You have still failed to understand the difference between the artificial leaf and the living body containing soul. Their functions are different. A living body grows in size, whereas the artificial leaf will not grow. They are two absolutely different things and cannot be compared.
Basic property of nature is that an activity of some form can be produced by potential difference. If an object is taken to a height, its gravitational potential increases and it starts moving downwards. Its activity stops when the energy given to it is dissipated in nature due to resistive forces. In the absenece of the resistive force, the activity will continue forever.
If an electric potential is given to an electric cell, it amounts to having given enrgy to the charge in it and will work till that energy is consumed.
If sound energy is created, it starts propagating in all directions and due to resistive forces in the collisions of air molecules will eventually die down.
Thus, all processes occurring in nature need generation of some type of potential difference which need to be created.
In the living body also, some form of potential difference is created which does the job of making the body grow by multiplication of the cells it is made of. So far scientists have not been successful in creating a living body. Recently, there was a news item that scientists were successful in creating life in a test tube using non-living chemicals. If this is true, eventually it will pave a way for understanding what is soul that produces living things.
Leaving aside the controversy of existence of some super human being called God, existence of soul as some form of potential difference in the body that does the job of growing the body and providing energy to its brain which is an electronic circuit for the living body to function cannot be denied.
Body does not keep on growing indefinitely. A person keeps growing upto some age and then lives much longer thereafter. I will try to explain this with the analogy of gravitational potential. If a ball is released from the height along the inclined plane, it keeps on going down. This can be compared to the growth of living things. But once it reaches the level ground, it continues to move forward with the velocity gained and finally stops when its energy is used up in overcoming resistance. In the same way, body grows upto a point and thereafater continues to live due to the gained momentum till its energy is used up in overcoming natural resistance.
In Yogas, its is claimed that length of life is measured not in terms of years, but in terms of respirations. Their theory is that if you conserve respirations, you can live longer. This is something like a scientific hypothesis.
All I have described above can be considered scientific hypothesis. There are many steps after the hypothesis to prove it as theory confirmed with experiments and finally a law. In science, there is no absolute truth. Scientists continuously strive to find truth and that is a never ending process.
To answer your querry in additional details:
Yes, the job of the soul is to give life to the body and brain and it is present in all living things like plants too. Soul is the biological potential difference like gravitational potential difference, electric potential difference, etc.
Leaf which the scientists created will not grow as it does not have soul.
I do not understand your querry "soul is already there in body". When I compared living body to a battery and soul to its voltage, one can say that voltage is already there in the battery. One can also say that battery was given the voltage by recharging. (True only for rechargeable battery). Human body is like a battery which is not rechargeable.