From Molecules to Organisms: What Plants Need to Grow
What plants need
Plants need light, water, air (carbon dioxide), and small amounts of dissolved minerals to grow well. Roots anchor the plant and absorb water and minerals; the stem carries water upward and food around the plant; leaves are the main places where light is captured. Flowers and cones are for reproduction, not feeding.
Where a plant’s mass comes from
The biggest trap in this standard is soil. A plant does not eat soil. Careful measurements show a plant in a pot can gain far more mass than the soil loses. The carbon in a tree’s wood came from carbon dioxide in the air, and the hydrogen came from water. Soil supplies minerals and support, which is why a plant in poor soil looks unhealthy even though soil is not its food.
Seeds and early growth
A seed contains stored food, so a seedling can sprout in the dark for a short time. It cannot stay healthy without light: it becomes pale, weak, and stretched out. A question claiming a plant “grew well” in a dark closet is a trap.
Worked example
Two identical plants sit by a window; one is watered and one is not. Predict and justify: the unwatered plant wilts because water carries materials through the plant and keeps cells firm. If instead both are watered but one sits in a closet, the difference is light energy used to make food, not water.
Rule of thumb
When asked why a plant grew or failed, check light, water, air, and minerals, then name which one changed.