Download Photosynthesis - NCEA Level 2 Biology

Photosynthesis
Photosynthesis
• All life on Earth is powered by the
sun.
• This light travelling 160 000 000
km from the sun is captured by
chloroplasts in green plants.
• Here it is turned into the energyrich foods and oxygen that all other
organisms depend on.
Chlorophyll
• This is found in the chloroplasts in
any part of the plant which is
green.
• Most photosynthesis takes place in
the leaves.
• Chlorophyll is found in the
thylakoids.
• These are stacked one on top
each other in piles called Grana.
Chlorophyll
• The grana stacks are joined to
each other by membranous
extensions of the thylakoids called
lamella.
• Photosynthetic pigments, enzymes
and carrier molecules are
embedded in the thylakoid
membranes.
• The clear fluid in the chloroplast is
called stroma.
Chlorophyll
• Chlorophyll is similar to
haemoglobin, the red pigment in
our blood except it is based around
magnesium.
• There are several different kinds of
chlorophyll.
• The most important one is
chlorophyll A.
• Other chlorophylls help to pick up
extra wavelengths of light.
Chlorophyll
• This energy is then passed to
chlorophyll A.
• Certain carotenoids known as
carotene and xanthophyll also do
this.
• Chlorophyll absorbs light in the red
and violet end of the visible
spectrum, and reflects green.
Photosynthesis E q uation
• The overall equation for
photosynthesis is:
Sunlight
6CO2 + 6H2O
C6H12O6 + 6O2
Chlorophyll
NADP - the Hydrogen
Carrier
• Nicotinamide Adenine Dinucleotide
Phosphate.
• This acts as the hydrogen carrier
in photosynthesis.
H2
NADP
NADPH2
H2
Photosynthesis
• Phtosynthesis takes place in 2
steps:
• The light phase
• The light independent phase
– This is known as the Calvin Cycle.
– Used to be called the Dark phase but
causes confusion as it still takes
place in the light.
– It is independent of light.
The Light Phase
• This is the photo part.
• It takes place in the thylakoids
• Chlorophyll absorbs light and uses
the energy to:
– Split water into hydrogen and
oxygen, the hydrogen is picked up by
NADP, the oxygen is a waste
product.
– Charge up ADP to ATP.
The Calvin Cycle
• This cyclic process occurs in the
stroma.
• Carbon dioxide is captured from
the air and fixed into a molecule in
the stroma (carbon dioxide
fixation)
• An important enzyme called
Rubisco (ribulose carboxylase)
catalyses the first step of fixation
by adding CO2 to ribulose
biphosphate.
The Calvin Cycle
• Rubisco is the most abundant
enzyme in chloroplasts.
• The product of this fixation is a 6C
substance, which is so unstable it
immediately splits into 2 molecules of
3- phosphoglycerate.
• This, along with electrons from
NADPH2 and the energy from ATP,
is turned into glyceraldehyde-3phosphate (G3P).
The Calvin Cycle
• Some of this G3P is returned to
the cycle
• The rest is used to make organic
compounds such as glucose,
lipids and proteins
The Relationship between
Photosynthesis and
Respiration
• Respiration takes place ALL the
time, so oxygen is taken in and
carbon dioxide is produced
continuously.
• Photosynthesis takes place in the
daylight hours, so carbon dioxide
is taken in and oxygen is
produced.
The Relationship between
Photosynthesis and
Respiration
• During the day there is usually
more photosynthesis than
respiration.
• The net result is that oxygen is
produced and carbon dioxide is
used during the day.
• During the night, oxygen is used
and carbon dioxide is released.
The Relationship between
Photosynthesis and
Respiration
• Compensation point – this is the
point where the amount of
photosynthesis is the same as the
amount of respiration.
• There is no net gain or loss of
gases.
• Ref pg 137 Pattern’s of Life
Absorption of Carbon
Dioxide
• If you keep adding CO2 to a
greenhouse, photosynthesis will
increase with increased light and
temperature.
• Eventually a limit is reached and
the rate levels off.
Absorption of Carbon
Dioxide
Factors that Affect
Photosynthesis
• Enzymes
– Photosynthesis is run by enzymes.
So any factor which affects enzymes
affects the rate of photosynthesis.
• Temperature
– At cold temperatures photosynthesis
is reduced. It speeds up as
temperature rises until an optimum is
reached. Eventually the enzymes
become denatured and
photosynthesis stops.
Factors that Affect
Photosynthesis
• Amount of Carbon dioxide
– Increase in CO2 will increase
photosynthesis up to a point.
• Light Intensity and Wavelength
– Chlorophyll uses red and blue
wavelengths of light. Carotene and
xanthophyll pick up different
wavelengths.
– Plants are adapted to different
intensities of light.
Factors that Affect
Photosynthesis
• Chlorophyll and minerals
– In general, the more chlorophyll, the
more photosynthesis. If plants lack
magnesium, their leaves go yellow
and do not photosynthesise. Also
need iron and other trace elements
from the soil.
Factors that Affect
Photosynthesis
• Absorption of Carbon Dioxide
– Linked to the opening and closing of
the stomata in the leaves, which is in
turn linked to water loss. If the leaf is
losing too much water it closes its
stomata.
• Sufficient Water
– Water is needed to keep the cells in
the leaf wet. Gases are absorbed
over a wet surface. Water also
needed for photosynthesis.