Biochemistry (Water and Life)

Water and Life
Water and Life

Water is found in all forms of life on Earth in some form or another. The human body is about 70% water, and other organisms, such as jellyfish, contain as much as 95% water. All of the oxygen that animals breathe had its origin as water. During photosynthesis (the process of using light to create food energy), plants break water apart to produce oxygen and food.

Water is one of the most abundant molecules on Earth. There are approximately 350 million cubic miles (1.4 billion cubic kilometers) of water on the planet. Nearly 97% of all water is found in the oceans, which cover two-thirds of the surface area of the planet.

About 90% of all fresh water is frozen in the ice in the North and South Poles and glaciers (large slow-moving masses of ice). Less than 1% of all the water on Earth is available for consumption, and most of it is found in aquifers (porous rock chambers holding fresh water) underground.

Chemistry of Water


Water is the most common substance on Earth, covering almost three quarters of the planet’s surface. Known by its chemical symbol, H2O, water is the only known substance on Earth that naturally exists as a gas, liquid, and solid. The vast majority of water, about 97%, is in the oceans.

The liquid form of water also exists in lakes, rivers, streams, and groundwater (water beneath Earth’s surface that is held between soil particles and rock, often supplying wells and springs). In its solid form, water makes up sheets of ice on the North and South Poles, and permanent snow.

Water also exists as water vapor (gas) in the atmosphere. The hydrosphere is the whole body of water that exists on or around Earth, which includes all the bodies of water, ice, and water vapor in the atmosphere. All life needs water to survive and the cells of all living things contain water.

Hydrologic Cycle

Hydrologic Cycle
Hydrologic Cycle

Water is in constant motion. Energy from the sun and the force of gravity drive the hydrologic cycle, which is the endless circulation of water between the land, oceans, and atmosphere (air surrounding Earth). Water also changes in form: from gas (water vapor), to liquid, to solid (ice). Rain and snow falling on the land runs off into streams and lakes, or soaks into soil and rocks.

Streams and rivers carry water downhill to lakes and, ultimately, to the ocean. Heat energy from the Sun transforms liquid water at the surface of lakes and oceans and other bodies of water into water vapor. Water vapor in the atmosphere rises and forms clouds. Cooling within clouds causes water vapor to become liquid once again. Rain and snow fall and the cycle begins anew.

The water budget

Earth’s water budget, the total amount of water on the planet, does not change over time. The hydrologic cycle is a closed system. Water is constantly moving and changing form, but it is neither created nor destroyed. With the exception of a very small amount of water added to the hydrologic system by volcanic eruptions and meteors from space, Earth’s total water supply is constant.

Physics of Water

Physics of Water
Physics of Water

Why is water wet? Many people will answer this question by simply saying, “Because it is.” The physical properties of water are fundamental to life and nature on Earth, and are often accepted as simple truths. Water is so common on Earth that its physical characteristics have a large impact on the physics of Earth in general. (Physics is the study of matter and energy, and of interactions between the two.)

Water covers almost three quarters of the planet’s surface. It is the only natural chemical substance that exists as a liquid, solid (ice), and gas (water vapor) within Earth’s normal temperature range. Water is liquid in a range critical for biological life (0–100°C, 32–212°F), and liquid water is present almost everywhere on Earth. Water’s ability to absorb heat regulates Earth’s climate and weather.

Phase changes

Matter exists in three states, or phases: solid, liquid, and gas. (Matter is anything that has mass and takes up space). Substances like water change from one phase to another at specific temperatures and pressures. Add heat (or pressure), and a substance begins to change from a solid to a liquid at its melting point. Add more heat, and the substance will begin to evaporate, to turn from liquid to gas, at its boiling point.

Biology of the Oceans

Biology of the Oceans
Biology of the Oceans

All organisms that live in the ocean are subject to the physical factors of the underwater environment. Some of the more important factors that affect marine (ocean) organisms are light levels, nutrients (chemicals required for growth), temperature, salinity (concentration of salt in the water), and pressure. In general, conditions in the ocean are more stable than those on land.

