Gas exchange system

Contrast the trachea of a mammal and the trachea of an insect

1. Mammals have just one trachea whereas insects have multiple trachea

2. Trachea of mammals have a larger diameter than trachea of insects

3. Mammal trachea made up of cartilage whereas insect trachea made up of chitin

4. Mammal trachea is longer than insect trachea

5. Mammal trachea branch into bronchi whereas insect trachea branch into tracheoles

Describe the difference in the composition of gases in inhaled and exhaled air.

Explain how these differences are caused.

1. inhaled air contains more oxygen that exhaled air

2. inhaled air contains less carbon dioxide than exhaled air

3. inhaled air contains less water vapour

4. water vapour diffuses from moist surface

5. respiration results in higher blood carbon dioxide and lower blood oxygen

6. oxygen enters blood and carbon dioxide leaves blood in alveoli by diffusion

describe the gross structure of the human gas exchange and how we breathe in and out

trachea, bronchi, bronchioles, alveoli

• 1. when you breathe in: the diaphragm contracts and moves down and the external intercostal muscles contract

  • contraction of diaphragm muscles flattens diaphragm

  • causes an increase in volume and pressure decrease in thoracic cavity (to below atmospheric), resulting in air moving in down pressure gradient

  2. when you breathe out: the diaphragm relaxes and internal intercostal muscles contract

  • diaphragm moves up and becomes dome shaped

  • contraction of intercostal muscles raises ribcage

  • causes a decrease in volume and a pressure increase in thoracic cavity to above atmospheric

  • pressure in lungs is higher than pressure outside

  • resulting in air moving out

apart from reduced elasticity, explain how changes to the lung tissue reduce the efficiency of gas exchange

1. alveolar walls thicken

   • so longer diffusion pathway

2. scarred tissue

   • reduces SA for gas exchange

role of diaphragm in breathing in

1. diaphragm contracts and moves down

2. increases volume in thorax and lowers pressure in thorax

3. air moves in down pressure gradient

   • Reduced pressure allows air to enter

role of diaphragm in breathing out

1. diaphragm moves up and becomes dome-shaped

2. reduces volume of thorax and increases pressure in thorax

3. so pressure in thorax is higher than the outside

how paralysis of diaphragm leads to breathing difficulties

• diaphragm will not contract and move down

• thoracic cavity/lung volume is not increased, so cannot breathe in

movement of ribs when a person breathes in

up and out

explain whether breathing out is active or passive

active because it involves contraction of muscles

Describe insect tracheal system

• Air enters through openings called spiracles and moves down into tubes called trachea

• Trachea branches into many tracheoles

• Tracheoles deliver the air to the respiring tissue

• Air diffuses into respiring tissue down concentration

three ways in which an insects tracheal system is adapted for efficient gas exchange

1. tracheoles have thin walls

   • so short diffusion distance to cells

2. large number of tracheoles

   • so short diffusion distance to cells

3. large number of tracheoles

   • so large surface area

4. Tracheae provide tubes full of air

   • so fast diffusion into insect tissues

5. Fluid in the end of the tracheoles that moves out during exercise

   • so larger surface area

Spiracle

the structure through which gases enter and leave the body of an insect

Tracheole

the small tubes that carry gases directly to and from the cells of an insect

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

1. oxygen used in respiration

2. oxygen moves down a diffusion gradient

The damesfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water.

Explain how the presence of gills adapts the damesfly to its way of life.

• Damselfly larvae has higher metabolic / respiratory rate

• so it uses more oxygen

explain 5 ways in which the structure of fish gills is adapted for efficient gas exchange

1. Gills have many lamellae / filaments so large surface area

2. Thin epithelium surface so short diffusion pathway

3. Countercurrent maintains concentration gradient along gill

   • equilibrium not reached

4. Circulation replaces blood saturated with oxygen

5. Ventilation replaces water as oxygen is removed

When a fish is removed from water their gill lamella stick together. Explain how this could be damaging to the fish.

• when the lamellae stick together the surface area for gas exchange is reduced

• This means that not enough oxygen is absorbed or not enough carbon dioxide is removed from the blood

counter-current mechanism

1. water and blow flow in opposite directions

2. blood always passing water with a higher oxygen concentration

3. diffusion gradient maintained throughout length of gill/lamella

describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.

details of breathing are not required.

the oxygen moves through the trachea, bronchi and bronchioles

• down a pressure and diffusion gradient

• across alveolar epithelium and capillary epithelium

how oxygen in the air in the alveoli enters the blood in the capillaries

the oxygen moves by diffusion across alveolar epithelium

Explain why a large number of small alveoli is more efficient in gas exchange than a smaller number of larger alveoli

• small alveoli has larger SA

  • so more diffusion

Forced expiration volume (FEV1) is the volume of air a person can breathe out in 1 second.

One of the severe disabilities that results from emphysema is that walking upstairs becomes difficult.

Explain how a low FEV1 value could cause this disability.

1. less CO2 removed

2. less oxygen uptaken

3. less respiration

features of xerophytic leaves

1. thicker cuticles

   • so increase in diffusion distance/slower rate of diffusion

2. hairs on leaves

   • increase in humidity/ decrease in WP gradient

3. curled leaves

   • increase in humidity/ decrease in WP gradient

4. sunken stomata

   • increase in humidity/reduction in air movement

Suggest and explain one way the leaf growth of xerophytic plants would be different from the leaf growth of sunflowers

Slow growth due to smaller number of stomata

Use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow only slowly

• Stomata close

• Therefore less CO2 uptake

• Therefore less photosynthesis

advantage of closing stomata to the plant when there’s no light

• water is lost through stomata

• reduces water loss and maintains water content of cells

how does CO2 in the air outside a leaf reaches the mesophyll cells inside the leaf

1. CO2 enters via stomata

2. Stomata is opened by guard cells

3. CO2 diffuses through air spaces down diffusion gradient

7 ways in which lungs are adapted for gas exchange

1. many alveoli to provide large SA

2. many blood capillaries provide large SA

   • so fast diffusion

3. alveoli walls are thin so short diffusion distance between alveoli and blood

4. flattened epithelium so short diffusion distance

5. ventilation:

   • brings in air containing a higher oxygen concentration and removes air with a lower oxygen concentration

   • so maintains diffusion/ concentration gradient

6. wide trachea for efficient flow of air

7. cartilage rings to keep airways open

name one way, other than ventilation, that helps maintain the difference in oxygen concentration

circulation of blood

how cuticle reduces water loss

cuticle is waxy, so its impermeable to water

how fish maintain a flow of water over their gills

1. mouth opens and floor of mouth lowered

   • water enters due to decreases pressure and increased volume

2. mouth closes and floor of mouth raised, which results in increased pressure and decreased volume

3. increased pressure pushes water over gills