Adaptation for gas exchange - All

Amoeba

• Thin cell membrane - short diffusion pathway to middle of the cell

• Unicellular - large SA:V

Flatworms

• Multicellular

• Flat - larger SA:V

• Flat - reduces diffusion pathway from body’s surface

Earthworms

• Multicellular

• Mucus - moist surface

• Blood vessels close to skin surface - reduces diffusion pathway

• Haemoglobin has high affinity for oxygen

Function of gill rakers

Protects gills from food and debris

Function of gill lamellae

Increase surface area of gill filaments

Counter current flow

• Blood flow and water flow in opposite directions

• Maximum saturation

• O2 concentration doesn’t reach equilibrium

• Ensures oxygen gradient is maintained

Parallel flow

• Blood flow & water flow in same direction

• Reach equilibrium

• O2 concentration reaches 50%

Ventilation in fish

• Mouth opens

• Buccal cavity floor lowers

• Volume increases, pressure decreases

• Mouth closes

• Buccal cavity floor raises

• Operculum opens & water is pushed over gills

Structure of trachea

• Cartilage prevents it from collapsing in negative pressure

• C shaped rings to allow flexibility for oesophagus to swallow food

• Covered in ciliated epithelial cells to sweep out dust & bacteria

Function of pleural membrane

• Surrounds lungs to make it air tight

• Secrete pleural fluid to reduce friction

• Protects lungs from ribs

Adaptations of alveoli

• Covered in surfactant - keeps surface moist

• Network of capillaries - maintaining diffusion gradients

• Capillary walls one cell thick - short diffusion pathway

Inhalation in humans

• Intercostal muscles contract

• Ribs move up and out

• Pleural membranes pulled out

• Diaphragm contracts and flattens

• Volume increases, pressure decreases

• Air moves down pressure gradient, into lungs

Exhalation in humans

• Intercostal muscles relax

• Ribs move down and in

• Pleural membranes relax

• Diaphragm relaxes and domes upwards

• Volume decreases, pressure increases

• Atmospheric pressure less - air moves out

Process of stomata opening

• Photosynthesis produces ATP

• ATP used in active transport of K+ ions into guard cells

• Soluble starch converted into insoluble malate

• Malate & K+ ions lower water potential in guard cells

• Water moves into guard cells via osmosis

• Guard cells expand as they move in. Uneven thickness of cells causes them to swell and expand, forming a stoma