Answer:
cell wall provides protection and structural support
Argyroneta aquatica because it is the only species of spider that lives entirely uder water
Answer:
The pressure differences on either side of the valve.
Explanation:
The heart valves open and close passively because of pressure differences on either side of the valve. When pressure is greater behind the valve, the leaflets are blown open and the blood flows through the valve. However, when pressure is greater in front of the valve, the leaflets snap shut and blood flow is stopped.
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