IB Bio A1.1 Water

• List reasons why water is a substance on which life depends.A1.1.1 - Water as medium of life.

  1. The first cells originated in water.2. Water is the "universal solvent" allowing it to dissolve and transport molecules around a body.3. Water is a metabolite in condensation and hydrolysis reactions.4. Water is a temperature buffer in bodies and ecosystems.5. Water maintains biological structures (such as phospholipid bilayer, proteins and DNA).

  
• Describe the structure of an atom.A1.1.2— Hydrogen bonds as a consequence of the polar covalent bonds within water molecules.

  Protons and neutrons make up the nucleus of the atom, while electrons orbit it in a "cloud".The electrons in an atom are attracted to the protons in the nucleus by an electromagnetic force in which the positive charge of the proton attracts the negative charge of the electron.

  
• Outline the formation of ionic bonds between atoms.A1.1.2— Hydrogen bonds as a consequence of the polar covalent bonds within water molecules.

  An ionic bond is an attraction between a positively charged ion and an negatively charged ion.

  
• Outline the formation of covalent bonds between atoms.A1.1.2— Hydrogen bonds as a consequence of the polar covalent bonds within water molecules.

  In a covalent bond, two atoms share one or more pair of electrons.

  
• Explain the sharing of electrons between atoms in a polar covalent bond.A1.1.2— Hydrogen bonds as a consequence of the polar covalent bonds within water molecules.


  In a polar covalent bond, the nucleus of one atom has more pull on the shared electrons than the other atom. As a result, it has a bigger electron cloud surrounding it. Because electrons have a negative charge and there are MORE ELECTRONS around this nucleus, there is a slight negative charge (ઠ-) on this nucleus. Because there are LESS ELECTRONS around the second atom's nucleus, there is a slight positive charge (ઠ+) on this nucleus

  
• State the location of the polar covalent bond within a water molecule.A1.1.2— Hydrogen bonds as a consequence of the polar covalent bonds within water molecules.

  There are two polar covalent bonds within a water molecule; one between the oxygen atom and each hydrogen atom.

  
• Explain the partial charges of the oxygen and hydrogen atoms within a water molecule.A1.1.2— Hydrogen bonds as a consequence of the polar covalent bonds within water molecules.

  The nucleus of the oxygen atom of a water molecules has more pull on the shared electrons than the hydrogen atom. As a result, it has a bigger electron cloud surrounding it. Because electrons have a negative charge and there are MORE ELECTRONS around the oxygen nucleus, there is a slight negative charge (ઠ-) on this nucleus. Because there are LESS ELECTRONS around the hydrogen atom's nucleus, there is a slight positive charge (ઠ+) on this nucleus

  
• Draw a water molecule, including notation to depict the partial charges of the atoms.A1.1.2— Hydrogen bonds as a consequence of the polar covalent bonds within water molecules.


  A water molecule consists of 2 hydrogen and 1 oxygen atom, hence…H2O. Within a water molecule, electrons are shared through polar covalent bonding between the atoms.

  
• Outline the cause of the formation of hydrogen bonds between water molecules.A1.1.2— Hydrogen bonds as a consequence of the polar covalent bonds within water molecules.

  The partially positive hydrogen atoms of one water molecule are attracted to the partially negative oxygen atom of a different water molecule, forming a hydrogen bond.

  
• Outline the consequences of the collective strength of hydrogen bonds between water molecules.A1.1.2— Hydrogen bonds as a consequence of the polar covalent bonds within water molecules.


  Water’s ability to make hydrogen bonds with itself and other charged molecules grants it a number of emergent properties such as cohesion, adhesion, solvency and a high specific heat. Collectively these property make water the primary medium of life.

  
• Define cohesion.A1.1.3— Cohesion of water molecules due to hydrogen bonding and consequences for organisms.

  Cohesion is the property of water in which it makes hydrogen bonds with itself, causing water molecules to stick together,

  
• Describe how water moves through the xylem of a vascular plant.A1.1.3— Cohesion of water molecules due to hydrogen bonding and consequences for organisms.

