Unit 1 - Structural Units & Functions

Lesson 2: Leaves


All trees, coniferous or deciduous, share several structural similarities. 

They all have

  • leaves

  • reproductive structures

  • trunk and branches

  • roots

These structures and their functions will be described in more detail in this unit of the course.


Leaves perform a number of functions, such as respiration, food storage, and photosynthesis. Some of these functions are explained on the next page.
Leaf appearance can vary depending on whether a tree is deciduous or coniferous. 

Click on the headings below to read about deciduous and coniferous leaves.           

In general, deciduous trees have broad leaves that fall from the tree every autumn. The maple leaf is a familiar example of this type of leaf. If a deciduous tree lives in a cold climate, it will drop its leaves prior to winter.

Why do deciduous trees lose their leaves? This adaptation allows trees to better survive the cold temperatures and lack of available water. If the tree did not shed its leaves, the fluids inside the leaf would freeze and the leaf cells would be damaged.

Furthermore, the shedding of leaves allows the tree to conserve all available water. The large flat surface of broad leaves allows water to easily escape from the tree. Although the loss of water from the leaf is a normal process that occurs during the growing season, it is not desirable at times when all available water is frozen, and hence unavailable to the tree.



Not all deciduous trees live in cold climates. They also found in warm regions of the world where there is no cold winter. These trees still lose their leaves during the year, usually right before the onset of the dry season. By losing their leaves before the dry season, trees can better conserve their water and protect themselves from very high temperatures.
Coniferous trees have needle-like or scale-like leaves that typically remain on the tree year round. The small surface area of needles allows coniferous trees to survive in harsh climates by reducing moisture loss and protecting against damage from wind and heavy snow. Conifer needles also tend to have waxy coatings that help to further protect against water loss.

These water conservation adaptations of the coniferous trees are very important to survival in cold climates because during the winter, most water is frozen and unavailable to the tree.