Download Photosynthesis

Photosynthesis
Light Energy
transduction
Chemical Energy (e.g. glucose)
-
Only photosynthetic organisms can do this (e.g. plants)
-
They are the ultimate source of chemical energy for all living organisms: directly or
indirectly.
Autotrophs are organisms, which can make their own food.
Hetrotrophs are organisms that need to eat other organisms.
Photosynthesis does not occur at night.
Carbon Dioxide
+
Water
light
chlorophyll
Glucose
+
Oxygen
6CO2
+
H2 O
light
chlorophyll
C6H12O6
+
6O2
Leaf structure in relation to photosynthesis
midrib
enlarged section
epidermal cell
waxing
cuticle
palisade cell
chloroplast
xylem vessel
mesophyll cell
phloem sieve tube
air space
guard cell
Order in leaf:
Waxing cuticle
wax layer – transparent to let light through – reduces water
loss.
Upper epidermis
for protection and structure. It is relatively transparent.
Palisade layer
tightly packed to stop light passing. Contain lots of chloroplasts
to make photosynthesis most efficient.
Spongy mesophyll layer
lets oxygen leave and CO2 enter and leave. Some
photosynthesis takes place but not a lot.
Lower epidermis
guard cell and stomata (pores) – allow gas exchange and water
loss.
Vein
composed of two layers.
Xylem takes water from roots to the leaf for photosynthesis.
Phloem takes products of photosynthesis around the plant.
Leaves are well adapted for the task of photosynthesis for a number of reasons:
1.
Their broad, flat shape offers a large surface area for absorbing light and CO2
2.
Most leaves are thin so gas diffusion is rapid.
3.
Air spaces in the spongy mesophyll layer allow good diffusion of gas.
4.
There are many stomata in the lower surface of he leaf, which allow the
exchange of O2 and CO2 with air outside the leaf.
5.
The palisade cells are tightly packed with chloroplasts and they have a tall
cylindrical shape. This allows the maximum amount of light to be trapped by the
cells.
6.
The veins, which contain xylem and phloem, supply the leaf cells with water and
mineral salts and they remove the products of photosynthesis.
7.
The cells of the upper epidermis lack chloroplasts so the maximum amount of
light passes through to the palisade cells beneath.
8.
Leaves tend not to overlap each other so that they can all get maximum sunlight.
9.
Leaves move so that they get maximum light.
Aerobic Respiration
Glucose
+
Oxygen
Carbon Dioxide
+
Water +
Energy
C6H12O6
+
6O2
6CO2
+
6H2O +
36ATP
Bicarbonate indicator (used to test for levels of CO2)
Yellow
more
CO2
Red
less
CO2
Exposed to daylight
A
B
C
D
Daylight excluded
Elodea (pond plant) only
Snail only
Elodea and snail
Control (nothing except solution)
Tube
A
B
Colour change
pale red dark red
pale red yellow
C
pale red
pale red
D
E
F
pale red
pale red
pale red
pale red
yellow
yellow
G
pale red
yellow
H
pale red
pale red
Purple/Dark Red
E
F
G
H
Elodea (pond plant) only
Snail only
Elodea and snail
Control (nothing except solution)
Explanation
Photosynthesis as there is daylight – less CO2
Aerobic respiration – snail has produced CO2
CO2 produced by snail is used by plant and O2 produced by
plant is used by snail
Nothing occurs naturally – light has no effect
No light for plant to photosynthesise
Snail still respires – light is irrelevant
Plant can’t photosynthesise but still respires. Both snail and
plant produce CO2 – more CO2.
Proves that light does not affect it.
Role of plant in photosynthesis
LIGHT
Excess O2 (waste)
is released into the
air.
stored
respired
light
water + CO2chlorophyllGlucose + O2
Carbon Dioxide
water
1.
Water enters by osmosis
2.
Water is carried up through the plant in Xylem vessels
3.
CO2 enters leaf through stomata by diffusion
4.
Water joins with CO2 to make Glucose and Oxygen.
5.
Some sugar is used in respiration, some is stored as starch and some is carried in
solution to other parts of the plant in the phloem. This is stored or respired.
6.
Oxygen produced is waste and is released into the air through stomata.
Use of Glucose produced by photosynthesis
Glucose is soluble, so can be carried easily around the plant. This is called translocation.
Glucose with
minerals such as
nitrates, can be
turned into amino
acids, which can
be turned into
proteins, which
are used for cell
structure and for
enzymes.
Built up into cellulose,
which is used to make
cell walls
Sucrose for fruits to
make them sweet.
Also, sucrose can be
used to transport
energy around the
plant. Glucose would
be used by cells before
reaching the correct
place – that is why it is
translocated as
sucrose.
The fruit is made so
that it can spread the
seeds.
Built into oil, which is
stored in the seeds as
an energy source. It is
used for the cell
membrane, structure
and for the wax
cuticle.
Respired by cells to
provide immediate
energy source
Stored as starch, which
is insoluble and
compact so can be
stored easily but can
be broken down again
whenever needed.
Seeds and roots may
have stored starch.
Glucose needs minerals to make amino acids. This is very important.
Glucose contains:
Amino Acids contain:
Carbon Hydrogen
Carbon Hydrogen
and Oxygen
Oxygen
and Nitrogen
For other things like oil, sucrose and cellulose, minerals are not needed.
Gas exchange
Night
As it is dark, no photosynthesis occurs, but respiration still takes place
Dusk/dawn
Dim light – little photosynthesis – enough to equal respiration, so
there is no net gas exchange.
Day
Bright light, so photosynthesis is faster than respiration. There is more
Carbon Dioxide taken in than Oxygen taken out.