Studied by 6 peopleList reasons why water is a substance on which life depends.
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).
Explain the sharing of electrons between atoms in a polar covalent bond.
the nucleus of one atom has more pull on the shared electrons than the other atom
as a result, the electrons spend more time with this atom, causing it to be slightly negatively charged
because the electrons spend less time with the other atom, it is said to be slightly positively charged
State the location of the polar covalent bond within a water molecule.
Water molecules are made up of one oxygen atom covalently bonded to two hydrogen atoms.
There are two polar covalent bonds within a water molecule; one between the oxygen atom and each hydrogen atom.
This means that oxygen is slightly negatively charged and the hydrogen atoms are slightly positively charged
Define Electronegativity.
A measure of how much an atomic nucleus attracts the electrons that are involved in a chemical bond.
Outline the cause of the formation of hydrogen bonds between 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.
Hydrogen bonds are indicated with dotted lines
Outline the consequences of the collective strength of hydrogen bonds between water molecules.
Water’s ability to make hydrogen bonds with itself and other charged molecules grants it a number of emergent properties
Collectively these property make water the primary medium of life.
Define cohesion.
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.
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 upward
3. 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.
The molecules on the surface are more attracted to other molecules of the liquid than to molecules in the surrounding air, as a result of cohesion.
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. (Water Skaters)
Surface tension allows organisms like water striders to “walk on water”
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 Capillary Action.
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
Usually caused when adhesion is greater than cohesion
Describe capillary action in plant tissue.
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.
Capillary action in soil is 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.
Describe how does Capillary Action benefit plants.
Capillary action occurs in sands and soils, drawing moisture above the water line.
As water is absorbed, it is also replaced by capillary action.
Plants also use capillary action to move water into cell walls, the cellulose fibres that compose the cell wall pull water into the spaces between them.
Prevents plant cells from drying out
Define hydrophilic molecules and why they behave like that.
Attracted to water
As they are also polar or have areas where there is uneven distribution of positive and negative charge
Dissolve in water
Define hydrophobic molecules and why they behave like that.
Are not attracted to water
They are also referred to as non-polar which is why they don’t attract to water
Dissolve in polar substances
Define adhesion.
The attraction of water to other polar or charged molecules
Define polar.
Polar means there is unequal sharing of electrons in a covalent bond between two atoms.
Explain why water is attracted to molecules that are polar or charged.
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.
State an example of the function of a molecule depending on it being hydrophilic and soluble.
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.
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.
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.
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.
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
List physical properties of water that are consequential for animals in aquatic habitats.
Buoyancy
Viscosity
Thermal conductivity
Specific heat capacity
Define Buoyancy
An upward force on an object in a fluid that opposes the weight (gravitational force).
If the buoyant force of the fluid is greater than the object's weight, the object will float.
Compare Buoyancy to air and water.
The high density of liquid water creates high buoyancy, allowing less dense materials to float.
Air, being much less dense than water, is much less buoyant as well.
Define Viscosity
The property of a fluid related to its resistance to flow.
Viscosity is due to the amount of friction the molecules of a liquid experience as they flow over each other.
A thicker fluid is more viscous than a thinner one
Compare viscosity of air to water to blood.
Air < Water < Blood
- Molecules 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.
Thermal conductivity is a measure of a material's ability to move heat across a temperature gradient.
Compare Thermal Conductivity to air and water
Water has a high thermal conductivity compared with other liquids (except liquid metals).
Air has a much lower thermal conductivity than water.
Outline a consequence to life of the thermal conductivity of air and water.
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.
Outline a consequence to life of the buoyancy of air and water.
Ringed Seal
Thick layer of blubber increases buoyancy in water as blubber is less dense than water
Black throated loon
Loons must continuously flap their wings when flying to keep themselves buoyant in the air
Outline a consequence to life of the viscosity of air and water.
Ringed Seal
Have tapered body to reduce friction when swimming through water
Black throated loon
Loons have streamlined bodies with flattened to reduce friction when diving
Outline a consequence to life of the specific heat capacity of air and water.
As a result of its high specific heat capacity, water heats up or cools down very slowly.
This provides for a stable internal environment and habitat of living things.
Because living body’s contain a lot of water, body temperature is slow to fluctuate when environmental temperatures change.
Water’s high specific heat capacity helps body temperature rise and fall slowly when external temperatures becomes very hot or cold.
Define specific heat capacity.
Specific heat capacity is the quantity of heat needed to raise the temperature of a chemical per unit mass.
Describe why water has a high specific heat capacity.
Water’s high heat capacity is caused by its numerous hydrogen bonds.
Each individual “bond” is weak, but there are so many of them that collectively a lot of energy must be added to break them all.
Compare the physical properties of water to those of air.
Water
greater buoyant force
greater viscosity
greater thermal conduction
greater specific heat capacity
Air
lower buoyant force
lower viscosity
lower thermal conduction
lower specific heat capacity
Describe how the black-throated loon (Gavia arctica) interacts with the physical properties of water in their habitat.
Buoyancy in water allows the bird to stay afloat without expending a lot of energy, however when flying through air the bird must expend energy to stay aloft, so it has large wings. Air is not viscous, so the loon can easily move through it when flying. The loon doesn’t lose as much body heat to the air because air has low thermal conductivity, but in water it has oiled feathers to keep water out. However, because the air has a low specific heat, its temperature changes as rapidly.
Describe how the ringed seal (Pusa hispida) interacts with the physical properties of water in their habitat.
Buoyancy in water allows the seal to stay afloat without expending a lot of energy. However, the water is viscous, so the seal has adaptations for streamlining as it swims through it. Water has a greater thermal conductivity than air, so the seal needs to insulate itself with blubber to maintain body temperatures. However, because the water has a high specific heat, the temperature of the water does not change as rapidly as the air around it, providing habitat stability for the seal. Seal pups live in underground insulated by trapped air.
Explain the hypothesis that asteroids are responsible for the origin of water on Earth.
Numerous planetary bodies, including asteroids and comets, containing large amounts of water.
asteroids up to a few hundred kilometers across seem the most likely sources of most of Earth’s water.
Studies of rocks that date to soon after the formation of Earth suggest that water may have begun to exist on Earth as early as 4.4 billion year ago.
State two reasons why water was retained on early Earth.
1. The distance of the Earth from the Sun keeps temperature on Earth below that needed to vaporize water.
2. Earth’s gravity keeps water from escaping the planet.
Explain why the presence of water is considered fundamental to the search for extraterrestrial life.
Water is essential for all life because functions as a solvent, allowing key chemical reactions to take place.
Other characteristics that make it a good habitat for life are its heat conduction, surface tension, and its high specific heat.
In fact, water is so vital to life that the presence of water is precedent to the search for extraterrestrial life.
Define “Goldilocks zone” in relation to the search for extraterrestrial life
Astrobiologists search for extraterrestrial objects that fall in a Goldilocks Zone,
meaning it is just the right distance from a star for water to remain at least periodically in liquid form on the surface.
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