Exchange and Transport Systems

Question 1

What is needed when organisms exchange substances with the environment?

Answer 1

• Cells need to take in oxygen for aerobic respiration and nutrients
• Need to excrete waste products like carbon dioxide and urea
• Most organisms need to stay at roughly the same temperature, so heat needs to be exchanged too

Question 2

Great surface area:volume ratio

Answer 2

This is the case for smaller organisms and it affects how quickly substances are exchanged

Question 3

Volume of a cylinder

Answer 3

Pi r2

Question 4

Volume of a sphere

Answer 4

4/3 Pi r3

Question 5

Diffusion equation

Answer 5

S.A x difference in concentration

Length of diffusion path

Question 6

Surface area of a sphere

Answer 6

4 Pi r2

Question 7

Features of specialised exchange surfaces

Answer 7

• Large surface area relative to volume of the organism which increases the rate of exchange
• Very thin so that the diffusion distance is short and therefore materials cross the exchange surface rapidly
• Selectively permeable to allow selected materials to cross
• Movement of environmental medium e.g. air to maintain diffusion gradient
• Movement of internal medium (transport system) e.g. blood in order to maintain diffusion gradient
• Being thin specialised exchange surface are easily damaged and dehydrated so located inside organism

Question 8

Single-celled organisms

Answer 8

• Substances can diffuse directly into or out of the cell across the cell-surface membrane
• Diffusion rate is quick beacuse of the small distances the substances have to travel
• Relatively large surface area, thin surface and short diffusion pathway so no need for specialised gas exchange system

Question 9

Multicellular Organisms

Answer 9

• Diffusion across membrane is too slow because…
• Some cells are deep within the body- big distance between them and outside environment
• Larger animals have a low surface area to volume ratio so it’s difficult to exchange enough substances to supply a large volume through a small outer surface
• So multicellular organisms need specialised exchange organs for transport

Question 10

Mass Transport

Answer 10

Efficient system to carry substances to and from their individual cells

Question 11

What does metabolic activity do?

Answer 11

Creates waste products to be transported away and metabolic activity inside cells creates heat

Question 12

How does body size affect heat exchange?

Answer 12

• Easy to lose heat if large surface area:volume
• Hard to lose heat if small surface area:volume
• Smaller organisms need a relatively high metabolic rate, in order to generate enough heat to stay warm

Question 13

How does body shape affect heat exchange?

Answer 13

• Compact shape means a small surface area: volume, minimising heat loss
• Less compact shape (bits sticking out) have a larger surface area:volume so increased heat loss from surface

Question 14

Adaptations for heat exchange

Answer 14

Whether an animal is compact or not depends on the temperature of its environment- animal’s body shape is adapted to suit its environment

Question 15

Behavioural and Physiological adaptations to aid exchange

Answer 15

• Animals with a high surface area:volume ratio tend to lose more water as it evaporates from their surface. This is a problem for animals living in hot regions where water evaporates quickly. Some small desert animals have kidney structure adaptations so they produce less urine to compensate.
• To support their high metabolic rates, small mammals living in cold regions need to eat large amounts of high energy foods such as seeds and nuts.
• Smaller mammals may have thick layers of fur or hibernate when weather gets cold.
• Larger organisms living in hot regions find it hard to keep cool as heat loss is slow. Elephants have large flat ears which increase surface area, allowing more heat loss. Hippos spend much of the day in the water (behavioural adaptation to help lose heat)

Question 16

Gas Exchange Surfaces

Answer 16

• Boundary between outside and internal environment of an organism
• Need oxygen and carbon dioxide to diffuse across exchange surfaces as quickly as possible
• Most gas exchange surfaces…
• Have a large surface area
• Thin (often one layer of epithelial cells) so short diffusion pathway
• Organism also maintains steep concentration gradient of gases across exchange surface, which increases rate of diffusion

Question 17

Gas exchange in fish

Answer 17

• Lower concentration of oxygen in water than in air
• So fish use the gas exchange surface (gills) to get enough of it

Question 18

Structure of Gills

Answer 18

• Water, containing oxygen, enters the fish through its mouth and passes out through the gills
• Each gill is made of lots of thin plates called gill filaments which give a large surface area for exchange of gases
• Gill filaments are covered in lots of tiny structures called lamellae, which increases surface area even more
• Lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion, between water and blood

