1. Plants and other autotrophs are
the producers of the biosphere
Photosynthesis nourishes almost all of the living world
directly or indirectly.
All organisms require organic compounds for energy
and for carbon skeletons.
Autotrophs produce their organic
molecules from CO2 and other inorganic raw materials obtained from the
environment.
Autotrophs
are the ultimate sure of organic compounds for all nonautotrophic
organisms.
Autotrophs
are the producers of the biosphere.
Autotrophs can be separated by the source of energy
that drives their metabolism.
Photoautotrophs
use light as the energy source.
Photosynthesis occurs in plants, algae, some other protists,
and some prokaryotes.
Chemoautotrophs
harvest energy from oxidizing inorganic substances,
including sulfur and
ammonia.
including sulfur and
ammonia.
Chemoautotrophy is
unique to bacteria.
unique to bacteria.
Autotrophs can be separated by the source of energy
that drives their metabolism.
Photoautotrophs
use light as the energy source.
Photosynthesis occurs in plants, algae, some other protists,
and some prokaryotes.
Chemoautotrophs
harvest energy from oxidizing inorganic substances,
including sulfur and
ammonia.
including sulfur and
ammonia.
Chemoautotrophy is
unique to bacteria.
unique to bacteria.
Heterotrophs live on organic
compounds produced by other organisms.
These organisms are the consumers of the biosphere.
The most obvious type of heterotrophs
feed on plants and other animals.
Other heterotrophs decompose and feed on dead organisms and on
organic litter, like feces and fallen leaves.
Almost all heterotrophs are completely dependent on photoautotrophs
for food and for oxygen, a byproduct of photosynthesis
2. Chloroplasts are the
sites of photosynthesis in plants
Any green part of a plant has chloroplasts.
However, the leaves are the major site of photosynthesis for
most plants.
There are about half a million chloroplasts per
square millimeter of leaf surface.
The color of a leaf comes from chlorophyll, the green pigment in the chloroplasts.
Chlorophyll plays an important role in the
absorption of light energy during photosynthesis.
Chloroplasts are found mainly in mesophyll cells forming the tissues in the interior of
the leaf.
O2
exits and CO2 enters the leaf through microscopic pores, stomata, in the leaf.
Veins deliver water
from the roots and
carry off sugar from
mesophyll cells to
other plant areas.
from the roots and
carry off sugar from
mesophyll cells to
other plant areas.
A typical mesophyll cell has 30-40
chloroplasts, each about 2-4 microns by 4-7 microns long.
Each chloroplast has two membranes around a central aqueous
space, the stroma.In the stroma are
membranous sacs,
the thylakoids.
membranous sacs,
the thylakoids.
These have an internal
aqueous space, the
thylakoid lumen or
thylakoid space.
aqueous space, the
thylakoid lumen or
thylakoid space.
Thylakoids
may be stacked
into columns called grana.
into columns called grana.