1.01 Exploring Life

1.02A Chemistry of Life Honors

1.02 Chemistry of Life

1.03 Earth’s Early Atmosphere

Zoology – The study of animals

Botany – The study of plants

Ecology – The study of living things in their environment

Microbiology – The study of microscopic organisms

Biochemistry – The study of chemical reactions in living things

Anatomy/Physiology – The study of the human body

Phenomena are observable events or occurrences (plural of phenomenon).

Observable

Science tries to answer the observable events of the world by analyzing, observing, and testing ideas.

Testable

A testable question has to be asked for science to answer it, using observation and experimentation. Observable and measurable empirical evidence has to be produced in order to be science.

Replicable

Empirical evidence can be replicated, or reproduced, and verified by other scientists if they conduct the same tests under the same conditions.

Reliable

When an experiment is repeated and has the same results, the evidence becomes more reliable. Reliability can also come from unbiased evidence.

Flexible

Science is always changing as experiments allow for new/more observations. Theories can be improved as new and current evidence are combined when new information is discovered.

Testable

Non-testable

“What gasses make up the atmosphere of earth?”

“What career should I pursue after I graduate?”

“What are the effects of high winds during a hurricane?”

“Should mining of phosphates be banned?”

Pseudoscience, or fake science, is any theory, methodology, or practice that doesn’t have scientific foundation.

Astrology is the belief that’s the positioning of the starts can determine one’s personality, future, and behavior.

Phrenology is the belief that one’s personality traits are readable by the bumps on their skull.

Reliability is science is important because people need to know real science for the greater good of knowledge, and that knowledge and science needs to be accurate.

• Has it been tested and observed many times by more than one group of scientists?
• Is the study or data completely documented, and does it follow the scientific method?
• Is the information full of facts and not biased?
• Is the information purely presented for public knowledge, avoiding having any commercial connections?
• Does the information come from a third party that is not profiting from the results of the study?
• Has the study been retested with the same results by other scientists?
• Are the results reported and published in a scientific journal?

Is the claim reliable?

Why or why not?

Advertisement Claim

This claim is not reliable.

This claim was purely presented for commercial use, wanting someone to buy it, paying someone to present this “science.” Also, when it says results are not typical, you know that it is not reliable because the results aren’t constant.

Experimental Claim

This claim is reliable.

This claim was performed by two different people three times, and all three times the results were very similar.

Scientific investigations are important because they help gather information and theories using a non-linear process.

Identify

Describe

Step one

Ask a question

The purpose of a scientific investigation is what you are trying to find out or the question you are trying to answer.

Step two

Do background research

It is important to find out and research what other scientists have already observed and discovered. Past investigations into your topic may lead to other questions that need answers.

Step three

Form a hypothesis

After obtaining background information, a hypothesis is needed about what you think will happen. Forming a hypothesis involves an understanding of current scientific knowledge and creativity to look at the problem or question in a way that will lead to the predicted outcome.

Step four

Test w/ an experiment

This is where you test your hypothesis to see if you were right or wrong about your outcome prediction. Every experiment has to have (at least) one variable that stays the same, and the other variables can remain the same or controlled. This allows you to see if a controlled change will affect the outcome (which the hypothesis predicts).

Step five

Analyze data

Analyzing data compares known and unknown data values. To make sure the results are valid, the experiment must be repeated several times. Consistent results over time and reproducible by other scientists (under the same conditions) means that an experiment is valid.

Step six

Conclusions

The data analysis will allow the scientist to ask themself whether their hypothesis was correct. Sometimes, the result is obvious. Having an incorrect hypothesis helps lead to new discoveries, and when the results are inconclusive, more research must be completed.

Independent Variable

This is the factor that you decide to change, allowing to focus on only the results of that change.

Dependent Variable

This is the factor that changes because of the independent variable. This is also called the outcome variable.

Controlled Variables

These are the factors that you decide to keep constant. This makes sure that whatever happens to the dependent variable is because of the independent variable.

