water, salt and lung surfactant, which makes it possible for the alveoli to remain inflated

Question 14

what is inspiration/inhalation?

Answer 14

• 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

Question 15

what is expiration/exhalation?

Answer 15

• 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

Question 16

how do you calculate the ventilation rate (volume of air someone takes in per minute)?

Answer 16

breathing rate (the amount of breaths per minute) x tidal volume (volume of air exchanged per minute)

Question 17

what is a spirometer and how does it work?

Answer 17

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

Question 18

how can the bell jar model demonstrate how the lung and diaphragm

Answer 18

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

Question 19

why do fish need a specialised gas exchange system?

Answer 19

• 1000x denser than air
• 100x more viscous
• has a much lower oxygen content

Question 20

how does the structure of the gills make them more efficient for gas exchange?

Answer 20

• 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

Question 21

what do some more primitive forms of fish use to ventilate their gills?

Answer 21

ram ventilation - continually move in water to pass it over the gills

Question 22

how does counter-current flow helps with the fish exchange system?

Answer 22

• 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

Question 23

how do the gills in bony fish stay ventilated?

Answer 23

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)

Question 24

how do you dissect a fish?

Answer 24

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

Question 25

what is the insect gas exchange surface?

Answer 25

microscopic air-filled pipes called tracheae

Question 26

what is the insect gas exchange system?

Answer 26

• air moves into the tracheae though pores on the insects surface called spiracles
• oxygen travels down the concentration gradient towards the cells
• carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere

Question 27

what do the tracheae branch off into and what are they filled with?

Answer 27

• smaller tracheoles, which have thin permeable walls and go to individual cells
• contain fluid, which oxygen can dissolve into
• oxygen then dissolves from this fluid into body cells (carbon dioxide is opposite)

Question 28

what is the process of rhythmic abdominal movements in insects?

Answer 28

• used to change volume of their bodies
• move air in and out of the spiracles due to changing pressures
• when insects are flying, thy use their wing movements to pump their thoraxes too
• increases the amount of oxygen entering

Question 29

how can you dissect an insect?

Answer 29

1) fix the insect to dissecting board, putting dissecting pins
2) to examine trachea, carefully cut and remove a piece of exoskeleton (insects hard outer shell) from along the length of its abdomen
3) use a syringe to fill the abdomen with saline solution
4) should be able to see a network of very thin. silvery tubes = tracheae
5) can examine under light microscope using wet mount
6) should be able to see rings of chitin in the walls of the trachea (there for support)