CH 4 LEDs and Photosynthesis Flashcards
Photosynthesis is the process by which plants convert light energy into the ______________they use as building blocks and —_________________stores.
Sugars
Energy
Membranes in plants called __________________do the heavy lifting, collecting ___________ ____________and passing it along to chemical processes inside the leaves that convert light, water, and carbon dioxide (CO2) from the air into _________________.
Chlorophylls
Light energy
Sugars
Water (H2O) + light (hv) + Carbon Dioxide (CO2) → ___________+ __________________.
→ Sugars + Oxygen (O2)
Again……..
Water (H2O) + _____________+ Carbon Dioxide (CO2) → Sugars + Oxygen (O2)
light (hv)
Photosynthesis can be broken down into two sub-processes: ________________ reactions and __________________ reactions.
light-dependent reactions
light-independent reactions.
It might be simpler to consider the light-dependent reactions _______________reactions because they use __________________ to break up a water molecule (H2O).
“water side”
light energy
The energy produced from these reactions is captured in two compounds that fuel the rest of the photosynthetic process:
________________________
Below is the simplified reaction: H20 + light → ATP + NADPH + O2
ATP (adenosine triphosphate)
NADPH (nicotinamide adenine dinucleotide phosphate).
As with everything in biology, the names can be confusing. “Light-independent reactions” are more commonly called “dark reactions,” though they don’t only occur at night as their name might imply. They just don’t require light, so it’s better to call them ____________________.
Light independent reactions
Light-independent reactions are also called the “_________________.” Melvin Calvin, James Bassham, and Andrew Benson discovered it while working together at University of California, Berkeley, but Calvin gets the name recognition.
“Calvin Cycle.”
In these reactions, ___________ is converted into sugars with the aid of the energy building blocks produced by the light-dependent reactions, ___________and ______________.
CO2
ATP and NADPH.
Because these reactions consume CO2, they can be considered
_____________________reactions.
Simplified, the carbon fixation reaction looks like this: ATP + NADPH + CO2 → Sugars + O2
Carbon Fixation
Simplified, the carbon fixation reaction looks like this:
______+ ________+ ___________→ Sugars + O2
ATP + NADPH + CO2
Both halves put together:
Light-Dependent Cycle H20 + light → ATP + NADPH + O2
Light-Independent Cycle ATP + NADPH + CO2 → Sugars Total
Two-Step Reaction?
Total Two-Step Reaction
H20 + light → ATP + NADPH + CO2 → Sugars + O2
There are several types of chlorophyll? Most green plants use chlorophyll _____and chlorophyll ______plus compounds called____________ to capture light for photosynthesis. There are also C1, C2, D, and F chlorophylls, but these are generally found in lower
A
B
Caretines
Chlorophyll is probably the best-known plant pigment. It’s _____________ in color and found in all plants and algae.
Chlorophyll’s job is to absorb ____________from the light _________to which the plant is exposed.
Green
Energy
Photons
In plants, chlorophylls absorb in the __________and ________ regions of visible light.
This may be why early LED manufacturers, who didn’t know better, produced grow lights with only red and blue emitters.
Red
Blue
One curiosity about chlorophyll is its close resemblance to hemoglobin, the human molecule that provides oxygen and carbon dioxide transport throughout the body. The primary difference between chlorophyll and hemoglobin is their center ion: hemoglobin has iron (Fe) at its center, while chlorophyll centers on ____________________otherwise, the molecules are strikingly similar.
Magnesium (Mg)
While partially true, plants don’t reflect 100% of the ___________________they receive—some is absorbed and some is reflected.
The reflected __________________can be absorbed by another leaf; thus, ____________________ scatters further into the garden’s canopy than red and blue.
Green light 3x
Many plants absorb as much as _________________of the green light they are given.
70% to 90%
Green light is absorbed deep within the leaf tissue by a group of compounds called ___________________ among which lycopene and beta-carotene are most well-known.
Carotenoids
lycopene and beta-carotene are two well-known well known carotenoids
lycopene and beta-carotene
Carotenoids cause plant leaves to ________________, increasing their ability to capture more light.
