PLANT & ANIMAL CELLS - VIDEOS

PLANT CELLS - VIDEO


ANIMAL CELLS - VIDEO

CELLS - CENTRIOLES #10

Centrioles - Organizing Chromosomes

Every animal-like cell has two small organelles called centrioles. They are there to help the cell when it comes time to divide. They are put to work in both the process of mitosis and the process of meiosis. You will usually find them near the nucleus but they cannot be seen when the cell is not dividing. And what are centrioles made of?Microtubules. 

Centriole Structure

A centriole is a small set of microtubules arranged in a specific way. There are nine groups of microtubules. When two centrioles are found next to each other, they are usually at right angles. The centrioles are found in pairs and move towards the poles (opposite ends) of the nucleus when it is time for cell division. During division, you may also see groups of threads attached to the centrioles. Those threads are called themitotic spindle. 

Relaxing When There's no Work

We already mentioned that you would find centrioles near the nucleus. You will not see well-defined centrioles when the cell is not dividing. You will see a condensed and darker area of the cytoplasm called the centrosome. When the time comes for cell division, the centrioles will appear and move to opposite ends of the nucleus. During division you will see four centrioles. One pair moves in each direction. 

Interphase is the time when the cell is at rest. When it comes time for a cell to divide, the centrioles duplicate. During prophase, the centrioles move to opposite ends of the nucleus and a mitotic spindle of threads begins to appear. Those threads then connect to the now apparent chromosomes. During anaphase, the chromosomes are split and pulled towards each centriole. Once the entire cell begins to split in telophase, the chromosomes begin to unravel and new nuclear envelopes begin to appear. The centrioles have done their job. 

CELLS - CHROMOSOMES #8

Chromosomes - Pull up Those Genes

Chromosomes are the things that make organisms what they are. They carry all of the information used to help a cell grow, thrive, and reproduce. Chromosomes are made up of DNA. Segments of DNA in specific patterns are called genes. Your genes make you who you are. You will find the chromosomes and genetic material in the nucleus of a cell. In prokaryotes, DNA floats in the cytoplasm in an area called the nucleoid. 

Loose and Tight

Chromosomes are not always visible. They usually sit around uncoiled and as loose strands called chromatin. When it is time for the cell to reproduce, they condense and wrap up very tightly. The tightly wound DNA is the chromosome. Chromosomes look kind of like long, limp, white hot dogs. They are usually found in pairs. 

Completing the Sets

Scientists count individual strands of chromosomes. They count individuals not every organism has pairs. You probably have 46 chromosomes (23 pairs). Peas only have 12. A dog has 78. The number of chromosomes is NOT related to the intelligence or complexity of the creature. There is a crayfish with 200 chromosomes. Does that make a crayfish five times smarter or more complex than you are? No. There are even organisms of the same species with different numbers of chromosomes. You will often find plants of the same species with multiple sets of chromosomes. 

Chromosomes work with other nucleic acids in the cell to build proteins and help in cell division. You will most likely find mRNA in the nucleus with the DNA. tRNA is found outside of the nucleus in the cytosol. When the chromosomes are visible, cells with two complete sets of chromosomes are called diploids (46 in a human). Most cells are diploid. Cells with only one set (23 in a human) are called haploid cells. Haploids are most often found in cells involved in sexual reproduction such as a sperm or an egg. Haploid cells are created in cell division termed meiosis. 

CELL - NUCLEUS #7

Cell Nucleus - Commanding the Cell

The cell nucleus acts like the brain of the cell. It helps control eating, movement, and reproduction. If it happens in a cell, chances are the nucleus knows about it. The nucleus is not always in the center of the cell. It will be a big dark spot somewhere in the middle of all of the cytoplasm (cytosol). You probably won't find it near the edge of a cell because that might be a dangerous place for the nucleus to be. If you don't remember, the cytoplasm is the fluid that fills cells. 

Life Before a Nucleus

Not all cells have a nucleus. Biology breaks cell types into eukaryotic (those with a defined nucleus) and prokaryotic (those with no defined nucleus). You may have heard of chromatin and DNA. You don't need a nucleus to have DNA. If you don't have a defined nucleus, your DNA is probably floating around the cell in a region called the nucleoid. A defined nucleus that holds the genetic code is an advanced feature in a cell. 

Important Materials in the Envelope

The things that make a eukaryotic cell are a defined nucleus and other organelles. The nuclear envelope surrounds the nucleus and all of its contents. The nuclear envelope is a membrane similar to the cell membrane around the whole cell. There are pores and spaces for RNA and proteins to pass through while the nuclear envelope keeps all of the chromatin and nucleolus inside. 

