Water

Question 1

Explain why water is considered the medium for life

Answer 1

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.

Question 2

Describe the structure of a water molecule and how it leads to hydrogen bonding

Answer 2

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.

Question 3

List the key functions of hydrogen bonding in biological systems.

Answer 3

• 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

Question 4

Define cohesion and adhesion in the context of water molecules, and explain their significance in plants

Answer 4

• 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

Question 5

Compare hydrophilic and hydrophobic molecules

Answer 5

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.

Question 6

Evaluate the importance of water as a solvent in biological systems.

Answer 6

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.

Question 7

Explain how the specific heat capacity of water contributes to temperature regulation in living organisms.

Answer 7

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.

Question 8

Analyze how the physical properties of water affect the survival of Arctic species like the ringed seal (Pusa hispida).

Answer 8

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.

Question 9

Describe the extraplanetary origin hypothesis for water on Earth.

Answer 9

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.

Question 10

Explain the concept of the “Goldilocks zone” and its significance in the search for extraterrestrial life.

Answer 10

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.

Question 11

Describe how surface tension allows pond skaters to move across water surfaces.

Answer 11

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.

Question 12

Compare the viscosity of water and air, and explain how this affects the black-throated loon’s movement.

Answer 12

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.

Question 13

Explain how the density of ice compared to liquid water affects aquatic ecosystems.

Answer 13

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.

Question 14

Describe how the high latent heat of vaporization of water contributes to temperature regulation in organisms.

Answer 14

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.

Question 15

Explain how water’s properties as a polar molecule affect its ability to dissolve substances.

Answer 15

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.

Question 16

Discuss how the thermal properties of water contribute to climate regulation on Earth.

Answer 16

Water’s high specific heat capacity and latent heat of vaporization allow it to absorb and release large amounts of heat with minimal temperature change. Oceans act as heat sinks, moderating temperatures and creating more stable climates in coastal areas. The water cycle, driven by these properties, also plays a crucial role in global heat distribution and weather patterns.

Question 17

Define viscosity and explain its significance in the movement of organisms like the black-throated loon and ringed seal.

Answer 17

Viscosity refers to the resistance of a fluid to flow. The viscosity of water is much higher than air, enabling the black-throated loon to fly through air with little friction. The body shapes of both the loon and seal are adapted for movement through water; the seal has flippers for propulsion, while the loon uses webbed feet that reduce drag as it moves through water.

Question 18

Why is water considered the medium for life?

Answer 18

Water is considered the medium for life because the first cells evolved in a watery environment, believed to be in the deep oceans near hydrothermal vents in the Earth’s crust. Water in its liquid state allows dissolved molecules to move around freely, enabling them to collide and react with each other. This property is crucial for most life processes, which occur in water. The strong link between water and life is so significant that scientists searching for extraterrestrial life look for evidence of water on other planets and moons as an indicator of potential life.

Question 19

How did the first cells originate in water?

Answer 19

The first cells are believed to have originated in water through a process where some water and solutes became trapped within a membrane near hydrothermal vents in the Earth’s deep oceans. Within this membrane-bound structure, chemical reactions began to occur, leading to the evolution of cells. The watery environment provided the necessary medium for these chemical reactions and allowed for the movement and interaction of molecules, which was essential for the development of early life forms.

Question 20

Why is liquid water crucial for life processes?

Answer 20

Liquid water is crucial for life processes because it allows dissolved molecules to move around freely, facilitating collisions and reactions between them. This property of water enables most biochemical reactions to occur efficiently. The ability of water to act as a solvent for many biological molecules is fundamental to cellular processes, including metabolism, signaling, and transport of nutrients and waste products. Additionally, water’s unique properties, such as its high specific heat capacity and ability to form hydrogen bonds, contribute to maintaining stable conditions necessary for life.

Question 21

How does the search for extraterrestrial life relate to water?

Answer 21

The search for extraterrestrial life is closely tied to the presence of water because of the strong link between water and life on Earth. Scientists looking for life on other planets and moons specifically search for evidence of water as a key indicator that life could have occurred there. This approach is based on the understanding that water is essential for life as we know it, providing the medium in which biological processes can occur. The presence of liquid water on a celestial body suggests the potential for habitable conditions and increases the likelihood of finding extraterrestrial life forms.

