2.2 Adaptations for Gas Exchange

Question 1

Is the surface area to volume ration higher in large or small organisms?

Answer 1

Small organisms. Their SA:v is large enough that diffusion through the body surface is sufficient to supply their needs. Distances within the body are small and transport by diffusion is again sufficient eg amoeba

Question 2

How are larger organisms adapted for gas exchange?

Answer 2

They have specialised surfaces eg giils or lungs. These surfaces have a large surface area, and are thin and permeable.

Question 3

How are earthworms adapted for gas exchange?

Answer 3

Their body is moist so gasses can dissolve and diffuse through their skin. Circulatory system and blood pigments.

Question 4

How have fish gills adapted for gas exchange?

Answer 4

Gills are composed of thousands of filaments. Filaments covered in lamellae (only a few cells thick) which contain blood capillaries. Large surface area and short diffusion distance. Each gill covered by a muscular flap (operculum). Mouth opens = decreased pressure = water flows in, down a pressure gradient. Mouth closes = increased pressure = water flows through the gill chamber & over the gills, out of the fish. O2 diffuses into the capillaries. Counter-current flow

Question 5

What is counter-current flow?

Answer 5

Blood flows in the opposite direction to the water. Blood at the end of the lamella is 80% or so saturated with oxygen, but the water it’s flowing past is 90 or 100% saturated so it can continue picking up oxygen until it’s 100% saturated. The system does not reach equilibrium, the diffusion gradient is maintained over the whole surface. More efficient than con-current flow.

Question 6

What is con-current flow?

Answer 6

Blood flows in the same direction as the water. The system reaches equilibrium so no further exchange can take place.

Question 7

How have terrestrial vertebrates adapted for gas exchange with air?

Answer 7

They have internal lungs which minimise loss of water and heat.

Question 8

How have amphibians adapted for gas exchange?

Answer 8

Infantile amphibians (tadpoles) have gills and also use their skin as a respiratory surface as they develop in water and undergo metamorphosis into the adult form. The inactive frog uses its moist, thin skin as a respiratory surface (gasses dissolve and diffuse into blood capillaries) but uses its lungs (thin with internal folding) when active.

Question 9

How have reptiles adapted for gas exchange?

Answer 9

Enlarge thoracic cavity to pull air into the lungs (expanding the rib cage or movement of internal organs). No muscular diaphragm.

Question 10

How have birds adapted for gas exchange?

Answer 10

Air sacs increase efficiency of lung ventilation by enabling air to pass in one direction through the lungs during inhalation AND exhalation. Also reduce body density for flight. Anterior (front) and posterior (back) air sacs. Inhalation > air into back air sacs > exhalation > air into lungs > 2nd inhalation > air into front air sacs > 2nd exhalation > air leaves the body

Question 11

Label the human respiratory system.

Answer 11

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Question 12

What enables ventilation in the human respiratory system?

Answer 12

Intercostal muscles, diaphragm, pleural membranes & pleural cavity. Create volume and pressure changes that allow a continuous exchange of gases & so maintaining concentration gradients.

Question 13

How have insects adapted for gas exchange?

Answer 13

Branched, chitin-lined system of tracheae with openings called spiracles. Tubes on the spiracles are in direct contact with individual cells and contain a small amount of fluid in which gasses are dissolved. Spiracles can be closed by valves to prevent water loss by evaporation.

Question 14

How have plants’ leaves adapted for gas exchange?

Answer 14

Thin Large surface area Permeated by air spaces

Question 15

Label a cross section of a leaf.

Answer 15

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Question 16

How have plants adapted for light harvesting?

Answer 16

Leaves have a large surface area and the ability to move through growth to the best position. Palisade cells are long and densely arranged in a layer. They contain many chloroplasts which arrange themselves according to light intensity. Light can pass through the spongey mesophyll.

Question 17

What does each part of the leaf do?

Answer 17

Cuticle prevents water loss Palisade cells contain lots of chloroplasts for photosynthesis Sponegy mesophyll allows light to pass through so it can reach the palisade cells Stomata allow water and gasses into and out of the leaf. Guard cells change shape to open and close the stomata and control gas exchange and water loss. (changes caused by turgidity - water in and out by osmosis)

Question 18

What is the malate theory?

Answer 18

Movement of potassium ions from the epidermal cells into the guard cells creates negative water potential in the gruard cells. Water then moves in by osmosis. The movement of the potassium ions is an active process requiring ATP.

Question 19

What are xerophytes?

Answer 19

A type of plant (cacti etc) that may open stomata at night instead of during the day in order to conserve water whilst other plants may close stomata during the day or night under drought conditions.