Substances (A)_____ in lipids diffuse through the membrane faster while substances that have a (B)____find if difficult to pass through the membrane.

Answer

To solve the question, we need to fill in the blanks with the appropriate terms based on the properties of substances in relation to cell membranes.

### Step-by-Step Solution:

1. **Understanding the Cell Membrane Composition**:
- The cell membrane is primarily composed of lipids, specifically phospholipids, which create a bilayer. This structure is crucial for the selective permeability of the membrane.

2. **Identifying Substance (A)**:
- Substances that can easily diffuse through the lipid bilayer are typically those that are lipid-soluble. These substances can dissolve in the lipid layer and pass through the membrane without the need for assistance.
- Therefore, for blank (A), we can fill it with **"lipid-soluble"**.

3. **Identifying Substance (B)**:
- In contrast, substances that have difficulty passing through the membrane are usually hydrophilic. Hydrophilic substances are water-soluble and cannot easily cross the lipid bilayer due to their polarity.
- These substances often require specific transport mechanisms, such as facilitated diffusion, to move across the membrane.
- Thus, for blank (B), we can fill it with **"hydrophilic"**.

4. **Final Answer**:
- The complete sentence would read: "Substances (A) **lipid-soluble** in lipids diffuse through the membrane faster while substances that have a (B) **hydrophilic** find it difficult to pass through the membrane."