When the cell is in a resting state there is something called chromatin in the nucleus. Chromatin is made of DNA, RNA, and nuclear proteins. DNA and RNAare the nucleic acids inside of the cell. When the cell is going to divide, the chromatin becomes very compact. It condenses. When the chromatin comes together, you can see the chromosomes. You will also find the nucleolus inside of the nucleus. When you look through a microscope, it looks like a nucleus inside of the nucleus. It is made of RNA and protein. It does not have much DNA at all. 

CELL NUCLEUS - QUIZ

CELLS - CYTOPLASM #6

Cytoplasm - Filling Fluid

Cytoplasm is the fluid that fills a cell. Scientists used to call the fluid protoplasm. Early on, they didn't know about the many different types of fluids in the cell. There is special fluid in the mitochondria, endoplasmic reticulum, Golgi apparatus, and nucleus. The only two 'plasms' left are cytoplasm (the fluid in the cell also called cytosol) and nucleoplasm (the fluid in the nucleus). Each of those fluids has a very different composition. 

The cell organelles are suspended in the cytosol. You will learn that the microfilamentsand microtubules set up a "skeleton" of the cell and the cytosol fills the spaces. The cytoplasm has many different molecules dissolved in solution. You'll find enzymes, fatty acids, sugars, and amino acids that are used to keep the cell working. Waste products are also dissolved before they are taken in by vacuoles or sent out of the cell. 

Special Fluids in the Nucleus

Nucleoplasm has a little different composition. Nucleoplasm can only be found inside of the nucleus. It doesn't have big organelles in suspension. The nucleoplasm is the suspension fluid that holds the cell's chromatin and nucleolus. It is not always present in the nucleus. When the cell divides, the nuclear membrane dissolves and the nucleoplasm is released. After the cell nucleus has reformed, the nucleoplasm fills the space again. 

More than Filling

The cytosol in a cell does more than just suspend the organelles. It uses its dissolved enzymes to break down all of those larger molecules. The products can then be used by the organelles of the cell. Glucose may exist in the cytosol but the mitochondria can't use it for fuel. The cytosol has enzymes that break glucose down into pyruvate molecules that are then sent to the mitochondria. 

CELLS - CONNECTION & COMMUNICATION #5

Connection and Communication

All living things communicate in one way or another. When you start looking at the world on a cellular level, you won't find communication in writing or words. Cellular communication is on a molecular level. This section talks about cells in a larger organism that are near each other. We don't cover the communication between single-celled organisms. They behave in different ways. 

Gap Junctions

Gap junctions are one type of cell connection. When two cells are right next to each other, their cell membranes may actually be touching. A gap junction is an opening from one cell to another. It's not a big opening, but it is large enough for cytoplasm to move from one cell to another. The connections are called channels and they act like tunnels for the movement of molecules. 

Desmosomes

Desmosomes are a second type of cell connection. They physically connect cells like the gap junction, but no opening is created. Proteins that bond the membrane of one cell to its neighbor create the desmosomes. You will find desmosomes in your skin cells. All of those proteins hold your skin together. The distance between the cells, however small, is about 10 times wider than the gap junction connections. 

Tight Junction

The last type of connection we will introduce is the tight junction. Tight junctions happen when two membranes actually bond into one. It makes a very strong barrier between two cells. Cells have some distance with a desmosome. Gap junctions allow molecules to pass. Tight junctions form solid walls. These types of connections are often found where one area needs to be protected from the contents of other areas. 

CELLS - MEMBRANE PROTEINS #3

Membrane Proteins - Bumpy Services We spoke a little about the cell membrane and its structure. We also discussed the lipid bilayer. That lipid bilayer is not smooth around the entire cell. You will find thousands (millions?) of proteins throughout the cell membrane. Some are just on the inside of the cell and some on the outside. A special few cross the cell membrane. Each type of protein has a specific purpose. There are also embedded proteins in the other membranes for cell organelles. A Tale of Two Types There are two types of proteins in the cell membrane -- peripheral proteins and integral proteins. As you can guess from the name, integral membrane proteins are permanently connected to the cell membrane. They have large sections embedded in the hydrophobic (middle) layer of the membrane. Peripheral proteins are not bonded as strongly to the membrane. They may just sit on the surface of the membrane, anchored with a few hydrogen (H) bonds. Integral proteins are the hard workers of the cell membrane. Some integral proteins cross the membrane and act as pathways for ions and molecules. Some of the ion movement may not require work (passive transport), but other processes require a lot of energy and pumping action (active transport). When you look at the whole membrane, there are very few integral proteins when compared to the number of peripheral ones. Discovering Structures This structure of the membrane with embedded proteins and a lipid bilayer was discovered in the early 1970's. Two scientists, Singer and Nicolson, first developed the theory of the "Fluid Mosaic Model." They used several different methods, such as the freeze-fracture technique and electron micrographs, to look closely at the cell membrane and its structure. They identified the proteins that sat on the surface, were sunk into the membrane, and the others that crossed the membrane. CELL MEMBRANES - QUIZ

CELLS - CELL WALL #4

Cell Wall - What's it for?

