How many cells are there in the human body?
The average human body contains around 30 trillion cells. However, depending on age, height, weight, health, environment and other factors, the number may vary from 10^12 to 10^16.
What are the main characteristics of human cells? Explain to me how they have evolved and what kind of differences there are in comparison with the cells of other living beings.
Here are the main points I would highlight regarding human cells and how they differ from cells of other organisms:

Human cells have evolved to be highly specialized to carry out specific functions in the body. Some key types of human cells and their functions include:
- Red blood cells: Carry oxygen throughout the body
- White blood cells: Important for immune function and fighting infection
- Neurons: Transmit signals in the nervous system
- Muscle cells: For movement and contraction
- Epithelial cells: Line the outer surfaces of organs and blood vessels

Compared to plant and animal cells, human cells have unique characteristics resulting from billions of years of evolution. Some key differences include:
- Human cells do not have cell walls made of cellulose like plant cells
- Human cells are more structurally complex with many specialized organelles and components to support complex life functions
- Human cells have a more advanced nucleus and genetic material allowing for greater control over cell processes
- Human cells have tighter regulation over growth and division to maintain health and prevent diseases like cancer

I hope this helps provide an overview of human cells and how they differ from cells of other living organisms. Please let me know if you would like more details or have any other questions. I'm happy to provide additional information or resources for learning more about this topic.