Gas exchange 6.1 -6.8

Question 1

How does a thick cuticle limit water loss?

Give an example of a plant that uses this method

Answer 1

Waxy cuticle = waterproof barrier
10% of water loss can occur through this route in regular plants

Thicker cuticle = less water loss

E.g holly

Question 2

How does rolling up of leaves prevent water loss?

Give an example of a plant that exhibits this

Answer 2

🔹stomata are located on lower epidermis
🔹rolling leaves so that lower epidermis faces in creates a region of trapped still air, this area becomes saturated with water vapour so has high water potential
🔹no water potential gradient between inside and outside of leaf

E.g Marram grass

Question 3

How do hairy leaves prevent water loss?

Give an example of a plant which uses this method

Answer 3

🔹On lower epidermis hairs trap still, moist air next to leaf surface

🔹Reduces water potential gradient

E.g one type of heather plant

Question 4

How does the location of stomata in pits and grooves help to limit water loss?

Give an example of a plant that uses this method

Answer 4

Trap still, moist air next to leaf which reduces water potential gradient

E.g pine trees

Question 5

How do insects limit water loss?

Answer 5

🔹Small SA:Vol
🔹Waterproof
🔹Spiracles

Question 6

What is tissue fluid?

Answer 6

The environment around the cells of multicellular organisms

Question 7

What is the relationship between metabolic rate, exchange of materials, and SA:vol

Answer 7

Higher metabolic rate = more exchange of materials = higher SA:vol required

Question 8

What is passive exchange?

Answer 8

No metabolic energy is required, e.g. osmosis and diffusion.

Question 9

What is active exchange?

Answer 9

Metabolic energy is required, e.g. by active transport

Question 10

Why can’t larger organisms rely on diffusion alone for the transport of materials?

Answer 10

Larger organism = smaller SA:vol

Question 11

What are the features of specialised exchange surfaces?

Answer 11

🔹Large SA:vol

🔹Very thin so that diffusion pathway is reduced

🔹Selectively permeable membrane to allow certain materials to cross

🔹A transport system to ensure the movement of the internal medium e.g. blood, to maintain a diffusion gradient

Question 12

What is Fick’s law?

Answer 12

SA x difference in concentration/

length of diffusion path

Question 13

What features of a plant limit water loss?

Answer 13

🔹Thick waxy cuticle 
🔹Rolling up of leaves
🔹Hairy leaves 
🔹Stomata in pits or grooves 
🔹Reduced SA:Vol of leaves

Question 14

Why do large mammals require the absorption of such a large volume of oxygen?

Answer 14

🔹Large volume of living cells means that a large volume of oxygen is required for respiration

🔹They maintain a high body temp. Which means they require high metabolic and respiratory rates

Question 15

Why are the lungs an internal structure

Answer 15

🔹They are delicate and require protection from the rib cage

🔹The body as a whole would lose a lot of water and dry out

Question 16

List the sequence of all the structures which air passes through

Answer 16

1) nose
2) trachea
3) bronchi
4) bronchioles
5) alveoli

Question 17

What supports the trachea and why?

Answer 17

Cartilage

To prevent the trachea collapsing as the air pressure inside falls when breathing

Question 18

What do the tracheal walls consist of?

Answer 18

Muscle, lined with ciliated epithelium and goblet cells

Question 19

What is the function of goblet cells?

Answer 19

Produce mucus to trap dirt particles

Question 20

What is the function of cilia?

Answer 20

Small hairs which move dirt laden mucus out of the airway so that they stay away from the lungs

Question 21

Why are there elastic fibres between the alveoli?

Answer 21

Allow the alveoli to stretch as they fill with air when breathing in.

They then spring back during exhalation I’m order to expel carbon dioxide.

Question 22

Why is diffusion of gases between alveoli and blood so fast?

Answer 22

🔹RBCs move slowly through capillaries
🔹RBCs are flattened against capillary walls reducing diffusion distance
🔹alveoli and capillaries are just 1 cell thick, reducing diffusion distance
🔹pulmonary capillaries and alveoli have a large SA
🔹concentration gradient is maintained by constant ventilation, heart pumping blood around body, and blood flow through pulmonary capillaries

Question 23

Describe how countercurrent flow maximises exchange (3)

Answer 23

🔹The flow of water is in the opposite direction to the flow of blood

🔹This maintains a concentration gradient across the entire length of the lamellae so diffusion can occur constantly

🔹which maximises exchange

🔹

Question 24

How do bony fish ventilate their lungs?

What happens to fish who cannot rely on this method of ventilation?

Answer 24

Using muscular contractions which cause water to move through the mouth over gills and out of the open opercula

Other fish ventilate gills by constant flow of water over them, meaning they must maintain a forward motion. If not they die.

Question 25

Why is water located at the ends of the tracheoles in insects?

Answer 25

Product of respiration from connecting cells

Question 26

What happens to gas levels when spiracles close?

Answer 26

CO2 increases
O2 decreases

As air cannot enter and CO2 produced in resp. cant leave

Question 27

How does the closing of spiracles lead to muscle fatigue?

Answer 27

Air can’t enter so respiration cannot occur to produce adequate energy/ATP

Question 28

How does the opening of spiracles benefit the insect (4)

Answer 28

🔹enable aerobic respiration
🔹repay oxygen debt
🔹break down lactate
🔹remove excess CO2

Question 29

How is the opening of spiracles disadvantageous to an insect?

Answer 29

It enables water loss through spiracles via evaporation

Question 30

Why does oxygen concentration in the trachea fall when spiracles are closed?

Answer 30

Oxygen used in respiration, so diffuses from trachea to tissues

No more oxygen able to enter organism

Question 31

How does anaerobic respiration affect water potential in the trachea?

Answer 31

Lactic acid is produced in cells so water potential decreases because lactate is soluble

Question 32

Define osmosis

Answer 32

The random net movement of water molecules from an area of high water potential to an area of low water potential

Question 33

Describe the tracheal system

Answer 33

Many trachea which branch into smaller tracheoles.

All trachea connect to exoskeleton.

At the ends are spiracles through which gases diffuse

Question 34

Define transpiration

Answer 34

Evaporation of water from leaves

Question 35

How is concurrent flow beneficial?

Answer 35

Less energy required

Question 36

How do cells lining the trachea protect alveoli?

Answer 36

Cells produce mucus that traps particles of dirt and bacteria

Cilia move these particles as they could cause infection if they entered alveoli

Question 37

List 2 reasons why plants growing on sand dunes need to have xerophytic features despite there being plenty of rainfall

Answer 37

The rain rapidly drains through the sand so roots cannot absorb the water

Sand dunes are usually windy, which reduces water potential, this increasing water potential gradient

Question 38

Why are high levels of CO2 bad?

Answer 38

1) CO2 asphyxiates/is toxic
2) lack of oxygen for aerobic respiration
3) lack of energy/ATP wich results in reduced muscle function as well as muscle fatigue