  1. Transpiration (evaporation) occurs through stomata of a leaf. As transpiration occurs, it creates negative pressure 2. The tension created by transpiration “pulls” water in the plant xylem, drawing the water upward3. Cohesion pulls up water molecules in a chain as the top-most water is pulled up and out of the stomata.

  
• Outline the cause of surface tension.A1.1.3— Cohesion of water molecules due to hydrogen bonding and consequences for organisms.


  The molecules on the surface are more attracted other molecules of the liquid than to molecules in the surrounding air. The net effect is an inward force that causes water to behave as if its surface were covered with a stretched elastic membrane.

  
• State a benefit to living things that results from surface tension.A1.1.3— Cohesion of water molecules due to hydrogen bonding and consequences for organisms.


  Surface tension allows organisms like water striders to “walk on water” and provides a stable environment for other organisms that live on or near the surface of water. To break through the surface of the water, enough force must be applied to break many hydrogen bonds simultaneously.

  
• Define adhesion.A1.1.4— Adhesion of water to materials that are polar or charged and impacts for organisms.


  The attraction of water to other polar or charged molecules is called adhesion.

  
• Define polar.A1.1.4— Adhesion of water to materials that are polar or charged and impacts for organisms.


  Polar means there is unequal sharing of electrons in a covalent bond between two atoms.

  
• Define ion.A1.1.4— Adhesion of water to materials that are polar or charged and impacts for organisms.


  An ion is an atom with different (unequal) numbers of electrons and protons.

  
• Compare cation and anion.A1.1.4— Adhesion of water to materials that are polar or charged and impacts for organisms.

  A cation has a positive charge because it has more protons than electrons (Na+)An anion has a negative charge because it has more electrons than protons (Cl-)

  
• Explain why water is attracted to molecules that are polar or charged.A1.1.4— Adhesion of water to materials that are polar or charged and impacts for organisms.

  The slight negative charge (δ-) of water oxygen atom is attracted to the [slight] positive charge of molecules that are polar or charged.The slight positive charge (δ+) of water hydrogen atom is attracted to the [slight] negative charge of molecules that are polar or charged.

  
• Outline the cause of capillary action.A1.1.4— Adhesion of water to materials that are polar or charged and impacts for organisms.

  Capillary action is the movement of water in through a narrow space, often in opposition to external forces like gravity. Adhesion of water to the walls of a vessel will cause an upward force on the liquid

  
• Describe capillary action in plant tissue.A1.1.4— Adhesion of water to materials that are polar or charged and impacts for organisms.


  Capillary action helps bring water from the roots all the way up to the branches and leaves. Adhesion of water to the xylem walls will cause an upward force on the water.

  
• Outline the cause and effect of capillary action in soil.A1.1.4— Adhesion of water to materials that are polar or charged and impacts for organisms.

  Capillary action in soil the primary force that enables the soil to retain water. In the same way that water moves upwards through a tube against the force of gravity; water moves upwards through soil pores, or the spaces between soil particles.

  
• Identify solvent and solutes of a solution.A1.1.5— Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals.

  Solvent: the liquid in which a solute dissolvesSolute: the substance that dissolves in a solvent

  
• Define solvation.A1.1.5— Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals.

  Solvation is the interaction of a solvent with the dissolved solute

  
• Explain why water is able to dissolve charged molecules.A1.1.5— Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals.


  Water is electrostatically attracted to ions.The slight positive charge (δ+) of of water hydrogen atom is attracted to the negative charge of an anion .The slight negative charge (δ-) of of water oxygen atom is attracted to the positive charge of a cation.

  
• Explain why water is able to dissolve polar molecules.A1.1.5— Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals.


  Polar molecules can form hydrogen bonds with water.The slight positive charge (δ+) of of water hydrogen atom is attracted to the negatively charged region of the solute.The slight negative charge (δ-) of of water oxygen atom is attracted to the positively charged region of the solute.

