B4- gas exchange in fish ✅, insects ✅ and plants ✅

explain how the body of a unicellular organism is adapted for gas exchange

1. thin flat shape → large SA:V ratio

2. thin → short diffusion distance to all parts of cells → rapid diffusion

why can a unicellular organism rely on gas exchange via diffusion but a multicellular organism can’t?

• unicellular → large SA:V ratio → short diffusion distances for substances to travel → can rely on diffusion

• multicellular → would take too long for gases to diffuse and reach all cells

describe the tracheal system of an insect

1. spiracles = pores on the surface that can open / close to allow diffusion

2. tracheae = large tubes full of air that allow diffusion

3. tracheoles = smaller branches from tracheae, permeable to allow gas exchange with cells

adaptations of insects tracheal system for gas exchange

• Tracheoles have thin walls → so short diffusion distance to cells

• Highly branched tracheoles→ so short diffusion distance to cells and large surface area

• Tracheae provide tubes full of air→ so fast diffusion

• contraction of abdominal muscles (abdominal pumping) changes pressure in body, causing air to move in and out → maintains concentration gradient for diffusion

• fluid in the end of tracheoles drawn into tissue by osmosis during exercise→ as fluid is removed, air fills tracheoles, so rate of diffusion to gas exchange surface increases as diffusion is faster through air

• The tracheal system also replenishes storage air sacs, which are important when the insect needs to conserve water.

explain structural and functional compromises in terrestrial insect that allow effect gas exchange while limiting water loss

1. thick waxy cuticle / exoskeleton → increases diffusion distance so less water loss via evaporation

2. spiracles can open to allow gas exchange and close to reduce water loss (evaporation)

3. hairs around spiracles → trap moist air, reducing water potential gradient so less water loss (evaporation)

describe and explain 3 ways gases are exchanges in a tracheal system

1. down a diffusion gradient

• respiration uses oxygen, creating low conc. oxygen at end of tracheoles

• oxygen diffuses from spiracles down conc grad to the cells (opposite occurs for CO₂)

2. abdominal pumping → down a pressure grad→ speeds up diffusion

• contraction of muscles in abdomen squeezes tracheae

• enabling mass transport of air in and out

• CO₂ forced out down pressure grad

• pumps more oxygen in

• also helps maintains greater diffusion grad which speeds up exchange of gases after exercise

3. water collects at end of tracheoles (due to respiration)

• during eg flying, muscle cells around tracheoles respire anaerobically and produce lactate

• lowers water potential of cells so water moves into cells by osmosis

• causes rate of gas exchange to increase bc: gases diffuse faster in air than through water, greater SA exposed to air, decreases pressure in tracheoles and as a result more air from atmosphere is drawn in

why do larger insects need abdominal pumping but smaller ones don’t

larger insects:

• speeds up diffusion of oxygen into body

• also helps removal of carbon dioxide

smaller insects:

• tiny size = large SA:V and short diff distances

• allowing enough oxygen to reach cells via diffusion down conc grads through tracheal system

explain how the leaves of dicotyledonous plants are adapted for gas exchange

• high density of stomata→ large SA for has exchange when opened by guard cells

• spongy mesophyll contains air spaces → large SA for gases to diffuse through

• thin → short diffusion distance

learn to label the cross section of a leaf

okay

when stomata are open, name 2 substances that diffuse in and 1 that diffuses out

IN:

1. oxygen

2. carbon dioxide

OUT:

1. water vapour

explain the structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss

1. thicker waxy cuticle

• increases diffusion distance so less evaporation

2. sunken stomata in pits / rolled leaves / hairs

• trap water vapour / protect stomata from wind

• so reduced water potential grad between leaf and air

• so less evaporation

3. spines / needles

• reduces SA:V ratio

define what a xerophyte is

a plant adapted to live in very dry conditions e.g. cacti and marram grass

explain how the gills of fish are adapted for gas exchange

1. gills made of many filaments covered with many lamellae

• increases the SA for diffusion

2. thin lamellae wall / epithelium

• so short diffusion distance between water / blood

3. lamellae have a large number of capillaries

• remove O2 and bring CO2 quickly so maintains concentration gradient

explain how the counter current flow increases/ aids gas exchange

1. blood and water flow in opposite directions through lamellae

2. so oxygen concentration is always higher in water than blood near

3. so maintains a concentration gradient of O₂ between water and blood

4. for diffusion along whole length of lamellae

why is parallel flow not as efficient for gas exchange in a fish

• equilibrium would be reached so oxygen wouldn't diffuse into blood along the whole gill plate

hard PPQs start here:

okay

explain the movement of oxygen into the gas exchange system of an insect when it is at rest

1. oxygen used in aerobic respiration

2. so oxygen concentration gradient established

3. so oxygen diffuses in down a concentration gradient

explain how abdominal pumping affects pressure in an insect abdominal and how this links to CO2 release (2)

1. abdominal pumping raised pressure in body

2. so CO2 moves down pressure gradient out of body

explain what causes O2 concentration in the tracheae to fall when the spiracles are closed (2)

• oxygen is used in respiration therefore diffuses from tracheae to tissues

• no more O2 can diffuse in

explain how the ventilation mechanism of a fish and the structure of its gills result in the efficient uptake of O2 from water (6)

1. filaments / lamellae

2. large SA

3. large number of capillaries

4. maintain a concentration gradient

5. thin epithelium

6. short diffusion distance

7. pressure changes from abdominal pumping

8. bring in more water / maintain gradient

9. countercurrent flow

10. diffusion along hole length / blood always meets water with a higher O2 concentration / equilibrium not reached

why is it easier to move water in one direction rather over a gas exchange system rather than in a tidal patten (2)

1. hate has a high density

2. so requires a large input of energy as difficult to push back out

a rise in the temperature of water decreases the amount of oxygen dissolved in the water. as the temperature rises, the rate of ventilation in a fish also rises. explain the advantage of this:

• metabolic rate increases with increase in temp

• so more oxygen required

OR

1. to provide the same amount of oxygen

2. need to have more water flowing over gills

other than SA:V ratio, describe and explain one way that uncontrolled cell division changes fish gills (3)

1. thicker epithelium between water and blood capillary

2. greater diffusion distance

3. less efficient gas exchange

describe 2 differences between the circulation of blood in fish and the circulation of blood in a mammal (2)

1. in fish→ 1 atrium, 1 ventricle vs in mammal→ 2 ventricles, 2 atria

2. in fish → blood does not return to heart after being oxygenated vs in mammal- blood returns to heart after being oxygenated

3. in fish→ one artery carrying blood away from heart vs in mammal→ aorta and pulmonary artery

4. in fish→ single circulatory system vs in mammal→ double circulatory system

other than a change in temperature, give one change the scientist could make to the environmental conditions to increase a flowers shelf life

1. increase humidity

2. decrease W.P grad between plant and air

3. less water lost via transpiration

adaptations of insects tracheal system for reducing water loss

• Spiracles- pores on the surface which can open and close

• The tracheal system also replenishes storage air sacs, which are important when the insect needs to conserve water.

• waxy exoskeleton made of chitin which is impermeable to water, preventing evaporation of water

• spiracles have hairs creates localised humidity by trapping a layer of water vapour, reducing water potential gradient and therefore water loss