Exchange Surfaces

What is an exchange surface?

A surface where substances are exchanged between an organism and its environment

Why do multicellular organisms need specialised exchange surfaces?

Low surface area to volume ratio makes diffusion too slow

What happens to surface area to volume ratio as size increases?

It decreases

Why is a low SA:V ratio a problem?

Diffusion cannot meet metabolic demands

How do large organisms overcome diffusion limitations?

Specialised exchange surfaces and transport systems

What four features make an exchange surface efficient?

Large surface area

Thin barrier

Good blood supply

Ventilation

Why does a large surface area increase diffusion rate?

More particles diffuse at the same time

Why must exchange surfaces be thin?

Short diffusion distance increases diffusion rate

Why does a good blood supply increase diffusion rate?

Maintains a steep concentration gradient

What is ventilation?

Movement of air or water over an exchange surface

Why is ventilation important?

Maintains a steep concentration gradient

What factors affect diffusion rate (Fick’s law)?

Surface area, concentration gradient, diffusion distance

What is diffusion?

Net movement of particles from high to low concentration

Why is oxygen needed by cells?

For aerobic respiration

Why must carbon dioxide be removed?

Toxic waste product of respiration

What is respiration?

Chemical reactions in cells that release energy

What gas exchange system do insects use?

Tracheal system

What are spiracles?

Openings that allow air in and out

What are trachea in insects?

Tubes that carry air through the body

What are tracheoles in insects?

Thin tubes where gas exchange occurs

How does oxygen reach insect tissues?

Diffusion through tracheoles directly to cells

Why is diffusion distance short in insects?

Tracheoles deliver oxygen directly to tissues

How is ventilation achieved in insects?

Abdominal pumping movements

How do insects reduce water loss?

Spiracles can close

What organ do fish use for gas exchange?

Gills

What are gill filaments?

Structures providing large surface area

What are lamellae?

Thin plates where gas exchange occurs

Why are lamellae thin?

Short diffusion distance

What is countercurrent flow?

Blood flows opposite to water

Why is countercurrent flow effective?

Maintains a steep concentration gradient along the whole gill

What is the trachea in humans?

Tube carrying air from mouth or nose to lungs

Why does the trachea contain cartilage rings?

Prevents airway collapse

What are bronchi?

Two branches of the trachea leading to lungs

What are bronchioles?

Smaller branching airways

Why do bronchioles have smooth muscle?

Control airflow by constriction or dilation

What are alveoli?

Tiny air sacs where gas exchange occurs

How do alveoli provide a large surface area?

Millions of alveoli in the lungs

Why are alveolar walls thin?

Short diffusion distance

Why are alveoli moist?

Gases dissolve before diffusing

Why do alveoli have a good blood supply?

Maintains a steep concentration gradient

What is lung surfactant?

Substance reducing surface tension and preventing alveoli collapse

Describe the structure of an alveolus

One-cell-thick squamous epithelium with elastic fibres, collagen fibres and surrounding capillaries

What is the function of elastic fibres in alveoli?

Allow stretching and recoil during breathing

What is the function of collagen fibres in alveoli?

Prevent over-expansion and bursting

How does oxygen move between alveoli and blood?

Diffuses into capillaries and binds to haemoglobin

How does carbon dioxide move between blood and alveoli?

Diffuses into alveoli to be exhaled

What capillary features aid gas exchange?

Thin walls, large surface area, slow blood flow, steep gradient, red blood cells close to wall

What does the pulmonary artery do?

Carries deoxygenated blood to the lungs

What does the pulmonary vein do?

Carries oxygenated blood to the heart

What is the role of capillaries in the lungs?

Allow gas exchange between alveoli and blood

What is ventilation?

Movement of air into and out of the lungs

What happens during inhalation?

Diaphragm contracts, ribs move up and out, volume increases, pressure decreases, air enters lungs

What happens during exhalation?

Diaphragm relaxes, ribs move down and in, volume decreases, pressure increases, air leaves lungs

Why does air enter the lungs?

Pressure inside lungs is lower than atmospheric pressure

What is elastic recoil?

Lungs returning to original shape after stretching

Why is elastic recoil important?

Helps force air out during exhalation

What is the difference between ventilation and gas exchange?

Ventilation moves air, gas exchange is diffusion of gases

What is asthma?

Inflammation and constriction of bronchioles

How does asthma affect ventilation?

Reduced airflow

How does asthma affect gas exchange?

Reduced oxygen uptake

What is pulmonary fibrosis?

Scarring of lung tissue

How does fibrosis affect diffusion?

Increases diffusion distance and reduces diffusion rate

What is a spirometer?

Device measuring lung volumes

What is tidal volume?

Volume of air inhaled or exhaled in one breath

What is vital capacity?

Maximum air exhaled after a deep inhalation

What is breathing rate?

Number of breaths per minute

How does lung disease affect spirometry?

Reduced tidal volume or vital capacity