Chapter 7 Plant Nutrition - Lecture Notes

Chapter 7: Plant Nutrition Students should be able to: 1.

Understand that photosynthesis is the fundamental process by which plants manufacture carbohydrates from raw materials. State the equation for photosynthesis Investigate and state the effects of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis. Describe intake of carbon dioxide and water by plants. Understand that chlorophyll traps light energy and convert it into chemical energy for formation of carbohydrates and their subsequent usage. Identify and label the cellular and tissue structure of a dicotyledonous leaf as seen in cross-section. #Understand the effect of lack of nitrate and magnesium ions on plant growth.

2. 3. 4. 5. 6. 7.

7.1 •

Photosynthesis Definition: Process by which plants manufacture carbohydrates from the raw materials of carbon dioxide and water. Chlorophyll

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Word Equation: Carbon Dioxide + Water  glucose + oxygen Light energy

Chlorophyll

6CO2 + 12 H 2 O → C 6 H 1 2 O6 + 6O2 + 6 H 2 O Light energy

7.2 •

Factors affecting photosynthetic rate (pg 121 of txtbk) These   

7.2.1

factors are Light Intensity Carbon Dioxide concentration Temperature

Light Intensity

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Photosynthetic rate

Light Intensity Explanation: • As light intensity ↑ from O to A ⇒ light is the limiting factor • Beyond A ⇒ rate of photosynthesis remains constant ⇒ light is no longer limiting factor. • So something else must have caused the rate to remain constant. What are they? Carbon dioxide conc and temperature

7.2.2

Temperature

Photosynthetic rate

Light Intensity Explanation: Photosyn is a process catalyzed by enzymes

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At higher temperatures, the enzymes are more active therefore rate of reaction is higher. However, beyond a certain range of optimum temperature, the enzymes start to denature thus rate of photosynthesis starts to decrease

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As temperature ↑ from 20°C to 30°C ⇒ photosynthetic rate ↑ but not as much ⇒ rate of photosynthesis remains more or less constant ⇒ temperature is not a limiting factor

7.2.3

Carbon Dioxide Concentration

Photosynthetic rate

Light Intensity Explanation: • As carbon dioxide concentration ↑ from 0.03% to 0.13% ⇒ photosynthetic rate ↑ by twice its original value ⇒ carbon dioxide concentration is the limiting factor • But atmospheric carbon dioxide concentration = 0.03% only • Only under lab conditions that carbon dioxide concentration > 0.03%  Under those conditions, a noticeable rise in photosynthetic rate is observed when temperature increases from 20°C to 30°C • Thus, carbon dioxide concentration is an important limiting factor.

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7.3

Intake of CO2 and H2O by plants (Pg 132 txtbk) Raw materials (H2O + CO2) Entry of H2O + mineral salts

Entry of CO2 Light

CO2 in leaf < CO2 in atm

Veins in leaf Form

Diffusion gradient forms Atm CO2  stomata  system of air spaces

CO2  dissolves in thin film of H2O on surface of mesophyll cells

Dissolved CO2  diffuses into cells

Fine branches ending among mesophyll cells Contains

Xylem

Phloem

Transport H2O + mineral salts soil  root  leaf Thru mesophyll of leaf

Diffuse from cell to cell

6CO2 12H2O

7.4 •

Function of chlorophyll Function of chlorophyll o Absorb light energy  convert to chemical energy Light

o 12H2O  6O2 + 24H (Light-Dependent Stage)

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o

Process is called photolysis= photo: light, lysis: breaking up of water molecules.

o The oxygen coming from RHS of the equation comes from H2O

7.5

Uses of Carbohydrates (txtbk pg 125)

Glucose in Green Leaves

7.6 Cellular & Tissue structure of a dicotyledonous leaf (txtbk pg 128-129) 7.6.1

Internal Structure of the Leaf Lamina

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7.6.2

Adaptations of Leaf to photosynthesis

Structure

Adaptation

Large surface area Thin Lamina

Absorb maximum light energy • Allows CO2 to reach inner cells rapidly. • Enables sunlight to reach all mesophyll cells. Chlorophyll absorbs and converts light energy to chemical energy used to manufacture sugars. More light energy can be absorbed near leaf surface. Allows rapid diffusion of CO2 to mesophyll cells. Open in sunlight, allowing CO2 to diffuse in and O2 to diffuse out of leaf. Xylem • Transports water and mineral salts to mesophyll cells

Chloroplasts found in all mesophyll cells More chloroplasts in upper palisade tissue Inter-connecting system of air spaces in mesophyll Stomata present in epidermal layers Veins containing xylem and phloem

Petiole (Leaf stalk)

Phloem • Transports sugars away from leaf Holds leaf in position to absorb maximum light energy

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#7.7 Effect of lack of minerals on plant growth (not in new syllabus 5100-2008) Mineral

Importance

Nitrates

Essential for synthesis of proteins, protoplasm, enzymes, nucleic acids Essential constituent of chlorophyll

Magnesium

Effect of lack of mineral • • •

Poor plant growth Leaves are few and pale green Seedlings eventually die

• •

Chlorophyll cannot be synthesized Chlorosis Yellow pigment deposited  leaves turn yellow

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