While cell membranes might be around every cell, cell walls made of cellulose are only found around plant cells. Cell walls are made of specialized sugars called cellulose. Cellulose provides a protected framework for a plant cell to survive. It's like taking a water balloon and putting it in a cardboard box. The balloon is protected from the outside world. Cellulose is called a structural carbohydrate (complex sugar) because it is used in protection and support. 

Cell walls also help a plant keep its shape. While they do protect the cells, cell walls and cellulose also allow plants to grow to great heights. While you have a skeleton to hold you up, a 100-foot tall redwood tree does not. It uses the strong cell walls to maintain its shape. For smaller plants, cell walls are slightly elastic. Wind can push them over and then they bounce back. Big redwoods need strength in high winds and sway very little (except at the top). 

Another Hole in the Wall

A cell wall is not a fortress around the delicate plant cell. There are small holes in the wall that let nutrients, waste, and ions pass through. Those holes are called plasmodesmata. These holes have a problem: water can also be lost. But even when the plant cell loses water, the basic shape is maintained by the cell walls. So if a plant is drooping because it needs water, it can recover when water is added. It will look just the same as when it started. 

More Than Walls in Plants

You may hear about cell walls in other areas of biology. Bacteria also have a structure called a cell wall. Fungi and some ptotozoa also have cell walls. They are not the same. Only plant cell walls are made out of cellulose. The other walls might be made from proteins or a substance called chitin. They all serve the same purpose of protecting and maintaining structure, but they are very different molecules. 

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CELLS - CELL MEMBRANES #2

Cell Membranes

We have been talking about cells being a unit of organization in biology. Let's look at the cell membrane and see how that membrane keeps all of the pieces inside. When you think about a membrane, imagine it is like a big plastic bag with some tiny holes. That bag holds all of the cell pieces and fluids inside the cell and keeps any nasty things outside the cell. The holes are there to let some things move in and out of the cell. 

Flexible Containers

The cell membrane is not one solid piece. Everything in life is made of smaller pieces and a membrane is no different. Compounds called proteins and phospholipidsmake up most of the cell membrane. The phospholipids make the basic bag. The proteins are found around the holes and help move molecules in and out of the cell. 

Scientists describe the organization of the phospholipids and proteins with the fluid mosaic model. That model shows that the phospholipids are in a shape like a head and a tail. The heads like water (hydrophilic) and the tails do not like water (hydrophobic). The tails bump up against each other and the heads are out facing the watery area surrounding the cell. The two layers of cells are called the bilayer. 

Ingrained in the Membrane

What about the membrane proteins?  Scientists have shown that the proteins float in that bilayer. Some of them are found on the inside of the cell and some on the outside. Other proteins cross the bilayer with one end outside of the cell and one end inside. Those proteins that cross the layer are very important in the active transport of ions and small molecules. 

Many Membranes

As you learn more about the organelles inside of the cell, you will find that most have a membrane. They do not have the same chemical makeup as the cell membrane. Each membrane is unique to the organelle. The membrane that surrounds a lysosome is different from the membrane around the endoplasmic reticulum. They are both different from the cell membrane. 

Some organelles have two membranes. A mitochondrion has an outer and inner membrane. The outer membrane contains the mitochondrion parts. The inner molecule holds digestive enzymes that break down food. While we talk about membranes all the time, you should remember they all use a basic phospholipid bilayer, but have many other different parts. 

CELLS MEMBRANE - QUIZ

CELLS - INTRO #1

WELCOME TO CELLS

You will carefully read each of the modules on the different cell organelles, discussing the structure & function.

Many of the modules will have a quiz at the end of the blog post.  Take the quiz & record on notebook paper to turn end at the end of the CELLS unit.

• your name
• name of the quiz
• the score
• PLEASE USE THE SAME PAPER FOR ALL CELL UNIT QUIZES.
• MODULE QUIZES - DUE @ END OF UNIT

Cells are the Starting Point

All living organisms on Earth are divided in pieces called cells. There are smaller pieces to cells that include proteins and organelles. There are also larger pieces called tissues and systems. Cells are small compartments that hold all of the biological equipment necessary to keep an organism alive and successful on Earth. 

