Active transport from outside to inside of molecules across a membrane requires :

Options

A. cyclic AMP
B. acetyl chlorine
C. lecithin
D. ATP

Answer

**Step-by-Step Solution:**

1. **Understanding Active Transport**: Active transport is a process that moves molecules across a cell membrane from an area of lower concentration to an area of higher concentration. This process requires energy because it is moving against the concentration gradient.

2. **Identifying the Energy Source**: In biological systems, the primary energy currency is adenosine triphosphate (ATP). Active transport mechanisms utilize ATP to provide the necessary energy to move molecules.

3. **Evaluating the Options**:
- **Cyclic AMP**: This is a secondary messenger involved in various cellular processes but does not directly provide energy for active transport.
- **Acetylcholine**: This is a neurotransmitter that plays a role in signal transmission but is not involved in the energy supply for active transport.
- **Lecithin**: This is a type of phospholipid that is part of cell membranes but does not provide energy for transport processes.
- **ATP**: This is the correct answer as it is the molecule that provides the energy required for active transport.

4. **Conclusion**: Therefore, the correct answer to the question is ATP, as it is essential for the active transport of molecules across a membrane.

**Final Answer**: ATP

---