Question 22

What causes the polarity of covalent bonds within water molecules?

Answer 22

The polarity of covalent bonds within water molecules is caused by the unequal sharing of electrons between oxygen and hydrogen atoms. The oxygen atom attracts electrons more strongly than the hydrogen atoms, resulting in a weak negative charge (δ-) on the oxygen atom and weak positive charges (δ+) on the hydrogen atoms. This uneven distribution of charge creates an asymmetrical shape and makes water a polar molecule.

Question 23

How do hydrogen bonds form between water molecules?

Answer 23

Hydrogen bonds form between water molecules as a result of their polarity. The weak positive charge (δ+) on a hydrogen atom of one water molecule is attracted to the weak negative charge (δ-) on the oxygen atom of an adjacent water molecule. These hydrogen bonds are constantly breaking and reforming, but when present in large numbers, they create a strong structure that gives water many of its unique properties.

Question 24

How should hydrogen bonds between water molecules be represented in diagrams?

Answer 24

Hydrogen bonds between water molecules should be represented using dotted lines between the hydrogen atom of one molecule and the oxygen atom of another molecule. The polarity should be indicated using the delta symbol (δ) with a plus sign (δ+) near the hydrogen atoms and a minus sign (δ-) near the oxygen atom. The covalent bonds within the water molecule should be shown as solid lines.

Question 25

Why is water considered a polar molecule?

Answer 25

Water is considered a polar molecule because it has one end that is negatively charged and one end that is positively charged. This separation of charge occurs due to the electrons in the covalent bonds being unevenly shared between the oxygen and hydrogen atoms. The oxygen atom, being more electronegative, attracts the electrons more strongly, creating a dipole within the molecule.

Question 26

What is the significance of hydrogen bonding in water for living organisms?

Answer 26

Hydrogen bonding in water is significant for living organisms because it contributes to many of water’s unique properties that make it essential for life. These properties include its ability to act as a universal solvent, its high specific heat capacity, its cohesive and adhesive properties, and its ability to form a surface tension. These characteristics enable water to support various biological processes, from cellular reactions to the transport of substances within organisms.

Question 27

What is cohesion in water molecules and how does it occur?

Answer 27

Cohesion in water molecules refers to the strong attraction between water molecules due to hydrogen bonding. Hydrogen bonds form between the slightly positive hydrogen atoms of one water molecule and the slightly negative oxygen atoms of adjacent water molecules. Although individual hydrogen bonds are weak and constantly breaking and reforming, the large number of these bonds creates a strong cohesive force between water molecules. This cohesion allows water to form droplets and enables it to move as a continuous column in plant xylem.

Question 28

How does cohesion in water molecules enable transport in plant xylem?

Answer 28

Cohesion in water molecules enables the transport of water under tension in plant xylem. The strong hydrogen bonds between water molecules create a continuous column of water from the roots to the leaves. As water evaporates from the leaves during transpiration, it creates a tension (negative pressure) that pulls the water column upwards. The cohesive properties of water allow this column to remain intact, even under significant tension, enabling water to be transported against gravity in tall trees. This process, known as the cohesion-tension theory, is crucial for water and mineral transport in plants.

Question 29

What is surface tension and how does it relate to hydrogen bonding in water?

Answer 29

Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. In water, it is caused by the cohesive forces between water molecules due to hydrogen bonding. At the surface of water, these hydrogen bonds are particularly strong because water molecules at the surface have fewer neighboring molecules to bond with, so they form stronger bonds with those around and below them. This creates a “skin-like” effect on the water’s surface, allowing some organisms to walk on water and creating unique habitats at the air-water interface.

Question 30

How does surface tension create habitats for organisms?

Answer 30

Surface tension creates unique habitats for organisms at the air-water interface. The “skin-like” effect on the water’s surface allows small insects like water striders (pond skaters) to walk on water without breaking the surface. This creates a distinct ecosystem where these insects can live, hunt, and reproduce. Additionally, surface tension allows small objects to float on water even if they are denser than water, supporting various microorganisms and providing a substrate for some aquatic plants. The surface film also traps organic matter, creating a food-rich environment for many aquatic organisms.

