Exchange

Question 1

What is the relationship between size of an organism and it’s sa:v ratio

Answer 1

As an organism increases in size, the sa:v ratio decreases as volume increases at a faster rate than surface area

Question 2

What are some adaptations that facilitate exchange as the ratio reduces

Answer 2

A flattened shape, so no cell is ever far from surface (flatworm, leaf) specialised exchange surface with large area to increase sa:v ratio (lungs, gills)

Question 3

What are some features of specialised exchange surfaces

Answer 3

Large surface area/ large sa:v , to increase rate of exchange, very thin, to shorten diffusion distance, selectively permeable

Question 4

What’s the relationship between sa:v ratio and metabolic rate

Answer 4

Organisms with high metabolic rate exchange more materials so need a larger sa:v ratio

Question 5

How to calculate the sa:v ratio

Answer 5

1. Work out SA 2. Work out volume 3. Divide sa by volume and put answer in the form x: 1

Question 6

Gas exchange in single celled organisms

Answer 6

They are small so have large sa:v ratio, oxygen is absorbed by diffusion across cell membrane and co2 from respiration diffuses out

Question 7

Describe the structure of the tracheal system of an insect

Answer 7

Insects have a network of tubes called tracheae which divide into smaller tubes called tracheoles which extend through the body tissue of an insect so 02 is brought directly to respiring tissues so there’s a shorter diffusion pathway

Question 8

What are the three ways respiratory gases move in and out of the tracheal system

Answer 8

Along a diffusion gradient, by mass transport and the ends of the tracheoles are filled with water

Question 9

Describe how gases move along a diffusion gradient in the tracheal system

Answer 9

When cells respire, 02 is used up so it’s conc falls at the ends of the tracheoles. This creates a diffusion gradient that causes 02 to diffuse from atmosphere into cells along tracheae/tracheoles. Co2 is produced during respiration which creates diffusion gradient and causes c02 to diffuse along trachea from cells to atmosphere

Question 10

What is the benefit of a diffusion gradient in the tracheal system

Answer 10

As diffusion in air is more rapid than in water, respiratory gases are exchanged quicker

Question 11

Describe mass transport in insects and why it’s useful

Answer 11

The contraction of the muscles in insects can squeeze the trachea, enabling mass movements of air in an out, this speeds up the exchange of respiratory gases

Question 12

Describe how the ends of the tracheoles being filled with water is significant

Answer 12

During periods of major activity, muscle cells around tracheoles carry out anaerobic respiration which produces lactate, which is soluble and lowers the water potential of muscle cells. Water therefore moves into muscle cells from tracheoles via osmosis. Means water in tracheoles decreases in volume which draws air into them. Means final diffusion is in air so is more rapid

Question 13

What does gas enter and leave trachea through in an insect

Answer 13

Tiny pores called spiracles on the body surface which may be opened and closed by a valve

Question 14

What is a limitation of the tracheal system

Answer 14

Relies on diffusion to exchange gases between environment and cells so to be effective the diffusion pathway must be short so this limits the size insects can attain

Question 15

Describe the structure of gills and pathway of water

Answer 15

The are made up of gill filaments, stacked in a pile with Gill lamellae at right angles to the filaments (increases SA) water is taken in through the mouth and forced over the gills and out through an opening on each side of the body

Question 16

What is countercurrent flow in fish gills

Answer 16

When the flow of water over Gill lamellae is in an opposite direction to the flow of blood within the capillaries of lamellae

Question 17

Describe countercurrent exchange and how it differs from parallel flow

Answer 17

Means a diffusion gradient for 02 uptake in maintained across the entire width of lamellae so around 80% of 02 in available water is absorbed into blood. If flow of water and blood was in same direction (parallel flow) diffusion gradient would only be maintained across part of lamellae sp 50% of 02 would be absorbed

Question 18

Adaptations of leaves for exchange

Answer 18

1. Many stomata so no cell is ever far to make for short diffusion pathway 2. Numerous interconnecting air spaces in mesophyll so gases readily come in contact with mesophyll cells 3. Large SA of mesophyll cells means rapid diffusion

Question 19

Explain how stomata have a role in water loss

Answer 19

Stomata are surrounded by guard cells which open and close pore/control gas exchange. Water is lost through evaporation so they guard cells close stomata to prevent water loss