Corn plant

pH of Liquids

Independent

The time in which a corn plant can grow

The liquid in which the pH is tested

Dependent

The height of the corn plant

The pH of the liquid

It is important to form a hypothesis at the beginning of the experiment because it means that everything that comes after that will be focused on proving that hypothesis.

A scientific law is a description of what we expect to happen in the natural world. They do not attempt to explain why, they just say how.

A scientific theory is a broad explanation of the natural world that is based on strong scientific support. They can be modified or overturned if new evidence is or discoveries are found.

Atomic Theory, Big Bang Theory, Theory of Plate Tectonics, Cell Theory, Kinetic Theory

Law of Conservation of Mass, Newton’s Laws of Motion, Law of Gravity, Law of Conservation of Energy

Data collection gives you the evidence needed to draw conclusions during a scientific investigation.

The x-axis is the location for the independent variable.

The y-axis is the location for the dependent variable.

What is the independent variable on this graph?

What is the dependent variable on this graph?

The independent variable is the time in minutes in which the tiger beetle is traveling.

The dependent variable is the distance in kilometers in which the tiger beetle is traveling.

What tips will you use when making graphs? =====>

Remember to add the unit being measured!

1.01 Exploring Life

1.02A Chemistry of Life Honors

1.02 Chemistry of Life

1.03 Earth’s Early Atmosphere

Carbohydrates, lipids, proteins, and nucleic acids

They all contain carbon atoms, which has a unique ability to repeatedly bond together. This allows them to form large molecules containing long chains, branching structures, or rings. Life’s diversity is based on carbon’s ability to form diverse molecular structure, including these four types of biological macromolecules.

Hydrophobic: lacking affinity for water, tending to not mix well with water

Monomer is a subunit that is combined to make polymers.

Polymers are larger molecules, bonding smaller molecules together into chains.

Name

Function(s)

1

Carbohydrate

Provides the cell with energy

2

Lipids

Stores energy

3

Proteins

Building blocks, transporting other substances, storage, etc.

4

Nucleic Acids

Carries genetic information

Name

2 examples

Image

Monosaccharide

Define: The smallest type of carbohydrate molecule.

Glucose and Fructose

In addition to providing energy, the carbon atoms in glucose can be used by the cells to build other important molecules, like fatty acids and amino acids. If the monosaccharides are not immediately used by the cells, they can be stored in larger carbohydrate molecules to be used later.

Disaccharide

Define: Carbohydrate molecules made up of two monosaccharide molecules, bonded together.

Sucrose (table sugar) and Lactose

Maltose is a disaccharide produced during the digestion of starch. It is made of two glucose molecules.

Polysaccharide

Define: Carbohydrate polymers made up of hundreds to thousands of monosaccharide units, bonded together.

Starch, Cellulose, Glycogen, Chitin

Main source of energy and structural for plants

Monosaccharides

Fats, Phospholipids, and Steroids

Fats are stored in the body in fat deposits, which serve as stored energy for the organism. Fat deposits under the skin can also provide insulation for an animal, while fat surrounding vital organs provides protection and cushion for the organs. Although fats, carbohydrates, and proteins all serve as energy sources, digesting fat macromolecules releases much more energy than an equal amount of the others. One gram of fat can provide about 38 kilojoules of energy, compared to around 17 kilojoules of energy from one gram of carbohydrate or protein.

Saturated

• Solid at room temperature

Unsaturated

• Liquid at room temperature
• Contains fewer hydrogen atoms on carbon chains

Phospholipids have 2 fatty acid tails instead of 3, and there is a phosphate group that give the phospholipids a hydrophobic and hydrophilic end.

Portion of a Cell Membrane

Define hydrophobic.

Lacking affinity for water, tending not to mix well with water

Which part of the phospholipid is hydrophobic?

The fatty acid tails are hydrophobic.

Define hydrophilic.

Has affinity for water, tends to mix well with water

Which part of the phospholipid is hydrophilic?

The glycerol head is hydrophilic.

Water can’t pass through the phospholipid tails, because they are hydrophobic. The head is hydrophilic, which means that it can be mixed with and touch water (water loving). The liquid inside and out of the cell can’t pass through because of the hydrophobic tail.

