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)

Trachea

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

Sites of gas exchange

alveoli in lungs and respiring cells around body

Nasal cavity

hollow space behind nose to warm and filter air

Lungs

main organs and responsible for gas exchange

Bronchus

Two short branches off trachea to carry air into lungs

Bronchioles

Airways made up of multiple branches, leading to alveoli

Thorax

between neck and abdomen

Alveoli

Tiny sacs of lung tissue where gas exchange takes place

Effective exchange surface

• Has a large surface area

• Good blood supply

• Well ventilated for gas exchange

• Thin, permeable membrane for diffusion

Capillaries

Small and thin blood vessels where gas exchange occurs, 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

• happens in the presence of oxygen

• occurs in mitochondria

• produces lots of energy

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

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)

1. movement

2. respiration

3. sensitivity

4. growth

5. reproduction

6. excretion

7. nutrition

   (+ active transport)

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)

• occurs in cytoplasm

• 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