GAS EXCHANGE IN FISH AND INSECTS

Question 1

How do single celled organisms exchange gases?

Answer 1

by diffusion through their outer body surface.
- they have a relatively large surface area, a thin surface and a short diffusion pathway.

Question 2

counter current system

Answer 2

• fish uses a countercurrent system for exchange of gases.
• blood flows over lamellae in one direction and water flows in opposite direction.
• this helps to maintain a large concentration gradient between water and blood.

Question 3

why is countercurrent system important

Answer 3

• ensures that equilibrium is not reached
• ensures that a diffusion gradient is maintained across the length of entire lamellae.

Question 4

fish gill anatomy

Answer 4

• water containing oxygen enters through its mouth and passes through the gills.
• the gills is made up of lots of thin plates called gill filaments which provides a bigger surface area for exchange of gases.
• the gill filament is covered with lots of tiny structures called lamellae which increases the surface area even more.
• the lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion.
• blood flows through lamellae in one direction and water flows in the opposite direction which us called the counter current principle which is very important to maintain a concentration gradient between water and blood.

Question 5

gas exchane in insects

Answer 5

• insects use a tracheal system for gas exchange which consists of trachea, tracheoles and spiracles.
• insects have microscopic air filled pipes called trachea .
• air moves into trachea via pores present in the surface called spiracles.
• oxygen moves down the concentration gradient towards the cells.
• the trachea is further branched into tracheoles which has a very thin permeable wall and is linked to every cells so that the oxygen reaches directly into the respiring cells.
• carbondioxide from the cells moves down its own concentration gradient to be released into the atmosphere.
• insects use a rhythmic abdominal movement to move air in and out of the spiracles.

Question 6

lactate and insects

Answer 6

• when insects are in flight, the muscle cell starts to respire anaerobically to produce lactate.
• lactate reduces the water potential of the cells.
• so water moves into the cells from the tracheoles by osmosis.
• so more air is drawn out from the atmosphere.

Question 7

gas exchange in dicotyledonous plants

Answer 7

• gas exchange in dicotyledonous plants takes place through mesophyll cells.
• plants need co2 for photosynthesis which prduces oxyegn as a waste gas and they need oxygen for respiration which produces co2 as a waste gas.
• the main gas exchange surface is the surface area of mesophyll cells in the leaf. they are well adapted for their function as they have a large surface area.
• mesophyll cells are inside the leaf so gases move in and out through special pores in epidermis called stomata.
• stomata opens to allow the exchange of gases and closes when the plant is losing too much water.
• guard cells contain the opening and closing of stomata.

Question 8

adaptation of insects to water loss

Answer 8

• if insects are losing too much water, they close the spiracles with their muscles.
• insects also have a waterproof waxy cuticle and tiny hairs over their spiracles to reduce evaporation.

Question 9

adaptation of plants to water loss

Answer 9

• stomata is kept open during the day to allow gaseous exchange. water enters the guard cells making them turgid and opening the stomatal pore. if plants start to get dehydrated, guard cells lose water and becomes flaccid which then closes the pore.

Question 10

adaptations for xerophytes

Answer 10

• stomata is sunken in pits that traps moist air which helps to reduce the concentration gradient between air and leaf which reduces the amount of water diffusing out of the leaf and evaporating air.
• a layer of hairs on the epidermis to trap moist air.
• curled leaves with stomata inside to protect them from wind(wind increases the rate of diffusion)
• reduced number of stomata so there is a fewer places for water to escape.
• waxy waterproof cuticles on leaves and stem to reduce evaporation.