General Botany I Physiology Lecture Notes PDF

‫بسم هللا الرحمن الرحيم‬ General Botany I Physiology Prepared by Prof assist Dr. Zeinab Ashour  What is plant physiology? Is the study of the function of cells, tissues, organs of plant; and the chemistry of these functions… But it is important to recognize that these functions de...

‫بسم هللا الرحمن الرحيم‬ General Botany I Physiology Prepared by Prof assist Dr. Zeinab Ashour  What is plant physiology? Is the study of the function of cells, tissues, organs of plant; and the chemistry of these functions… But it is important to recognize that these functions depend on structures. Photosynthesis Control all cell functions Store solutes to determine the osmotic potential of cell Respiration Diffusion and permeability Cytoplasm Where many biochemical reactions take place  OUR COURSE ❑Diffusion, osmosis and permeability PLASMA MEMBRANE ❑Colloids in plants CYTOPLASM ❑PHOTOSYNTHESIS CHLOROPLAST ❑RESPIRATION MITOCHONDRIA ❑ENZYMES IN ALL COMPARTMENTS  evaluation 10 mark midterm Exam 15 mark for Oral Exam and assignments 20 mark for Practical Exam 60 mark For Final written exam ▪ All cells are enclosed in a membrane that serves as outer boundary, separating the cytoplasm from the external environment. ▪ This plasma membrane allows the cell to take up or retain certain substances while excluding others. ▪ Various transport proteins embedded in the plasma membrane are responsible for this selective transport of solutes across the membrane. All biological membranes have the same basic molecular organization. ▪ They consist of a double layer (bilayer) of phospholipids combined (interspersed) with proteins. The composition of the phospholipids and the properties of the proteins vary from membrane to membrane, conferring on each membrane its unique functional characteristics. ▪ ▪ Phospholipids are class of lipids in which two fatty acids covalently linked to glycerol, which is covalently linked to a phosphate group. Also attached to this phosphate group is a variable component such as serine, choline, glycerol, or inositol. The fatty acids consider as non- polar tails and they vary from head components which are highly polar; consequently, phospholipids molecules display both hydrophilic and hydrophobic properties. The nonpolar hydrocarbon chains of the fatty acids from a region that is exclusively hydrophobic and that excludes water.  The proteins associated with the lipid bilayer are of two types, integral and peripheral (they have also been called intrinsic, or extrinsic, respectively). Integral proteins are embedded in the lipid bilayer. So that one part of the protein interact with the outside of the cell, another part interacts with the hydrophobic core of the membrane, and a third part interacts with the interior of the cell, the cytosol.  Peripheral proteins are attached to the membrane surface by non-covalent bonds. Peripheral proteins have several roles in membrane function. For example, they are involved in interactions between the plasma membrane and components of the cytoskeleton, such as microtubules.  How the plasma membrane controls permeability to the different substances? The plasma membrane is characterized by its selective permeability that is they allow the passage of certain substances and prevent the passage of others.  Permeability to non-ionized substances In general, the non-ionized solutes enter and leave the cell by diffusion. Diffusion can be simply defined as the movement of particles of matter due to their own kinetic energy. The direction of movement of these particles is from the region of their higher concentration to the region of their lower concentration in order to equalize the concentration of the two regions. Even after equilibrium is reached the diffusion continues in both directions at equal rates  1- Size Small and non-polar substances diffuse directly through membrane without need any help such as gases CO2 and O2 (called passive simple diffusion). Large substances need assistance (help) of membrane proteins such as channels or carriers to diffuse through it (called passive facilitated diffusion).  2- Solubility in oily materials Substances showing the greatest affinity for oil are substances which penetrate rapidly. If two substances have equal lipid solubility, then the larger molecules penetrate more slowly than smaller molecules. From these and other findings, it can be said that the protoplasmic membrane appears to be not a simple lipid membrane, but it has been suited to the penetration of small molecules and to hinder the penetration of large molecules.  Permeability to ionic substances: Although ions are very small in size compared with the large molecules of non-ionized substances, but they diffuse through the plasma membranes at a much slower rate. In spite of the low rate of diffusion of the ions, the cells continue to take up an ion even if the concentration of this ion inside the cell is higher than the concentration in the external medium. It may be concluded, therefore, that the entrance of ionic substances into the cells is not (not all time) a passive diffusion process.  In this process, the diffusion needs energy so that the ions can move against a concentration gradient i.e., from the dilute to the concentrated side. This type of absorption is called active absorption (active transport). Metabolic energy and transmembrane protein (pump)are involved in this active transport. The accumulation of ions or molecules in the cytosol through the action of transport proteins consumes metabolic energy.  Selective uptake of ions. Living cells seem to have the ability to distinguish between the different ions; absorbing and accumulating and rejecting others. It has been found that monovalent cations such as K+ are absorbed and accumulated more rapidly than polyvalent cations such as Ca2+. Even among ions with the same valence, the cells prefer some of them to others. Most plants, for example, accumulate K+ more than Na+, Cl-, Br-, and NO3- are also accumulated more rapidly than SO42-.