Oxygen comes out of the stomata during photosynthesis through the process known as

Step 1: Analyze the question During photosynthesis, oxygen is produced as a by-product inside the leaf. The question asks how it leaves through the stomata.

Step 2: Explain the concept

• Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration, with no energy needed.
• Osmosis is the movement of water across a semi-permeable membrane, so it does not apply to a gas.
• Transpiration pull is the force that draws water up the xylem as water vapour is lost from leaves. It is about water, not oxygen.
• Active transport moves substances against a concentration gradient and uses energy (ATP). Gas exchange in leaves does not need this.

Step 3: Apply it to the leaf

1. Photosynthesis in the chloroplasts of the mesophyll cells produces oxygen.
2. The concentration of oxygen inside the leaf becomes higher than in the outside air.
3. Oxygen moves down this concentration gradient through the open stomata into the atmosphere.
4. No energy is used, and the movement is a passive process: diffusion.

Step 4: Answer The correct option is A. diffusion.

Exam tip: Remember that gases move by diffusion. Whenever a question is about oxygen, carbon dioxide, or water vapour moving through stomata, think diffusion. Osmosis is only for water across membranes, and active transport needs energy against a gradient.