Why are cactuses spiky?
For grown-ups: the science
Cactuses have spikes because the spikes help them save water, shade their stems, and protect them.
In most cacti, spines are modified leaves. Reducing leaf surface area lowers water loss through transpiration. Photosynthesis happens mainly in the green stem, which commonly stores water; spines can provide shade, reduce airflow near the surface, and deter many herbivores.
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Transcript
A cactus stands in a hot, dry desert. Why does it have so many spikes?
Most cactus spikes are leaves that changed shape over a very long time. Tiny, narrow spikes lose much less water than wide leaves.
The cactus's thick green stem catches sunlight and makes food. It also stores water for dry days.
Spikes make a little shade on the stem. They can also help keep hungry animals from taking a bite.
So cactus spikes help save water, make shade, and protect the cactus. What a smart way to live in a dry place!