Question 31

What are some adaptations of organisms that take advantage of water’s cohesive properties?

Answer 31

Organisms have evolved various adaptations to take advantage of water’s cohesive properties:
- Plants have developed vascular systems with narrow xylem vessels that maximize the cohesive forces of water, enabling efficient water transport.
- Some insects, like water striders, have hydrophobic legs that allow them to utilize surface tension to move on water surfaces.
- Some plants, like lotus leaves, have developed highly hydrophobic surfaces that use water’s cohesive properties to create a self-cleaning mechanism (the lotus effect).
- Certain fish species lay their eggs on the underside of the water surface, using surface tension to keep the eggs in place and oxygenated.

Question 32

What is adhesion in relation to water molecules?

Answer 32

Adhesion refers to the ability of water molecules to bond via hydrogen atoms to other molecules that are polar or charged, such as cellulose. This property is distinct from cohesion, which involves water molecules bonding to each other. Adhesion plays a crucial role in various biological processes, particularly in plants, where it enables water movement through the xylem and soil.

Question 33

How does adhesion contribute to water movement in plants?

Answer 33

Adhesion contributes to water movement in plants by enabling water to move up the xylem during transpiration. Water molecules adhere to the cellulose in the cell walls of xylem vessels, creating a continuous column of water from the roots to the leaves. This adhesion, combined with the cohesion between water molecules, allows water to be pulled upwards against gravity, facilitating the transport of water and dissolved minerals throughout the plant.

Question 34

What is capillary action and how does it relate to adhesion?

Answer 34

Capillary action is the ability of a liquid to flow against gravity in narrow spaces without the assistance of, and in opposition to, external forces like gravity. It occurs due to the combination of adhesive and cohesive forces. In the context of water, adhesion causes water to stick to the sides of a narrow tube or space, while cohesion pulls more water molecules along. This phenomenon is crucial in both soil water movement and water transport within plant tissues.

Question 35

How does capillary action function in soil?

Answer 35

In soil, capillary action allows water to be drawn up through narrow channels between soil particles. Water adheres to the soil particles due to their charged or polar nature, and cohesion between water molecules pulls more water upwards. This process enables water to move from wetter to drier areas of soil, helping to distribute moisture more evenly and making water available to plant roots even when the water table is below the root zone.

Question 36

What is the role of capillary action in plant cell walls?

Answer 36

Capillary action in plant cell walls enables water to flow through plant tissue. The spaces between cellulose fibers in plant cell walls act as capillary tubes, drawing water from xylem vessels. This process allows water to move laterally across plant tissues, ensuring that cells throughout the plant have access to water. It’s particularly important for maintaining cell turgor and facilitating the transport of water to areas not directly connected to the xylem, such as leaf mesophyll cells.

Question 37

Why is water considered a universal solvent?

Answer 37

Water is considered a universal solvent due to its polarity. The polar nature of water molecules allows them to form hydrogen bonds with other polar molecules and ions, causing them to dissolve. This property enables water to dissolve a wide variety of hydrophilic molecules, including many biological molecules essential for life processes. As a result, water serves as the medium for most metabolic reactions and facilitates the transport of substances within organisms.

Question 38

How do the solvent properties of water affect enzyme function?

Answer 38

The solvent properties of water are crucial for enzyme function. Most enzymes catalyze reactions in aqueous solutions, where water provides the medium for substrates and enzymes to interact. Water molecules can form hydrogen bonds with polar and charged amino acids in the enzyme’s active site, helping to maintain the enzyme’s three-dimensional structure. Additionally, water can participate in many enzymatic reactions, acting as a reactant or product. The aqueous environment also allows for the easy movement of substrates and products to and from the enzyme’s active site.

Question 39

What is the difference between hydrophilic and hydrophobic molecules in relation to water?

Answer 39

Hydrophilic molecules are “water-loving” and can form hydrogen bonds with water, allowing them to dissolve easily. These include polar molecules and those with positive or negative charges. Hydrophobic molecules are “water-hating” and cannot form hydrogen bonds with water. They are typically non-polar molecules with no positive or negative charge. In biological systems, hydrophilic molecules are often involved in reactions and transport in aqueous environments, while hydrophobic molecules play crucial roles in structures like cell membranes.

