Cellular Respiration: Aerobic Respiration vs. Anaerobic Respiration

C6H12O6 + 2 NAD+ + 2 ADP + 2 P -----> 2 pyruvic acid, (CH3(C=O)COOH + 2 ATP + 2 NADH + 2 H+

by Tiffanie Branch


What is Cellular Respiration?

Cellular respiration is defined as the conversion of fuel into energy and nutrients within the mitochondria and cytosol of cells. This series of biochemical reactions is also called a “metabolic pathway.” Two types of cellular respiration exist: aerobic, or respiration in the presence of oxygen, and anaerobic, or respiration without oxygen.

Aerobic respiration requires oxygen as a reactant, and creates energy more efficiently than anaerobic respiration. It produces between 36 and 38 molecules of adenosine triphosphate (ATP), six molecules of water, and six molecules of carbon dioxide.

To understand aerobic respiration, think of what happens when we eat and breathe. We take in food, which breaks down with glucose for our cells to use. Breathing gives our bodies the oxygen necessary to convert that glucose into energy. Our bodies expel the leftovers from the process as water, carbon dioxide, and energy. The expressed chemical equation for this interaction can be defined as:

C 6 H 12 O 6 + 6 O 2 --> 6 CO 2 + 6 H 2 O + ATP
Cellular Respiration formula


What Is Aerobic Respiration?

Aerobic respiration is comprised of three major steps:

1. Glycolysis

2. The Citric Acid Cycle

3. Oxidative Phosphorylation

During glycolysis, glucose breaks down into two pyruvate molecules. This requires two reduced nicotinamide adenine dinucleotide molecules (NAD+) and two ATP. The products of glycolysis result in two pyruvate molecules, two oxidized nicotinamide adenine dinucleotide molecules (NADH), and four ATP (which is a gain of two ATP). This part of the process takes place in the cytosol of the cell.

C6H12O6 + 2 NAD+ + 2 ADP + 2 P -----> 2 pyruvic acid, (CH3(C=O)COOH + 2 ATP + 2 NADH + 2 H+
This is what glycolysis looks like

The citric acid cycle, also known as the Krebs cycle, represents the second step of aerobic cellular respiration. One pyruvate from glycolysis oxidizes into acetyl coenzyme A (acetyl CoA) within the mitochondrial matrix. This part of the process is called a “cycle” since just one molecule of pyruvate completes the cycle. With two pyruvates produced, the cycle begins again. The double cycling yields two ATP, as well as NADH and oxidized flavin adenine dinucleotide (FADH2).

This releases stored energy into active energy + CO2

The third and final step, oxidative phosphorylation, takes place in the inner mitochondrial membrane. Some textbooks might refer to this as the electron transport chain. NADH and FADH2 are electron carriers. They use those electrons, as well as oxygen, to convert adenine diphosphate (ADP) to ATP. While this happens, NADH creates hydrogen gradient when the NADH loses its hydrogen, thus making it NAD+. This allows it to be reused in glycolysis. The products of this are NAD+, H2O, and 32 to 34 ATP.

What Is Anaerobic Respiration?

The second type of cellular respiration, anaerobic respiration, contains two steps.

Glycolysis occurs the same way it does in aerobic respiration. Biologists describe the second step as fermentation, which results in alcohol. The alcohol derives from pyruvate produced by glycolysis, and can ferment into either ethanol or lactate (lactic acid). Anaerobic respiration only yields two ATP, and the entire two-step process takes place in the cytosol. Yeast involves this form of respiration to help make wine and other alcohols. It also occurs during exercise as lactic acid builds up in muscles due to low oxygen supply.


Cellular respiration comes in two forms: aerobic and anaerobic. Aerobic respiration goes through glycolysis, the citric acid (Krebs) cycle, and oxidative phosphorylation (the electron transport chain). Anaerobic respiration goes through glycolysis and fermentation. Aerobic respiration occurs with greater efficiency producing 36-38 ATP, while anaerobic respiration only produces 2 ATP.

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What Are Endothermic And Exothermic Reactions?

What are endothermic and exothermic reactions? Our StudyGate experts know everything there is to know about that, and would be happy to share their knowledge with you! They can answer any of your quick questions, or even help you prepare for a test! First, let’s cover the basics before we move on to the harder stuff.


Endothermic? Exothermic? What Does That Mean?

Let’s break these words down.

