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Chapter 17

Plant Nutrition


Historical Background

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

Light Energy

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

Electromagnetic spectrum

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.

Photosynthetic Pigments

Chlorophylls most abundant and important pigments.

Two types

Chlorophyll a

Primary photosynthetic pigment

Chlorophyll b

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.

The Chloroplast

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

Photosystem I

Photosystem II


Light – Independent Reactions

Carbon fixation

Calvin cycle


5 – carbon sugar called ribulose bisphosphate


3 – carbon called phosphoglycerate

PGAL is phosphoglyceraldehyde

Factors Affecting Photosynthesis

Light intensity



Mineral availability

Photosynthesis and Cellular Respiration

Occur simultaneously in light

Comparison of photosynthesis and respiration

Figure 17-9, page 347

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Special Cases

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

CAM Plants

Crassulacean acid metabolism

Take in CO2 at night when temperature are low

Prevent water lose in hot and dry environments

Food-Making in Bacteria



Heterotrophic Plants


Mistletoe, parasite of oaks


Dodder plant also parasitic

Cannot photosynthesize


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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