1600’s Jan van Helmont, Flemish physician
New plant material came directly from water ?
1770’s Joseph Priestley, English chemist
Plant grows in air of blown out candle
1776 Antoine Lavoisier French chemist
Oxygen given off by plants
Jan Ingenhousz, Dutch physician
Found plants give oxygen to air only in sunlight
Jean Senebier, Swiss clergyman
Found that plants take in carbon dioxide during growth in sunlight
1800’s scientists had identified the basic requirements for plant growth
Carbon dioxide, water, and light
Most energy enters the earth’s biosphere through photosynthesis. Botanists estimate that 150 billion tons of sugar are produced yearly by plants.
Process of capturing and transforming the energy of sunlight into chemical energy.
Green plants use carbon dioxide and water to make glucose, and they release oxygen.
Autotrophs – capable of making food from simple inorganic substances.
Two types: both use carbon dioxide as a source of carbon to make food.
Photoautotrophs – use light energy to drive the reactions to make their food
Chemoautotrophs – bacteria oxidize inorganic chemicals for the energy to drive their food-making reactions
Heterotrophs – can not make their own food
Sunlight know as radiation.
Radiation travels in waves.
Wavelength – crest to crest.
Sunlight is a mixture of all visible wavelengths.
Sunlight known as white light.
Prism and a spectrum of light
Visible light = ROYGBIV
Amount of energy
Absorption of light
Visible light makes up only a small portion of the electromagnetic spectrum. At increasing wavelengths, there are: infrared rays, which are heat radiations; UHF waves, which are used for FM radio and television; and radio waves. At decreasing wavelengths, there are ultraviolet rays, X rays, and gamma rays.
Chlorophylls most abundant and important pigments.
Primary photosynthetic pigment
Carotenes and xanthophylls
Absorb light and transfer the energy to chlorophyll a
Carotenes, xanthophylls, and chlorophylls are embedded in the thylakoid membranes of the chloroplasts.
Some believe that just because the leaves are green, they use green light for photosynthesis. What we see as color is reflected light. Chlorophyll reflects light in the green-yellow range and absorbs light in the violet-blue and orange-red ranges.
Photosynthesis occurs in the chloroplasts
Chloroplasts are organelles containing photosynthetic membranes
Photosynthetic membranes are arranged in the form of flattened sacs called thylakoids
Stacks of thylakoids are called grana
The regions between the grana make up the part of the chloroplast known as stroma
Chloroplasts can be divided into three classes on the basis of their pigment content. The chloroplasts of plants, green algae, and the euglenoids contain chlorophyll’s a and b and carotenoids. The chloroplasts of brown algae, diatoms, and dinoflagellates have chlorophylls a and c, carotenoids, and yellowish-brown pigments. Those of red algae contain chlorophyll a, carotenoids, and phycobilins.
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Reactions of Photosynthesis
Only a same portion of light energy is transformed into chemical energy.
Reaction summarizes the conversion of light energy into chemical energy:
6CO2 + 12H2O à C6H12O6 + 6O2 + 6H2O
Figure 17-6, page 344
Light-dependent reactions must take place during daylight, the light-independent reactions may take place both day and night.
Light – Dependent Reactions
Figure 17-1, page 345
Light – Independent Reactions
5 – carbon sugar called ribulose bisphosphate
3 – carbon called phosphoglycerate
PGAL is phosphoglyceraldehyde
Factors Affecting Photosynthesis
Photosynthesis and Cellular Respiration
Occur simultaneously in light
Comparison of photosynthesis and respiration
Figure 17-9, page 347
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C 4 Plants
Extra photosynthetic pathway
Acts as a CO2 pump
More rapid fixation
Needs more energy
Grow best in high light intensity
Sugar cane and corn
Crassulacean acid metabolism
Take in CO2 at night when temperature are low
Prevent water lose in hot and dry environments
Food-Making in Bacteria
Mistletoe, parasite of oaks
Dodder plant also parasitic
A common insectivorous plant found in the Northeast is the sundew. Its leaves are covered with hairlike tentacles. The tip of each tentacle has a drop of sticky fluid containing digestive enzymes. Insects attracted to the fluid become entrapped in it and are digested.
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