Chapter 6: Exchange

Question 1

Features of specialised exchange surfaces

Answer 1

• Very thin (short diffusion distance).
• Selectively permeable
• Large surface area to volume ratio
• Movement if the environmental medium (to maintain diffusion gradient)
• Transport system to ensure the movement of the internal medium (to maintain diffusion gradient)

Question 2

Equation for diffusion

Answer 2

SA X Difference in conc.
/
Length of diffusion path.

Question 3

Gas exchange in single called organisms

Answer 3

They have a large SA to V ratio.

Oxygen is absorbed by diffusion across their body surface and carbon dioxide diffuses out across their body surface.

Question 4

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

Answer 4

• Along diffusion gradient.
• Mass transport.
• Ends of tracheoles are filled with water.

Question 5

How does water enter and leave the tracheae?

Answer 5

Through tiny spores called spiracles.

Question 6

How do spiracles work?

Answer 6

Opened and closed by a valve.

Question 7

What are the limitations of the tracheal system?

Answer 7

-Relies mostly on diffusion.
So short diffusion path needed. Therefore, insects are small. The diffusion pathway limits the size that insects can attain.

Question 8

What is the gas exchange in insects?

Answer 8

They have evolved tracheae.

Question 9

What are the tracheae supported by?

Answer 9

Strengthened rings.

Question 10

What do tracheae divide into?

Answer 10

Dead end tubules called tracheoles.

Question 11

How do respiratory gases move in and out of the tracheal system along a diffusion gradient?

Answer 11

(1) When cells respire, and so oxygen is used up. It’s concentration towards the ends of the tracheoles falls.
(2) This creates a diffusion gradient. This causes oxygen to diffuse from the atmosphere, along the tracheae and tracheoles to cells.
(3) Carbon dioxide is produced by cells during respiration.
(4) This creates a diffusion gradient in the opposite direction.
(5) This causes carbon dioxide to diffuse along the tracheoles, and trachea to the atmosphere.

Question 12

Is diffusion quicker in gas or liquid?

Answer 12

Gas.

Question 13

How do respiratory gases move in and out of the tracheal system by mass transport?

Answer 13

(1) Contraction of muscles in insects squeeze the trachea enabling mass movements of air in and out.

Question 14

How do respiratory gases move in and out of the tracheal system when the ends of the tracheoles are filed with water?

Answer 14

(1) During major activity the muscle cells around tracheoles carry out anaerobic respiration.
(2) This produces lactate. This is soluble and lowers the water potential.
(3) So water moves into cells from the tracheoles by osmosis.
(4) The water in the ends of the tracheoles decreases in volume and in doing so draws air further into them.
(5) This means final diffusion pathway is in gas phase, not liquid and so more quicker. This increases rate at which air moves into tracheoles.

BUT LEADS TO GREATER WATER EVAPORATION.

Question 15

What is the structure of the gills?

Answer 15

Gills are made up of gill filaments, at right angles to them are gill lamellae. This increases surface area of the gills.

Question 16

What is countercurrent flow?

Answer 16

The flow of water and blood is in opposite directions.

Question 17

What does the countercurrent exchange principle ensure that?

Answer 17

• Blood that is well loaded with oxygen meets water, which has its maximum concentration of oxygen. So oxygen diffuses from the water to the blood.
• Blood with little oxygen meets water which has most oxygen removed. Diffusion occurs from the water to blood.

Question 18

What would occur with parallel flow?

Answer 18

Diffusion gradient is only maintained for half the distance across the gill lamellae. So only half of the oxygen diffuses from the water into the blood.

Question 19

What adaptions do leaves have for rapid diffusion?

Answer 19

• Large surface area of mesophyll cells for rapid diffusion.
• Many stomata.
• Numerous interconnecting air spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells.

Question 20

How is the gas exchange in plants similar to that of insects?

Answer 20

• Diffusion occurs in gas phase.

- No living cell is far from external air.

Question 21

Where is the majority of stomata located?

Answer 21

Underside of leaf.

Question 22

What happens when water loss would be excessive?

Answer 22

The stomata close.

Question 23

What is each stroma surrounded by?

Answer 23

Pair of guard cells.

Question 24

How do terrestrial organisms lose water?

Answer 24

By evaporation.

Question 25

Which features of an efficient gas exchange conflict with the need to conserve water?

Answer 25

Thin, permeable and large area.

Question 26

What adaptation shave insects evolved to reduce water loss?

Answer 26

Small surface area to volume ratio. Waterproof coverings. Spiracles. THIS MEANS AN INSECT HAS A INTERNAL NETWORK OF TUBES INSTEAD OF USING BODY SURFACE TO DIFFUSE GASES.

Question 27

What are xerophytes?

Answer 27

Plants which are adapted to living in areas where water is in short supply.

Question 28

Modifications of leaves where rate of water loss is high.

Answer 28

- Thick cuticle. E.g. Holly - Rolling up of leaves= Protects lower epidermis and so traps region of still air. This area has high water potential so there is no gradient. E.g. Marram grass - Hairy leaves= Traps still, moist air next to leaf surface so reduced gradient. E.g. Type of heather plant. - Stomata in pits or grooves= Trap still, moist air next to leaf surface and reduce gradient. E.g. Pine trees. - Reduced surface area to volume ratio of leaves.

Question 29

Why are lungs located on the inside of the body?

Answer 29

Air is not dense enough to support and protect the delicate structures. Body would lose a lot of water.

Question 30

Describe the process of inspiration.

Answer 30

(1) External intercostal muscles contract, internal intercostal muscles relax. (2) Ribs move upwards and outward, increasing the volume of the thorax. (3) The diaphragm contracts, causing it to flatten. This also increases the volume of the thorax. (4) An increase in volume means there is a decrease of pressure. (5) As a result, atmospheric pressure is now greater than pulmonary pressure and so air is forced into the lungs.

Question 31

Describe the process of expiration.

Answer 31

(1) Internal intercostal muscles contract, external intercostal muscles relax. (2) Ribs move downwards and inwards, decreasing the volume of the thorax. (3) Diaphragm relaxes and bulges upwards. This further decreases the volume of the thorax. (4) Decreased the volume of the thorax means the pressure increases. (5) Pulmonary pressure is greater than atmospheric pressure, so air forced out of lungs.

Question 32

Ventilation definition.

Answer 32

Movement of air in and out of the lungs.

Question 33

Pulmonary ventilation rate calculation (dm^3min^-1) =

Answer 33

Tidal volume (dm^3) X Breathing rate (min^-1)

Question 34

What are the main parts of the human gas exchange?

Answer 34

``` Lungs Trachea Bronchi Bronchioles Alveoli ```

Question 35

Why is diffusion between the alveoli and the blood very rapid?

Answer 35

- Red blood cells are slowed as they pass through pulmonary capillaries, allowing more time for diffusion. - Blood flow through pulmonary capillaries maintains a conc. gradient. - Alveoli and pulmonary capillaries have a large total SA. - Always a steep concentration gradient due to constant ventilation.

Question 36

What are the two stages of digestion?

Answer 36

Physical breakdown. | Chemical breakdown.

Question 37

What is physical breakdown?

Answer 37

Larger pieces breakdown into smaller pieces by teeth. This provides larger surface area for chemical digestion and makes it possible to ingest food. Food is churned in stomach and this physically breaks it up.

Question 38

Three types of digestive enzymes.

Answer 38

Carbohydrases: Hydrolyse carbohydrates to monosaccharides. Lipases: Hydrolyse lipids into glycerol and fatty acids. Proteases: Hydrolyse proteins to amino acids.