Thicken
should a plant begin to shut down chlorophyll absorption due to light overexposure, _____________________can continue to drive photosynthesis.
Green light
____________, ______________, and ______________are the primary colors of light;
when they are mixed together in computer monitors and televisions, they can recreate every color including white.
Including 5% to 10% green emitters in an LED grow light makes it easier for the gardener to see problems that might otherwise be masked by the light’s purplish-pink color.
Red, blue, and green
Infrared: Emerson Enhancement Effect
In 1957, Robert Emerson conducted experiments regarding what wavelengths most efficiently drive photosynthesis.
He noticed that photosynthesis dramatically drops off at ___________nm and above. This was considered strange since chlorophyll isolated in a beaker absorbs light well above this point.
Photosynthesis reductions above __________nm became known as the “___________________.”
680nm
680nm
Red drop effect
This led Emerson to additional experiments showing that plants respond disproportionately to the combination of ___________________ and ___________________.
infrared light and red wavelengths.
He observed a dramatic increase in ___________________ rates when plants were exposed to red light and infrared light at the same time. This phenomenon became known as the “Emerson enhancement effect.”
Photosynthesis
Emerson’s experiments showed that using small amounts of infrared spectrum in combination with other reds can increase our _______________________. It’s not often when one plus one equals an output greater than two!
Be sure to look for an LED grow light that includes ___________
spectra so you can benefit from this effect.
yields
Infrared
Typical photosynthesis charts show the ___________________ response curve at each wavelength within PAR spectrum, with some consideration given to what is absorbed by the different carotenoids.
Chlorophyll
But there is more to the picture: other light spectra, commonly called ________________________________, are also needed for healthy plant growth. ___________________________ regulate plant growth as well as development processes such as controlling internodal stretching.
Signaling wavelengths 2x
While you can grow plants without them, plants grown without _______________________won’t yield as heavily and may develop weak stalks and stems—not the best for the big, heavy harvests you desire.
Signaling Spectra
_____________________is an extremely important plant growth regulator that functions in the red end of the visible light spectrum.
Phytochrome
While it has no role in ___________________, phytochrome controls internodal elongation and flowering initiation (photoperiodism).
Photosynthesis
The best understood of the plant-signaling compounds, phytochrome has two active states:
___________________________
___________________________
phytochrome red (Pr)
phytochrome far red (Pfr)
phytochrome red (Pr) absorbs light around ________nm to ________nm
phytochrome far red (Pfr) absorbs light at ________nm to _______nm.
650nm to 670nm
705nm to 740nm.
Note that the___________ absorption is outside of the PAR spectrum range.
Pfr
The ratio between Pr and Pfr, which convert back and forth depending on the light they receive, affects the plant’s physical shape, including its ____________.
Height
Plants use ___________ to sense infrared light hitting their stems, much of which passes straight through the leaves while the accompanying _____________ is absorbed by the leaves.
Phytochrome
Red light
To develop their normal shape, plants must receive specific ratios of _____________and ____________light on their stems; without enough ___________,the plants will sense that they are being blocked from the light and will stretch (increase internodal distance) to search for it.
Red and infrared
Infrared
_________-__________plants, discussed in chapter 6, also rely on phytochrome to initiate flowering.
Flowering begins when a sufficient quantity of_____ converts back to the ________form, a process that requires about _______hours of uninterrupted darkness.
Short day
Pfr
Pr
12
That’s why short-day plants grown outdoors begin to flower when day lengths shorten sometime after _________ __________, and it’s why indoor growers switch to a ______hours-on/ _____hours-off light cycle for flowering short-day plants.
Summer solstice
12 / 12
On the research front, growers have been experimenting with using ______________to extend “day” length during the flowering phase.
Why lengthen the “day?” So that your plants have more time to turn _______ into _________and so they can then use those sugars to grow stronger stems and bigger yields.
Phytochrome
Light
Sugar
Short-day plants generally require _______hours to convert Pfr to Pr.
Growers have been able to increase yields by keeping the lights on for _____or ________hours then finishing the light cycle with infrared light only for periods ranging from a few seconds to a few minutes.
