8-1
Energy and Life
Energy
- the ability to do work
- all activities depend on some kind of energy; this
includes the activities of living things
- without the ability to obtain and use energy, life would
cease to exist
Where does the energy that
living things need come from?
A.
Autotrophs and Heterotrophs
Plants (autotrophs) use light energy from the sun to produce food
Animals (heterotrophs) obtain energy from food they consume
Mushrooms (heterotrophs) obtain food from organisms they
decompose
*****to live, all organisms (plants and animals) must release the
energy in sugars and other compounds
B.
Chemical Energy and ATP
Forms of energy include: light, heat, electricity
- energy is stored in chemical compounds
- all cellular activities are powered by chemical fuel
1.
ATP and ADP
ATP (adenosine triphosphate)
- a chemical compound that living things use to store
energy
- consists of:
adenine – a nitrogen-containing
compound
ribose – a 5-carbon sugar
3 phosphate groups
ADP (adenosine diphosphate)
- structurally similar to ATP, but contain s only 2
phosphate groups
- small amounts of energy can be stored by adding a
phosphate group to ADP and converting it to ATP
C.
ATP and Glucose
- cells regenerate ATP from ADP by using energy
stored in carbohydrates like glucose
- ATP moves energy more efficiently than it stores it
- One molecule of glucose stores 90 times more
chemical energy than one molecule of ATP
8-2 An overview of
Photosynthesis
Photosynthesis
the process by which plants use the energy from sunlight to convert
CO2 and H2O to O2 and sugars and starches
A.
Investigating photosynthesis
Experiments of many scientists contributed to our understanding of
photosynthesis
1. Van Helmont’s experiment (1643)
- carefully measured a plant’s intake and weight increase and
concluded that trees gain most of their mass from water
- his experiment accounts for the water portion of the carbohydrate
produced by photosynthesis
2. Priestley’s experiment (1771)
- using a bell jar, candle, and a living plant, he found
that plants release O2
3. Jan Ingenhousz (1779)
- found that aquatic plants produce O2 bubbles in the
light, but not in the dark, concluding that plants need
sunlight to produce O2
*****These 3 experiments and others performed later,
revealed that in the presence of light, plants change CO2 and
H2O into carbohydrates and release O2
B. The Photosynthesis Equation
Photosynthesis uses the energy of sunlight to convert H2O
and CO2 into O2 and high-energy sugars
light
Carbon dioxide + water  glucose + oxygen
6CO2
light
+ H2O  C6H12O6 + 6O2
- plants use the sugars to produce more complex carbohydrates
(starches)
- plants obtain CO2 from the air or water in which they grow
C.
Light and Pigments
- you have to understand how plants capture the energy of
sunlight in order to understand how they use raw materials to
produce complex sugars
- photosynthesis requires light and chlorophyll, the
pigmented molecule found in chloroplasts
- there are 2 types of chlorophyll; chlorophyll a and
chlorophyll b
- chlorophyll absorbs light energy at different wavelengths
within the visible spectrum
chlorophyll a (violet and red)
chlorophyll b (red and blue)
- chlorophyll does not absorb light in the green spectrum
(this is why plants are green) and very little in the yellow and
orange spectrum.
- Any compound that absorbs light also absorbs the
energy from that light which is transferred directly to
electrons in the chlorophyll molecule
- This increases the energy level in the chlorophyll
electrons and these high-energy electrons make
photosynthesis work
8-3 The Reactions of
Photosynthesis
A. Inside the Chloroplast
- where photosynthesis takes place
- thylakoids are sac-like membranes arranged in stacks
called grana
- the thylakoids contain clusters of chlorophyll and other
pigments and proteins known as photosystems that capture the
energy of sunlight
- photosynthesis takes place in two stages; the lightdependent reaction which takes place in the thylakoids and the
light-independent reaction (Calvin cycle) which takes place in the
region outside the thylakoid membranes (stroma)
The Reactions of Photosynthesis
B. NADPH (nicotinamide adenine dinucleotide
phosphate)
- a special carrier molecule that transports the highenergy electrons that result from the capture of energy from
sunlight in chlorophyll
- NADP+ accepts and holds 2 high-energy electrons
with a H+
- This converts NADP+ to NADPH trapping the
energy of sunlight in chemical form
- NADPH carries this energy to chemical reactions
elsewhere in the cell such as building needed carbohydrates
like glucose
C. Light-dependent Reactions
- require sunlight
- produce O2 gas and convert ADP and NADP+ into
the energy carriers ATP and NADPH
STEPS
Step A
- Pigments in photosystem II absorb light
- energy from the light is absorbed into electrons increasing
their energy levels
- these high-energy electrons move into the electron
transport chain
Step B
- high-energy electrons move from the electron transport
chain to photosystem I.
- Electron energy is used to move hydrogen ions from the
stroma into the inner thylakoid
Step C
- Pigments in photosystem I use light energy to reenergize
the electrons.
- NADP+ picks up these high-energy electrons at the outer
thylakoid surface along with a hydrogen ion and becomes
NADPH
Step D
- Inside of the thylakoid membrane fills up with positively
charged hydrogen ions making the outside of the thylakoid
membrane negatively charged and the inside positively
charged
Step E
- Hydrogen ions cannot cross the membrane but requires a
membrane protein called ATP synthase which allows them
too pass through it.
- As they pass through it, ATP synthase converts ADP to
ATP
D. The Calvin Cycle (light independent or dark
reaction)
- the Calvin Cycle uses ATP and NADPH to produce highenergy sugars
- it takes place in the stroma of chloroplasts
- it does not require direct light
STEPS
Step A
- Six CO2 molecules enter from the atmosphere and combine
with six 5-carbon molecules to form twelve 3-carbon molecules
Step B
- The twelve 3-carbon molecules are converted to higher energy
forms powered by ATP and NADPH
Step C
- Two of the 3-carbon molecules are converted to sugars and
other compounds
Step D
- the remaining ten 3-carbon molecules are converted back
to 5-carbon molecules to be used in the next cycle
***** Six CO2 molecules are used to produce one
6-carbon sugar molecule
D. Factors Affecting
Photosynthesis
1. Shortage of water
- can slow or stop photosynthesis
2. Temperature
- photosynthetic enzymes work best at 0-35 degrees
Celsius
- above or below that, enzymes could be damaged and
at very low temperatures, photosynthesis could stop
completely
3. Light intensity
- increase in light intensity increases the rate of
photosynthesis
- at a certain intensity level, plants will reach a
maximum rate of photosynthesis
- this maximum intensity level will vary from plant
type to plant type