Download PDF Physicochemical and Environmental Plant Physiology FOURTH EDITION
by Park S. Nobel
Sinopsis
Figure 1-1 depicts a representative leaf cell from a higher plant and illustrates the larger subcellular structures. The living material of a cell, known as the protoplast, is surrounded by the cell wall. The cell wall is composed of cellulose and other polysaccharides, which helps provide rigidity toindividual cells as well as to the whole plant. The cell wall contains numerous relatively large interstices, so it is not the main permeability barrier to the entry of water or small solutes into plant cells. The main barrier, known as the plasma membrane (or plasmalemma), is found inside the cell wall and surrounds the cytoplasm. The permeability of this membrane varies with the particular solute, so the plasma membrane can regulate what enters and leaves a plant cell. The cytoplasm contains organelles such as chloroplasts and mitochondria, which are membranesurrounded compartments in which energy can be converted from one form to another. Chloroplasts, whose production and maintenance is a primary function of plants, are the sites for photosynthesis, and mitochondria are the sites for respiration. Microbodies, such as peroxisomes and ribosomes, are also found in the cytoplasm along with macromolecules and other structures that influence the thermodynamic properties of water. Thus, the term cytoplasm includes the organelles (but generally not the nucleus), whereas the term cytosol refers to the cytoplasmic solution delimited by the plasma membrane and the tonoplast (to be discussed next) but exterior to the organelles.
In mature cells of higher (evolutionarily advanced) plants and many lower plants, there is a large central aqueous compartment, the central vacuole, which is surrounded by a membrane called the tonoplast. The central vacuole is usually quite large and can occupy up to about 90% of the volume of a mature cell. Because of the large central vacuole, the cytoplasm occupies a thin layer around the periphery of a plant cell (Fig. 1-1). Therefore, for its volume, the cytoplasm has a relatively large surface area across which diffusion can occur. The aqueous solution in the central vacuole contains mainly inorganic ions or organic acids as solutes, although considerable amounts of sugars and amino acids may be present in some species. Water uptake by this central vacuole occurs during cell growth and helps lead to the support of a plant.
Content
- Cells and Diffusion
- Cell Structure
- Diffusion
- Membrane Structure
- Membrane Permeability
- Cell Walls
- Water
- Physical Properties
- Chemical Potential
- Central Vacuole and Chloroplasts
- Water Potential and Plant Cells
- Solutes
- Chemical Potential of Ions
- Fluxes and Diffusion Potentials
- Characteristics of Crossing Membranes
- Mechanisms for Crossing Membranes
- Principles of Irreversible Thermodynamics
- Solute Movement Across Membranes
- Light
- Wavelength and Energy
- Absorption of Light by Molecules
- Deexcitation
- Absorption Spectra and Action Spectra
- Photochemistry of Photosynthesis
- Chlorophyll—Chemistry and Spectra
- Other Photosynthetic Pigments
- Groupings of Photosynthetic Pigments
- Electron Flow
- Bioenergetics
- Gibbs Free Energy
- Biological Energy Currencies
- Chloroplast Bioenergetics
- Mitochondrial Bioenergetics
- Energy Flow in the Biosphere
- Temperature and Energy Budgets
- Energy Budget—Radiation
- Heat Conduction and Convection
- Latent Heat—Transpiration
- Further Examples of Energy Budgets
- Soil
- Leaves and Fluxes
- Resistances and Conductances—Transpiration
- Water Vapor Fluxes Accompanying Transpiration
- CO2 Conductances and Resistances
- CO2 Fluxes Accompanying Photosynthesis
- Water-Use Effi iency
- Plants and Fluxes
- Gas Fluxes above Plant Canopy
- Gas Fluxes within Plant Communities
- Water Movement in Soil
- Water Movement in the Xylem and the Phloem
- Soil–Plant–Atmosphere Continuum
