3.1.1 Exchange Surfaces

Question 1

Why do organisms require exchange surfaces?

Answer 1

all organisms require:
-oxygen and glucose(as as source of energy) in aerobic respiration and other metabolic reactions
-need to excrete CO2 and urea
-proteins for growth and repair
-fats to make membranes and energy stores
-minerals to maintain water potential and enzyme action

Question 2

Why is diffusion alone enough to supply needs of a single-celled organism?

Answer 2

-lower metabolic activity so less oxygen demand/co2 production
-the SA:vol ratio is large
-quick diffusion rate because of the short distances the substances have to travel

Question 3

Why is diffusion across the cell membrane too slow in multicellular organisms?

Answer 3

-higher metabolic activity/levels of activity, so use up oxygen and glucose faster
-larger animals have lower SA:vol ratio so its difficult to exchange enough substances to supply a large vol to a small outer surface.
-amount of energy used up means they have higher oxygen demands in muscle cells and produce more CO2
-distance between cells and exchange substance is too far for diffusion to take place because some cells are deep within the body

Question 4

Volume and SA formulas

Answer 4

SA of cube: (6 x L^2)
Vol of cube:(L^3)
SA of cuboid: 2(bh + bl +hl)
vol of cuboid= hbl
circumference= 2pi r
area of circle= pi r^2

Question 5

Specialised exchange surfaces

Question 6

Increased SA

Answer 6

-provides space for molecules to pass through
i.e root hair cells which help increase rate of absorption of water + mineral ions from the soil, or villi in the small intestine

Question 7

Thin layers

Answer 7

-usually one cell thick
-reduces the diffusion distance and improves efficiency
i.e each alveolus are made up of thin, flat cells called the alveolar epithelium. helps decrease diffusion distance of O2 and CO2 and increases RoR

Question 8

Good blood supply and ventilation

Answer 8

the steeper the conc gradient, the faster the diffusion
-ensures substances are constantly delivered to and removed from the exchange surface which maintains conc gradient
i.e alveoli is surrounded by a large capillary network, so the blood can take O2 and brings more CO2. lungs are also ventilated so air in alveolus is being replaced.
Gills are the gas exchange surface in fish where O2 and CO2 are exchanged between the fish’s blood + surrounding water. -large network of capillaries and well ventilated with fresh water

Question 9

The mammalian gas exchange system

Question 10

Structure of the gas exchange system

Answer 10

-air enters the trachea
-splits into bronchi, one in each lung
-splits into smaller tubes called bronchioles
-have alveoli at their ends(small air sacs) = provide large SA for diffusion
-ribcage, intercostal muscles and diaphragm work together to move air in and out

Question 11

What is the gas exchange organs in mammals?

Answer 11

the lungs
-help get oxygen into the blood(for respiration) and to get rid of carbon dioxide(made by respiring cells) from the body

Question 12

features of mammals

Answer 12

-small SA:vol ratio and a very large volume of cells
-high metabolic rate because they are active and maintain their body temp independent of the environment

Question 13

Goblet cells

Answer 13

-line the airways + secrete mucus
-the mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli

Question 14

Cilia

Answer 14

-hair like structures on the surface of epithelial cells lining the airways
-beat the mucus secreted by goblet cells upward away from the alveoli towards the throat where it is swallowed(prevents lung infections)

Question 15

Elastic fibres

Answer 15

-in the walls of the structures of the gas exchange system to help the process of breathing out
-when inhaling, lungs inflate and fibres stretch
-when exhaling, the fibres recoil to help push the air out

Question 16

Smooth muscle

Answer 16

-in the walls of the structures of the gas exchange system and allows the diameter of the lumen in bronchi/bronchioles to be controlled
-relaxes to make tubes wider during exercise(less resistance to ventilation and air can be exhaled and inhaled easier)
-less air remains in the lungs

Question 17

Cartilage

Answer 17

• c shaped(tracheal) rings in the walls of the trachea and bronchi(complete) to provide support
  -strong but flexible(stops trachea and bronchi collapsing and ensure it stays open when you inhale and pressure drops)

