Light & Photosynthesisor

“You light up my life”

A/H 100G

J.G. Mexal

CO2 capture

Basic Photosynthetic Reaction

• CO2 + H2O CH2O + O2

• 1.47 lb 0.60 lb 1.00 lb 1.07 lb

λ

PhotosynthesisAction Spectra of Lights vs Chl a & b Absorption

Incandescent light

Cool whitefluorescent light

Chlorophyll A & B

PhotosynthesisLight Compensation and Saturation Points

Net Ps (mgCO2/cm2/h)

2000 4000 6000

Light Intensity (fc)

C.P.

S.P.

Photosynthesis

Sun vs Shade Leaves

Epidermis

Palisade Mesophyll

Spongy Mesophyll

Epidermis

Stomata

Sun Shade

Photosynthesis

Pathways for Photosynthesis

• C-3 = most crops

• C-4 = arid shrubs, grasses, pineapple

• CAM = succulents – (crassulacean acid metabolism)

Photosynthesis

C3, C4, and CAM Plants

C3 Plants C4 Plants CAM Plants

Spinach Corn Agave

Beans Bermuda grass Jade plant

Bentgrass Russian thistle Pineapple

Mulberry 4-wingsaltbush

Sansevieria

Chile Pigweed Cacti

Photosynthesis

Characteristics of C3 and C4 PlantsCharacteristic C3 Plants C4 Plants

Tissue w/ chloroplasts Mesophyll Mesophyll &bundle sheaths

Transpiration High Low

Optimum T 15-25C 30-40C

Light intensity (saturation) 3,000 fc 6,000+ fc

Photorespiration Measurable Not measurable

Compensation point 30-70 ppm CO2 0-10 ppmCO2

Ps pathways 1 2

Ps @ hi T & hi light Low High

Photosynthesis

Simplified C3 Pathway

Photosynthesis

C3 Leaf StructurePalisade mesophyll

Spongy mesophyll

Epidermis

VeinVein

PhotosynthesisLight Compensation and Saturation Points

PhotosynthesisInteraction between CO2 and Light Intensity

1,300 ppm CO2

1600 ppm CO2

360 ppm CO2

Light Intensity

Photosynthesis Rate

Photosynthesis

Simplified C4 Pathway

Spatial Separation

Photosynthesis

Simplified C4 Pathway

Photosynthesis

C4 Leaf StructureBundle sheath cells

Mesophyll

Vein

PhotosynthesisDistribution of C4 Plants/ Oecologia 23:1-12:1978

Percent of Grass Taxa Percent of Dicot Taxa

PhotosynthesisC3 & C4 Response to Light Intensity

Light Intensity

Photosynthesis

Sugarcane- C4

Clover- C3

Tobacco- C3

Philodendron-C3

Photosynthesis

Simplified CAM Pathway

3-carbon compound

Temporal Separation

Photosynthesis

Simplified CAM Pathway

PhotosynthesisWhat is this?????

Things to Know

• What happens to all the light striking the earth’s surface

• Light attributes– Quality

– Quantity

– Duration

• Plant pigments– Imp. Wavelengths

– Actions

• Photoperiod response– Long-day

– Short-day

– Day-neutral

– Important dates (why?)

• Ps Reaction– Basic

– C3, C4, CAM

Quiz Questions

• Give the basic photosynthesis reaction and where does it take place?

• Describe the characteristics of C-3 and C-4 plants. Give examples of a C-3 and C-4 plant.

• Describe the differences between a C-4 and CAM plant. Give an example of a CAM plant.

• What is a ‘short-day plant’? ‘long-day plant’? ‘day-neutral plant’?

• How do plant ‘tell time’? What’s the reaction?• Why do C-4 plants have a higher rate of photosynthesis.

Describe leaf morphology of both.

Light and Photobiology

Electromagnetic Spectrum

y = 19176x-0.9376

R2 = 0.99

0

20

40

60

80

300 400 500 600 700 800 900

Energy (kcal/cm

Wavelength (nm)

PhotosynthesisLeaf Tissues & Function

• Tissue– Epidermis

– Guard cells & stomates

– Chlorophyll- containing cells

– Veins

• Primary Functions– Protective cells (keep

water within leaf)

– Allow CO2 & O2

diffusion for Ps & Rs– Manufacture ATP &

glucose– Translocate H2O and

nutrient to, and CHO & AA away from, the leaves