Question 40

How do the solvent properties of water contribute to transport in plants and animals?

Answer 40

The solvent properties of water are essential for transport in plants and animals. In plants, water dissolves minerals and nutrients from the soil, allowing them to be transported through the xylem to other parts of the plant. In animals, blood plasma, which is mostly water, dissolves and transports various substances including glucose, amino acids, hormones, and waste products throughout the body. The ability of water to dissolve gases also enables the transport of oxygen and carbon dioxide in blood and cellular fluids.

Question 41

Why are some biological molecules hydrophobic, and what roles do they play?

Answer 41

Some biological molecules are hydrophobic because their functions depend on them being insoluble in water. For example, phospholipids in cell membranes have hydrophobic hydrocarbon tails that form the hydrophobic core of the membrane. This hydrophobic nature is crucial for maintaining the integrity and selective permeability of cell membranes. Other examples include some vitamins (A, D, E, K) and hormones (steroid hormones) that are lipid-soluble, allowing them to pass through cell membranes easily. The hydrophobic nature of these molecules is essential for their specific biological functions.

Question 42

What is specific heat capacity and how does it affect aquatic habitats?

Answer 42

Specific heat capacity is the amount of energy required to raise the temperature of 1 kg of a substance by 1°C. Water has a high specific heat capacity (4200 J/kg/°C) compared to air (1000 J/kg/°C). This property provides stable aquatic habitats as water temperatures change more slowly than air temperatures. It allows aquatic organisms to maintain constant body temperatures and provides optimal conditions for enzyme activity. For example, the ringed seal (Pusa hispida) can survive year-round in arctic and sub-arctic regions due to the stable sea temperatures maintained by water’s high specific heat capacity.

Question 43

How does the thermal conductivity of water compare to air, and what are the implications for aquatic animals?

Answer 43

The thermal conductivity of water is almost 30 times higher than that of air. This means water conducts heat much more efficiently than air. For aquatic animals like the black-throated loon (Gavia arctica), this presents a challenge in maintaining body temperature. To adapt, these birds have evolved features like feathers that trap an insulating layer of air, helping them regulate body temperature while diving for prey. In contrast, seals like the ringed seal rely on a layer of blubber for insulation, as it’s more effective in the highly conductive aquatic environment.

Question 44

What is buoyancy and how do aquatic animals adapt to it?

Answer 44

Buoyancy refers to the ability of an object to float in water. Aquatic animals must adapt to overcome or utilize buoyancy. The black-throated loon, for instance, has evolved solid bones, unlike the hollow bones of most bird species. This adaptation increases the bird’s weight and helps compress air out of its lungs and feathers during dives, allowing it to overcome buoyancy and dive effectively. Conversely, the ringed seal uses its blubber layer not only for insulation but also to improve buoyancy, helping it float more easily in its aquatic habitat.

Question 45

How does the viscosity of water affect aquatic animals, and how does it compare to air?

Answer 45

Viscosity refers to a fluid’s resistance to flow. Water has a much higher viscosity than air, which affects how animals move through it. Both the black-throated loon and the ringed seal have evolved body shapes that allow them to move efficiently through water despite its higher viscosity. The loon uses webbed feet to propel itself, with the feet positioned laterally to reduce drag. The seal has flippers adapted for efficient propulsion through water. In contrast, the loon’s ability to fly through air with less friction demonstrates the lower viscosity of air compared to water.

Question 46

How do the physical properties of water contribute to the formation of ice, and what are the implications for aquatic habitats?

Answer 46

Water has the unique property of being less dense as a solid (ice) than as a liquid. This causes ice to float on water, forming an insulating layer above liquid water in aquatic habitats. The thermal conductivity of ice is much lower than that of liquid water, which helps trap thermal energy below the ice. This property is crucial for aquatic life in cold climates, as it allows organisms like the ringed seal to survive under ice sheets. The floating ice provides a habitat both on its surface and in the warmer water beneath, essential for the seal’s survival in arctic environments.

