Chapter 3 - Water and Life

Life on Earth developed underwater for 3 billion years before expanding to land. Water is the substance that enables life as we know it on Earth, as well as perhaps on other worlds. All recognizable creatures are mainly made of water and live in a water-dominated world.

Water covers three-quarters of the Earth's surface. Although the majority of this water is liquid, it is also found on Earth as a solid (ice) and a gas (water vapor).

Water is the only common material on Earth that exists in all three physical states of matter in its natural environment. Furthermore, the solid form of water floats on the liquid form, which is a unique characteristic derived from water.

The ratio of ice to liquid water is shifting as the Earth warms due to climate change. The melting of Arctic sea ice and glaciers has an impact on life on, beneath, and around them.

Warmer seas and a thinner ice pack in the Arctic are causing phytoplankton (microscopic aquatic photosynthetic organisms) blooms, which can be seen from orbit as the “cloudy” saltwater, as shown in the image attached.

However, organisms that rely on Arctic ice are suffering. For example, the number of black guillemots in Alaska is falling as a result of the rising environment and shrinking Arctic sea ice. The structure of a water molecule enables it to interact with other molecules, including ions.

Water is so common to us that we often miss its many amazing properties. Water's distinctive behavior may be traced back to the structure and interactions of its molecules, continuing the subject of emergent characteristics.

When studied on its own, the water molecule appears to be deceptively simple. It has the form of a broad V, with two hydrogen atoms connected to an oxygen atom by single covalent connections.

Because oxygen is more electronegative than hydrogen, the electrons in covalent bonds spend more time near oxygen than near hydrogen; these are polar covalent bonds.

Because of the uneven distribution of electrons and water's V-like form, it is a polar molecule, which means that its total charge is unbalanced.

Because of the unequal distribution of electrons and the V-like form of water, it is a polar molecule, which means that its total charge is unevenly distributed.

In water, the oxygen molecule contains two areas of partial negative charge (-), while each hydrogen molecule has two regions of partial positive charge (+).

Water's characteristics are caused by the attraction of oppositely charged atoms in distinct water molecules: One molecule's partially positive hydrogen attracts a neighboring molecule's partially negative oxygen.

A hydrogen bond holds the two molecules together as shown in the image attached.

Because of hydrogen bonding, water molecules remain near to one another. Although the arrangement of molecules in a sample of liquid water is continually changing, many of the molecules are linked by numerous hydrogen bonds at any given time.

Water is more organized than most other liquids due to these connections. The hydrogen bonds keep the material together as a whole, a process known as cohesion.

Cohesion caused by hydrogen bonding aids in the movement of water and dissolved nutrients in plants against gravity.

Water travels from the roots to the leaves via a network of water-conducting cells. As water evaporates from a leaf, hydrogen bonds cause water molecules leaving the veins to tug on molecules farther down, and the upward pull is carried all the way to the roots via the water-conducting cells.

Adhesion, or the adhering of one material to another, is also important. Water's hydrogen bonding to the molecules of cell walls helps to counteract gravity's downward pull.

• The term surface tension is related to cohesion, referring to a measure of how difficult it is to stretch or break the surface of a liquid. At the interface between water and air is an ordered arrangement of water molecules, hydrogen-bonded to one another and to the water below, but not to the air above.

Kinetic energy, or the energy of motion, is present in everything that moves. Atoms and molecules have kinetic energy because they are always moving, but not always in the same direction.

The larger a molecule's kinetic energy, the faster it travels. Thermal energy is the kinetic energy associated with the random movement of atoms or molecules.

Temperature and thermal energy are connected, but they are not the same thing. Temperature indicates the average kinetic energy of molecules in a body of matter independent of volume, whereas thermal energy reflects total kinetic energy and hence relies on the volume of the substance.