The structure in the cell that controls the movement of substances in and out of the cell is the

Step 1: Analyze the question The question asks which cell structure controls what enters and leaves the cell. The key phrase is "in and out of the cell", meaning the boundary between the cell's inside and its outside.

Step 2: Explain the concept The cytoplasmic membrane (also called the cell membrane or plasma membrane) surrounds the cell. It is selectively permeable, also called partially or differentially permeable. This means it lets some substances pass freely, such as water, oxygen and carbon dioxide, and restricts others. Substances cross it by:

• Diffusion
• Osmosis
• Active transport

Step 3: Check each option

• A. Cytoplasmic membrane: It forms the outer boundary of the cell and controls the movement of substances in and out. ✔
• B. Nuclear membrane: It controls movement between the nucleus and the cytoplasm only, not in and out of the whole cell. ✘
• C. Protoplasm: This is the whole living content of the cell (cytoplasm and nucleus). It is not a controlling barrier. ✘
• D. Endoplasm: This is the inner, more fluid part of the cytoplasm. It has no control over substances entering or leaving the cell. ✘

Step 4: Answer The correct option is A. cytoplasmic membrane.

Exam tip: Match the membrane to the boundary it guards. The cell membrane guards the cell, the nuclear membrane guards the nucleus. If a question says "in and out of the cell", think cell membrane and selective permeability.