Starting with “endothermic”, the prefix “endo” means “within, inner, absorbing, or containing”, and the prefix “exo” means “outside, or out of”. Of course, the word “thermic” means “heat”. So, if we put it all together, an endothermic reaction is one that takes in heat, and an exothermic reaction is one that gives off heat.


Endothermic and Exothermic Reactions: The Definitions

Here are the official definitions of endothermic and exothermic reactions:

Endothermic reaction: Any chemical reaction or change in which energy in the form of heat is absorbed

Exothermic reaction: Any chemical reaction or change in which energy in the form of heat is released

How Do They Work?

On a molecular level, chemical reactions happen when the reactant molecules collide with enough energy to break down existing chemical bonds so that new ones can form. Every chemical reaction includes the same components: two or more reactants and a change in energy. To explain how endothermic and exothermic reactions work, let’s look at a couple of simple examples, starting with endothermic reactions.


Endothermic Reaction: Melting Ice

What Are Endothermic And Exothermic Reactions

The melting of ice is a common endothermic reaction. Here’s what happens.

Water molecules are arranged in a rigid state (ice). Next, we add heat, which is a form of energy. Let’s say we leave our ice sitting in the sun. The sun gives off heat, and the ice absorbs this heat as a form of energy. This energy breaks down the rigid bonds in the ice, and causes the water molecules to move quicker and collide more often. As a result, the temperature of the ice rises and it turns into water! Basically, melting ice is an endothermic reaction because the ice absorbs (heat) energy, which causes a change to occur.

Other examples of endothermic reactions:

  • Photosynthesis: Plants absorb the heat energy from sunlight and convert it into ATP and NADPH (energy storage molecules found within chloroplasts in a plant cell) while also giving off oxygen.
  • Evaporation: Heat excites water molecules, causing them to collide faster and change state from liquid to gas.
  • Sublimation: Dry ice, the solid form of carbon dioxide, has a lower temperature than ice. When it is exposed to higher temperatures, the dry ice changes directly from a solid to a gas.


Exothermic Reaction: Combustion

What Are Endothermic And Exothermic Reactions

Next, we’ll talk about fire, or combustion, a classic example of an exothermic reaction.

A fire needs three things to start in a chain reaction: Fuel- standard diesel fuel has a chemical formula similar to: What Are Endothermic And Exothermic Reactions. Oxygen’s chemical formula is  What Are Endothermic And Exothermic Reactions

And, of course, heat is the final ingredient. Our reactants are the chemicals in the fuel and oxygen, and the heat is our required energy source.

Let’s say we’re having a bonfire at the beach. You pile the wood in the fire pit. Then, you add some gasoline on top of it, and light a match. The heat from the match causes the carbon and hydrogen molecules in the fuel to collide with the oxygen molecules at a very high rate. Then, the speed at which bonds are being broken down and remade causes combustion, or, fire, which gives off carbon dioxide and other chemical compounds in the form of smoke. So, smoke and heat (lots of it) are the products of this exothermic reaction. To summarize, two or more chemical reactants are put together, and energy is added to allow the chemical bonds to break down and reform at a high rate. This high speed chain reaction releases large amounts of heat.

Other examples of exothermic reactions:

  • Condensation: Think of a glass of cold water. As time passes and water temperature drops, the gas molecules (water vapor) around that glass slow down and change state from gas to liquid as they collect on the surface of the glass. This is an exothermic reaction because heat is technically given off in order for the gas to cool and change state.
  • Oxidation: Take a piece of metal and get it wet. Over time, the water molecules on the metal’s surface bond with the oxygen in the air. Small amounts of heat from this reaction are given off as the metal itself begins to rust.

Endothermic and Exothermic Reactions: A Review

  • Endothermic reactions absorb heat to bring on a chemical change. Photosynthesis, evaporation, sublimation, and melting ice are great examples.
  • Exothermic reactions are chemical changes that release heat. Combustion and oxidation are the more common examples of this.
  • When deciding whether a reaction is endothermic or exothermic, ask yourself if more heat is added or taken away in a particular reaction.

And now you know the basics! If you’re looking for extra help with a chemistry assignment, or would like more detailed explanations, click the buttons below! Then, you can register for a free StudyGate account, post emergency homework questions, find a tutor to meet with online! Whether you’re looking to improve your grades or simply expand your knowledge, StudyGate has everything you need!

