Answer:True
Explanation:
Nerve impulse must reach a certain threshold in a neuron before action potential can be generated to intiate conduction of action potential.
Therefore if mutiple impulses are generated and these are not upto thresholds , no matter how strong the stimulI are-NO ACTION POTENTIAL WILL BE GENERATED.
THIS IS ALL OR NONE PRINCIPLE
The all or none hypotheses can be best explain with flushing of the water closet after using it. If required volume of water is not pumped into the water closet storage above, no matter how long the handle is push, FLUSHING WILL NOT TAKE PLACE.Thus the threshold volume of water must be met.
C) As the trait will then pass to others without it and through natural selection will become abundant
Answer:
The answer is A.
Explanation:
B) Nucleotides and amino acids can act as extracellular signal molecules:
ATP is made of adenosine (a type of nucleotide) and used in cell signalling called "purigenic signalling" and amino acids are also used as signal molecules.
C) Some signal molecules are transmembrane proteins:
Transmembrane acts as receptors for smaller signal molecules so this can also be accepted as true.
D) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription:
That is also true, some of the hormones can cross lipid membrane of the cells and bind directly to the intracellular (inside-of-a-cell) proteins.
Lastly; dissolved gasses such as nitric oxide can activate proteins such as guanylyl cyclase so this choice is <u>false</u>.