name ____________________
Principles of Biology – Photosynthesis Study Guide
Obtain a Glencoe Biology book. Read pages 242 through 248 to complete the following.
Carbohydrates, in the form of simple sugars, like glucose are broken
apart by organisms to make ATP. Heterotrophs must consume sugars, but
autotrophs can make their own. They do this by trapping energy from
sunlight to make carbohydrates in a process called photosynthesis.
Most plants are green because they contain chlorophyll,
chlorophyll found in
chloroplasts of some cells. The first step in photosynthesis is trapping energy
from the sun.
sun This energy is then converted into chemical energy. Besides
energy, these two things are needed for photosynthesis to occur: H2O & CO2.
Write the balanced chemical equation for photosynthesis here:
Light Energy + 6CO2 + 6H2O C6H12O6 + 6O2
How many molecules of carbon dioxide are required? 6 How many
molecules of carbohydrates are produced? One (1) What gas is produced as
a waste? Oxygen
The “light reactions” are the photo part of photosynthesis; during the
light reactions, H2O is split into H & energy (or O).
O) The Calvin cycle is the
synthesis part of photosynthesis, during which carbon dioxide and the H from
water are combined to form glucose/sugars.
glucose/sugars
Complete the 3 main steps for the light reactions: (see fig. 10.8)
1. Electrons from chlorophyll lose energy, which is used to make ATP
(used in Calvin Cycle.
Cycle
2. Water breaks up into H & O.
3. Additional electrons, along with H+ form another energy molecule,
called NADPH.
NADPH
Complete the steps to the Calvin cycle: (see fig. 10.9)
1. The C from carbon dioxide is “fixed” to a 5-Carbon molecule to form
a 6-carbon molecule.
2. This 6-carbon molecule splits into 2 33-carbon molecules,
molecules called PGA.
3. The PGA is changed to PGAL (2 33-Carbon sugars)
sugars),
rs) using NADPH
and ATP energy.
4. Some PGAL are left in the Calvin cycle, some are used to form other
carbohydrates.
carbohydrates
In summary, the light reactions make energy molecules, and split water. The
Calvin cycle combines CO2 with H to make carbohydrates.
carbohydrates
Predict what would happen to the rate of photosynthesis if we could increase
the concentration of CO2. The rate will go up.
up What if we could decrease the
concentration of CO2? The rate would decrease.
(as long as plenty of light and water are present)
How do photosynthetic plants enable us to use the energy from the sun?
Convert sun’
sun’s energy into food energy
What would happen to animal life on earth if all plants suddenly died?
All animals die, due to decrease in O2 and food.
food
Compare the chemical reaction of photosynthesis to the chemical reaction of
respiration: They are opposites (as different kinds of energy). The reactants
reactants
of one is/are the products of the other.