Light

The amount of light in a certain location controls the growth of the single-celled marine algae called phytoplankton. Phytoplankton are the base of the marine food chain, meaning they are the food for other organisms, who then are the food for higher organisms and so forth.

These plants convert sunlight and water into the carbohydrates (sugars) they feed on in a process called photosynthesis. Unlike land, where plants generally live on surfaces, in the ocean, light travels through the water allowing phytoplankton to grow over a vertical distance of nearly 500 feet in some locations (about 150 meters).

Coastlines

Coastlines
Coastlines

Coastlines are boundaries between land and water that surround Earth’s continents and islands. Scientists define the coast, or coastal zone, as a broad swath (belt) of land and sea where fresh water mixes with salt water. Land and sea processes work together to shape features along coastlines. Freshwater lakes do not technically have coastal zones, but many of the processes (waves, tides) and features found along ocean coastlines also exist in large lakes.

Coastal zone features

All coastlines include a thin strip of land that is submerged at high tide and exposed at low tide, called the shoreline. The coastal zone, however, extends far inland from the shore, across lowlands called coastal plains, and far seaward to the water depth where ocean waves do not reach the seafloor. The coastal zone includes lagoons, beaches, estuaries, tidal wetlands, tidal inlets, river deltas, barrier bars and islands, sand bars, and other shallow-water ocean features.
  • Lagoons: Shallow, salt-water bays between barrier islands and the mainland. 
  • Beaches: Sand deposits along shorelines. Intense waves wash fine-grained mud from coastal sediments (particles of sand, gravel, and silt) leaving only sand-sized grains of resistant minerals like quartz and calcium carbonate. Beaches are common on the seaward side of barrier islands where wave energy is intense. 
  • Estuaries: The mouths of rivers and streams that receive a pulse of saltwater with the tides. 
  • Tidal wetlands (flats): The broad areas of marshy wetlands around lagoons and estuaries that flood with salt water during high tides.
  • Tidal inlets: Openings through which water and sediment are washed in and out of lagoons by daily tides. 
  • Deltas: Deposits of sediments at the mouths (ends) of rivers that flow into the ocean. 
  • Barrier bars and islands: Long mounds, or bars, parallel to the shore into which near-shore ocean currents carry and deposit sand. Eventually, some barrier bars grow tall enough to stay exposed at high tide and become barrier islands. The outer banks of North Carolina as well as Galveston, Mustang Island, and South Padre Island in Texas are examples of barrier islands. 
  • Sand bar: A ridge of sand in rivers or along the coast built up by water currents.

Currents and Circulation Patterns in the Oceans

Currents and Circulation Patterns in the Oceans
Currents and Circulation Patterns in the Oceans

The oceans are in constant motion. Ocean currents are the horizontal and vertical circulation of ocean waters that produce a steady flow of water in a prevailing direction. Currents of ocean water distribute heat around the globe and help regulate Earth’s climate, even on land. Currents carry and recycle nutrients that nourish marine (ocean) and coastal plants and animals.

Human navigators depend on currents to carry their ships across the oceans. Winds drive currents of surface water. Differences in temperature and salinity (saltiness) cause water to circulate in the deep ocean. The rotation of the Earth, the shape of the seafloor, and the shapes of coastlines also determine the complex pattern of surface and deep ocean currents.

Ocean water is layered. The shallowest water, called surface water, is warmer, fresher, and lighter than deep water, which is colder, saltier, and denser. The boundary between surface and deep water is a thin layer marked by an abrupt change of temperature and salinity. This layer, called the thermocline, exists in most places in the oceans. Surface and deep water only mix in regions where specific conditions allow deep water to rise or surface water to sink.

El Niño and La Niña

El Niño
El Niño

El Niño and La Niña are changes in the winds and ocean currents of the tropical Pacific Ocean that have far-reaching effects on global weather patterns. Together, El Niño and La Niña are extremes that make up a cycle called the El Niño Southern Oscillation (ENSO). An oscillation is a repeated movement or time period. El Niño and La Niña events do not occur in a regular or seasonal pattern; instead, they repeat about every two to seven years and last for a few months.

