10: Photosynthesis Flashcards
Which two factors affect photosynthetically active radiation in plants?
- type of light received
2. wavelengths received
What are the 4 main pigments in plants?
- Chlorophyll A
- Chlorophyll B
- Carotenoids
- Anthocyanin
Which are the 2 photosynthetically active pigments?
Chlorophyll a and b - predominantly a
Describe chlorophyll as photosynthetically active pigments
(A & B) Green pigments that help capture the sun’s energy by absorbing a lot of blue and red light and reflecting the other light wavelengths
Describe carotenoid pigments and list the two kinds
Orange pigments that are leftover in the leaf after the chlorophyll exits in the fall
- absorb mostly blue light and reflect the rest
- carotene
- xanthophyll
Describe anthocyanin pigments
Red pigment located inside the vacuole that does NOT contribute to the light dependent reactions and is purely a colour
Where is chlorophyll located?
Embedded in stacked membrane sacs (thylakoids) within chloroplasts of mesophyll cells
Also located in guard cells
T or F: Chlorophyll is a green pigment that reflects green light and absorbs blue and red light?
TRUE photosynthesis does not use green light
Which chemical is the key component of the chlorophyll molecule? What is attached to it?
Magnesium in the centre of the chemical rings with CH2 and CH3s attached
What is the chemical formula for photosynthesis?
6CO2 + 6H2O inputted into the chlorophyll and in the presence of light energy and enzymes –> C6H12O6 (glucose) + 6O2 + water
What are the inputs required for photosynthesis?
Carbon dioxide
Water
Sunlight
Enzymes
What are the products of photosynthesis?
Oxygen gas
Glucose (sugar)
Water
What are the two distinct steps of photosynthesis?
- Light reactions
2. Light independent reactions
What are thylakoids?
Stacked membrane sacs inside the chloroplasts of mesophyll cells that contain chlorophyll
The site of the light reaction step of photosynthesis
Describe the light reaction step of photosynthesis
- Rxns take place in the thylakoid membranes (Grana)
- light energy is captured and converted to ATP and NADPH
- Oxygen is produced by the water burning and released out the stoma into the atmosphere
Describe the light independent reaction step of photosynthesis
- The Calvin Cycle (C3 cycle) take place in the stroma of chloroplasts
- ATP & NADPH produced by the light runs are fed into the calvin cycle to fix the atmospheric CO2 into a 3-Carbon compound
- This requires RuBisCO ENZYME
- products of the CC = starch and glucose
What is ATP?
Adenosine Triphosphate
- temporarily, short-lived stored energy of biological systems
- the energy produced the light rxn stage of photosynthesis that cells need to do their work - cells cannot use the sugar directly, it needs to be converted into ATP
Describe how photosynthesis happens in leaves?
Light passes through the transparent epidermal cells on the surface of the leaves and into the thylakoid membranes in the chloroplasts
and CO2 comes in through the stoma and diffuses into the liquid environment inside the cells and moves into the chloroplasts
water is produced by PS and transpiration can also leave the stoma
Describe the stroma
The liquid filling of the chloroplasts that surrounds the thylakoids
Where the high energy compounds (ATP & NADPH) and CO2 enter to be converted into sugar
What are the 2 structures of chloroplasts?
- Grana: all the thylakoids
2. Stroma: fluid filling in chloroplasts
Where does the light dependent reaction occur?
In the grana (all the thylakoids)
How are solar panels similar to leaves?
They capture solar energy and convert it to a form of energy that can be used or stored just like plants
What are C3 plants? How does photosynthesis occur?
Plants that contain 3-carbon compounds where photosynthesis, carbon fixation and the Calvin cycle occur in a SINGLE chloroplast
When does photorespiration occur?
When temperate plants close their stomata early in the afternoon due to periods of very hot dry weather because the threat of water loss is too high
What is photorespiration?
When the stomata is closed early causing a lack of CO2 intake, the enzyme RuBisCO which usually captures CO2 in the Calvin cycle to produce sugar will use O2 instead –> up to half of the fixed carbon produced is returned as free CO2 and not sugar (CO2 is a waste product)
What are the damages of photorespiration?
Loss of CO2 intake can lead to damage because it’s required for photosynthesis
What are C4 & CAM plants? Give examples of each
Plants adapted to environments where CO2 may be limited (hot and dry) so they STORE CO2 in a chemical form inside the ‘leaf’ cells to be available for photosynthesis even if the stomata is closed
ex C4: corn, tropical grasses
ex CAM: cacti, jade, stonecrops, orchids, bromeliads
How does photosynthesis occur in C4 plants?
