U1: Photosynthesis is
the production of
carbon compounds in
cells using light
energy
Requires a photosynthetic pigment (chlorophyll) and can only occur in certain
organisms (plants, certain bacteria).
U2: Visible light has a
range of wavelengths
with violet the
shortest wavelength
and red the longest
Range of visible light wavelengths: 400 to 700 nm.
U3: Chlorophyll
absorbs red and blue
light most effectively
and reflects green
light more than other
colours
When chlorophyll absorbs light, it releases electrons which are used to
synthesise ATP (chemical energy).
Red Orange Yellow Green Blue Indigo Violet
U4: Oxygen is
produced in
photosynthesis from
the photolysis of
water
Step 1: Light Dependent Reactions
● Light is absorbed by chlorophyll -> ATP (chemical energy)
● Photolysis: photo - light; lysis - disintegration.
−
+
𝐻2𝑂 → 4𝑒 + 4𝐻 + 𝑂2
●
H and ATP are used in the light independent reactions. 𝑂2is released
from stomata as a waste product.
U6: Energy is needed
to produce
carbohydrates and
other carbon
compounds from
carbon dioxide
Step 2: Light Independent Reactions
● ATP and hydrogen (carried by NADPH) -> site of the light independent
reactions
𝐻 + 𝐶𝑂2 → 𝑐𝑜𝑚𝑝𝑙𝑒𝑥 𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑𝑠
●
The ATP provides the required energy to power these anabolic
reactions and fix the carbon molecules together
Skill: Drawing an
● The absorption spectrum indicates the wavelengths of light absorbed by
absorption
each pigment;
spectrum for
● The action spectrum indicates the overall rate of photosynthesis at each
chlorophyll and an
wavelength of light;
action spectrum
Correlation: Both display: two main peaks – a larger peak at the blue region (~450
for photosynthesis nm) and a smaller peak at the red region (~670 nm); a trough in the green / yellow
portion of the visible spectra (~550 nm).