How El Niño and La Niña Occur

El Niño events occur when the trade winds and equatorial current south of the equator in the Pacific Ocean lessen in intensity. The trade winds, or trades, are strong, steady winds that blow from east to west and drive strong west-flowing ocean currents on either side of the equator. (The trade winds are named for their role in propelling sailing ships carrying cargo to trade around the world.) The equatorial current is a sustained pattern of water flowing westward near the equator. Less dramatic La Niña episodes occur during the opposite conditions, when the tropical winds and currents are unusually strong.

During normal, non–El Niño conditions, the trade winds and equatorial current in the southern Pacific push warm surface water to the west and allow cold water from the deep ocean to rise along the coast of South America. The southeasterly (northwest-blowing) trades south of the equator usually pile a mound of warm water around the islands of Indonesia, and create a zone of cool water that rises called an upwelling off the coasts of Peru and Ecuador.

Fish (Saltwater)

Fish (Saltwater)
Fish (Saltwater)

There are over thirty thousand different species of fish, and they are the most numerous vertebrates. Vertebrates are animals that have a bony spine that contains a nerve (spinal) chord. Vertebrates usually have an internal skeleton that provides support and protection for internal organs. This spine and skeleton allow vertebrates to move quickly and to have great strength.

Fish usually live surrounded entirely by water. They all have gills for breathing and fins for swimming. Most fish are ectotherms, which means that their bodies are nearly the same temperature as the water in which they live. About 60% of all fish live entirely in saltwater, while the rest live in freshwater or both freshwater and saltwater.

One of the most remarkable things about fish is their diversity. Fish can be very large, like the whale sharks that can reach 90,000 pounds (41,000 kilograms) or very small, like gobies that can weigh as little as 0.0004 ounce (0.1 gram). They have a variety of diets, including plants, other fish, invertebrates (animals without a backbone) and microscopic plankton (free-floating plants and animals).

Geology of the Ocean Floor

Geology of the Ocean Floor
Geology of the Ocean Floor

Geology is the study of the solid Earth and its history. Marine geology is the study of the solid rock and basins that contain the oceans. The rocks and sediments (particles of sand, gravel, and silt) that lie beneath the oceans contain a record book of Earth’s past.

Topographic features (the physical features of the surface of Earth) and geologic processes in the ocean basins hold the keys to plate tectonics, a fundamental theory of geology that explains the movement of the continents and seafloor over time. (A plate is a rigid layer of Earth’s crust and tectonics is the large scale movements of the crust.) Only when scientists began to successfully probe the secrets of the seafloor in the mid-twentieth century did they begin to understand the complex workings of the solid Earth.

If marine geology is the study of the ocean soup bowl, then oceanography is the study of the broth, and marine biology is the study of the vegetables and meat in the broth. These three branches of ocean science are closely linked. The mountains and valleys of the seafloor, together with the continental margins (edges), act to guide ocean currents (a steady flow of water in a prevailing direction) that in turn regulate global climate.

Islands

An island
An island

Islands are land areas smaller than a continent that are completely surrounded by water. Islands range in size from islets (small islands) barely exposed at high tide, to vast landmasses almost the size of continents. Islands exist in all the ocean basins (the deep part of the ocean floor), along coastlines, and in freshwater lakes and rivers.

Islands come in many sizes and shapes, but they all share the same defining characteristics. There are more similarities than differences between a huge arctic island like Greenland and a small tropical one like Guam.

Islands are isolated. The water around them controls their climate and weather. The British Isles, which include Great Britain and Ireland, have a mild climate for their northern location because they lie in the path of the warm Gulf Stream current (a current is a steady flow of water on a prevailing direction).

