Gas exchange in Fishes, Insects and Plants

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Counter Current in Fish

- Water containing oxygen enters the fish thought the mouth and pass out through the gills.

- Each gill is made out of thin plates called gill filaments, they are covered by tiny structures called lamellae, which increase the gas exchange surface area even more.

- Lamellae consists of lots of blood capillaries that carry deoxygenated blood.

- Blood and the water flow in opposite way, this is called the counter current system which maintains a large concentration gradient between water and the blood in capillaries.


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Insects use Tracheae to exchange gas

- Insects have air-filled pipes called tracheae.

- Air moves in the tracheae through pores on the surface called spiracles.

- Oxygen travels down the concentration gradient towards the cell.

- Oxygen directly diffuses into respiring cells ( oxygn is not transferred).

- Carbon dioxides are released in the atmosphere through the spiracles.

- They have a rhythmic abdominal movement to move air in and out of the spiracles.


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Gas exchange in Plants

- Photosynthesis requires CO2, which produces oxygen as a waste gas. They need oxygen for respiration. which produces CO2 as a waste gas.

- The gas exchange surface of plants are mesophyll cells on the leaf ( they create a large S.A).

- Mesophyll cells are inside the leaf, gas moves in and out of it through pores in the epidermis called stomata.

- The stomata can open to allow exchange of gas, and close if the plant is losing too much water.

- It’s the function of guard cells to open and close the stomata.


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- Some plants are specially adapted to for life in warm, dry or windy habitats, where water loss is a problem.


- Stomata **** in pits to trap moist air.

- A layer of "hairs" on the epidermis to trap moist air. 

- Curled leaves to trap moist air and protecting it from the wind.

- A reduced number of stomata to reduce water loss.

- Waxy, waterproof layer on the leaf to reduce water evaporation.

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