Hydrogen Bonds in Water and Plant Cells (Arabic PDF)

‫بسم هللا الرحمن الرحيم‬  HYDROGEN BONDS  Hold water molecules  Extraordinary Properties together that are a result of hydrogen bonds.  Each water molecule can form a maximum ◦ Cohesive behavior of 4 hydrogen...

‫بسم هللا الرحمن الرحيم‬  HYDROGEN BONDS  Hold water molecules  Extraordinary Properties together that are a result of hydrogen bonds.  Each water molecule can form a maximum ◦ Cohesive behavior of 4 hydrogen bonds ◦ Resists changes in temperature  The hydrogen bonds ◦ High heat of vaporization joining water ◦ Expands when it freezes molecules are weak, ◦ Versatile solvent about 1/20th as strong as covalent bonds.  They form, break, and reform with great frequency  Hydrogen bonds hold the substance together, a phenomenon called cohesion  Cohesion is responsible for the transport of the water column in plants  Cohesion among water molecules plays a key role in the transport of water against gravity in plants  Adhesion, clinging of one substance to another, contributes too, as water adheres to the wall of the vessels. Hydrogen bonds hold the substance together, a phenomenon called cohesion Water and plant cells  Water and Plant Cells  80-90% of a growing plant cell is water  The actual cellular water content varies with cell type and physiological condition. - This varies between types of plant cells - Carrot has 85-95% water - Wood has 35-75% water - Seeds have 5-15% water Water and Plant Cells The physical and the chemical properties of water make it suitable for many purposes in plants. It is the medium in which diffusion of solutes takes place in plant cells. Water uptake can lead to cell expansion and also the generation of intracellular hydrostatic pressures, which can help support plants. It is well suited for temperature regulation because it has a high heat of vaporization, a high thermal capacity per unit mass, and a high thermal conductivity for a liquid. Water is also an extremely good general solvent, in part owing to the small size of its molecules. Its polar character makes water suitable for dissolving other polar substances. Its high dielectric constant makes it a particularly appropriate solvent for ions.  Plant continuously absorb and lose water - Lost through the leaves called transpiration  Water Transpiration  The evaporation of water into the atmosphere from the leaves and stems of plants.  It occurs chiefly at the leaves while their stomata are open for the passage of CO2 and O2 during photosynthesis.  Transpiration is not simply a hazard of plant life. It is the "engine" that pulls water up from the roots to: – supply photosynthesis (1%-2% of the total) – bring minerals from the roots for biosynthesis within leaf – cool the leaf.  Water (A) Hydrogen bonds between water molecules results in local aggregations of water Carbohydrate molecules chains Proteins (B) Theses are very short lived, break up rapidly to form more random configurations Due to temperature variations in water Phospholipids Properties of Water 1. Water is Liquid at 2. Water is the Room Temperature. Universal Solvent. - Low Mr Molecules are – Water “dissolves” polar usually gasses at RT. molecules - O2, Mr=32=gas – Water allows chemical - H20, Mr=18=liquid! reactions to occur Molecular refraction =Mr ‫االنكسار او تكسر الجزيئات‬ Properties of Water 3. Water is Cohesive 4. The temperature of – Water sticks to sides water rises and falls slowly – Water fills vessels – This prevents sudden or dramatic changes – Water molecules cling, – One calorie will raise 1g of but also rearrange, this water 1 degree C. allows water to flow – This is over two times the amount of energy required for other covalent molecules – Protection and Buffer Properties of Water 5. Water has a high heat 6. Frozen water is less of Vaporization dense than liquid water – Water to steam requires a – Lakes freeze from the top lot of energy down – This property helps – Allows for ice activities moderate the earth’s – Protects organisms in temperature Lakes – Life as we know it would not exist if we were all gasses.