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What Are Prokaryotic and Eukaryotic Cells?

What Are Prokaryotic And Eukaryotic Cells

So, what are prokaryotic and eukaryotic cells?

A cell is the smallest structural and functional unit of an organism. The most basic cell is made up of a nucleus (the part of the cell that controls all its functions), cytoplasm (the jellylike substance that surrounds the nucleus), organelles (smaller cell structures that perform a specific cell function), and a cell membrane (the  wall through which materials pass in and out of the cell). There are two types of cells: prokaryotic and eukaryotic.


What Are Prokaryotes and Eukaryotes?

First of all, a prokaryote is a unicellular (one cell) organism which does not have a nucleus with a membrane or specialized organelles. They look like this:

What Are Prokaryotic And Eukaryotic Cells
Prokaryotic Cell



As you can see, this particular prokaryote has DNA without a nucleus, a cell membrane and a cell wall, ribosomes (organelles that synthesize proteins), cytoplasm to hold it all in place, and a flagellum that the cell uses to move.

A Eukaryote is a multi-cellular organism that has a nucleus with a membrane, and specialized organelles that each perform a specific function. This is what it looks like:

What Are Prokaryotic And Eukaryotic Cells
Eukaryotic Cell


The eukaryotic cell is more complex than a eukaryotic cell. A membrane surrounds the nucleus. There are many different organelles in the cytoplasm that perform different functions. For example, the mitochondrion creates energy for the cell to use. The lysosome processes waste material. The rough endoplasmic reticulum is where many different types of proteins are processed and put together in processes called transcription and translation. Next, the smooth endoplasmic reticulum manufactures lipids and metabolizes sugars and other materials for the cell to use later. Ribosomes create proteins. The cell coat and cell membrane protect the cell and allow materials to pass in and out.  All the cell’s genetic material, chromatin, is kept in the nucleus. As you can see, eukaryotic cells are much more complex compared to prokaryotes.


What is the difference between Prokaryotic and Eukaryotic cells?

There are quite a few differences between prokaryotic and eukaryotic cells.

Eukaryotic cells usually include:

  • A defined nucleus
  • They have more than one chromosome
  • A true membrane around the nucleus
  • Are usually multicellular
  • Handle genetic recombination through Meiosis and the fusion of gametes
  • And include more complex organelles such as lysosomes, peroxisomes, microtubules, and two endoplasmic reticulums

In comparison, prokaryotic cells contain:

  • DNA strands not contained in a nucleus
  • One chromosome and plasmids to help with cell division
  • No nuclear membrane
  • Usually unicellular
  • Genes recombine through cell division and binary fission
  • No complex organelles other than ribosomes


What Is An Example of A Prokaryotic Cell?

Most bacteria and algae fall are prokaryotic cells. This includes the bacterium tuberculosis and E. coli, shown below. As you can see, flagella cover the cell body and enable movement.

What Are Prokaryotic And Eukaryotic Cells
E. coli.


What Is An Example of A Eukaryotic Cell?

Eukaryotic cells include plant and animal cells. An animal cell is pictured below. Plant and animal cells are mostly similar with the exception of a strong cell wall and chloroplasts in plant cells.

What Are Prokaryotic And Eukaryotic Cells
Animal Cell



Eukaryotic cells have a nucleus filled with chromatin (genetic material), specialized organelles such as lysosomes, mitochondria, endoplasmic reticulums, ribosomes, and a cell wall. Then, their genetic material recombine through Meiosis and the fusion of gametes. Most eukaryotic cells belong to animals and plants. Prokaryotic cells contain DNA strands and ribosomes that are held in place with cytoplasm. Prokaryotes recombine their DNA through binary fission, a process where DNA is copied and split off into two new cells. In addition, many prokaryotic cells have flagellum, or long structures that help the cell move. Examples of prokaryotes include E. coli. and tuberculosis.

This is is a basic explanation of prokaryotic and eukaryotic cells. StudyGate is home to a huge community of science experts that would love to provide even more details about cells, the specific detailed function of each organelle within a cell, and so much more. Our tutors are very passionate about science and are available to help, whenever you’re ready! If you’re looking for science help, one-on-one tutoring, and a place to study with your friends, click the button below and start learning today!


