When cells communicate by the signaling process, one cell produces a signaling molecule that must be received by the signal receptor on or in the responding cell. Signaling molecules are often called ligands, a general term for molecules that bind specifically to other molecules (such as receptors).
The heart and the arteries of a person, both contracts to pump the blood throughout the body. The aorta, which is the largest artery of the human body, pumps the blood from the heart to the entire body of a person. The oxygen-rich blood is pumped out of the left ventricle when its contraction into the aorta, from where it is transported to the whole body.
Hence, the given statement is true.
Answer: alternative A
Explanation: The deeper the layer in water, the <u>less light reaches it</u>. In deeper layers, therefore, it becomes difficult, if not impossible, to photosynthesis to occur. Having in mind that <u>phytoplankton and photosynthetic organisms depend on photosynthesis to survive,</u> they won't appear in such dephts.
Celluar respiration breaks down glucose and photosynthesis makes glucose.
