Download Photosynthesis

Photosynthesis
Chloroplasts




Chloroplasts are the sites of
photosynthesis.
All green parts of a plant, including green
stems and unripened fruit, have
chloroplast, but leaves are the major site
of photosynthesis in most plants.
500,000 chloroplasts per square
millimeter of leaf surface.
Plants are the primary producers of food
for all land animals.
Chloroplasts



It is the light energy absorbed by
chlorophyll that drives the synthesis of
food molecules in the chloroplast.
Chloroplasts are found mainly in the
cells of mesophyll, the tissue in the
interior of the leaf.
Carbon dioxide enters the leaf, and
oxygen exits, by way of microscopic pores
called stomata.
Why green???

Plants are green because the chlorophyll
pigments inside the chloroplast organelles
absorb most all wavelength of visible light
except that in the 510nm to 550nm
range.
In the Presence of Light

In the presence of light, the green
parts of plants produce
carbohydrates (glucose) and oxygen
from carbon dioxide and water.
Light Reactions


We can simplify the equation by indication
only the net consumption of water:
6 CO2 + 6 H2O + light energy  C6H12O6 + 6 O2
Light Reactions cont.

The two stages of photosynthesis
are known as the LIGHT
REACTIONS (the photo part of
photosynthesis) and the CALVIN
CYCLE (the synthesis part)
Light reaction: Take-up water and
produces oxygen
 Dark reaction (Calvin cycle): Takes-up
carbon dioxide and makes glucose

Calvin Cycle (dark reactions)




It is in the dark reactions that plants make
glucose.
The glucose made will be used to power the
metabolism of the plant, growth, etc.
Some glucose will be used to make cellulose,
another carbohydrate that is used for structural
support.
What glucose is not used, will be stored as
amylose / amylopectin (plant starch)


Interesting to note that humans have evolved the
capacity to produce and enzyme in saliva called
amylase.
Remember that in animals, glucose consumed but
not metabolism will be stored as lipids (FAT) for
later energy needs.
Edible starches are found in a very diverse array of plants, primarily in
storage organs such as tubers and seeds. Starch is synthesized in
specialized plastids known as amyloplasts and also in chloroplasts.
Starch is a major component of the "average" dietary intake of man
and animals. Calculated in calories, about four-fifths of the worlds
food is provided by three grain crops (maize, wheat and rice) and
three tuber crops (potato, yam and cassava). On a dry-weight basis
starch is by far the major component of the edible portions of these
crops, providing between 60% to 90% of the dry weight. As well as its
uses in nutrition, starch is also an important component in
manufacturing a wide range of industrial products such as paper,
textiles and building materials. Furthermore, chemically modified
starch and starch derivatives are used widely throughout industry.
World-wide, maize represents the major commercial source of starch,
whereas wheat starch is of only minor significance in the starch
industry.
Photosynthesis is not exclusively a plant kingdom chemical
process to make organic compounds for life…
Photosynthetic Protists
Photosynthetic Bacteria (Cyanobacteria)
The End