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Understanding Isaac Newton and his Three Laws of Motion

Isaac Newton and the Three Laws of Motion

Sir Isaac Newton, English author, mathematician, theologian, astronomer, and physicist, wrote his Philosophiæ Naturalis Principia Mathematica, a book that changed the way scientists thought about mechanics and the way we interact with the physical universe. In Principia, Newton outlines his laws of motion and universal gravitation- laws that describe movement as a direct result of the surrounding environment. These three laws are a crucial part of physics, and we’ve provided three simple examples to help you in your understanding of Isaac Newton and his Three Laws of Motion!


The First Law Of Motion

Newton’s first law of motion states:

“Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.”


This is also known as Newton’s law of inertia. You may have learned it as the following: “Every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force” When an object moves, that movement will continue until something else causes it to stop. The opposite is also true- when an object is stationary, it will remain that way until something causes it to move. The following gif best explains Newton’s first law:

Newton's Laws of Motion


Now then. Here we see a giraffe traveling along in a tiny car. According to Newton’s first law of motion, the moving car should continue to move…unless something else causes it to stop moving. That’s where the wall comes in- that’s an external force. When the car hits the wall, it changes state and stops moving.

But wait, there’s more.

You’ll notice that the giraffe is also in motion. When the wall stops the car, the giraffe continues to move. In this case, the car is the external force that acts upon the giraffe. The giraffe continues to move until it has no where else to go. The car causes it to change state and come to a complete stop.

To summarize:

The car and giraffe move together,

When the car hits the wall, it changes state and stops moving. It becomes inert (can’t move). The giraffe continues to move.

The stationary car acts upon the still-moving giraffe. It causes the giraffe to change state and come to a complete stop.


The Second Law Of Motion

Newton’s second law of motion states:

“The relationship between an object’s mass (m), it’s acceleration (a), and the applied force (F) is F = ma.”

Acceleration and force are vectors. This means that they both have a certain magnitude (power) and direction (In this law the direction of the force vector is the same as the direction of the acceleration vector).

When a constant force acts on an object at rest, the object begins to accelerate, or change its velocity (how fast it’s going). When a constant force acts on an object in motion, it can cause that object to either speed up, slow down, or change direction.

High force = high mass + high acceleration

Low force = low mass + low acceleration

High force = low mass + high acceleration

Low force = high mass + low acceleration

A wonderful example of Newton’s second law of motion comes to us from the action-packed climax of The Avengers.

In this scene, a nuclear missile is headed straight for New York! The missile is an object in motion traveling with a high amount of force (high mass + high acceleration). Luckily, the one and only Tony Stark (in his Iron Man suit) is quickly traveling in the same direction, trying to divert the missile.

At 0:35, Tony accelerates and grabs the missile. As you can see when he catches up to it, he and the missile travel at the same rate of acceleration. Then, at 1:16 he exerts a constant upward force on the missile, which causes it to gradually change direction and travel upwards, narrowly missing the city. As they ascend, Tony and the missile gradually travel at the same speed, and they travel through the portal. The missile’s mass (heavy), multiplied by its acceleration (high), causes the missile to exert a high amount of force as it slams into the ship and explodes!


The Third Law Of Motion

Newton’s third law of motion states:

“For every action, there is an equal and opposite reaction.”

In other words, when a force is exerted in one direction, the same force is exerted in the opposite direction. Think of a few everyday examples:

  • When you jump, a force is being exerted on your body, which makes you go UP. At the same time, an equal force is being exerted DOWN on the ground. Essentially, you and the ground are pushing off of one another, and the result is this: 
  • When you go swimming, and you kick your legs as you move through the water, what happens? Your legs exert a force on the water, and the water exerts the same force against your legs. As a result, you travel in one direction, and the water travels in the opposite direction in the form of ripples.
  • Do some push-ups. Your hands exert a downward force on the ground, and the ground exerts an upward force on you, causing you to rise and fall.
  • Go outside and watch the birds fly around. Each time they flap their wings, they exert a downward force on the surrounding air. At the same time, the air exerts an upward force on the bird’s wings. This causes the bird to gain altitude, and before you know it, they have achieved flight!


And those are Issac Newton’s three laws of motion in a nutshell! Of course, these are basic definitions and examples- StudyGate has tons of knowledgeable tutors that can provide all kinds of detailed explanations about Newton’s laws and so much more! We’ve got tutors for biology, chemistry, physics, astronomy- whatever you need!  If you’re looking for some more science help, click on the buttons below to get started!

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