Function

Many steroids are hormones that control a number of the body's metabolic processes.

Molecular structure of a steroid

Example(s)

Cholesterol is the most abundant steroid and is the starting material for most other types of steroids. Cholesterol is found throughout your body and it is important for synthesizing other steroids, such as male and female hormones.

Molecular structure: what atoms does it contain?

The macromolecules in this category all share a similar structure of four linked rings of carbon atoms.

They are used for structure, transporting other substances, storage, signaling from one part of an organism to another, movement, and defense against foreign substances.

Proteins denature when specific conditions, such as temperature and pH, are stable. When they break, chemical reactions can occur within the protein and change the shape of the molecule. After this happens, the protein can no longer do its job or serve it’s function.

Proteins are made up of many amino acids. Even if only one of those acids change or are different, the function of the protein can completely change because it doesn’t have the same structure anymore.

The number and arrangement of amino acids in the chain determines the properties and functions of the protein.

Protein Example

Function

1. Insulin

Hormone for sugar metabolism

1. Cytochrome c

Enzyme for cell respiration

1. Hemoglobin

Oxygen transport in blood

The monomer, or building blocks, of protein are amino acids.

Molecular structure: what does the shape look like?

As amino acids bond together to form a large protein molecule, it naturally twists and bends into its unique shape.

Molecular structure of an amino acid

Molecular structure: what atoms does it contain?

A carboxyl group (-COOH), an amino group ), one single hydrogen, and an “R” group which is different on every amino acid.

The side chain/R group is the only part of the molecular structure that varies between the 20 different amino acids that make up a protein. The side chain may contain carbon, hydrogen, oxygen, or other atoms, and it is always attached to the central carbon atom of the amino acid by a single covalent bond.

Enzymes are special proteins that increase the rate of a reaction by decreasing the amount of energy needed to get a reaction started.

Enzymes belong to the protein macromolecule group.

The function for a catalyst is to increase the speed of a reaction. The molecule doesn’t get used up in the reaction.

Without an enzyme, there is a lot more energy needed and used when a chemical reaction occurs. With an enzyme, the amount of potential energy needed and used decreases significantly.

Yes

What would the optimal pH be for Enzyme B in this graph? (type your answer in the box below)

7

If temperature or pH is altered in a way, the enzyme is denatured and no longer able to speed up the reactions. Another thing that can interfere with an enzyme's ability to speed up a reaction is an enzyme inhibitor. Enzyme inhibitors are substances that bind to an enzyme and change its shape or block its ability to interact with the chemical reaction.

Sometimes the substances in a chemical reaction bind to an active site on the enzyme, helping the reaction to occur faster. An inhibitor may have a similar shape to the substances in the reaction, allowing it to bind to the active site and interfere with the enzyme's function.

Hot temperatures

Hot temperatures can slow down an enzyme’s activity. If the enzyme undergoes hot temperatures, then it can slow down and denature.

Warm temperatures

Warm temps can speed up an enzyme’s activity (Ex: low grade fevers), but we don’t want them getting too hot!

Cold temperatures

Cold temps slow down an enzyme’s activity. This can be reversed if the enzyme is warmed back up to its optimal temperature, but if the temp continues to drop to freezing it can sometimes denature.

Change in pH

A change in pH can slow down the enzyme’s activity and cause it to denature.

Enzyme Inhibitors

Enzyme inhibitors can block the active site and denature the ability to speed up the reaction. The inhibitors have similar shape to the reaction substances, which allows it to bind and interfere with the speeding up of the chemical reaction.

Concentration of enzymes and substrates

If the amount of enzyme or substrate increases, the activity will be faster. If the amount decreases, the activity will be slower.

Nucleic acids carry the genetic information needed to build organisms.

1. DNA

1. RNA

DNA contains an organism's genetic information and is usually found within a cell's nucleus.

The RNA molecules transport the genetic coding from the DNA to other parts of the cell where proteins are built.

The monomer of a nucleic acid is a nucleotide.

What are the three main components of a nucleic acid monomer?

