Well, the food is in the environment. I would like to compare it with how bacteriae feed (however my biology is quite rusty), that is, they engulf their food and they "digest" -- not the proper term, since there are no organs to do real digestion -- it.
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I think it's the second one or first one
Answer:
on channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.
The ability of cells to communicate through chemical signals originated in single cells and was essential for the evolution of multicellular organisms. In multicellular organisms, cells send and receive chemical messages constantly to coordinate the actions of distant organs, tissues, and cells. Cells can receive a message, transfer the information across the plasma membrane, and then produce changes within the cell in response to the message. Single-celled organisms, like yeast and bacteria, communicate with each other to aid in mating and coordination. Cellular communication has developed as a means to communicate with the environment, produce biological changes, and, if necessary, ensure survival.
Process of Electron Transport Chain (ETC), is a series of transferring from electron donors to their acceptors. It basically means a transfer from high energy molecule to a low-energy molecule. This process of extracting energy by transfer is classified as a chemical reaction and we see it is the path taken of cellular respiration (NADH) and FADH2) and in photosynthesis, NADPH. It starts with an electron, NADH and FADH2, when the electron donors release a proton gradient and it creates an imbalance. Think of it as a see-saw with one heavy person on one end and a lighter one on the other end. The protons actually attempt to defuse back across this see-saw of a membrane and it releases energy during the cross over which we call Chemiosmosis.
Autonomic nervous system (ANS) is the branch of the nervous system that provides unconscious control of basic body processes that is consists of two divisions; the sympathetic and parasympathetic. These two divisions have opposing effects on the internal organs they innervate. The Parasympathetic nervous system is the division that balances the actions of the sympathetic nervous system by slowing body processes, returning the body to homeostasis once a stressor has passed. The Sympathetic nervous system is the emergency system. Its major function is the fight-or-flight response in reaction to a threat. It speed-up key body processes to prepare the body for physical action.
