Download 1.17 * Energy Flow and Photosynthesis

1.17 – Energy Flow and
Photosynthesis
Homework Pg. 76 #2-6
Light from the sun is the ultimate source of
energy for most living things
Organisms can’t use light directly. They have to
capture solar energy and store it as chemical
energy in carbohydrate molecules, such as
glucose, and then transfer the energy from
glucose to ATP.
The absorption of light energy and the production
of glucose occur though photosynthesis
Autotrophs – an organism (such as a plant) that
obtains energy directly from light
• they make their own food
Heterotrophs – an organism (such as an animal)
that obtains energy by eating other organisms
• they can’t make their own food
Photosynthesis: The Process
Photosynthesis occurs in the chloroplasts, which
are found in the leaves of plants
Chloroplasts contain an inner and outer
membrane and have little compartments called
thylakoids.
Thylakoids stack on top of each other to form a
structure called a granum.
A protein-rich fluid called stroma fills the rest of
the space.
Chlorophyll, a green pigment, is found in the
thylakoid membranes.
Chlorophyll molecules absorb light energy and
begin the process of photosynthesis.
The equation for photosynthesis is:
6 CO2(g) + 6 H2O(l) + light energy → C6H12O6(aq) + 6 O2(g)
Photosynthesis occurs in 2 steps:
1. The Light Reactions
• Require light in order to happen
• Photosynthesis begins when the chlorophyll
molecules in the thylakoid membranes trap
light and transfer its energy to ATP molecules
2. The Calvin Cycle
• Reactions of photosynthesis in which carbon
dioxide molecules are used to produce glucose
• The carbon atoms in glucose come from the
carbon atoms in CO2
• The ATP molecules made in the light reactions are
required for the Calvin Cycle to occur
– This energy is transferred to the glucose that is
produced
• This part of the reaction can occur without
sunlight, so it is referred to as the dark reactions
Accessory Pigments
A multicoloured pigment in chloroplast membranes
that assists chlorophyll in absorbing light E
• Ex. Carotenoids (orange), xanthophylls (yellow),
anthocyanin (red)
In spring and summer, leaves look green because of
the high [chlorophyll] in the chloroplast membranes
When temperatures cool down, leaves stop producing
chlorophyll and the molecules of chlorophyll that are
already there start to break down
• This allows the bright colours of the accessory
pigments to show