Answer:
Relative velocity simply means velocity relative to a certain observe point, in this case, the river shore.
This is a type of complex movement; a boat is moving with a certain velocity, let's say 8 m/s. However, the river this boat moves on also has its velocity, let's say 2 m/s. Since the shore isn't moving, the velocity of the boat relative to the shore will be simple resultant velocity of the boat's and the river's velocities.
Let's illustrate this with two examples:
1) if the boat is moving downstream both are moving in the same direction, so the resultant will be 8 m/s + 2 m/s = 10 m/s.
So, any spectator looking at the boat from the shore will think its velocity is 10 m/s, when in reality it's 8 m/s.
2) if the boat is moving upstream, these two velocities have opposite directions, so the resultant will be 8 - 2 = 6 m/s
So, as a short summary, relative speed is an object's speed in regard to another chosen referent point.
Answer:
1. Signaling molecule
2. Signaling receptors
Explanation:
Hormones, growth factors, neurotransmitters, etc. serve the function of signaling molecules for cells. These molecules are released by one cell and bind to the receptors present on/in the target cells to elicit the desired response. Thereby, the signaling molecules serve in cell-cell communication.
For example, insulin hormone synthesized and released from beta cells of pancreas binds to its cell surface receptors present on the surfaces of liver cells and muscle cells to stimulate the uptake of the glucose from the blood.
Likewise, neurotransmitters released from the presynaptic neuron bind to receptors present on the membrane of postsynaptic neuron and serve to carry the nerve impulse to the postsynaptic neuron.
The answer is A. ecology
Hope this helps!