Each nucleotide is made up of a nitrogenous base, a sugar, and a phosphate group.

Molecular Structure

DNA serves as the master copy of an organism's genes. RNA copies sections of the DNA molecule and then carries the copies outside the nucleus. The genetic instructions provided by these copies direct the construction of protein molecules.

Double Stranded

Contain Cytosine & Guanine

Found only in the nucleus

DNA

Both

DNA

Contains Deoxyribose

Contains Thymine

Made of nucleotides

DNA

DNA

Both

Contains Uracil

Single Stranded

Contains Ribose

RNA

RNA

RNA

Carbohydrates

Lipids

Proteins

Nucleic Acids

Monomer

(base unit)

Monosaccharides

None

Amino Acids

Nucleotides

Properties

When dissolved in water, like inside a cell, monosaccharide molecules form a ring structure.

Lipid molecules do not mix well with water (hydrophobic).

Proteins can only properly function under specific conditions, such as a small range of temperature and pH.

A DNA molecule is actually made up of two nucleotide chains that spiral around an imaginary axis. This shape is called a double helix.

Function(s)

Store glucose as an energy reserve, sometimes provide structural support for cells.

Can be used to provide energy, insulation, or control of a body’s metabolic functions.

Used for a variety of different functions, such as structure, storage, signaling, movement, transporting, and defense substances

Contain the genetic information that codes for the cell’s structure and activities.

Examples

Starch, cellulose, glycogen,

Cholesterol, sex hormones, fats

Enzymes, antibodies

DNA, RNA

1.01 Exploring Life

1.02A Chemistry of Life Honors

1.02 Chemistry of Life

1.03 Earth’s Early Atmosphere

Macromolecules are held together by chemical bonds. Covalent bonds form between monomers that make up carbohydrates, such as glucose and fructose, in order to build polymers.

Macromolecules provide energy and structure to living things and their cells.

Organic compounds are carbon-based molecules.

A valence electron is an electron located in the outermost occupied energy level in an atom. These are the electrons that participate between chemical bonding between atoms.

A carbon atom can form up to four covalent bonds with other atoms. This can be four single bonds, two single bonds and a double bond, or one single bond and one triple bond.

The term dehydration synthesis describes any process where two substances bond together by the removal of water. This is the chemical reacting that bonds monomers together to build polymers. During this reaction, water molecules are formed by the atoms that are removed from the monomers.

The opposite of dehydration synthesis is hydrolysis. This is the chemical reaction that breaks polymers down into smaller monomer units. During this reaction, a water molecule is split into OH and H, which are added back to the monomers as the bond between the monomers is broken.

Starch molecules are long, straight chains of glucose molecules, where all the glucose molecules are turned the same direction.  Some types of starch do contain some branching in their glucose chains. Starch is the principal polysaccharide used by plants to store glucose, to be used later as an energy source. Plants often store starch in seeds or other specialized organs. When humans consume starch, like rice, beans, wheat, corn, and potatoes, a specific enzyme found in saliva helps break down the starch into individual glucose molecules. This allows the glucose to be absorbed into the bloodstream and distribute it to energy-needing areas.

Glycogen is a branched chain of glucose molecules. The glucose molecules in glycogen are all facing the same direction. The branches in glycogen molecules tend to be shorter and more frequent than any branching that may occur in some starch molecules. Glycogen is the polysaccharide molecule used to store glucose in animals. If some of the glucose from the broken-down starch needed to be stored for later use, they are stored in the glycogen. The excess glucose bonds to the glycogen, forming branches. This allows animals and humans to store glucose primarily in the liver and muscle tissue to have glucose ready to break down energy when needed.

Cellulose is made up of long chains of glucose molecules, bonded together in an alternating manner, where every other glucose is turned in an opposite direction. The way the glucose molecules are arranged allow for a hydrogen bond to form between the cellulose molecules. These series of hydrogen bonds that form between the closely packed cellulose molecules provide a rigid and stable structure, used to give strength to plant cell walls. Cellulose is responsible for the rigidity and strength in leaves, stems, bark, and other plant structures. Cellulose/plant fiber can’t be digested by humans and most animals, passing through the digestive tract without being digested. This helps exercise the digestive track, keeping it healthy and clean.

