As (a)_____ can not pass through the non polar lipid bilayer, they require (b)____to facilitate their transport across the membrane.

Answer

To solve the question, we need to fill in the blanks with appropriate terms related to the transport of molecules across the cell membrane.

### Step-by-Step Solution:

1. **Understanding the Cell Membrane Structure**: The cell membrane is primarily composed of a lipid bilayer, which has hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails. This structure creates a barrier for certain types of molecules.

2. **Identifying 'A'**: The question states that 'A' cannot pass through the non-polar lipid bilayer. This indicates that 'A' must be a type of molecule that is not compatible with the hydrophobic environment of the lipid bilayer.
- **Conclusion**: 'A' is a **polar molecule** (as polar molecules are hydrophilic and cannot easily pass through the hydrophobic lipid bilayer).

3. **Identifying 'B'**: The question mentions that 'A' requires 'B' to facilitate its transport across the membrane. Since polar molecules cannot pass through the lipid bilayer directly, they need assistance.
- **Conclusion**: 'B' is a **carrier protein** (as carrier proteins help transport polar molecules across the membrane through facilitated diffusion).

### Final Answer:
(a) **polar molecule**
(b) **carrier protein**

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