Kelp and Seaweed

Seaweed
Seaweed

From the tiniest of bacteria to the massive blue whale, the world’s oceans and freshwater support a tremendous variety of life. Often, a beachcomber will find rubbery plants washed up on the shoreline. These exotic-looking plants are seaweed. A dive below the surface of coastal waters in some areas of the world, such as California, reveals a world of towering plants that sway gently in the ocean current. These giants are one form of seaweed called kelp.

Kelp make up only about 10% of all the known seaweed species. The many varieties of seaweed present in the world’s fresh- and saltwater provide a habitat and even a food source for creatures. Humans benefit from seaweed as well. For thousands of years in Far East countries like Japan, seaweed has been an important part of the diet, in the form of soup stock, seasoning, and as an integral part of sushi. In addition, seaweed is useful in the laboratory. The artificial growth surfaces used to raise bacteria rely on a seaweed component as a thickening agent, similar to that found in gelatin.

Characteristics of seaweed

The leafy-looking seaweed that grows in ocean waters is a type of algae. Other forms of seaweed look grass-like or feathery. Algae are plants; that is, they contain the chemical chlorophyll that converts energy from the Sun into food substances that the plant uses to grow. Algae range in size from microscopic single cells (the fundamental unit of all living things) to huge numbers of cells assembled together to form a much bigger organism. Seaweed is the large collection of algae cells, or macroalgae.

Layers of the Ocean

Layers of the Ocean
Layers of the Ocean

Oceanographers (scientists who study the oceans) often divide the ocean into horizontal layers. They use the physical characteristics of the water such as temperature, density, and the amount of light at different depths to classify these layers. The most important factor is the density of the water, which is determined by the combination of salinity (the amount of salt in the water) and temperature.

All ocean water is salty, but some contains more salt than others. The water that is saltier is heavier and sinks, while the water that is less salty is lighter and floats. Similarly, warmer water is lighter than colder water, so it floats on top of colder water.

Oceanographers generally categorize the ocean into four layers: the epipelagic zone, the mesopelagic zone, the bathypelagic zone, and the abyssopelagic zone. The word “pelagic” refers to the open ocean, away from the coast. The prefix epi means “surface”; the prefix meso means “middle”; the prefix bathy means “deep”; and the prefix abysso means “without bottom.” In addition, the transition zone between the epipelagic and the mesopelagic is often called the thermocline.

Marine Invertebrates

Marine Invertebrates
Marine Invertebrates

Invertebrates are animals that do not have a bony internal skeleton, although many do have hard outer coverings that provide structure and protection. More than 90% of all animals are invertebrates and they are classified into at least 33 major groups, or phyla. Nearly every phylum of invertebrates has members that live in the oceans.

Six phyla of invertebrates that are commonly found in the oceans are: Porifera (sponges); Cnidaria (corals, jellyfish, and sea anemones); Annelida (segmented worms); Molluska (snails, clams, mussels, scallops, squid, and octopuses); Arthropoda (crabs, shrimp, barnacles, copepods, and euphausids); and Echinodermata (sea stars, sea urchins, and sea cucumbers). Each phyla is divided into smaller groups called classes, which is then split into families and then species.

Phylum Porifera

The sponges are the least complex multicellular animals. They generally live attached to a surface and have three basic shapes, encrusting, vase-like, and branching. Sponges live in intertidal (between the tides) zones as well as in the deep ocean. They can be a few inches (centimeters) to 10 feet (3 meters) in diameter. There are nearly 10,000 species of sponges and all but two families are only found in ocean environments.

Marine Mammals

Marine Mammals
Marine Mammals

Mammals are vertebrates (animals with a backbone) that share characteristics of nursing their young with milk, breathing air, having hair at some point in their lives, and being warm-blooded. Marine mammals are the species of mammals that depend on the oceans for all or most of their lives.

There are about 115 different species of marine mammals. Marine mammals vary from the small sea otter to the giant blue whale. Some of them live in groups, like dolphins, while others are solitary, like polar bears. All marine mammals share four characteristics:
  • They have a streamlined body shape that makes them excellent swimmers.
  • They maintain heat in their bodies with layers of fat called blubber.
  • They have respiratory (breathing) systems that allow them to stay underwater for long periods of time. 
  • They have excretory (waste) systems that allow them to survive without drinking freshwater. Instead they obtain the water they need from the food they eat.

