Transporting substances across a membrane from an area of lower concentration to an area of higher concentration requires -

Options

A. energy
B. phospholipid
C. Diffusion
D. Facilitated diffusion

Answer

To solve the question, "Transporting substances across a membrane from an area of lower concentration to an area of higher concentration requires -", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Concentration Gradient**:
- When substances move from an area of lower concentration to an area of higher concentration, they are moving against the concentration gradient. This is an important concept in understanding how substances are transported across membranes.

**Hint**: Remember that moving against the concentration gradient is not a natural process and requires energy.

2. **Identify the Type of Transport**:
- The movement of substances from low to high concentration is classified as active transport. Active transport is different from passive transport, where substances move from high to low concentration without the need for energy.

**Hint**: Active transport requires energy input, while passive transport does not.

3. **Recognize the Role of Energy**:
- Active transport requires energy, typically in the form of ATP (adenosine triphosphate). This energy is necessary for the movement of substances against their concentration gradient.

**Hint**: Think of ATP as the "fuel" that powers active transport processes.

4. **Evaluate the Other Options**:
- The question also mentions phospholipids, diffusion, and facilitated diffusion.
- **Phospholipids** are components of the cell membrane but do not provide energy for transport.
- **Diffusion** is a passive process where substances move from high to low concentration.
- **Facilitated diffusion** is also passive and involves the movement of substances through a membrane protein, again from high to low concentration.

**Hint**: Distinguish between active and passive processes to eliminate incorrect options.

5. **Conclude the Correct Answer**:
- Based on the understanding that transporting substances from lower to higher concentration requires energy, the correct answer is **energy**.

### Final Answer:
Transporting substances across a membrane from an area of lower concentration to an area of higher concentration requires **energy**.