Question 19

Counter-current system

Answer 19

• In the gills of a fish, blood flows through the lamellae in one direction and water flows over them in the opposite direction
• Counter-current system means that the water with a relatively high oxygen concentration always flows next to blood with a lower concentration of oxygen
• Means that a steep concentration gradient is maintained over the whole length of the gill between the water and blood (as much oxygen diffuses from water into blood)
• If flow was parallel, concentration of oxygen would be 50/50

Question 20

Gas exchange in dicotyledonous plants

Answer 20

• Plants need CO2 for photosynthesis, which produces O2 as a waste gas
• Need O2 for respiration, which produces CO2 as a waste gas
• Main gas exchange surface is surface of mesophyll cells in the leaf (well adapted, large surface area)
• Gases move in and out through special pores in the epidermis (mainly lower epidermis) called stomata
• Stomata open to allow exchange of gases and close if plant is losing too much water
• Guard cells control opening and closing of stomata

Question 21

Gas exchange in insects

Answer 21

• Terrestrial insects have microscopic air-filled pipes called tracheae which they use for gas exchange
• Air moves into the tracheae through pores on the surface called spiracles
• Oxygen travels down the concentration gradient towards the cells
• Tracheae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells
• Means that oxygen diffuses directly into respiring cells- insect’s circulatory system doesn’t transport O2
• Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere
• Insects use rhythmic abdominal movements to move air in and out of the spiracles

Question 22

Limiting water loss in Insects

Answer 22

• Close spiracles using muscles if losing too much water
• Waterproof, waxy cuticle all over body and tiny hairs around spiracles, both of which reduce evaporation
• Small surface area:volume ratio

Question 23

Limiting water loss in plants (Stomata)

Answer 23

• Stomata are usually kept open during day to allow gaseous exchange
• Water enters the guard cells, making them turgid, which opens stomatal pore
• If plant starts to get dehydrated, guard cells lose water and become flaccid, which closes the pore
• Waterproof covering

Question 24

Limitng water loss in Xerophytes

Answer 24

• Plants adapted for life in warm, dry or windy habitats where water loss is a problem
• Stomata sunk in pits to trap water vapour, reducing concentration gradient of water between leaf and air (this reduces evaporation of water from leaf)
• Layer of hairs on the epidermis to trap water vapour round the stomata
• Curled leaves with the stomata inside, protecting them from wind (windy conditions increase rate of diffusion and evaporation)
• Reduced number of stomata, so there are fewer places for water to escape
• Thicker waxy, waterproof cuticles on leaves and stems to reduce evaporation

Question 25

Plants adaptations for rapid diffusion

Answer 25

• Many small pores called stomata, and so no cell is far from stoma so diffusion pathway is short
• Numerous interconnecting air-spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells
• Large surface area of mesophyll cells for rapid diffusion

Question 26

Structure of gas exchange system

Answer 26

• As you breathe in, air enters the trachea
• Trachea splits into 2 bronchi- one bronchus leading to each lung
• Each bronchus then branches off into smaller tubes called bronchioles
• Bronchioles end in small air sacs called alveoli (this is where gases are exchanged)
• Ribcage, intercostal muscles and diaphragm all work together to move air in and out

Question 27

Intercostal muscles

Answer 27

• Found between ribs
• Internal intercostal muscles are on inside of extrenal intercostal muscles

Question 28

Ventilation

Answer 28

• Consists of inspiration and expiration
• Controlled by movements of diaphragm, internal and external intercostal muscles and ribcage

Question 29

Inspiration

Answer 29

• External intercostal and diaphragm muscles contract
• Causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic cavity (space where lungs are)
• As volume of thoracic cavity increases, lung pressure decreases to below atmospheric pressure
• Air will always flow from an area of higher pressure to an area of lower pressure (down a pressure gradient) so air flows down trachea and into lungs
• Inspiration is an active process- requires energy

Question 30

Expiration

Answer 30

• External intercostal and diaphragm muscles relax
• Ribcage moves downwards and inwards, and the diaphragm curves again
• Volume of thoracic cavity decreases, causing air pressure to increase to above atmospheric pressure
• Air is forced down the pressure gradient and out of the lungs
• Passive process-no energy required