Question 18

KEY STRUCTURES

Question 19

nasal cavity

Answer 19

-large SA with good blood supply, which warms air to body temp
-hairy lining which secretes mucus to trap pathogens and protect lung tissue from infection
-moist surfaces which increase the humidity of the upcoming air to reduce evaporation from exchange surfaces

Question 20

Trachea

Answer 20

-main airway carrying clean, warm, moist air through c-shaped cartilage rings(for flexibility to not constrict oesophagus behind it)
-also has smooth muscle, elastin fibres, goblet cells and ciliated epithelium

Question 21

Bronchi

Answer 21

-trachea divides in the chest cavity to form the left+right bronchi, similar structure as trachea i.e same cartilage rings but fully ringed + smaller pieces
-more structural support and keeps airways open for efficient airflow
(rest of specification features are same)

Question 22

bronchioles(larger,smaller,smallest)

Answer 22

-bronchi divide
-no cartilage rings
-has smooth muscles(walls of bronchioles constrict and dilate to change amount of air reaching the lungs)
-has elastic fibres
-only bigger bronchioles have goblet cells + ciliated epithelia

Question 23

alveoli

Answer 23

-tiny air sacs which are the main gas exchange surfaces of the body
-unique to mammalian lungs
-no cartilage, smooth muscle, goblet cells or cilia
-consist of a layer of flattened, thin epithelial cells along with some collagen+elastin fibres
-elastic tissue to stretch when air is drawn in and return to normal shape to help squeeze air out(elastic recoil of lungs)

Question 24

adaptations of alveoli

Answer 24

AREA:
-Large SA= large numbers of alveoli
-elastic fibres= stretch to increase SA and recoil to help force out air
-surfactant reduces cohesive action between water molecules + prevents alveoli collapsing
- more space for molecules to pass
DISTANCE:
-thin walls= both the alveoli and the capillaries have walls that are one cell thick
- short diffusion distances
GRADIENT:
-good blood supply= capillaries close to alveolar wall so blood supply constantly replenished
-good ventilation= oxygen constantly replenished and CO2 constantly removed
- maintaining a steep conc gradient

Question 25

What is on the inner surface of alveoli?

Answer 25

thin layer of water, salts and lung surfactant(makes it possible for the alveoli to remain deflated because it reduces surface tension)
-oxygen dissolves in the water before diffusing into the blood
-water can evaporate into the air in the alveoli(adaptations help reduce water loss)

Question 26

What is ventilation?

Answer 26

inspiration and expiration controlled by the movements of the diaphragm, intercostal muscles and ribcage

Question 27

Structures involved in ventilation

Answer 27

-ribcage= semi rigid case in which pressure can be lowered in respect to the air outside it
-diaphragm= broad, domed sheet of muscle forming the floor of the thorax
-external/internal intercostal muscles= found between the ribs
-thorax= lined by pleural membrane which surrounds lung
(space between them is called pleural cavity and is usually filled with thin layer of lubricating fluid so the membranes can slide over each other and you can breathe).

Question 28

Inspiration

Answer 28

-energy using, active process
-the external intercostal and diaphragm contract, causing ribcage to move up and outwards and the diaphragm to flatten and lower, increasing vol of thorax
-as vol increases, the lung pressure decreases to below atmospheric pressure
-causes air to flow in through the lungs(through nasal passages, trachea, bronchi, and bronchioles into the lungs) to equalise pressure

Question 29

Expiration

Answer 29

-passive process(doesn’t use muscle contraction, rinçage falls due to gravity and lungs are elastic so will recoil)
-external intercostal and diaphragm relax
-ribcage moves downwards and inwards and the diaphragm moves up to it resting domed shape
-elastic fibres in the alveoli return to normal length
-thorax volume decreases, causing the air pressure to increase above atmospheric pressure
-air is forced out the lungs
-can exhale forcibly using energy, internal intercostal muscles contract to pull the ribcage down and in and the abdominal muscles contract to force the diaphragm up.

Question 30

What is a spirometer?

Answer 30

machine that can be used to investigate breathing patterns or different aspects of lung volume

Question 31

What readings can a spirometer give?