Question 47

What is the hypothesis for the extraplanetary origin of water on Earth?

Answer 47

The hypothesis suggests that Earth’s water originated from asteroids. When Earth formed about 4.5 billion years ago, conditions were too hot for water vapor to condense into liquid water. Scientists believe that asteroids, and the meteorites that break off from them, brought water to Earth. Many asteroids contain ice and other organic materials that could have contributed to the evolution of life on Earth.

Question 48

What evidence supports the asteroid hypothesis for Earth’s water origin?

Answer 48

Two types of ancient meteorites provide evidence for the asteroid hypothesis:
- Carbonaceous chondrites, one of the oldest groups of meteorites in the solar system, contain hydrogen isotopes similar to those found in seawater.
- Eucrite achondrites, another group of ancient meteorites, contain ratios of hydrogen isotopes similar to those found on Earth.
These similarities in isotope composition support the idea that asteroids could be the source of Earth’s water.

Question 49

How did water from asteroids become liquid water on Earth’s surface?

Answer 49

During asteroid impacts with Earth, water vapor would have been released. This vapor would have been trapped by Earth’s gravity. As Earth’s temperatures cooled, they became low enough to allow this water vapor to condense and form liquid water. The liquid water was then retained on the surface by Earth’s gravity.

Question 50

What are the two main reasons for the retention of water on Earth?

Answer 50

The two main reasons for the retention of water on Earth are:
- Gravity: Earth’s gravitational force was strong enough to keep water from escaping into space.
- Temperature: Earth’s temperature cooled sufficiently to allow water vapor to condense into liquid form, which could then be retained on the surface.

Question 51

Why is the abundance of water over billions of years significant for life on Earth?

Answer 51

The abundance of water over billions of years of Earth’s history has allowed life to evolve. Water is crucial for the existence of life as we know it. Its presence in liquid form on Earth’s surface for such a long period has provided a stable environment for life to develop and diversify. This long-term availability of water has been a key factor in the evolution of complex life forms on our planet.

Question 52

Why is water crucial in the search for extraterrestrial life?

Answer 52

Water is considered essential for life as we know it. Living organisms depend on water for their existence, so the presence of liquid water is a key requirement for any planet to potentially support life. Scientists searching for extraterrestrial life specifically look for evidence of water on other planets and moons as an indicator that life could exist there. This approach is based on our understanding of life on Earth and the fundamental role water plays in biological processes.

Question 53

What is the “Goldilocks zone” and why is it important in the search for extraterrestrial life?

Answer 53

The “Goldilocks zone,” also known as the habitable zone, is the area around a star where temperatures are favorable for water to exist in liquid form. It’s named after the story of Goldilocks and the three bears, where conditions are “just right.” This zone is crucial in the search for extraterrestrial life because liquid water is considered essential for life as we know it. Planets in this zone are neither too hot (where water would evaporate) nor too cold (where water would freeze), but have the potential for liquid water on their surface.

Question 54

How does a planet’s distance from its star relate to the Goldilocks zone?

Answer 54

A planet’s distance from its star directly affects its temperature and, consequently, its ability to maintain liquid water. To be in the Goldilocks zone, a planet must be at the correct distance from its star - not too close and not too far. If a planet is too close to its star, it will be too hot for liquid water. If it’s too far, it will be too cold. The exact boundaries of this zone depend on the star’s size and energy output.

Question 55

What are exoplanets and how do they relate to the search for extraterrestrial life?

Answer 55

Exoplanets are planets located outside our solar system, orbiting other stars. In the search for life beyond our solar system, scientists are particularly interested in exoplanets located within the Goldilocks zone of their respective stars. These planets have the potential for liquid water on their surface, making them prime candidates in the search for extraterrestrial life.

Question 56

How do scientists detect the presence of water on exoplanets?

Answer 56

Scientists use a technique called transit spectroscopy to analyze exoplanets. This method examines the light passing through a planet’s atmosphere as it transits in front of its star. By analyzing the wavelengths of light being absorbed or deflected, scientists can determine the elements and molecules present in the planet’s atmosphere. If the analysis indicates the presence of water vapor, it suggests that the planet may have liquid water on its surface, making it a potential candidate for harboring life.