12
13 - 14
Infrared light
This ___________ period of infrared light jumpstarts the Pfr-to-Pr conversion process, allowing the plants to convert enough Pfr to Pr during a shortened night cycle to continue vigorous _______________.
Some growers also report that this process allows them to grow the same-sized plants but harvest their crop a few days to weeks sooner than without the
Short
Flowering
Cryptochrome is similar to phytochrome in that it’s a photosensor, though it captures _______, __________ and a small amount of UV-A light.
Blue
Violet
_________________also assists in regulating the physical size and shape of plants, both alone and in combination with _______________.
Cryptochrome
Phytochrome
Cryptochrome affects the plant’s “___________________,” which is how the plant perceives night and day, as well as being responsible for ___________________—the process that causes plants to turn toward the light.
Sunflowers provide an example of this effect: their flowers track the sun from the east in the morning to the west in the evening.
Circadian clock
Phototropism
Most current LED grow lights have sufficient _________________ to activate cryptochrome photosensors without added UV light.
Blue light
There are three bands of UV light: ________, _________, and ________.
UV-A
UV-B
UV-C
UV-A:
Wavelength______________nm
Type of wavelength_____________
Applications:___________________
DNA effect_______________
Key Point___________________
400 -320 nm
Long
Black light
Indirect DNA damage
Excites cryptochrome
UV-B
Wavelength______________nm
Wavelength type_____________
Application________________
DNA effect_________________
KEY points__________________
320-280nm
Medium
Phototherapy
Direct DNA damage
Causes sunburns
UV-C
Wavelength_________________nm
Wavelength type______________
Application________________
DNA effect
Key Points_________________
200-280 nm
Short
Germicidal
DIRECT DNA damage
Mostly filtered by environment , very harmful
If indoor gardeners supplement with UV light, it should to be _____________In some plants, UV-B is thought to increase ______________ and ___________________.
UV-B
Flavonoids
Terpenoids
_________________are compounds that are responsible for many of the vibrant colors of the plant, which in nature help to attract beneficial insects that can aid in pollination. ______________ also inhibit certain plant pathogens.
Flavonoids
________________ are responsible for aromatic plant smells. From eucalyptus trees to cinnamon, ____________ are the compounds you smell.
Terpenoids
When investigating LED grow lights that contain UV, find out from the manufacturer what wavelength of UV is used in the light. Some LED grow lights use inexpensive _____________LEDs so they can say their products contain “UV light.” Helpful UV-B LED emitters are still very expensive and so are less common in LED grow lights.
UV-A
One way to add UV to your garden is to supplement your LED grow light with one or more UV _____________( s). These generally emit a bit of UV-A along with UV-B and come in various sizes and output strengths, and they are generally a less-expensive solution than LED grow lights that include expensive UV-B emitters.
Tanning lights
We can exceed the light requirements of our plants with modern LED grow lights. When exposed to too much light intensity, plants shut down photosynthesis through a process called _________________.
Photoinhibition
Photoinhibition is a serious problem: not only are the plants not converting light into ____________so they can grow, they actually spend energy to defend themselves through a process called “___________________”that disperses excess energy from over-stimulated_____________molecules.
Sugars
Feedback deexcitation
Chlorophyll
Feedback de-excitation also releases dangerous _______________ inside the plant, which attack chlorophyll molecules and other structures within the plant.
Free-Radicals
One way to understand what “too much light” means to plants is to learn about a total daily light limit called the ____________________
Daily light integral (DLI)
The DLI is the total amount of ____________________ (1 million _____________) received by a plant during a single light period.
Light moles
Micro moles
The maximum DLI that can be achieved outside in full sun is about ________________moles/ day.
This level should never be exceeded indoors.
60
Many commercially grown plants have published _______________. Take the time to look up the DLI for the plants you’re growing indoors. Exceeding this limit can make the plants shut down and start spending energy to protect themselves instead of producing harvests.
DLI limits
To calculate the DLI, measured in total micromoles per day, for your garden. The light used for this example provides 1000 micromoles of light intensity during a 12-hour photoperiod:
Divide by 1,000,000 to convert from micromoles to moles of light:
43,200,000 µmol/ day ÷ 1,000,000 = 43.2 moles/ day
