Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth? Select the correct answer using the code given below.

Answer: (c) 1, 2 and 4 only

Volcanic action, respiration and decay all release CO₂; photosynthesis alone removes it.

Statement by statement

1. ✓ ADDS CO₂ Volcanoes release CO₂ from magma — the carbon cycle’s slow geological source.

2. ✓ ADDS CO₂ Most living cells (plants too) break down food and release CO₂.

3. ✗ REMOVES CO₂ Photosynthesis takes CO₂ from the air and fixes it into sugar — the opposite direction.

4. ✓ ADDS CO₂ Decomposers break down dead matter and release its carbon as CO₂ (or methane without oxygen).

The idea

Sort every process into one of two boxes. Does it put carbon dioxide into the air, or take it out? Only photosynthesis (and the ocean dissolving the gas) takes it out. Everything that breaks down or burns carbon compounds puts it in.

Into the air: respiration, decay, burning, volcanoes → Out of the air: photosynthesis, dissolving in sea water

The trap

Plants do release CO₂ (at night, by respiration), so “photosynthesis” can feel like a source. The process itself only absorbs it.

Also know

The carbon cycle has a fast part (plants, animals, air, surface ocean: years to decades) and a slow part (rocks, fossil fuels: millions of years; deep ocean: centuries to thousands of years). The largest store of carbon on Earth is in rocks such as limestone. Burning fossil fuel moves carbon from the slow part into the fast part.