LECTURE #7: Plant Nutrition and Photosynthesis

I. PLANT NUTRITION

1. For a plant to survive and grow, it must be nourished: (Fig 37.1)

a. CO₂, H₂O, and minerals

b. O₂ for cellular respiration

2. Essential nutrients: (Table 37.1) (Fig. 37.2)

a. macronutrients = elements that plants need in relatively large amounts.

b. micronutrients = elements that plants need in very small amounts.

3. Roots and shoots are anatomically adapted for absorbing essential nutrients. (Fig 37.6)

a. cellular respiration in roots produces CO₂, which reacts with H₂O to give H⁺ + HCO₃^-.

b. H⁺ ions displace positively charged minerals on surface of fine soil particles.

4. Nitrogen assimilation is the process of nitrogen intake by plants. (Fig 37.9)

a. atmospheric nitrogen enters the soil.

b. nitrogen fixing bacteria in soil produce nitrogenase.

(this enzyme reduces N₂ by adding hydrogen ions to form ammonia (NH₃).

(this process is very ATP expensive to bacteria—8 ATP/NH₃).

(All of Earth’s life depends on nitrogen fixation by prokaryotes.)

c. in soil, NH₃ (ammonia) picks up another H to form ammonium (NH₄⁺).

d. plants can absorb NH₄⁺, but they take in NO₃^- more readily.

e. NO₃^- (the main source of nitrogen) is formed by nitrifying bacteria.

f. absorbed NO₃^- is transported in xylem to leaves, or converted back to NH₄⁺ first.

g. NO₃^- is reduced to NH₃ and incorporated into amino acids before transport to in leaves

5. Rhizobium is a bacteroid in nodules of legume roots that are symbiotic. (Fig 37.11)

a. the bacteria supply the legume with fixed nitrogen.

b. the legume supplies the bacterium with sugar and other organic compounds.

6. look at carnivorous plants (Fig 37.14, page 727).

II. PHOTOSYNTHESIS (Life on earth is solar-powered)

A. AUTOTROPHS

1. Organisms that can manufacture their own organic compounds from inorganic raw materials taken from the environment.

2. Most autotrophs are photosynthetic (photoautotrophs). (A few are chemosynthetic).

3. Photosynthetic plants are by far the most important autotrophs.

B. HETEROTROPHS

1. Organisms that are incapable of manufacturing their own organic compounds, and therefore must obtain prefabricated material from the "PRODUCERS"

2. Most heterotrophs must have complex digestive systems to breakdown relatively large organic matter into components that can be absorbed and reassembled.

3. Bacteria, fungi, protozoa, and animals are common heterotrophs. (hetero = other)

C. PHOTOSYNTHESIS (Fig 10.2)

1. Chloroplasts in the leaves are the major site of photosynthesis in most plants.

2. Chloroplasts are mainly in the mesophyll, the green tissue in the interior of leaf.

3. A typical mesophyll cell has 30-40 chloroplasts that are lens-shaped (like RBCs).

4. Chlorophyll is in the thylakoid membranes of chloroplasts.

5. In the presence of light, chloroplasts convert CO₂ + H₂O ® O₂ + organics (glucose).

6. O₂ comes from the H₂O (van Niel).

7. Photosynthesis: the two stages of this vital process: (Fig 10.4)

a. the light reactions:

(1) light absorbed by chlorophyll transfers electrons from H₂O to NADP⁺ (acceptor).

(2) NADP⁺ is reduced to NADPH by adding a pair of electrons and H⁺.

(3) H₂O is split in the process, giving rise to O₂.

(4) light also drives photophosphorylation (ADP to ATP).

(5) thus, the light reaction produces NADPH and ATP.

b. the Calvin Cycle: (i.e., the dark reaction, since it does not require light).

(1) utilizes the high-energy products of light reaction to convert CO₂. (i.e., carbon fixation)

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