Plankton

beach with plankton
beach with plankton

Plankton is a general term that includes plants, animals, and bacteria that drift through lakes and the oceans. Plankton are the foundation for all life in the ocean and produce much of the oxygen that sustains life on Earth. Plankton represents a diverse and large group of organisms.

Often, the only factor that the nearly ten thousand different species of plankton have in common is their poor swimming ability. Rather than control where they are moving, like fish, whales, and turtles, plankton simply float wherever the water currents take them. In fact, the word plankton is derived from the Greek word planktos, meaning “to wander.”

Studying and classifying plankton

Biologists identify and count plankton found in water samples. Several different methods are used to collect plankton from water samples, the most common of which includes the use of plankton nets. Most plankton nets are made of nylon or synthetic material that is produced so that the size of the holes between the fibers is uniform. The most common shape for a plankton net is cone-shaped, and the large end of the cone is attached to a metal net ring.

Tides

Tides
Tides

Tides are the alternating rise and fall of bodies of water, relative to land. Each 24-hour period, there are two high tides and two low tides. The arrival times and heights of the tides change every day and follow a pattern over days, months, and seasons.

The shape of a coastline, water depth, shape of the seafloor (bathymetry), weather, and other local factors affect the heights and arrival times of tides at specific locations. The daily tides bring ocean nutrients that nourish brackish-water (slightly salty) plants and wildlife that live in tidal wetlands.

Explaining the tides

Humans in maritime (sea-going and coastal) societies have always recognized and measured the daily, monthly, and yearly pattern of water level rise and fall along coastlines. Navigation, construction, and fishing in coastal areas require precise knowledge of the local tides, and tide prediction is an ancient science. The ancient Hawaiian “moon calendar” charts the tides and relates them to fishing and agricultural harvests.

Waves

Waves
Waves

Wind creates waves. As an air current (moving stream of air) moves over an undisturbed water surface, friction between air and water creates a series of waves that move across the surface. The size of the waves depends on the wind speed, the duration of the wind, and the distance over which the wind blows. (The distance of open water surface that the wind blows over is called the fetch.) A week-long tropical storm in the Pacific Ocean might produce waves as tall as three-story houses; a ten minute gust blowing across a small lake might make waves that are only a few inches tall.

Waves move away from their point or area of origin in widening circles, like ripples moving away from a pebble dropped into a pool. In an ocean basin (the deep ocean floor), waves from many different wind events are moving across the sea surface at any given moment. When sets of waves meet they interact to form new patterns. By the time they reach the coastline, waves have been affected by many wind events.

Ocean waves may appear that the water is moving forward but in actuality the water is moving in a circle as the water molecules lift and fall. (A molecule is the smallest unit of a substance that has the properties of that substance.) Imagine floating in the ocean in a raft.

Deltas

Deltas
Deltas

Deltas are deposits of sediments (particles of sand, gravel, and silt) at the mouths of rivers that flow into the ocean. The mouth of a river is the end where the body of water flows into the sea. Deltas are shaped by interactions of the river’s fresh water with the ocean water, tides, and waves. Throughout history, deltas have been important places for human settlement. They are also vital habitats for many animals and plants.

In the fifth century B.C.E, Greek naturalist Herodotus coined the name delta to describe the triangular shape of the sediments deposited at the end of the Nile River. The capital Greek letter delta (∆) resembles a triangle. Most deltas are triangular in shape because rivers deposit larger amounts of sediment where they meet the sea, then fan out into the mouth of the sea to deposit the remaining sediment.

Formation of Deltas

As rivers flow through their beds (a channel occupied by a river), the water breaks up rocks and pebbles, which the river then carries with it as it flows. These pieces of rock, sediment, include sand, pebbles, and silt. When the fast-flowing waters of the river reach the ocean, they push against the ocean water.

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