3.3.1 + 3.3.2 SA:V Ratio And Gas Exchange

Question 1

Examples of substances exchanged between organisms and the environment

Answer 1

Respiratory gases eg. Oxygen and carbon dioxide
Nutrients eg. Water, glucose, amino acids
Excretory products eg. Urea, excess amino acids
Heat

Question 2

What is passive exchange

Answer 2

Requires no energy from ATP eg. Simple and facilitated diffusion, osmosis

Question 3

What is active exchange?

Answer 3

Requires energy from ATP eg. Active transport

Question 4

Where does exchange take place?

Answer 4

Exchange surfaces, usually plasma membranes

Question 5

What is the surface area to volume ratio?

Answer 5

The relationship between the size of an organism and its surface area

Question 6

What happens to the SA:V ratio as the size of the organism increases?

Answer 6

It decreases (small surface area in comparison to volume), so larger organisms need to have adaptations to make exchange more efficient.

Question 7

How are large organisms adapted to increase SA:V ratio?

Answer 7

Villi and microvilli to absorb digested food
Alveoli/bronchioles for gas exchange in mammals
Spiracles and tracheoles for gas exchange in terrestrial insects
Gill filaments and lamellae for gas exchange in fish
Thin wide leaves for gas exchange in plants
Many capillaries in the capillary network

Question 8

Why do large animals especially need to have adaptations?

Answer 8

They have a small surface area to volume ratio and a fast metabolism.

Question 9

What are the structures in the human gas exchange system?

Answer 9

Trachea
Bronchus
Bronchioles
Alveoli
Diaphragm
Lungs

Question 10

What are antagonistic pairs of muscles?

Answer 10

One contracts as the other relaxes to enable movement.

Question 11

What are the muscles involved in ventilation?

Answer 11

Intercostal muscles
Diaphragm

Question 12

What happens during inspiration?

Answer 12

External intercostal muscles contract
Internal intercostal muscles relax
Rib cage moves up and out
Diaphragm contracts and flattens
Air pressure in lungs initially drops then increases above atmospheric pressure as air moves in
Lung volume increases
Air moves in

Question 13

What happens during expiration?

Answer 13

External intercostal muscles relax
Internal intercostal muscles contract
Rib cage moves down and in
Diaphragm relaxes and domes
Air pressure in lungs decreases as air moves out
Lung volume decreases
Air moves out

Question 14

What is pulmonary ventilation?

Answer 14

The total volume of air that is moved into the lungs in one minute.

Question 15

What is the tidal volume?

Answer 15

Volume of air normally taken in per breath at rest

Question 16

What is the ventilation rate?

Answer 16

Number of breaths taken in one minute

Question 17

What is the pulmonary ventilation equation?

Answer 17

Pulmonary ventilation = tidal volume x ventilation rate

Question 18

How is the alveolar epithelium adapted for efficient gas exchange?

Answer 18

Increase the surface area of the lungs
Walls are very thin/ only one cell thick so creates a short diffusion distance
Many capillaries provide good blood supply to maintain high concentration gradient

Question 19

How do terrestrial insects limit water loss whilst still maximising gas exchange?

Answer 19

They have a small surface area to volume ratio where water can evaporate from (spiracles)
Have a lipid layer on their exoskeleton, making them waterproof
Spiracles can open and close to reduce water loss and are very small

Question 20

What is the gas exchange system in insects?

Answer 20

Tracheal system

Question 21

What are the structures in the tracheal system?

Answer 21

Spiracles
Tracheal
Tracheoles

Question 22

What are spiracles

Answer 22

Round openings on the surface of the insects body that allow oxygen and carbon dioxide to enter and exit the trachea. They can open and close to reduce water loss.

Question 23

What are trachea in insects

Answer 23

A network of internal tubes within the insect. They have rings to keep them open and strengthen them.

Question 24

What are tracheoles

Answer 24

Branches of trachea to extend throughout insect to provide oxygen and remove carbon dioxide from all respiring cells

Question 25

How is gas exchanged along a diffusion gradient in insects?

Answer 25

When cells are respiring, oxygen is used up and carbon dioxide is produced, creating a concentration gradient from the tracheoles to the atmosphere. Oxygen diffuses into cells from the atmosphere, and carbon dioxide diffuses into the atmosphere from cells, by simple diffusion.

Question 26

How is gas exchanged by mass transport in insects?

Answer 26

Insects contract and relax abdominal muscles to squeeze trachea and increase mass movement of air.

