Unit: Leaves The Energy Powerhouse of the Plant

“…tubular, needlelike, feathery, cupped, sticky, fragrant, smooth or waxy…” Leaves are diverse and are adapted for their needs and growth

Some Leaf statistics… A maple tree with 100,000 leaves has a combined surface area greater than the size of 6 basketball courts Globally, leaves produce more than 200 billion tons of sugar a year; that’s 2200 lbs X 1,000,000,000… WOW!

Structure & function of leaves Leaf Structure – the wide, flat plant organ designed to absorb as much sunlight as possible Leaf Function - to absorb light and produce sugar through photosynthesis

Photosynthesis = “light” and “putting together” Plants use light energy to put carbon dioxide (from the air) and water (gathered from the roots) to make sugar Oxygen is also given off The sugar produced by photosynthesis is used for energy to make other plant tissues Photosynthesis is a series of biochemical reactions that occurs in the presence of chlorophyll, the green pigment that makes leaves green!

Chloroplasts - the plant cell organelle that is the location for photosynthesis “ Energy –capturing solar cells and sugar factories”

The “raw materials” for photosynthesis enter the plant through these locations: Stomates – tiny holes on the underside of leaves that let carbon dioxide enter and water exit Roots – the site of water absorption Stems – the site where water and minerals travel from the roots to the leaves via Xylem – ‘tubes’ that bring water and minerals from the roots to the leaves Phloem – ‘tubes’ that bring food (sugar) from the leaves to all plant parts

How does Photosynthesis work? …remembering the Visible Spectrum… (ROYGBJ) Color is seen because it is reflected by a pigment, any substance that absorbs light So, green leaves absorb all the other colors, but reflects the green wavelength we are able to see

Leaf Transpiration “the loss of water vapor” from the plant Water lost contributes to the Water Cycle Plants wilt when too much water is lost by transpiration or when there is not enough water absorbed by the roots During transpiration, water moves out of the plant through its stomates (plural: stomata)

Why leaves change color in the Fall… Spectacular autumn foliage is not all about “leaf peeping”! Chlorophyll, the pigment needed for photosynthesis that gives leaves their green color, stops being produced The withdrawal of nitrogen and phosphorus, needed for photosynthesis, are taken from the leaves and used for winter storage in twigs and branches while they are dormant Colors seen in the fall are no longer hidden by the chlorophyll’s green color

Bright and beautiful colors are the result of chlorophyll production“shutdown ” Carotenoid pigments – yellow + orange, seen in maples Anthocyanin pigments – pink, red and purple, seen in sugar and red maples, sassafras, sumac trees Tannins – brown, seen in oaks, beech, and other trees

Weather conditions affect fall colors Warm and sunny days with cool nights promote red autumn colors Freezing, rainy, cloudy weather conditions reduce leaf color intensity “leaf peepers” look for “peak” colors and foliage reports to plan trips to the New England States Check out for a look at the foliage travel report!

Leaf Abscission means leaves fall in Deciduous Trees Enzymes in leaves cause cell death at the base of leaf petioles The xylem still brings water to the leaf, but… The phloem pathway for sugar flow is blocked as photosynthesis stops for the winter The abscission zone forms a protective layer called suberin, which protects the tree from insects, disease, and dehydration The abscission zone is the site of leaf “fall”, and the leaf’s petiole separates from the stem

Falling leaves leave “Sleeping trees” - Senescence Senescence is the breakdown of cell contents and membranes – for trees, this happens at the abscission zone Leaves falling let trees enter a winter dormant period while the trees rest Fallen leaves on the forest floor decompose The soil is “restocked with nutrients” and becomes food for soil organisms like worms and bacteria

Strange, beautiful and functional leaves Tendrils are string-like leaves that “help the plant climb or support weak stems” Thorns and spines keep plants from losing water and protects them from hungry animals (except Eeyore, the thistle eater) Succulent leaves store water Reproductive leaves have “babies” – plantlets with roots and leaves Insect-Trapping leaves include the popular Venus Fly Traps and Pitcher Plants