A.1.1 Molecules - WATER Flashcards
Why did the first cells origin in water? Why is water a substance on which life depends?
First cells originated in water because:
1. Water blocked harmful UV rays
2. Provided a stable medium for aquatic organisms due to high specific heat capacity -> requires large amount of energy to change temperatures
3. Enzymes have an optimal temperature, so the water buffers the temperature of the cell so metabolic reactions can occur and the enzyme doesn’t denature
All living organisms require water to survive because:
1. Water forms a large proportion of living organisms
2. Water in the cytoplasm is the medium in which most processes of life occur
3. Biological enzymes must be dissolved in water
Outline the formation of hydrogen bonds between atoms
Hydrogen bonding is the electrostatic forces of attraction that form BETWEEN water molecules due to the polarity of water molecules.
It is weaker, and represented by a dotted line.
Describe a water molecule – why is it polar covalent? Draw the water molecule, using the correct notation.
Water is a polar covalent molecule due to the UNEQUAL SHARING OF ELECTRONS, which results in a permanent dipole.
Oxygen is partially negative, and hydrogen is partially positive.
The maximum number of hydrogen bonds that can be formed by one molecule of water is FOUR.
Outline the consequences of the collective strength of hydrogen bonds between water molecules
- High Heat Capacity and Thermal Stability: Hydrogen bonds allow water to absorb and release large amounts of heat with minimal temperature change. This high heat capacity stabilizes temperatures in aquatic environments and helps regulate the Earth’s climate.
- High Boiling and Melting Points: The strong hydrogen bonding in water requires a significant amount of energy to break these bonds, leading to high boiling and melting points compared to similar-sized molecules.
3.High Surface Tension: Hydrogen bonding at the surface of water molecules creates strong cohesive forces, resulting in high surface tension. This allows insects and small animals to walk on water surfaces and aids capillary action in plants.
- Density Anomalies: Water’s density decreases upon freezing due to the formation of a crystalline lattice with open hexagonal structures. This unique behavior of water explains why ice floats on liquid water and helps insulate aquatic environments.
- Solvent Properties: Water’s ability to form hydrogen bonds makes it an excellent solvent for polar and ionic compounds. It enables the dissolution of many essential biological molecules, facilitating chemical reactions and nutrient transport within living organisms.
Define cohesion
Cohesion is the electrostatic attraction between water molecules, due to hydrogen bonding, which is due to the polarity of the water, becuase of the partial positive hydrogen and partial negative oxygen.
Describe how water moves through the xylem of a vascular plant
Cohesion allows for the transport of water under tension in the xylem of plants.
- Water is transported in the xylem
- From roots to leaves
- Evaporation of water from the leaves pulls up water under tension in a continuous column of water
Outline the cause of surface tension
Surface tension is the result of cohesive forces between molecules at the surface of a liquid. It’s primarily caused by the imbalance of forces acting on molecules at the liquid-air interface compared to those within the bulk of the liquid
Cohesive forces are attractive interactions between molecules of the same substance. In a liquid, molecules are attracted to neighboring molecules by various intermolecular forces, such ashydrogen bonding (in the case of water).
State a benefit to living things that results from surface tension
Surface tension can cause small objects, like water droplets or insects, to adopt certain shapes that minimize their surface area, such as spherical droplets or the way insects “float” on water surfaces.
Some insects can use water surfaces as a habitat
Define adhesion
Adhesion is the attraction of water to polar or charged materials.
Outline the cause of capillary action. Describe capillary action in plant tissue. Outline the cause and effect of capillary action in soil.
- Water moves up to the roots in the soil by capillary action as its attracted to the charged soil particles
- Water is attracted to the polar molecules of cellulose (glucose) of the cell walls
- Water is drawn upwards in the xylem through capillary action
Explain why water is able to dissolve charged and polar molecules.
Water is a universal solvent – it can dissolve both polar and ionic substances.
- It forms hydrogen bonds with charged substances
- It isolates and surrounds ionic substances to form hydration shells
Outline the solvation of hydrophilic and hydrophobic substances
Solvation refers to the process of surrounding solute molecules with solvent molecules to form a homogeneous solution. The behavior of hydrophilic (water-attracting) and hydrophobic (water-repelling) substances in water is governed by the polarity of the molecules involved.
State an example of the function of a molecule depending on it being hydrophobic and insoluble.
An example of a molecule whose function depends on its hydrophobic and insoluble nature is cholesterol. Cholesterol is a lipid molecule that plays a crucial role in maintaining the structure and fluidity of cell membranes and serves as a precursor for the synthesis of important molecules such as steroid hormones and bile acids.
State an example of the function of a molecule depending on it being hydrophilic and soluble.
An example of a molecule whose function depends on its hydrophilic and soluble nature is glucose, a simple sugar that serves as a primary source of energy for many living organisms.
Outline the role of water as a medium for metabolism.
- Water contributes to the formation of cell membranes
- The spontaneous formation of bilayers as phospholipid heads interact with water, and tails try to avoid water - Water impact the folding of proteins
- Water drives the folding of amino acid chains ad different types of amino acids seek and avoid interacting with water
- Hydrophobic side chains in the protein’s interior, and hydrophilic side changes exposed on the protein’s surface
- Function-reliant shape - Water surrounds DNA to support the double helix
- Cells must be able to follow the careful instructions encoded by DNA
- Passes instructions onto further future cells
