Leaf growth patterns

Take students outdoors where there are several bushes and trees.
Show students how to identify the pattern of leaves on the branches of trees or bushes - look a little way down the stem where the leaves are more spaced out. In the winter, when deciduous leaves have dropped, look at the pattern of the leaf buds. Draw on paper/portable white board to make the pattern clear.

Alternate: one leaf emerges from one side of the stem, the next leaf along from the other side.
Opposite: two leaves emerge from the same place on the stem, but on different sides.
Whorled: several leaves emerge from the same place on the stem.

Identify the trees as they are studied.
I found this free Vancouver Street Trees iphone App which identifies trees on Vancouver streets by location.

Students can use a map to mark where they found each kind of pattern.
Or they can make a Venn diagram of the plants they find and the growth pattern(s) they exhibit.
Note that different students may see different patterns in the same tree. Sometimes the patterns are not clear, especially if the leaves are close together at the tip of the stem.

Extension: look at the patterns of the veins in leaves (opposite or alternate) and compare to the leaf growth pattern from the stem in the same plant.

Discussion:
Although leaves have different patterns in how they grow, all the patterns ensure that the leaves are well spaced out around the stem. This allows each leaf to catch as much light as possible for the plant.
Through evolution, leaves that spread their leaves out were at an advantage over other plants, and this adaptation persisted.

The actual mechanism for leaf growth patterns (called phyllotaxis) involves a molecule called auxin, and is a current area of research.
Auxin is constantly flowing up the stem towards the growing tip. Where there is a lot of auxin, a new leaf grows. Auxin is drawn towards where a new leaf is growing, and is pulled away from the surrounding areas, depleting them of auxin. This means, as more auxin moves up the stem, it collects in areas further away from the last leaf. Once enough auxin builds up a new leaf grows, on the other side of the stem from the last leaf.
See this webpage for a visual: https://www.researchgate.net/figure/Model-for-the-role-of-polar-auxin-t…

The growth of all living things is a result of their molecules flowing, interacting and changing, setting up patterns that we see in the structure of plants and animals e.g. patterns of ribs or body segments.