Water Flashcards
Explain why water is considered the medium for life
The first cells evolved in a watery environment, likely near hydrothermal vents in deep oceans. Water in its liquid state allows dissolved molecules to move around, so they are easily able to collide and react with each other. Most life processes occur in water. Scientists looking for life on other planets and moons look for evidence of water to suggest that life could have occurred there.
Describe the structure of a water molecule and how it leads to hydrogen bonding
Water is composed of one oxygen atom and two hydrogen atoms. The sharing of electrons is uneven, resulting in a weak negatively charged region (δ-) on the oxygen atom and weak positively charged regions (δ+) on the hydrogen atoms. This separation of charge creates a dipole, making water a polar molecule. The polarity allows hydrogen bonds to form between the positive and negatively charged regions of adjacent water molecules.
List the key functions of hydrogen bonding in biological systems.
- Dissolving of solutes in water
- Cohesion and adhesion of water molecules
- Base-pairing between DNA strands
- Secondary and tertiary levels of protein structure
- Tensile strength in cellulose and collagen
- Interactions between mRNA and tRNA during protein synthesis
- Surface effects on membranes between polar phosphate groups and water
Define cohesion and adhesion in the context of water molecules, and explain their significance in plants
- Cohesion: Strong attraction between water molecules due to hydrogen bonding. Allows columns of water to move under tension (mass transport) through the xylem of plants.
- Adhesion: Bonding of water molecules to other polar or charged molecules, such as cellulose. Enables water to move up the xylem during transpiration and through narrow channels in soil and plant cell walls by capillary action
Compare hydrophilic and hydrophobic molecules
Hydrophilic molecules are “water-loving,” polar or charged, and can form hydrogen bonds with water, allowing them to dissolve. Hydrophobic molecules are “water-hating,” non-polar, cannot form hydrogen bonds with water, and tend to group together due to hydrophobic interactions.
Evaluate the importance of water as a solvent in biological systems.
Water is regarded as the universal solvent. Highly soluble molecules (e.g., sodium chloride, urea, glucose, amino acids) can be easily transported within organisms. Some molecules’ functions depend on being hydrophobic and insoluble (e.g., phospholipids in cell membranes). Less soluble molecules like oxygen require special transport mechanisms (e.g., combining with hemoglobin). Most enzymes require water to hold their shape, improve stability, and catalyze reactions in aqueous solutions.
Explain how the specific heat capacity of water contributes to temperature regulation in living organisms.
Water has a high specific heat capacity (4200 J/kg/°C) due to numerous hydrogen bonds. It takes a lot of thermal energy to break and build these bonds, so water temperature does not fluctuate greatly. This provides stable aquatic habitats and helps maintain constant temperatures optimal for enzyme activity in organisms.
Analyze how the physical properties of water affect the survival of Arctic species like the ringed seal (Pusa hispida).
High specific heat capacity maintains stable sea temperatures. Ice’s lower density allows it to float, creating habitats on and below ice sheets. The thermal conductivity of ice is lower than liquid water, trapping heat below and increasing sea temperature. The seal’s blubber provides insulation and improves buoyancy.
Describe the extraplanetary origin hypothesis for water on Earth.
Earth was initially too hot for liquid water. Scientists hypothesize that water originated from asteroids and meteorites, particularly carbonaceous chondrites and eucrite achondrites, which contain ice and hydrogen isotopes similar to Earth’s water. Upon impact, these bodies released water vapor that condensed as Earth cooled, forming liquid water retained by gravity.
Explain the concept of the “Goldilocks zone” and its significance in the search for extraterrestrial life.
The Goldilocks zone is the area around a star where temperatures allow liquid water to exist on a planet’s surface. It’s neither too hot nor too cold, hence “just right.” Scientists search for exoplanets within Goldilocks zones of other solar systems as potential candidates for hosting life, using techniques like transit spectroscopy to analyze their atmospheres.
Describe how surface tension allows pond skaters to move across water surfaces.
Surface tension is created by hydrogen bonds between water molecules at the air-water interface. These bonds form a sort of film on the body of water, allowing insects such as pond skaters to move across the surface without breaking through.
Compare the viscosity of water and air, and explain how this affects the black-throated loon’s movement.
The viscosity of water is much higher than that of air. This allows the black-throated loon to fly through air with little friction. However, the loon’s body shape and webbed feet are adaptations that help it move efficiently through the more viscous water. The lateral location of its feet reduces drag as it moves through water.
Explain how the density of ice compared to liquid water affects aquatic ecosystems.
Ice is less dense than liquid water, causing it to float. This creates an insulating layer on top of bodies of water, allowing aquatic life to survive underneath even in freezing conditions. If ice sank, bodies of water would freeze from the bottom up, making survival difficult for many aquatic organisms.
Describe how the high latent heat of vaporization of water contributes to temperature regulation in organisms.
Water’s high latent heat of vaporization means a large amount of energy is required to convert liquid water to water vapor. This property allows for effective cooling through evaporation, such as sweating in mammals or transpiration in plants, helping organisms regulate their body temperature.
Explain how water’s properties as a polar molecule affect its ability to dissolve substances.
Water’s polarity allows it to dissolve many ionic compounds and polar molecules. The slightly negative oxygen atoms attract positive ions, while the slightly positive hydrogen atoms attract negative ions. This property makes water an excellent solvent for many biological molecules and cellular processes.
