4.1. [cont] Biological molecules: DNA & Water

Biological molecules 

#4 is DNA

#5 is water

4. DNA

DNA is the molecule that carries genetic material in most organisms.

• two strands coiled together to form a double helix 
• each strand contains chemicals called bases 
• cross-links between the strands are formed by pairs of bases 
• the bases always pair up in the same way: 
• A with T
• C with G 

DNA double helix

5. Water

Water is a solvent in organisms.

• Mosts cells contain 75% water.
• Many substances move around a cell when they are dissolved in water.
• Many reactions take place in water.

• Digestion: 
• food can be digested ONLY in liquid form - enzymes need to be in water to catalyze reactions
• Excretion: 
• excretory products, like urea, are dissolved in water to dilute them --> allows for removal from body
• Transport systems 
• Bloodstream = plasma + cells. Plasma is 92% water and transports CO2, urea, digested food, hormones
• Plants:
• in xylem, water transports mineral ions
• in phloem, water transports sugars and amino acids for use or storage

Try this!

[source: workbook]

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