Grades 3–5 · Organisms
How can a bulb grow new leaves after winter?
A true bulb is a short underground shoot surrounded by thick, fleshy leaf bases. Inside are a small growing bud and stored food. The bulb is living plant tissue, not just a seed with a large coat.
In the diagramA bulb stores resources around a budfood storegrowing budshort stemFleshy leaf bases supply early growth; roots take in water and minerals.
During the previous growing season, green leaves used light energy to make sugars. Some of that material was moved into the bulb and stored. After a resting period, the plant can use stored resources while new roots and leaves begin to grow.
A new shoot therefore does not need to make all its food before it can reach the light. Stored material helps supply early growth. Once the leaves unfold, they can make more sugars and help refill the store.
Light, temperature and the plant’s stage of growth help control the cycle. Many spring bulbs form a flower bud before the spring display. Roots still take in water and minerals, but soil is not the source of the light energy stored in the bulb’s food.
About this explanation
Starting knowledge: Know that leaves make sugars in light and plants have roots and shoots.
Sources
- University of Minnesota Extension — Planting bulbs, tubers and rhizomes