Question 20

Why is there a conflict in exchange in insects

Answer 20

Water evaporates easily from the surface of their bodies and they become dehydrated but for efficient gas exchange, they need a thin, permeable surface with large area (conflict with need to conserve water)

Question 21

What are adaptations of insects for efficient gas exchange and to limit water loss

Answer 21

There’s a small sa:v to minimise area from where water could be lost, waterproof coverings (chitin with waterproof cuticle) and spiracles which can be closed at rest to reduce water lost

Question 22

What are xerophytes

Answer 22

Plants adapted to living in areas where water is in short supply

Question 23

List the adaptations of xerophytes to limit water loss

Answer 23

1. Thick cuticle (creates waterproof barrier) 2. Rolling up of leaves 3. Hairy leaves 4. Sunken stomata 5. Reduced sa:v of leaves

Question 24

Describe how rolling of leaves prevents water loss

Answer 24

It protects the stomata on the lower epidermis and a region of air is trapped. This become saturated with water vapour which increases its water potential. This means there is no water potential gradient between inside and outside of the leaf so no water is lost

Question 25

How does hairy leaves and having stomata in pits/grooves prevent water loss

Answer 25

Traps moist air next to leaf surface so water potential gradient between inside and outside leaf is reduced so less water is lost via evaporation

Question 26

How does a lower sa:v reduce water loss in leaves

Answer 26

Means slower rate of diffusion so less water is diffused out

Question 27

Structure of the human gas exchange system (pathway of oxygen)

Answer 27

Trachea (airway supported by rings of cartilage. Walls made of muscle lined with ciliates epithelium), lungs, bronchi (divisions of trachea, produce mucus to trap dirt, have cilia), bronchioles( muscle lined with epithelial cells which allows them to constrict) alveoli

Question 28

What is the surface over which gas exchange takes place in the lungs

Answer 28

The alveolar epithelium/ alveolar membrane

Question 29

Describe features of the alveolar epithelium

Answer 29

Between the alveoli are collagen and elastic fibres, elastic fibres allow alveoli to stretch as they fill with air and spring back when breathing out

Question 30

Describe the process of inspiration

Answer 30

1. External intercostal muscles contract, internal relax 2. Ribs are pulled upwards and outwards, increasing vol of thorax 3. Diaphragm muscles contract, causing it to flatten (also increasing vol of thorax) 4. Increased vol of thorax leads to decreased pressure in lungs 5. Atmospheric pressure now greater than pulmonary so air is forced into the lungs from higher to lower pressure/down a pressure gradient

Question 31

Describe the process of expiration

Answer 31

1. Internal intercostal muscles contract, external relax 2. Ribs move downwards and inwards, decreasing volume in the thorax 3. Diaphragm muscles relax and vol of thorax further decreases 4. Decreased vol of thorax increases pressure in the lungs 5.
   Pulmonary pressure now greater than atmosphere and so air is forced out of the lungs

Question 32

Why is diffusion of gases in the alveoli rapid

Answer 32

Red blood cells are slowed as they pass through pulmonary capillaries (more time for diffusion) large sa, steep concentration gradient, walls of alveoli and capillaries are v thin so diffusion distance short, red blood cells flattened against capillary walls so short diffusion distance

Question 33

What are some risk factors of lung disease

Answer 33

Smoking, air pollution, genetic makeup, frequent infection, occupation

Question 34

What are some restrictions on cigarettes to reduce lung disease

Answer 34

Age restrictions, increased tax, no advertising, plain packaging (no brands), images of sick people

Question 35

Describe how co2 in the air outside a leaf reaches mesophyll cells inside the leaf

Answer 35

Carbon dioxide enters via stomata, which are opened by guard cells. Co2 diffuses through air spaces, down a diffusion gradient

Question 36

Describe how 02 in the air reaches capillaries around the alveoli

Answer 36

Air passes through trachea, bronchi and bronchioles down a pressure gradient. Air crosses the alveolar epithelium down a diffusion gradient

Question 37

Describe the pathway by which 02 goes from an alveolus to the blood

Answer 37

Diffuses across the alveolar epithelium and capillary epithelium/endothelium

Question 38

Why is having more 02 useful for fish

Answer 38

Can be used in respiration