Question 27

How is gas exchanged in insects using water-filled tracheoles?

Answer 27

When in flight, the muscle cells respire anaerobically to produce lactate. This lowers water potential of cells so water moves from tracheoles to cells by osmosis. This decreases volume of water in tracheoles, which is replaced by air which is drawn in due to low pressure.

Question 28

How is the tracheal system adapted for efficient gas exchange?

Answer 28

Large number of highly branched tracheoles provide a large surface area for efficient gas exchange. Short diffusion distance as walls of tracheoles are thin, and there is a short distance between spiracles and tracheoles. Oxygen used up in respiring cells sets up a concentration gradient to provide a large concentration gradient for diffusion.

Question 29

How are single celled organisms adapted for efficient gas exchange?

Answer 29

Have a flattened shape so no part of it is far from the edge of he cell, providing a short diffusion distance, and increases SA:V ratio. Food vacuole to maintain concentration gradient by lowering concentration of food in the cytoplasm.

Question 30

Structures in gas exchange system in fish

Answer 30

Gills Gill filaments Gill lamellae

Question 31

How are fish adapted for efficient gas exchange?

Answer 31

Many gill filaments stacked up in a pile that are covered in gill lamellae, all of which provide a large surface area The walls of the lamellae are one cell thick, which provides a short diffusion distance. Gills have a rich blood supply due to a capillary network in every lamellae to maintain high concentration gradient. The countercurrent flow mechanism maintains a high concentration gradient.

Question 32

Describe what the countercurrent flow mechanism is

Answer 32

Water flows over the gills in the opposite direction to the flow of blood in the capillaries This means blood is always passing water with a higher oxygen concentration so maintains concentration gradient Mains diffusion occurs throughout the entire length of the gill lamellae Ensures that equilibrium is not reached

Question 33

What are the structures in a leaf?

Answer 33

Upper epidermis Palisade mesophyll Spongy mesophyll Stomata Lower epidermis Guard cells

Question 34

What moves in and out of the stomata?

Answer 34

Oxygen diffuses out of the stomata from photosynthesis Carbon dioxide diffuses into the stomata for photosynthesis Water evaporates out of the stomata during transpiration

Question 35

Why do stomata need to open and close?

Answer 35

To minimise water loss by evaporation from leaves to the environment, so they close at night when photosynthesis is not taking place and gas is not needed.

Question 36

How are leaves adapted for efficient gas exchange?

Answer 36

Stomata open and close to allow gas to enter and exit the leaf, and no cell is far from stomata as there are a large number of them. This provides a short diffusion distance. Spongy mesophyll latter has air spaces to allow gas to move around easily to come into contact with photosynthesising mesophyll cells. Guard cells control opening and closing of stomata to maintain concentration gradient. Thin and flat leaves to increase surface area to volume ratio.

Question 37

What is a xerophytic plant?

Answer 37

Adapted to live in environments with limited water, so have structural features to enable efficient gas exchange to occur whilst limiting water loss.

Question 38

What are the adaptations of xerophytes to reduce water loss?

Answer 38

Curled leaves and hair-covered stomata to trap water to increase humidity and decrease water concentration gradient. Thicker cuticle to reduce rate of evaporation Longer root network so bale to reach water at further distance Less stomata so less water loss Thick stems so able to store more water Pointed spines minimise surface area for water loss

Question 39

Spirometer

Answer 39

Measures lung capacity by patients exhaling into it to produce a spirometer trace.

Question 40

FEV

Answer 40

Forced expiratory volume- maximum volume of air that can be breathed out in one second

Question 41

Tidal volume

Answer 41

Volume of air inhaled and exhaled at rest

Question 42

Forced vital capacity

Answer 42

Maximum volume of air that can be inhaled or exhaled

Question 43

Total lung capacity

Answer 43

Vital capacity + residual volume

Question 44

Residual volume

Answer 44

Volume of air left in lungs after expiration

Question 45

What are the effects of athsma/bronchitis on gas exchange?

Answer 45

Obstruction of the airways that disrupts breathing Muscle wall of bronchitis and bronchioles contract to secrete more mucus Diameter of airways reduced so flow of air reduces Decreased FEV Low energy as not enough oxygen delivered to alveoli, blood and respiring cells

Question 46

What are the effects of emphysema/pulmonary fibrosis on gas exchange?

Answer 46

Breakdown of alveoli walls Alveoli fuse together so reduced SA:V ratio Walls dilate and thicken which increases diffusion distance Less oxygen enters the blood Leads to an increased ventilation rate.