Active & Passive Transport in Plants: A Comprehensive Guide

Active Transport

Active transport moves substances across membranes from lower to higher concentration, against the concentration gradient. This process requires cellular energy (ATP) and a carrier protein.

The substance binds to the carrier protein's receptor site on one side of the membrane. ATP changes the protein's shape, releasing the substance on the other side. Active transport occurs only in living, respiring cells.

Factors influencing active transport:

• ATP Production: Increased ATP production increases active transport rate.
• Temperature and Oxygen: These affect respiration and ATP production, thus impacting transport rate.
• Mitochondria: Cells with more mitochondria have higher transport rates due to increased ATP production.
• Poisons: Respiratory poisons like cyanide halt ATP synthesis and active transport.

Stomata: Structure and Function

Stomata are openings in the plant epidermis, primarily on leaves. Each stoma is surrounded by two guard cells.

Stomata facilitate gas exchange (carbon dioxide and oxygen during photosynthesis and respiration) and transpiration (water vapor release).

Stomatal Opening and Closing

Stomatal opening and closing depend on the turgor pressure of guard cells. They typically open during the day and close at night.

Daytime: Water enters guard cells via osmosis, increasing turgor pressure. The inelastic inner wall causes the cells to bend and the pore opens.

Nighttime: Water loss from guard cells decreases turgor pressure, closing the pore.

Respiration and ATP

Food contains chemical energy. Respiration releases this energy by breaking down food (e.g., glucose) in cells. This energy is stored in mitochondria as adenosine triphosphate (ATP).

ATP consists of adenine, ribose, and three phosphate groups. It's formed by bonding adenosine diphosphate to a phosphate group in the cytoplasm, absorbing energy from glucose.

ATP powers various energy-requiring reactions.

Uses of ATP

• Cell division and growth
• Synthesis of proteins, fats, and vitamins
• Nerve impulse conduction and muscle movement
• Maintaining body temperature
• Active transport of molecules or ions
• Cellular response to chemical stimuli (e.g., nerve cell receptors)
• Organ activity coordination (e.g., insulin regulating blood sugar)