Unit 1 - Structural Units & Functions

Lesson 3: Functions of Leaves

The tree's leaves perform many important functions:

  • medicinal uses
  • food for people and animals
  • reduce noise pollution
  • they help reduce the Greenhouse Effect
  • provide shade
  • provide recreation
  • shelter for wildlife
  • remove pollutants from the air
  • perform photosynthesis
  • help with the process of transpiration and respiration
  • storage for food




Below, you can read about four important life processes performed by the leaves of the tree.







Photosynthesis
is a  biochemical reaction through which all green plants, including trees, make their food.
The process of photosynthesis requires water and carbon dioxide and then uses light energy from the sun to make glucose and oxygen.
The roots absorb the water from the ground, which is then transported to the leaves. Holes on the underside of the leaves, called stomata, allow the carbon dioxide to pass into the leaf.  The chlorophyll in the leaf absorbs the light energy needed to turn the raw ingredients of water and carbon dioxide into glucose and oxygen.
The oxygen made from photosynthesis is released back into the atmosphere through the leaf stomata, becoming a critical component of the air we breathe.
The glucose made during photosynthesis is used by the tree for energy to live, grow and repair.
Click here to watch a video on photosynthesis. 
Then take the quiz to test your knowledge.

Transpiration
is the process in which water, absorbed by the roots, is transported to the stomata, where it changes to vapor and is released into the atmosphere.  Transpiration is simply the evaporation of water from the leaves.

Click here to watch a video on the trees in the Amazon and transpiration.




In many ways, respiration is the opposite of photosynthesis.  Trees take the sugars, produced during photosynthesis, and oxygen in order to produce energy for tree growth.

Respiration in trees can be compared to inhaling air into our lungs; photosynthesis is compared to exhaling.




The leaves function as the food storage for the tree; short and long term. 

On a short term basis, during the daytime, sugars accumulate in the leaves; starch is then produced and stored in the chloroplasts.

At night, the starch is broken down into glucose and converted to transportable forms like sucrose.

It  has also been shown that food is stored in the leaves until they wither and die.  This food is exported to the stem before the leaf falls and is then used in the development of the next shoot.