Answer 31

-Tidal volume= volume of air in each breath(usually about 0.4dm cubed which uses about 15% of the vital capacity of the lungs)
-Vital capacity= max volume of air that can be breathed in/out
-Breathing rate= how many breaths are taken per unit time(usually per minute)
-Oxygen uptake= the rate at which a person uses up oxygen(the number of dm cubed per minute)

Question 32

Extra components of the lung volume

Answer 32

-Inspiratory reserve volume= max volume of air you can breathe in over and above a normal inhalation
-Expiratory reserve volume= extra volume of air you can force out of your lungs above tidal volume
-residual volume= volume of air that is left in your lungs when you have exhaled as hard as possible(cannot be measured directly)
-total lung capacity= sum of the vital capacity and the residual volume

Question 33

How to use a spirometer

Answer 33

-a spirometer has an oxygen-filled chamber with a movable lid
-the person using the spirometer breathes through a tube connected to the oxygen chamber
-as the person breathes the lid moves up and down

Question 34

How are the movements on a spirometer recorded?

Answer 34

-recorded by a pen attached to the lid of a chamber which writes on a rotating drum, creating a spirometer trace
OR
-spirometer can be hooked up to a motion sensor which uses the movements to produce electronic signals which are picked up by a data logger
-soda lime in the tube that the person breathes into absorbs CO2.

Question 35

Why does the total volume of gas in the chamber decrease over time?

Answer 35

air that is breathed out is a mixture of O2 and CO2 BUT
C02 is absorbed by the soda lime and the oxygen in the chamber is used in respiration when the person inhales

Question 36

How to get a valid spirometry reading

Answer 36

-The person using it must wear a nose clip to ensure that they can only breathe in and out through the mouth, so all the air they breathe goes through spirometer
-machine must also be airtight

Question 37

Analysing data from spirometers
Breathing rate

Answer 37

the amount of peaks in a set time represent 10 breaths per minute(min -1)

Question 38

Analysing data from spirometers
tidal volume

Answer 38

change from time to time, depending on ‘at rest’ phase or ‘peak’ phase etc
-measure the difference between the top and bottom of the trace in terms of the volume of air in the lungs(in dm cubed)

Question 39

Analysing data from spirometers
vital capacity

Answer 39

measure highest peak from the lowest point to highest point (in dm cubed)

Question 40

What problems do fish have with gas exchange?

Answer 40

-water is more viscous + dense than air and has a lower O2 conc
-have a high oxygen demand but a small SA:V ratio means diffusion would not be enough to supply oxygen
-skin is an impermeable membrane so gases cannot diffuse through

Question 41

How do fish overcome exchange problems?

Answer 41

they have gills so they do not have to use up much energy moving dense water in and out of lung-like systems

Question 42

Structure of gills

Answer 42

-each gill is made up of gill filaments/primary lamellae which provide a big SA for gas exchange and increase rate of diffusion
-gill filaments covered by gill plates/secondary lamellae which further increase SA
-each gill supported by gill arch with lots of capillaries(good blood supply) and thin surface layer of cells to shorten diffusion distance
-gill rakers, in most bony fish, on inner side of arch that strain water flowing past

Question 43

Challenges with gills

Answer 43

-for efficient gas exchange, fish needs to maintain a constant flow of water over gills
-diffusion is slower in water than air

Question 44

Steps of gill irrigation

Answer 44

-the mouth opens(operculum is shut)and the buccal cavity floor is lowered, increases volume and decreases pressure compared to outside of the fish, so water is sucked into the cavity down a pressure gradient
-opercula cavity expands and raises the floor of the buccal cavity, decreases the volume and increases the pressure higher than the opercula cavity, which forces water out of the buccal cavity and across gill filaments down pressure gradient
-mouth closes(buccal and opercular cavity constrict) operculum flaps open and opercular cavity moves inwards, which increases pressure and decreases volume,
forces the water over the gills and out of operculum, flaps close again
-opens its mouth and cycle restarts

Question 45

The counter-current system

Answer 45

-blood flows through the gill plates in one direction and water flows over in the opposite direction
-ensures that water with a relatively higher oxygen concentration always flows next to blood with a lower concentration oxygen
-maintains a steep concentration gradient(prevents equilibrium) so as much oxygen as possible diffuses into the blood

Question 46

How is gas exchange in fish effective?

Answer 46

-tips of adjacent gill filaments overlap to increase resistance to the flow of water over the gill surfaces and slow movement of water for more time
-counter-current system

Question 47

Why is it hard for insects to have a gas exchange system?

