11.1. Overview of photosynthesis
In plants, energy in light is absorbed by chlorophyll and then transferred into
the chemical energy of the molecules formed during photosynthesis. These
molecules are used by the plant to produce ATP during respiration.
Non-photosynthetic organisms feed on the molecules produced by plants and
then also use them to make ATP during respiration.
Site of photosynthesis:
The leaf is the main photosynthetic structure in eukaryotic plants. Chloroplasts
are the cellular organelles within the leaf where photosynthesis takes place.
Structure of the leaf
Leaves are adapted to bring together the 3 raw materials of photosynthesis
(water, carbon dioxide and light) and remove their products (oxygen and
glucose).
These adaptations include…
1. Large surface area - to absorb as much sunlight as possible.
2. An arrangement of the leaves on the plant that minimises overlapping
and so avoids the shadowing of one leaf by another.
3. Thin - as most light is absorbed in the first few micrometres of the leaf
and the diffusion distance for gases is kept short.
, 4. Transparent cuticle and epidermis - to allow light through to the
photosynthetic mesophyll cells beneath.
5. Long, narrow upper mesophyll cells packed with chloroplasts that collect
sunlight.
6. Numerous stomata for gaseous exchange - so that mesophyll cells are
only a short diffusion pathway from one.
7. Stomata that open and close in response to changes in light intensity.
8. Many air spaces in the lower mesophyll layer to allow rapid diffusion in
the gas phase of carbon dioxide and oxygen.
9. A network of xylem that brings water to the leaf cells, and phloem that
carries away the sugars produced during photosynthesis.
An outline of photosynthesis
Overall equation:
6CO2 + 6H2O →→→→ C6H12O6 + 6O2
LIGHT
, Photosynthesis is a complex metabolic pathway involving many intermediate
reactions.
Photosynthesis definition: the process of energy transferral in which some of
the energy in light is conserved in the form of chemical bonds.
There are three main stages to photosynthesis:
1. CAPTURING OF LIGHT ENERGY: by chloroplast pigments such as
chlorophyll.
2. THE LIGHT-DEPENDENT REACTION (LDR):
● Some of the light energy absorbed is conserved in chemical bonds.
● During the process an electron flow is created by the effect of light
on chlorophyll, causing water to split (photolysis) into protons,
electrons and oxygen.
● The products are reduced NADP, ATP and oxygen.
3. THE LIGHT-INDEPENDENT REACTION (LIR): in which these protons^
(hydrogen ions) are used to produce sugars and other organic molecules.
Structure and role of chloroplasts in photosynthesis
In eukaryotic cells, photosynthesis takes place within the chloroplast
organelles. These are typically disc-shaped, 2-10μm long, and 1μm in diameter.
In plants, energy in light is absorbed by chlorophyll and then transferred into
the chemical energy of the molecules formed during photosynthesis. These
molecules are used by the plant to produce ATP during respiration.
Non-photosynthetic organisms feed on the molecules produced by plants and
then also use them to make ATP during respiration.
Site of photosynthesis:
The leaf is the main photosynthetic structure in eukaryotic plants. Chloroplasts
are the cellular organelles within the leaf where photosynthesis takes place.
Structure of the leaf
Leaves are adapted to bring together the 3 raw materials of photosynthesis
(water, carbon dioxide and light) and remove their products (oxygen and
glucose).
These adaptations include…
1. Large surface area - to absorb as much sunlight as possible.
2. An arrangement of the leaves on the plant that minimises overlapping
and so avoids the shadowing of one leaf by another.
3. Thin - as most light is absorbed in the first few micrometres of the leaf
and the diffusion distance for gases is kept short.
, 4. Transparent cuticle and epidermis - to allow light through to the
photosynthetic mesophyll cells beneath.
5. Long, narrow upper mesophyll cells packed with chloroplasts that collect
sunlight.
6. Numerous stomata for gaseous exchange - so that mesophyll cells are
only a short diffusion pathway from one.
7. Stomata that open and close in response to changes in light intensity.
8. Many air spaces in the lower mesophyll layer to allow rapid diffusion in
the gas phase of carbon dioxide and oxygen.
9. A network of xylem that brings water to the leaf cells, and phloem that
carries away the sugars produced during photosynthesis.
An outline of photosynthesis
Overall equation:
6CO2 + 6H2O →→→→ C6H12O6 + 6O2
LIGHT
, Photosynthesis is a complex metabolic pathway involving many intermediate
reactions.
Photosynthesis definition: the process of energy transferral in which some of
the energy in light is conserved in the form of chemical bonds.
There are three main stages to photosynthesis:
1. CAPTURING OF LIGHT ENERGY: by chloroplast pigments such as
chlorophyll.
2. THE LIGHT-DEPENDENT REACTION (LDR):
● Some of the light energy absorbed is conserved in chemical bonds.
● During the process an electron flow is created by the effect of light
on chlorophyll, causing water to split (photolysis) into protons,
electrons and oxygen.
● The products are reduced NADP, ATP and oxygen.
3. THE LIGHT-INDEPENDENT REACTION (LIR): in which these protons^
(hydrogen ions) are used to produce sugars and other organic molecules.
Structure and role of chloroplasts in photosynthesis
In eukaryotic cells, photosynthesis takes place within the chloroplast
organelles. These are typically disc-shaped, 2-10μm long, and 1μm in diameter.
