Answer:Valves stop blood flowing backwards
Explanation: Valve are flags of tissue that control the direction of the blood in our heart.,it prevent the backwards flow of blood. valves regulate blood from flowing back into the atria.The right and left atrio-ventricular valves prevent blood from flowing backwards into atria. When the ventricle is full,the valve prevent backwards flow of blood.
Answer:
no.........................
If a lot of tryptophan is present, the operon will be repressed.
Under intermediate amounts of tryptophan, the change to stop codons would cause the ribosome to stall and therefore would mimic as if there were no tryptophan present.
If no tryptophan present, the operon would be maximally expressed.
a - True. The ribosome would always be stalled in the leader sequence - so this wouldn't matter. However, the operon would still be transcribed because the repressor would be active (remember Trp operon is controlled both by attenuation and repression). True as long as there's not much tryptophan to activate the repressor!
b- True - With no tryptophan the repressor isn't engaged and the ribosome is stalled in the leader sequence.
c- Matters about how much tryptophan is available. So True if there's lots of tryptophan available.
d- I would choose this one as all of the above could be true depending on the levels of tryptophan.
