Gas Exchange

Question 1

What factors affect rate of diffusion?

Answer 1

Large Surface Area
Large Concentration Gradient
Short diffusion pathway

Question 2

State Fick’s Law

Answer 2

Rate of Diffusion is proportional to Surface Area x Difference in concentration divided by length of diffusion pathway

Question 3

Explain the adaptations of Gas exchange in a Single celled organism

Answer 3

The Exchange Surface is the whole body surface - cell surface membrane

Large Surface Area as the organism is small so it has a high SA:VOL ratio

Short diffusion pathway - gases only dissuade through membrane to enter cell

Conc gradient maintained - Oxygen used up in respiration which maintains low conc. Of Oxygen

Question 4

What is the role of Spiracles in Insects?

Answer 4

They are the openings on either side of the body through which gases can enter and leave by diffusion

Question 5

What are the function of the valves in Insects?

Answer 5

Used for opening and closing spiracles

Question 6

What are tracheae in Insects?

Answer 6

A series of long tubes held open by rings of chitin through which air passes

Question 7

What are tracheoles?

Answer 7

Smaller branched tubes with no chitin that air passes along ending in muscles of the insect

Question 8

What is the function of Air Sacs

Answer 8

Used for pumping air in/out of the tracheal system in very active insects

Question 9

Explain the adaptations of Gas exchange in insects

Answer 9

The exchange Surface is the tips of the tracheoles

Large Surface Area - Large No. Of highly branched Tracheoles

Short diffusion pathway - tracheoles have thin walls

Concentration Gradient - Oxygen used in aerobic respiration in body cells so lower conc. inside cell

Question 10

How does Gas Exchange work in an insect

Answer 10

Oxygen diffuses through spiracle, down tracheae and tracheoles into body cells. Carbon Dioxide goes in opposite direction. Tips of tracheoles have water in which oxygen dissolves in from tips of tracheoles to body cells. This is enough for small insects

Question 11

How does Gas exchange differ for large insects

Answer 11

VENTILATION MECHANISM

As oxygen needs to be supplied quicker, spiracles will close and air sacs are squeezed using muscles ina abdomen which pushes air further into tracheoles.

Question 12

What happens when wing muscles are working hard?

Answer 12

Respiration will become partly anaerobic and lactate builds up (lactate = solute so affects water potential), lowers water potential in muscle cells, so water in tracheoles goes into muscle cells by osmosis. This reduces diffusion distance as oxygen diffuses directly from air into muscle cell without dissolving

Question 13

Give 2 adaptations to reduce water loss in insects

Answer 13

Insects have an exoskeleton that is covered in a waxy waterproof cuticle

Spiracles can close using valves when insect is not active

Question 14

Explain the Counter Current Principle

Answer 14

Blood + Water flow in opposite directions

Water with a high oxygen concentration will always flow next to blood with a relatively low oxygen concentration which maintains a concentration gradient and allows diffusion to occur across the whole length of the gill lamellae.

Question 15

Explain the adaptations for gas exchange in Fish

Answer 15

The gas exchange Surface is the gill lamellae

Large Surface area due to large No. of highly branched gill filaments with many gill lamellae

Short diffusion pathway - very close at exchange surface. The lamella wall is a thin layer of squamous cells and the capillary wall is one cell thick

Concentration Gradient - Ventilation Mechanism continuously flowing oxygenated water over surface and remixing deoxygenated

Transport mechanism bringing deoxygenated blood and removing oxygenated blood.

Counter current maintain conc Gradient for diffusion to occur across whole gill lamellae

Question 16

Explain Ventilation in Fish during Inspiration

Answer 16

Mouth opens. Floor of pharynx is pulled down, increasing the volume inside and decreases pressure. Water flows in

Question 17

Explain Ventilation in Fish during Expiration

Answer 17

Mouth closed. Floor of pharynx pulled up. Decreases volume inside and increases pressure, squeezing water through the gills

Question 18

What is the function for Palisade mesophyll

Answer 18

Main region for photosynthesis in upper parts of the plant

Question 19

What is spongy mesophyll

Answer 19

They are many large spaces air spaces

Question 20

Explain the adaptations for gas exchange in a plant

Answer 20

Exchange surface - surface of mesophyll cell

Large Surface area - many mesophyll cells in contact with many air spaces

Diff in conc. gradient - Gases used up as soon as they enter the cell in respiration or photosynthesis

Short diffusion pathway - Gases only diffuse through cell wall + membrane to enter cell

Question 21

Explain the Structure of the Human Gas exchange System

Answer 21

Air enters the trachea which is supported by rings of cartilage. Stops the trachea collapsing during pressure changes. The trachea divides into a left + right bronchus which further divides into smaller tubes called bronchioles which at the end have alveoli (air sacs)

Question 22

Explain the adaptations for gas exchange in Humans

Answer 22

Exchange Surface - The Alveolar Epithelium

Large Surface - Many Alveoli

Diff in Conc. Gradient - ventilation brings fresh air with high O2 conc. into alveoli and removes stale air with low O2 conc.

The continuous blood flow means there is a low conc. of O2 in the capillaries at the alveoli maintain a concentration gradient.

Short Diffusion Pathway - Alveolus wall is a single layer of squamous cells called Alveolar Epithelium. Capillary is the same but called the capillary endothelium and both lead to short diffusion pathway

Question 23

What are the structures needed for ventilation in humans?

Answer 23

External + internal intercostal muscles between ribs and diaphragm. They work as an antagonistic pairs ( 1 contracts + other relaxes)

Question 24

Explain the mechanism of breathing of Inspiration

Answer 24

• Muscles of diaphragm contract, diaphragm flattens
• External Intercostal Muscles (between ribs) contract, rib cage moves up and out.
• Volume of thoracic cavity increases
• Pressure decreases below atmospheric pressure
• Air sucked into lungs from high to low pressure

Question 25

Explain the mechanism of breathing out Expiration

Answer 25

• Muscles of diaphragm relax, diaphragm returns to domed position
• Internal Intercostal Muscles (between ribs) contract, ribcage moves down and in
• Volume of thoracic activity decreases
• Pressure in thoracic activity increases above atmospheric pressure
• Air forced out from high to low pressure

Question 26

Explain the rate of heat loss with small organisms

Answer 26

They have a large SA:VOL ratio. They lose a lot of heat to environment relative to size; high rate of heat loss. To compensate, the have high rates of respiration as heat is a by product of respiration

Question 27

Explain rate of heat loss for Large organisms

Answer 27

They have a small SA:VOL ratio . They have a lower rate of heat loss so rates of respiration tend to be lower

Question 28

How do insects prevent water loss?

Answer 28

• Open and close spiracles (prevent evaporation)- Covered in a waxy cuticle

Question 29

How do the stomata help prevent water loss?

Answer 29

When cells have a lot of water they are turgid and when cells don’t they are flaccid. Flaccid guard cells close the stomata

Question 30

In photosynthesis in plants, what gas is needed?

Answer 30

Carbon dioxide

Question 31

What are the ways that insects control water loss?

Answer 31

• Waxy outer cuticle- They can close their spiracles- Water is trapped around the spiracles by hairs