Nervous System
<span>Respiratory System
</span><span>Circulatory System
</span><span>Digestive System
</span><span>Urogenital System
</span><span>Endocrine System
</span><span>Immune System</span>
Polar<span> molecules
water molecules have a weak, partial negative charge at one region of the molecule (the oxygen atom in water) and a partial positive charge elsewhere (the </span>hydrogen<span> atoms in water).The force of attraction is called a </span>hydrogen bond<span>.</span>
Lichens have been described as "dual organisms<span>" because they are symbiotic associations between two (or sometimes more) entirely different types of microorganism - a fungus (termed the mycobiont) a green alga or a cyanobacterium (termed the photobiont).
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