Answer 47

-tough exoskeleton
-do not usually have blood pigments that can carry oxygen

Question 48

How does ventilation take place in insects?

Answer 48

-have an air filled tracheal system which supplies air directly to the respiring tissues
-air enters via a pore called the spiracle in abdomen
-carried up the body by trachea(lined with chitin) + smaller tracheoles(open at the end and lined with water so gas exchange can occur, no chitin)
-when at rest, tracheoles are lined with tracheal fluid which limits air penetration, so no gas exchange is taking place
-tracheal fluid increases water potential higher than in the body cells(do anaerobic respiration which produce lactic acid and reduces water potential) so fluid moves out of tracheoles via osmosis
-oxygen dissolves into the tracheal fluid and diffuses into cells
-C02 diffuses out of cells into tracheoles/trachea and out of spiracles, which increases SA of diffusion of gases
-exchange can also occur across the thin tracheole walls

Question 49

Spiracles

Answer 49

-small pores on the sides of the insect’s abdomen where gases and water vapour enters and leaves
-can open/close(controlled by sphincter) to prevent water loss
-normally closed when insect is inactive and oxygen demands are low

Question 50

How do spiracles help provide oxygen more rapidly?

Answer 50

-the spiracle closes and air is pumped into the system by muscular movements of the abdomen/thorax
-this changes the pressure in the trachea + tracheoles so air is drawn in/forced out

Question 51

Trachea

Answer 51

-largest tubes in insect respiratory system and they carry air into the body
-tubes are lined by spirals of chitin, which keep them open if bent or pressed
-chitin makes up the cuticle and is relatively impermeable so little gas exchange happens in trachea
-supported by strengthened rings to prevent collapsing

Question 52

Tracheoles

Answer 52

-smaller, narrower branches of trachea
-single, elongated with no chitin so they are freely permeable to gases
-can run through tissues + in between cells, so is where most gas exchange takes place
-give a large SA for gas exchange

Question 53

Tracheal fluid

Answer 53

-limits the penetration of air for diffusion
-when oxygen demands build up, a lactic acid build up in the tissues results in tracheal fluid moving into cells by osmosis, lactic acid decreases water potential of cells = exposes more SA for gas exchange

Question 54

Alternative methods for increasing level of gas exchange

Answer 54

-rhythmic abdominal movements to change the volume of their bodies to move air in and out of spiracles
-in flying insects, wing movement pumps thorax
-in larger insects, there are air sacs that help mechanically pump air through the system(usually have higher energy demand)

Question 55

Dissecting tool and their properties

Answer 55

Scalpels-have sharp detachable blade + used for making fine cuts
Dissecting scissors- used for precise cutting, safer than scalpels because blades are less likely to snap under pressure, and can be easier to avoid damaging tissue underneath
Dissecting pins -used with a wax filled dissecting tray to pin specimen in place
Tweezers -useful for holding and manipulating smaller parts of specimen

Question 56

How should dissecting tools be kept?

Answer 56

-clean, sharp and free from rust(blunt tools don’t cut well and are more dangerous)

Question 57

Dissecting fish gills

Answer 57

1) place fish on cutting board/dissecting tray
2) push back the operculum and use scissors to remove gills
3) cut each gill arch through the bone at the top + bottom
4) gill filaments should become visible
5) Scientific drawing of gills, must be labelled

Question 58

Dissecting insects

Answer 58

(must be humanely killed and better if it is a bigger insect i.e cockroach)
1) fix insect onto dissecting board, can use pins in legs to keep it in place
2) carefully cut + remove a piece of the exoskeleton along the length of its abdomen to examine tracheae
3) use syringe to fill abdomen with saline solution –} should be able to see network of thin, silver-grey tubes(tracheae)
4) can mount trachea on a wet mount microscope slide and examine them under a light microscope –} should see rings of chitin in tracheal walls(for support)

Question 59

Breathing instructions to person using a spirometer

Answer 59

breathe in as much as you can and then force out as much air as possible

Question 60

Chitin

Answer 60

-lines trachea in insects
-impermeable in gases, so they cannot diffuse in and out
-tough so it supports trachea and stops it from collapsing