Make Like a Tree and Leaf

This production of oxygen enables life on earth as we know it. What do leaves do? H20 + CO2 + light CH2O + O2 Leaves use light energy to break apart water and carbon dioxide molecules and recombine them as sugar and oxygen. This production of oxygen enables life on earth as we know it.

Plant matter is basically derived from thin air! What do leaves do? H20 + CO2 + light CH2O + O2 The sugars produced by photosynthesis are converted into all plant tissues, from leaves to flowers to wood. Plant matter is basically derived from thin air!

How do they do it? Light H2O H2 + O Each chlorophyll has 4 nitrogens and a magnesium at its center H2 + O The chlorophyll molecule acts like a net, catching photons. In the first of two steps, the photon energy cleaves a water molecule into H2 and O by charge-separation reactions.

How do they do it? CO2 H2 + O “Rubisco” enzyme CH2O + O2 (Ribulose-1,5-bisphosphate carboxylase/oxygenase) CH2O + O2 In the second step, the cleaved water molecule is combined with CO2 to produce simple sugars and oxygen. This is done by the Rubisco enzyme in an extremely complex process called the Calvin cycle.

(Ribulose-1,5-bisphosphate carboxylase/oxygenase) How do they do it? CO2 H2 + O “Rubisco” enzyme (Ribulose-1,5-bisphosphate carboxylase/oxygenase) CH2O + O2 The oxygen is respired as a waste product and the sugars are incorporated as the building blocks of all plant tissue.

Where is chlorophyll within the leaf? Leaf cross section Plant cell Chlorophyll is contained in organelles called chloroplasts within plant cells. Chloroplasts have their own DNA, because...

Where did chlorophyll originate? …chlorophyll is thought to have evolved in cyanobacteria, and 1-2 billion years ago a cyanobacterium was engulfed by an amoeba (becoming a chloroplast), resulting in what we now call algae. Algae is the ancient ancestor of all land plants.

Why are leaves green? Chlorophyll mainly absorbs light in the red and blue spectra, and reflects light in the green spectrum. Plants with red leaves have an abundance of pigments (anthocyanins) which mask the underlying green color.

How do leaves regulate transpiration? Stoma Leaves perform a balancing act with water. Some is needed for photosynthesis, and some is needed for cooling. This is regulated by stomata, which are microscopic variable apertures. They also control CO2 and O2 exchange.

How do leaves regulate transpiration? Conifer stomata If a leaf is drought stressed it closes its stomata, but then it cannot photosynthesize. Plants adapted to wet habitats (western hemlock) have poor stomatal control and cannot survive dry climates.

How do leaves regulate transpiration? Plants adapted to hot and dry habitats (such as cacti) open their stomata at night and finish photosynthesis by day. Consequently, cactus tissue is sour in the morning and sweet in the evening.

How do leaves know when to drop? In deciduous trees, changing environmental conditions (cold, shortened days, drought, insect attack, etc.) activate enzymes that first form protective layer on the main stem, then dissolve cell walls at the base of the leaf. Coniferous trees shed and re-grow needles continuously.

What causes fall colors? Before dropping leaves, plants “resorb” nutrients. Because chlorophyll is rich in nitrogen, it is broken down and saved by the plant, leaving other pigments (red anthocyanins and yellow carotenes) which were always there but masked by the green of the chlorophyll.

Questions?