Chitin is a rigid polysaccharide, similar to cellulose in its alternating arrangements of glucose molecules. It differs from cellulose by having amino groups (NH₂) bonded to its glucose molecules. Because of its strength, it is used to form the exoskeleton of all arthropods: insects, spiders, lobsters, and crabs. These protective exoskeletons, or anything else made of chitin, cannot be digested by animals.

A fatty acid is a long chain of carbon and hydrogen atoms, with a carboxylic acid group on one end of the molecule. The carbon chain is usually between 12 and 18 carbon atoms long, and it may contain single or double bonds between the carbon atoms. Some functions include forming fat molecules, controlling inflammation, brain health and development, maintaining fluidity of cell membranes, and preventing blood clots.

A fatty acid chain with only single bonds between the carbon atoms is called “saturated,” and a chain that contains some double bonds is called “unsaturated.” Saturated fatty acid chains are straight, which allows them to pack tightly together. Because of this, saturated fats, like the fat found in meat, require a higher temperature to melt. This means they tend to be solid at room temperature. Unsaturated fatty acid chains are “kinked” because they bend where the double or triple bonds are locate in the carbon chain. Unsaturated fats are usually liquid at room temperature and are often called oils.

A glycerol molecule has the formula C₃H₈O₃. Dehydration synthesis occurs in order to attach fatty acid molecules to the glycerol molecule, removing a hydrogen atom from the glycerol molecule and oxygen and hydrogen atoms from the fatty acid to form a water molecule. This process leaves an available location for a covalent bond to form between the glycerol and fatty acid.

Steroids are important because they play a role in essential biological processes, such as immune response, regulating metabolism, and reproduction. Cholesterol is an important steroid in our bodies because it is used to make most of the other steroids that we need. Our bodies build cholesterol molecules in the liver, and we also acquire it from the food we eat. It is possible to have too much cholesterol in our bodies, which can be unhealthy, but a certain amount of cholesterol is important for our bodies to properly function.

Testosterone (hormone) can be made from cholesterol. The structure of testosterone looks like cholesterol, but without the branch stretching out of the polymer. There is also less hydrogen and instead of a hydrogen and oxygen single bond at the bottom, there is a oxygen double bond. The testosterone is the two bottom monomers.

Phospholipids have two fatty acid molecules and one phosphate group bonded to the glycerol molecule. This structure gives phospholipids a hydrophobic end and a hydrophilic end to the molecule.

Having hydrophobic and hydrophilic ends to the molecule allow phospholipids to serve as a major component of cell membranes. The phospholipids are arranged in a double layer within the membranes, which allows the hydrophilic ends of the molecules to come in contact with the water inside and outside the cell.

A cell’s membrane is made up of two layers of phospholipids. The hydrophobic fatty acid ends of the molecules face toward the center of the membrane. The phosphate groups on the other ends of the phospholipid molecules are hydrophilic, so they can interact well with the water inside and outside of the cell.

Proteins are used for structural support, movement, signaling from one part of an organism to another, transporting other substances, increasing the rate of chemical reactions, and defense against foreign substances.

Cells build their proteins from 20 different amino acids. There are other amino acids that have important functions within cells, but they are not used to build proteins.

When two amino acids form a bond between the carboxyl group of one and the amino group of another, this bond is called a peptide bond. This bond is formed by dehydration synthesis, and the reaction involves the help of an enzyme.

A protein molecule is made up of one or more chains of amino acids twisted and folded in a unique three-dimensional shape. Many proteins form a roughly spherical shape, while some are long and fibrous in shape.

This method uses chemical symbols and numbers to tell you which elements are in a compound and how much of each element is present.

A subscript is a small number next to the abbreviated element that shows how many atoms of a specific element there are. For example, O₂ means there are two oxygen atoms covalently bonded to each other. (A subscript of 1 is never used because we can assume if an element has no subscript, then there is only one of that element.)