  
• Outline the solvation of hydrophilic and hydrophobic substances.A1.1.5— Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals.

  Hydrophobic means water fearing. Because they are not polar or charged, hydrophobic molecules will not dissolve in water. They are insoluble. Hydrophilic means water loving. Because they are polar or charged, hydrophilic molecules will dissolve in water. They are soluble.
• State an example of the function of a molecule depending on it being hydrophilic and soluble.A1.1.5— Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals.

  Because of they have hydrophillic amino acids, enzymes can dissolve in cytoplasm where they are used to catalyze chemical reactions in the cell.

  
• State an example of the function of a molecule depending on it being hydrophobic and insoluble.A1.1.5— Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals.


  Because of their hydrophobic tail, phospholipids will form bilayers in water, with the tails not exposed to water.

  
• Outline the role of water as a medium for metabolism.A1.1.5— Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals.

  Cytosol is the liquid part of the cytoplasm, a structure common to all cells. It is composed of about 80 percent water and also contains dissolved salts, fatty acids, sugars, amino acids, and proteins such as enzymes. These substances must be dissolved in water in order to carry out the metabolic processes required to keep the cell alive.

  
• Describe the role of water as a medium for transport in vascular plants.A1.1.5— Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals.

  Water is used to transport molecules through the body of vascular plants. Dissolved mineral ions are transported in the xylem from roots to leaves Dissolved sugars produced in photosynthesis are transported in the phloem from source to sink

  
• Describe the role of water as a medium for transport in animal blood.A1.1.5— Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals.

  Water is used to transport molecules through the body within the blood of animals. Blood plasma transports Salt ions Amino acids Proteins Glucose Waste products of metabolism A small amount of dissolved gasses

  
• Define physical property.A1.1.6— Physical properties of water and the consequences for animals in aquatic habitats.


  A physical property is a measurable behavior or characteristic of matter that exists without the matter reacting or interacting with other things.

  
• List physical properties of water that are consequential for animals in aquatic habitats.A1.1.6— Physical properties of water and the consequences for animals in aquatic habitats.

  BuoyancyViscosityThermal conductivitySpecific heat capacity

  
• Outline the cause and effect of buoyancy.A1.1.6— Physical properties of water and the consequences for animals in aquatic habitats.

  Cause:an upward force applied to an object that is immersed in a fluid. Effect: If the buoyant force of the fluid is greater than the object's weight, the object will float.

  
• Outline the cause and effect of viscosity.A1.1.6— Physical properties of water and the consequences for animals in aquatic habitats.

  Cause:Viscosity is due to the amount of friction the molecules of a liquid experience as they flow over each other. Effect:A thick fluid is more viscous and a thin fluid is less viscous.

  
• Compare viscosity of air to water to blood.A1.1.6— Physical properties of water and the consequences for animals in aquatic habitats.

  Air < Water < BloodMolecules in air have little friction as they flow over each other, so air is not viscous.Molecules in water can form hydrogen bonds with each other, increasing the friction and viscosity.Cells and dissolved solutes in blood cause even more friction as the blood flows, increasing viscosity.
• Define thermal conductivity.A1.1.6— Physical properties of water and the consequences for animals in aquatic habitats.

  Thermal conductivity is a measure of a material's ability to move heat across a temperature gradient.

  
• Compare less conductive to more conductive materials.A1.1.6— Physical properties of water and the consequences for animals in aquatic habitats.


  Less ConductiveHeat slowly moves through the material.Better at insulation and preventing heat loss.More ConductiveHeat rapidly moves through the material.Better for absorbing and transferring heat.
• Outline a consequence to life of the thermal conductivity of air and water.A1.1.6— Physical properties of water and the consequences for animals in aquatic habitats.

  Marine mammals are exposed to both air and water. The animal will lose more body heat to the environment when in water than in air because water rapidly absorbs and removes heat from the body. As a result, these animals have large layers of blubber which insulate their body heat sources (muscles) from the environmental. Fat is less conductive of thermal energy than water, so the animal is able to retain more body heat than it would be able to without the blubber.