C4 plants have 2 distinct kinds of chloroplasts:
- mesophyll chloroplasts
- CO2 is quickly converted into malate or aspartate (C4 intermediate)
- occurs in the thin-walled mesophyll cells and is then passed to the thick-walled bundle sheath cell - bundle sheath chloroplasts
- Surrounds the vascular bundle (different physically)
- where the Calvin cycle occurs
- takes the 4-C acid to make CO2 as in the regular CC by RuBisCO enzyme creating sugar
T or F: C4 plants can have photosynthetic rates 2-3x higher than those of C3 plants in hot sunny environments? Why/why not?
True because the stomata will be closed in the temperate plants and photorespiration will occur rather than the regular photosynthesis that will be happening in the C4 plants
How does photosynthesis occur in CAM plants?
- Photosynthesis and initial carbon fixation occurs at NIGHT and a 4-C acid is stored in the cell’s vacuole during the daytime
- Calvin Cycle operates as usual in the chloroplasts during the day using the stored 4-C acid (malic acid) to convert it into CO2 to be used for photosynthesis during the daytime when stomata are closed
- oxygen is released in the daytime when the sun burns the water and the stomata are open
What are the main differences between C3, C4, & CAM photosynthesis?
C3:
- 1 type of chloroplast with CO2 conversion in the stroma
- most temperate climate plants
C4:
- 2 distinct types of chloroplast
- MC: produces C4 molecules
- BSC: does the CC
- hot and dry climates
CAM:
- 1 chloroplast where malic acid is produced and the CC occurs
- hot and dry climates
T or F: There is approximately 400ppm CO2 in our atmosphere currently? And plants extract huge amounts daily?
True
How much water is needed for photosynthesis? And is it a limiting input?
less than 1% is required so no, it is not limiting
What are the 6 different light qualities?
- Daylight
- Incandescent
- fluorescent
- halogen
- Cool white LED
- warm white LED
Describe the quality of daylight
- broadspectrum light (all visible wavelengths)
- intensity is even across the wavelengths
- direct sunlight is highly intense
Describe the quality of incandescent light
- Most of the colder wavelengths are low intensity
- Produce high intensity red lights
- Produce heat
Describe the quality of fluorescent light
Provide good light but intensity is focused in green-red
Green light is useless to plants
Orange is slightly useful
Not bad light for us, but NOT GOOD for plants
Describe the quality of Halogen light
Burn a lot more power - more red
More of the red wavelengths, not much blue
Describe the quality of cool white LED light
Produce a lot of blue light - high intensity
And in green range
Little in the red light
Describe the quality of warm white LED light
High green light intensity
More red light intensity
What is light quality?
describes the wavelengths present (ex. red, blue, green)
What is light intensity?
How much energy is contained in the wavelengths
How does a clear summer day compare to the brightest indoor lights being on in terms of light intensity?
Sunlight on a clear day has 70,000 lux vs. the 1200 lux of the indoors
What is the unit for light intensity?
lux
T or F: Most plants need more than 30% of full sunlight to survive
FALSE. Most plans ONLY need 30% of the full sunlight
What are the two terms for sugar transport in plants?
- Source-to-sink translocation
2. Pressure Flow Hypothesis
What are the sources of sugar and what are the sinks for sugar?
Source: chloroplast
Sink: roots or fruits
Describe the pressure flow hypothesis
- Sugar is produced by PS and is loaded into the phloem and unloaded where it is needed (sinks) with help from the companion cells
- Water will move from the xylem to the phloem by OSMOSIS to dilute the sugar, creating osmotic pressure to drive the phloem sap (sugars) downward to the roots or fruits to be stored as starch
Where is sugar stored if the rate of photosynthesis is higher than the translocation of sugar?
Sugar is stored as starch in the chloroplasts of the leaves TEMPORARILY
Describe starch
A complex carbohydrate consisting of many glucose units joined together
a storage form of glucose
What is the process that converts starch back into glucose?
Digestion
Explain the process of digestion of starch into glucose
Starch molecules are digested by enzymes (AMYLASE) to be converted back into glucose
At which temperature will enzymes become ineffective and why?
32 degrees because they are proteins so they will melt
What controls the activity of enzymes?
Temperature
