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Alveoli are folded to increase their surface area to volume ratio, so more volume of air can diffuse in from the blood and and in from the bronchioles. The lining of the alveoli walls are also moist so th...

Independent variable: the one that you change. 

Dependent variable: the one that you measure. 

For example, a scientist wants to find out whether a diet including oats makes a horse run fast...

When the neurone is stimulated, the Na+ channels open to allow influx of sodium ions down its electrochemical gradient. This makes the inside of the cell less negative. When threshold voltage (-55m...

inactive pathogens 

white blood cells produce antibodies 

these antibodies can be then quickly released whrn the immune system comes into contact with the live pathogen and destoy it 

Via osmosis, water travels down the concentration gradient to an area of lower water concentration and higher concntration of other substances.