Summary
Summary Module 3.1: Exchange and transport
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OCR biology A level A summary of key concepts ranging from specialised exchange surfaces, to ventilation in mammals and fish.
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EXCHANGE SURFACES Ventilation in mammalsInspiration – energy
Specialised surfaces 1) Diaphragm contracts, flattening + lowering
- Diffusion for single celled organisms as ↑ SA:V and ↓ 2) External intercostal contract = ribs up + out
metabolic activity = ↓O2 demand/CO2 produced 3) ↑ volume of thorax + ↓ pressure
- Larger have small SA:V + ↑ metabolic rate, distance 4) Air drawn in and equalises pressure
for diffusions too far, not meet demand
- Conflict gas exchange + water loss (evaporation) Expiration – passive process
- O2 dissolves in water before diffusing 1) Diaphragm muscles relax + moves up
2) External intercostal relax = ribs down + in
Features 3) Elastic fibres in alveoli return to normal
1) Increased surface area – SA:V ratio 4) ↓ volume of thorax + ↑ pressure
2) Thin layers – fast, efficient diffusion 5) Air moves out to equalise pressure
3) Blood supply – constant exchange + gradient
4) Ventilation – maintain concentration gradient Exhale forcibly using energy
- Internal intercostal contract pull ribs down fast
SA: V = SA / V Sphere SA = 4r2 Sphere V= 4/3r3 - Abdominal contract, diaphragm up, ↑ thorax p
Mammalian gas exchange The first breath
- 15-20x greater, lungs stretched, not return to original
- Lung surfactants (phospholipid) stop alveoli sticking
- Surfactants develop at 30 weeks, premature have
artificial surfactants sprayed to prevent damage
Asthma attack
1) Bronchiole lining release histamine, inflame epithelial
2) Stimulate goblet cells to make excess mucus
3) Smooth muscle in bronchiole contracts (narrow)
Asthma medicines
Trachea - Preventers = steroids daily to ↓ airway sensitivity
- Incomplete cartilage rings – stop airway collapse + - Relievers = immediate relief
food down oesophagus (smoke paralyses cilia) - Chemical attach to smooth muscle (relax + dilate)
- Ciliated epithelium, goblet prevent bacteria
Measuring lung capacity
Bronchioles 1) Peak flow meter = rate air is expelled (asthma)
- Bronchus cartilage, cilia, smooth muscle 2) Vitalographs = amount of air breathed out + speed
- Smooth muscle, no cartilage (< 1mm) 3) Spirometer = breathing vol, O2 used up, soda lime
- Muscle contracts + bronchioles close absorbs CO2, line down, healthy, sterilised, no leaks
- Flattened cells = some exchange
Alveoli
- Elastic recoil forces air out
- Inner surface – water, salts, lung surfactants (inflate)
- Macrophages combat pathogen (200-300m)
Cartilage Smooth Elastic Goblet Cilia
Trachea ✓ ✓ ✓ ✓ ✓
Bronchi ✓ ✓ ✓ ✓ ✓
Large bronch ✕ ✓ ✓ ✓ ✓
Small bronch ✕ ✕ ✓ ✕ ✕
Alveoli ✕ ✕ ✓ ✕ ✕
Breathing rate = number of breaths per minute
Pleural cavity Ventilation rate = total vol of air inhaled in 1 minute
- Lung = double membrane (pleural membrane) Residual volume = vol of air left in lungs after strongest
- Pleural cavity (between membranes) filled with exhalation (not measured directly), continuous exchange
pleural fluid – lubricates so layers slide over as Total lung capacity = vital capacity + residual vol
breathe, adhere outer lung by water cohesion
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