1.5 The Respiratory System 🫁

Respiratory system

System of organs to maintain gas exchange

Gaseous exchange

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

Trachea

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

Sites of respiration

respiring cells around body

Nasal cavity

hollow space behind nose to warm and filter air

Lungs

main organs 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

between ribs, moving 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

particles and bacteria stick and move out towards back of throat

Cilia

ciliated epithelial cells, fine hairs that beat to move mucus

Diffusion

movement of particles from region of high concentration to region of low 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, optimised by effective involuntary muscular action

Need for transport and exchange systems

large organisms have smaller sa:v ratios so are unable to directly obtain substances from environment

Large surface area to volume ratio

faster diffusion rates as more room to diffuse through membrane

Alveoli adaptations

• Large surface area as many alveoli are present

• Good blood supply

• Thin, moist and permeable walls

• large diffusion gradient due to lower concentration in capillaries

Moist lining of alveolus

gases dissolve in moisture helping them to pass across

Wall of capillary

one cell thick to optimise diffusion between alveoli and blood

Permeable walls

allows gasses to pass through easily

Many blood vessels surrounding alveoli

maintain a constant diffusion gradient for gas exchange

Site of gas exchange

alveoli in mammals and stomata in plants

Gas exchange in plants

carbon dioxide is taken in and exchanged for oxygen, regulated by guard cells

Leaf adaptations as a respiratory surface

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

• surrounded by air spaces to increase surface area

• cell membranes are also thin, moist and permeable

• occurs in spongy mesophyll

Uses of energy

• active uptake/ transport

• movement

• growth

• reproduction

• maintain constant body temp

Aerobic respiration

• happens in the presence of oxygen

• occurs in mitochondria

• produces lots of energy

Fermentation (yeast)

• can happen in presence or absence of oxygen

• occurs in plant and yeast cells

• boil and add layer of oil to remove oxygen

Word equation for fermentation (yeast)

Glucose → carbon dioxide + ethanol + little energy

Uses of fermentation (yeast)

making of bread and alcoholic drinks

Enzymes in yeast

work at optimum temperatures and can become denatured

Limewater test

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

Exothermic reaction

releases energy to its surroundings, usually heat

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

extra oxygen 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

• intercostal muscles relax, ribs move down and in

• thorax decreases in volume and increases in pressure, forcing air out of lungs

• diaphragm relaxes, returning to domed shape

Bell jar model

• rubber sheet moves down to increase volume inside glass jar

• causes decrease in pressure

• balloons inflate as air enters until pressures are equal

Limitations of the bell jar model

• ribs and intercostal muscles are not represented

• diaphragm shape is flat and pulled down rather than domed

• balloons contain open space instead of 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 (increased respiration)

• larger volume of air needed for gas exchange

• body increases rate and depth of breathing (+ heart rate)

Recovery time

time taken for breathing rate to return to normal after exercise