Plant Transport

• Diffusion is the net movement of ions or solute molecules from a region of higher concentration to a region of lower concentration, down a concentration gradient
• Diffusion in gases: Gas molecules move from a region of higher concentration to that of a lower concentration until they are evenly spread
• Diffusion in liquids: Dissolved particles of a substance in a liquid move from a region where they are more concentrated to a region where they are less concentrated until they are evenly distributed
• Importance of Diffusion:

  • Initially, the concentration of a substance outside the cell is higher than inside the cell
  • The particles diffuse across the cell membrane
  • An equal concentration of the substance inside and outside the cell is attained
• Living cells continuously use up oxygen during aerobic respiration

  • The concentration of oxygen inside the cell falls
  • Oxygen molecules diffuse into the cell until the oxygen concentration is raised again
  • During respiration, carbon dioxide is produced
  • The concentration of carbon dioxide rises and creates a concentration gradient
  • Oxygen is supplied to Amoeba by diffusion, enabling metabolic wastes such as carbon dioxide to be excreted out
• Factors affecting the rate of diffusion:

  • Temperature: An increase in temperature results in a higher rate of diffusion
  • Size of particles: Small molecules or ions diffuse faster than large ones
  • Thickness of the barrier: Thicker cell walls result in a slower rate of diffusion
  • Concentration gradient: The greater the concentration gradient, the higher the rate of diffusion
  • Surface area: The rate of diffusion into a cell depends on the total surface area of the cell membrane
• Osmosis is the diffusion of water across a selectively permeable membrane, from a high water potential to a low water potential
• Osmotic potential is represented by (ΨS) and is a measure of the potential of water to move from one cell to another as influenced by solute concentrations
• Turgor pressure: The outward pressure which the cell sap exerts against the inside wall of the cell

  • In plant cells, if the cell sap has a lower water potential than that of the surrounding fluids, water from the outside enters by osmosis
  • Turgor is a state when a cell is firm or turgid due to water entering the cell, causing it to swell
• Pressure potential: Turgor pressure that develops against the cell walls as a result of water entering the vacuole of the cell
• Water potential is denoted by the Greek letter Ψ (PSI) and is expressed in units of pressure called megapascals (MPA), measuring the potential energy in water
• Importance of turgor in plants:

  • Changes in turgor of the guard cell causes the opening of the stomata
  • Changes in turgor of the pulvinus causes the folding of leaflets in the mimosa
• Plasmolysis: Loss of water through osmosis which is accompanied by the shrinkage of protoplasm away from the cell wall, leading to wilting
• Active transport is an energy-consuming process by which substances are transported from regions of low concentration to regions of high concentration against a concentration gradient
• drying - most primitive way para indi mag ban os
• turgid - swelling
• flaccid - shrinking
• water potential - diluted - concentrated
• hypotnic - lower concentration of solute
• hypertonic - high concentration of solute
• osmosis - hypotonic - hypertonic
• in dicot plants, if the stoma opens, then guard cell is swollen
• if stoma is closing, then vacuole is shrunk
• an advantage of opening of guard cells is that CO2 will be entering which is a raw material for photosynthesis
• disadvantage of opening of guard cell is the exit of water
• cytolysis - swelling of protoplasm
• shrinkage of protoplasm leads to wilting
• if cell is exposed to hypotonic environment, plant will absorb water from the soil
• if cell is exposed to hypertonic solution, soil will absorb water from plants
• uniport - one type of substance
• symport - 2 types substances enter w/ the same direction
• antiport - one enters, one exit