Essential Plant Processes: Nutrition, Transport, and Leaf Function

Plant Nutrition

Photosynthesis: The process by which plants manufacture carbohydrates from raw materials using energy from light.

Key Aspects of Photosynthesis and Respiration

• Chlorophyll: Transfers light energy into chemical energy stored in molecules, essential for the synthesis of carbohydrates.
• Carbohydrate Use and Storage: Aside from using complex carbohydrates to create the plant's structure, plants store carbohydrates or use them for energy to grow.
• Respiration: To utilize stored carbohydrates, plants take the glucose formed during photosynthesis and combine the carbohydrate with oxygen—a process called respiration—to release energy.
• Role of Chlorophyll and CO₂: Chlorophyll is required because it helps absorb the light needed for photosynthesis. Carbon dioxide (CO₂) is important because it is converted into sugars, such as glucose.

Factors Affecting the Rate of Photosynthesis

The rate of photosynthesis is affected by varying light intensity and temperature:

• Light Intensity: Without sufficient light, a plant cannot photosynthesize very quickly, even if there is plenty of water, carbon dioxide, and a suitable temperature.

Features of the Leaf

Key structures within the leaf facilitate essential plant functions:

• Palisade Mesophyll: Primary site for the distribution of chloroplasts and photosynthesis.
• Stomata, Spongy Mesophyll Cells, and Guard Cells: Facilitate gas exchange (CO₂ intake and O₂ release).
• Xylem: Provides transport of water and minerals, and structural support.
• Phloem: Responsible for the transport of sugars and organic nutrients.

Essential Mineral Ions

Nitrate Ions (Nitrogen Source)

Nitrate ions are crucial as they provide nitrogen, which the plant uses to synthesize its own amino acids for protein production.

Magnesium Ions (Chlorophyll Production)

Plants use magnesium ions specifically to manufacture chlorophyll in their leaves.

Effects of Mineral Deficiency

Deficiency in essential ions, such as nitrate or magnesium, compromises plant growth. Specifically, the plant's photosynthetic ability is limited, leading to stunted development.

Transport in Plants

Plants utilize specialized transport systems—continuous tubes called xylem and phloem—to move food, water, and minerals throughout the organism.

Xylem Function

The basic function of xylem is to transport water and dissolved mineral nutrients from the roots to the shoots and leaves. The roots, stems, and leaves are interconnected, forming a continuous system of water-conducting channels that reach all parts of the plant. Water is transported upwards through the xylem vessels.

Phloem Function

Phloem carries sugars and other organic nutrients, synthesized by the plant (primarily in the leaves), to the rest of the plant for storage or immediate use.

Root Hair Cells

Root hair cells are specialized for the absorption of water and minerals from the soil. They possess a large number of mitochondria, which supply the necessary energy for active transport of minerals.

Transpiration

Transpiration is defined as the loss of water vapor from plant leaves. This occurs through the evaporation of water at the surfaces of the mesophyll cells, followed by the diffusion of water vapor through the stomata.

Environmental Effects on Transpiration Rate

• Temperature: Higher temperatures cause the guard cells (which control the stomatal openings) to open, increasing the rate of water release. Colder temperatures cause these openings to close.
• Relative Humidity: As the relative humidity of the air surrounding the plant rises, the concentration gradient for water vapor decreases, causing the transpiration rate to fall.