Prefix

Meaning

Example

di-

two

sulfur dioxide (SO₂)

tri-

three

nitrogen trifluoride (NF₃)

tetra-

four

carbon tetrachloride (CCl₄)

penta-

five

phosphorus pentachloride (PCl₅)

hexa-

six

sulfur hexafluoride (SF₆)

Macromolecules are held together by covalent bonds.

The disaccharide Sucrose is formed by glucose and fructose.

1.01 Exploring Life

1.02A Chemistry of Life Honors

1.02 Chemistry of Life

1.03 Earth’s Early Atmosphere

Numerous conditions make Earth an ideal home for its diverse inhabitants. For example, it has liquid water, an optimal distance from the sun, and an atmosphere that contains a mix of important elements and molecules.

Temperature? (hot, cold, mild)

Earth was (probably) very hot.

Protective atmosphere? (yes or no)

The earth was constantly bombarded with comets and asteroids. (no)

Presence of water? (yes or no)

Earth cooled enough for the surface to solidify and for water vapor to fall as rain. This allowed permanent oceans to form. (yes)

Presence of oxygen? (yes or no)

There was little to no oxygen. (no)

Atmospheric gases (list)

The atmosphere was primarily made up of carbon dioxide, water vapor, and nitrogen. There may have been tiny amounts of carbon monoxide, hydrogen sulfide, and hydrogen cyanid.

Organic molecules are carbon-based molecules. Some are small, simple molecules, while others are long, branching molecules containing hundreds of atoms.

Organic molecules are important to life on Earth, so scientists are very interested in the origin of the very first organic molecules.

Theories suggested that earth was able to build small organic molecules from inorganic molecules in the atmosphere. The spontaneity of the chemical reactions was thought to occur because of the limited amount of oxygen and large amounts of energy provided. The scientists argued that the greater amounts of oxygen gas is why we don’t observe these reactions today, because oxygen interferes with the reactions that would form carbon-based organic molecules.

UV radiation and lightning provided the atmosphere with large amounts of energy.

Theories suggest that some of the first organic molecules formed on Earth may have been amino acids and nucleotides (monomer of DNA/RNA).

Because of the great amounts of oxygen gas in the atmosphere, we can’t observe these reactions today. Oxygen interferes with the reactions that would form carbon-based organic molecules.

In 1953, Stanley Miller and Harold Urey of the University of Chicago tested the Oparin-Haldane hypothesis by simulating Earth's early atmospheric conditions in a laboratory.

Their experiment produced a variety of amino acids and other small organic molecules.

The gas mixture used to represent the early atmosphere contained water (H₂O), hydrogen (H₂), methane (CH₄), and ammonia (NH₃).

Miller and Urey discovered 21 amino acids and other organic molecules present in the liquid.

Oparin and Haldane proposed that lightning and the intense radiation that penetrated the thin primitive atmosphere provided the energy needed for these reactions. Other scientists propose that deep-sea vents may have provided the energy and chemical molecules needed to form the first organic compounds.

It is possible that some of these organic molecules arrived on the early Earth on meteorites and comets from space. Scientists have found organic compounds, including amino acids, in modern meteorites that have landed on Earth. 

Scientists have observed that chemical bonds sometimes form between small organic compounds on hot surfaces. Scientists speculate that ocean water containing small organic molecules, like those formed in the Miller-Urey experiment, splashed onto hot sand, clay, or rock. As the water evaporated on the hot surface, the small organic compounds could have bonded together. Although they have not been able to build large protein molecules in this way, scientists have been able to form smaller chains of amino acids using this method.

All living organisms contain genetic information, stored in DNA and RNA molecules, which directs the functions of cells. The general coding and structure of these molecules is universally shared by all organisms. 

Some scientists hypothesize that some of the first large organic molecules to form and self-replicate were RNA molecules, with DNA molecules forming much later. This is called the RNA world hypothesis. These early RNA molecules were probably smaller than the RNA molecules in our cells today. They would have contained the codes for building specific protein molecules from the amino acids present on Earth at that time. Proteins are necessary components of all living cells.

A catalyst is a substance that increases the rate of reaction without undergoing any permanent change.