Question 31

Forced Expiration

Answer 31

• External intercostal muscles relax and internal intercostal muscles contract, pulling the ribcage further down and in
• Movement of 2 sets of intercostal muscles is said to be antagonistic (opposing)
• Requires energy

Question 32

Alveoli

Answer 32

• Microscopic air sacs where gas exchange occurs (millions found in the lungs)
• Alveoli surrounded by a network of capillaries

Question 33

Respiratory gases in tracheal system

Answer 33

• Along a diffusion gradient- cells respire, oxygen is used up so concentraion towards ends of tracheoles falls
• This creates a diffusion gradient that causes gaseous oxygen to diffuse from the atmosphere along the trachea and tracheoles to the cells
• CO2 is produced during respiration which creates diffusion gradient in opposite direction
• Causes gaseous CO2 to diffuse along the tracheoles and trachea from cells to atmosphere (diffusion more rapid in air than in water)
• Mass transport= contaction of muscles in insects can squeeze the trachea enabling mass movements in and out
• This further speeds up exchange of respiratory gases
• During major activity, muscle cells around tracheoles respire (carry out some anaerobic respiration)
• This produces lactate which is soluble and lowers water potential of muscle cells
• Water therefore moves into cells from tracheoles by osmosis
• Water in ends of tracheoles decreases in volume and in doing so draws air further into them
• Means final diffusion pathway is in a gas rather than a liquid , so diffusion is more rapid
• Increases rate at which air moves and evaporation

Question 34

Alveoli Structure

Answer 34

• Wall of each alveolus is made from a single layer of thin, flat cells called alveolar epithelium
• Walls of capillaries are made from capillary endothelium
• Walls of alveoli contain a protein called elastin
• Elastin is elastic- helps alveoli to return (recoil) to their normal shape after inhaling and exhaling air
• Reduced distance, thin walls, steep concentration gradient, large surface area

Question 35

Movement of oxygen and carbon dioxide through the gas exchange system

Answer 35

• Air (containing oxygen) moves down the trachea, bronchi and bronchioles into the alveoli
• This movement happens down a pressure gradient
• Oxygen then moves into the blood where it can be transported round the body (happens down a diffusion gradient)
• Carbon dioxide moves down its own diffusion and pressure gradients, but in the opposite direction to oxygen so that it can be breathed out

Question 36

Gas exchange in the Alveoli

Answer 36

• Oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium, and into a compound called haemoglobin in the blood
• Carbon dioxide diffuses into the alveoli from the blood

Question 37

Factors affecting the rate of diffusion

Answer 37

• Thin exchange surface- alveolar epithelium is only one cell thick so short diffusion pathway (speeds up diffusion)
• Large surface area- there a millions of alveoli which speeds up rate of gas exchange
• Steep concentration gradient of oxygen and carbon dioxide between the alveoli and the capillaries, which increases the rate of diffusion
• Constantly maintained by flow of blood and ventilation

Question 38

Tidal Volume

Answer 38

Volume of air in each breath

Question 39

Ventilation Rate

Answer 39

Number of breaths per minute

Question 40

Forced Expiratory Volume (FEV1)

Answer 40

Maximum volume of air that can be breathed out in one second

Question 41

Forced Vital Capacity (FVC)

Answer 41

Maximum volume of air it is possible to breathe forcefully out of the lungs after a really deep breath in

Question 42

Effect of lung diseases on gas exchange

Answer 42

• TB, fibrosis, asthma and emphysema all reduce the rate of gas exchange in the alveoli
• Less oxygen is able to diffuse into the bloodstream, the body cells recieve less oxygen and the rate of aerobic respiration is reduced
• Means less energy is released and sufferers often feel tired and weak

Question 43

What are restrictive diseases and how to interpret on graph?

Answer 43

• Diseases which make it difficult to fully breathe in (fibrosis)
• On graph, FVC would be severely reduced because it’s hard to get air into lungs
• FEV1 is likely to high compared to FVC beacuse someone with a restrictive disease is able to breathe out fairly normally

Question 44

Risk factors

Answer 44

• Something that increases chance of getting a disease, doesn’t mean you will definitely get it though
• Also other factors need to be taken into consideration when drawing conclusions

Question 45

Correlations of Lung Diseases

Answer 45

Question 46

Risk Factors of Lung Disease

Answer 46