1.5 The Respiratory System

Respiratory system

System of organs to maintain gas exchange

Gaseous exchange

oxygen is taken in and exchanged for carbon dioxide (waste product of respiration)

Sites of gas exchange

alveoli of the lungs and respiring cells around the body

Lungs

main organs and responsible for gas exchange

Nasal cavity

hollow space behind nose to warm and filter air

Trachea

allows air to pass through and supported by rings of cartilage to prevent collapsing

Bronchus

Two short branches off trachea to carry air into lungs

Bronchioles

Airways made up of multiple branches, leading to alveoli

Alveoli

Tiny sacs of lung tissue where gas exchange takes place

Effective exchange surface

Has a large surface area, a good blood supply, is well ventilated for gas exchange and has a thin membrane for diffusion

Capillaries

Small and thin blood vessels where gas exchange occurs, they consist of a single layer of cells

Diaphragm

thin sheet of muscle to help control breathing, pulls down and contracts to become flat so air can easily enter

Intercostal muscles

in between ribs which move rib cage during breathing

Pleural membrane

Double-layered membrane that encloses and protects each lung to reduce friction

Pleural fluid

Fluid necessary to prevent friction between the pleural membranes

Mucus and cilia

particles and bacteria stick to move them out and to the back of the throat

Diffusion

movement of substances from a higher concentration to a lower concentration

Adaptations of the respiratory system

Large surface area due to multiple branches of bronchioles and many alveolar sacs, good blood supply for quick diffusion, well ventilated, ventilation is optimised by effective involuntary muscular action

Need for transport and exchange systems

Larger organisms have smaller surface area to volume ratios and are unable to directly obtain useful substances from their environment like single-celled organisms can

Large surface area to volume ratio

Leads to faster diffusion rates, more room for particles to diffuse through membrane

Purpose of gas exchange

Organisms need oxygen for aerobic respiration, they also need to remove carbon dioxide which is a waste product in some organisms

Alveoli adaptations

• Large surface area - many alveoli are present

• Thin, moist and permeable walls

• Permeable walls

• Good blood supply

• A large diffusion gradient - concentration in alveoli is higher than capillaries so oxygen moves to the blood

Moist lining of alveolus

gases dissolve in moisture helping them to pass across, which increases the rate of diffusion

Wall of capillary

one cell thick to optimise diffusion between the alveoli and the blood

Permeable walls

allows gasses to pass through easily

Many blood vessels surrounding alveoli

maintain a constant diffusion gradient for gas exchange so oxygen is taken out and carbon dioxide in

adaptations for exchange

Alveoli in mammals, guard cells and spongy mesophyll in plants

Gas exchange in plants

Carbon dioxide diffuses into plant in exchange for oxygen that diffuses out, regulated by guard cells to open and close stomata

Leaf adaptations as a respiratory surface

• pores called stomata to open/close and regulate gas exchange

• surrounded by air spaces to increase surface area for diffusion and gas exchange

• cell membranes are also thin, moist and permeable

• occurs in spongy mesophyll

Aerobic respiration

Cell respiration which happens in the presence of oxygen in the mitochondria of the cell, in animals and plants

Anaerobic respiration

Cell respiration which happens in the absence of oxygen

Fermentation

Anaerobic respiration in plant and yeast cells which produces ethanol and carbon dioxide

Word equation for fermentation

Glucose -> carbon dioxide + ethanol + little energy

Uses of fermentation

The manufacture of bread and alcoholic drinks

Anaerobic respiration in yeast practical

• Boil the glucose solution to sterilise it and remove any oxygen, leaving behind the glucose needed for anaerobic respiration

• Cool before adding the yeast (high temperatures will kill it)

• Place a layer of oil on top of the glucose solution to prevent oxygen entering

• Yeast will respire anaerobically producing alcohol, heat and carbon dioxide that can be collected in limewater

Factors affecting respiration in yeast practical

1. Mix yeast into a solution of glucose and water - this provides the glucose and oxygen needed for respiration.

2. Leave at room temperature for 1 hour.

3. Place mixture in a test tube.

4. Place a boiling tube over the test tube and invert - the test tube will now be upside down.

5. Place in water bath at 10°C.

6. Measure the height of the bubble at the top of the test tube.

7. After 30 minutes, measure the height of the bubble at the top of the test tube.

8. Repeat steps 2 to 7 at different temperatures (e.g. 20°C, 30°C, 40°C and 50°C).

9. Calculate the change in bubble height and record results

Factors affecting respiration in yeast results

optimum temperature will produce largest bubble of CO₂ after 30 minutes, respiration will have happened fastest

Limewater test

CO₂ bubbled in limewater cause a change from colourless to a milky (cloudy precipitate)

Exothermic reaction

releases energy to its surroundings, usually heat

Use of energy (7 life processes)

movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition (+ active transport)

Aerobic respiration

happens in the presence of oxygen and releases lots of energy

Word equation for aerobic respiration

Glucose + oxygen -> carbon dioxide + water + energy

Balanced chemical equation for aerobic respiration

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Anaerobic respiration

happens in the absence of oxygen (strenuous exercise) and produces little energy

Word equation for anaerobic respiration

Glucose → lactic acid + little energy

Oxygen debt

amount of extra oxygen the body needs after exercise to react with lactic acid

Inhalation

1. intercostal muscles contract, ribs move up and out

2. thorax increases in volume and decreases in pressure, causing air to enter lungs

3. diaphragm contracts, moving downwards

Exhalation

1. intercostal muscles relax, ribs move down and in

2. thorax decreases in volume and increases in pressure, forcing air out of the lungs

3. diaphragm relaxes, returning to domed shape

Bell jar model

• When the rubber sheet moves down, the volume inside the glass jar increases.

• This increase in volume causes a decrease in pressure.

• The lungs (balloons) inflate as air enters until the pressures inside and outside are equal

Limitations of the bell jar model

1. The ribs and intercostal muscles are not represented in the model

2. Space between lungs and wall of thorax is large rather than small

3. Diaphragm shape is not flat and pulled down but domed and it flattens

4. Balloons contain open space opposed to many alveoli

Composition of inhaled air

21% Oxygen, 0.04% Carbon Dioxide, 78% Nitrogen, water vapor varies

Composition of exhaled air

16% Oxygen, 4% Carbon Dioxide, 78% Nitrogen, saturated with water vapour

Effects of exercising

• muscles require more energy causing increased respiration

• a larger volume of air is needed to replace oxygen used and remove carbon dioxide

• to supply this the body increases the rate and depth of breathing

• also leads to increased heart rate

Recovery time

time taken for breathing rate to return to normal after exercise