One important reaction that RNA helps to catalyze is the building of new RNA molecules. Before this discovery was made, the long-held view was that only proteins could serve as biological catalysts.

If RNA is able to self-catalyze, this means that early RNA molecules may have been able to self-replicate without the help of other molecules. If early RNA molecules were able to copy themselves to build new RNA molecules, this helps to explain why all organisms share the same genetic code.

These early single-celled organisms were prokaryotes, a small simple type of cell that lacks a true nucleus. These cells lived and evolved on Earth all alone for 2 billion years. They have continued to evolve and flourish on a changing Earth, and in turn they have played an important role in the changes taking place.

The first prokaryotic cells lived on an Earth that had little to no oxygen in its atmosphere. This means that the chemical processes that occurred within the cells, providing energy necessary to keep them alive and functioning, did not require oxygen.

These cells were heterotrophs that had to obtain their energy by taking in nutrients as food.

Heterotrophs are organisms that must eat or consume other organisms, plants, animals, or both, to get energy.

Scientists speculate that their food was the rich assortment of organic molecules thought to be present in the ocean water at that time.

Cells

Interesting Fact

Methanogens

Single celled organisms that produce methane (CH₄) in a form of anaerobic respiration. They are common in wetlands, marine sediment, and in the guts of many animals.

Thermophiles

Single-celled organisms that live at extremely high temperatures, between 45 and 80 degrees Celsius (113 and 176 degrees Fahrenheit). They can be found in hot springs and deep-sea vents. Scientists believe thermophilic bacteria may have been some of the first cells on Earth.

Halophiles

Organisms that thrive in environments with very high concentrations of salt. Many conduct photosynthesis. They can be found in places with salt concentrations five times greater than that of the ocean, such as the Great Salt Lake and the Dead Sea.

Cyanobacteria

Photosynthetic prokaryotes that live in the water. They are the most abundant bacteria on the planet and release large amounts of oxygen into the atmosphere. Even though these bacteria cells are very small, they often grow together in large colonies that can be seen with the naked eye. Cyanobacteria can be found in almost every conceivable environment, from oceans to fresh water to moist soil. These photosynthetic cells are essential to ocean ecosystems, serving as the autotrophs at the base of many marine food chains.

Fossil evidence shows that the earliest and most abundant autotrophic cells were ancestors of modern-day cyanobacteria. They are considered to be one of the largest and most important groups of bacteria on Earth today. 

 Their ancestors were just as important to the evolution of Earth because they released large amounts of oxygen into the atmosphere. Photosynthesis uses carbon dioxide gas as a reactant and gives off oxygen gas as a product.

As the number of cyanobacteria and other autotrophs increased on Earth over millions of years, the amount of oxygen in the atmosphere also increased.

The aerobic autotrophs and heterotrophs became the dominant life forms on the planet and evolved into all of the diversity of life now visible on Earth.

Microspheres are tiny bubbles filled with groups of molecules, able to maintain an internal environment different from their surroundings. Microspheres are tiny bubbles filled with groups of large organic molecules; they can form under very specific conditions.

Microspheres are not cells, but they do share some characteristics with cells. These bundles of molecules can maintain an internal environment different from the surroundings outside the bubble. They also have a simple way of storing and releasing energy.

These bundles of molecules expand by absorbing additional molecules until they reach an unstable size, and then they split into smaller microspheres. This division is not true reproduction or cell division, but it may be a precursor (predecessor) to it.

If RNA molecules could self-replicate, it would mean that whenever a microsphere split, the early genetic coding in the RNA would pass to the newly formed microspheres. This could be a predecessor to how cells pass on their genetic information today and may help explain why all organisms share a universal genetic code.

Scientists have found fossils of microscopic bacterial cells in rocks that are more than 3.5 billion years old. They believe that Earth’s atmosphere contained very little oxygen at the time, so these bacterial cells were probably able to survive without it.

2.2 billion years ago

1.01 Exploring Life

1.02A Chemistry of Life Honors

1.02 Chemistry of Life

1.03 Earth’s Early Atmosphere