Download photosynthesis - Teaching Biology Project

PHOTOSYNTHESIS
What is Photosynthesis?
Photosynthesis is the chemical change which happens in
the leaves of green plants. It is the first step towards
making food not just for plants, but ultimately for every
animal on the planet as well.
Photosynthesis needs:
•
•
•
•
chlorophyll (in chloroplasts of leaves)
carbon dioxide (from the air)
water (from the soil) (carried by the xylem)
sunlight energy
Photosynthesis produces:
• glucose (which can be stored as starch)
(transported around plant by phloem)
• Oxygen (by-product)
Formula for Photosynthesis:
Where does Photosynthesis take
place?
As you can see there are two kinds of mesophyll cells - palisade mesophyll
and spongy mesophyll. The mesophyll cells contain tiny bodies called
chloroplasts which contain a green chemical called chlorophyll.
Chlorophyll enables the light energy from sunlight to be converted into
chemical energy for the photosynthesis reaction.
Internal Structure of a leaf
Chloroplast
Electron Micrograph of a chloroplast
in the Mesophyll Cells of the Leaf
Leaf
tissue
Photosynthesis involves 2 steps: Both
steps take place in the Chloroplasts of
the mesophyll cells
Light Dependent Phase
•Light energy absorbed by chlorophyll.
•Water (H2O) is split, oxygen is
released and the hydrogen joins into a
hydrogen carrier molecule.
•Energy is released
Takes place in the Grana
(membranes) of the chloroplast
Light Independent Phase
•Hydrogen + Energy combine with carbon
dioxide to form carbohydrates in the form of
glucose
•Takes place in the stroma of the chloroplast
The Photosynthesis
Equation
6CO2 + 6H20 = C6H1206 + 602
(1 molecule of glucose)
It must be balanced
i.e. the same number of atoms on each side of the equation
Factors limiting photosynthesis
The speed at which photosynthesis takes
place depends on :
• Light
• Temperature
• Carbon Dioxide Level
Factors limiting Photosynthesis
• Without enough light a plant cannot photosynthesise very fast, even
if there is plenty of water and carbon dioxide. Increasing the light
intensity will make photosynthesis faster.
• Sometimes photosynthesis is limited by the level of carbon dioxide.
Even if there is plenty of light a plant cannot photosynthesise if it has
run out of carbon dioxide.
• Temperature can be a limiting factor too. If it gets too cold the rate
of photosynthesis will slow right down; equally, plants cease to be
able to photosynthesise if it gets too hot.
If you plot the rate of photosynthesis against the levels of these three limiting
factors you get graphs like the ones below.
Maximising Growth
• Understanding the factors that limit
photosynthesis enables greenhouse farmers to
maximise the conditions for plant growth. They
often use paraffin lamps inside the greenhouse
because burning paraffin produces carbon
dioxide as well as heat, and so makes
photosynthesis proceed faster. They may also
use artificial light to enable photosynthesis to
continue beyond daylight hours.
Day or Night?