A main purpose of a cell is to organize. Cells hold a variety of pieces and each cell has a different set of functions. It is easier for an organism to grow and survive when cells are present. If you were only made of one cell, you would only be able to grow to a certain size. You don't find single cells that are as large as a cow. Also, if you were only one cell you couldn't have a nervous system, no muscles for movement, and using the internet would be out of the question. The trillions of cells in your body make your life possible. 

One Name, Many Types

There are many types of cells. In biology class, you will usually work with plant-like cells and animal-like cells. We say animal-like because an animal type of cell could be anything from a tiny microorganism to a nerve cell in your brain. Plant cells are easier to identify because they have a protective structure called a cell wall made of cellulose. Plants have the wall; animals do not. Plants also have organelles like the chloroplast (the things that make them green) or large water-filled vacuoles. 

We said that there are many types of cells. Cells are unique to each type of organism.  Humans may have hundreds of types of cells. Some cells are used to carry oxygen (O₂) through the blood (red blood cells) and others might be specific to the heart. If you look at very simple organisms, you will discover cells that have no defined nucleus (prokaryotes) and other cells that have hundreds of nuclei (multinucleated). The thing they all have in common is that they are compartments surrounded by some type of membrane. 

Add to your notes:
cell chart

CELL - VOCABULARY

The cell is the basic unit of life. All organisms are made up of cells (or in some cases, a single cell). Most cells are very small; most are invisible without using a microscope. Cells are covered by a cell membrane and come in many different shapes. The contents of a cell are called the protoplasm.

ANIMAL CELL

The following is a glossary of animal cell terms:

cell membrane - the thin layer of protein and fat that surrounds the cell. The cell membrane is semipermeable, allowing some substances to pass into the cell and blocking others.

centrosome - (also called the "microtubule organizing center") a small body located near the nucleus - it has a dense center and radiating tubules. The centrosomes is where microtubules are made. During cell division (mitosis), the centrosome divides and the two parts move to opposite sides of the dividing cell. The centriole is the dense center of the centrosome.

cytoplasm - the jellylike material outside the cell nucleus in which the organelles are located.

Golgi body - (also called the Golgi apparatus or golgi complex) a flattened, layered, sac-like organelle that looks like a stack of pancakes and is located near the nucleus. It produces the membranes that surround the lysosomes. The Golgi body packages proteins and carbohydrates into membrane-bound vesicles for "export" from the cell.

lysosome - (also called cell vesicles) round organelles surrounded by a membrane and containing digestive enzymes. This is where the digestion of cell nutrients takes place.

mitochondrion - spherical to rod-shaped organelles with a double membrane. The inner membrane is infolded many times, forming a series of projections (called cristae). The mitochondrion converts the energy stored in glucose into ATP (adenosine triphosphate) for the cell.

nuclear membrane - the membrane that surrounds the nucleus.

nucleolus - an organelle within the nucleus - it is where ribosomal RNA is produced. Some cells have more than one nucleolus.

nucleus - spherical body containing many organelles, including the nucleolus. The nucleus controls many of the functions of the cell (by controlling protein synthesis) and contains DNA (in chromosomes). The nucleus is surrounded by the nuclear membrane.

ribosome - small organelles composed of RNA-rich cytoplasmic granules that are sites of protein synthesis.

rough endoplasmic reticulum - (rough ER) a vast system of interconnected, membranous, infolded and convoluted sacks that are located in the cell's cytoplasm (the ER is continuous with the outer nuclear membrane). Rough ER is covered with ribosomes that give it a rough appearance. Rough ER transports materials through the cell and produces proteins in sacks called cisternae (which are sent to the Golgi body, or inserted into the cell membrane).

smooth endoplasmic reticulum - (smooth ER) a vast system of interconnected, membranous, infolded and convoluted tubes that are located in the cell's cytoplasm (the ER is continuous with the outer nuclear membrane). The space within the ER is called the ER lumen. Smooth ER transports materials through the cell. It contains enzymes and produces and digests lipids (fats) and membrane proteins; smooth ER buds off from rough ER, moving the newly-made proteins and lipids to the Golgi body, lysosomes, and membranes.

vacuole - fluid-filled, membrane-surrounded cavities inside a cell. The vacuole fills with food being digested and waste material that is on its way out of the cell.

PLANT CELL

The cell is the basic unit of life. Plant cells (unlike animal cells) are surrounded by a thick, rigid cell wall.

The following is a glossary of plant cell anatomy terms.

amyloplast - an organelle in some plant cells that stores starch. Amyloplasts are found in starchy plants like tubers and fruits.

ATP - ATP is short for adenosine triphosphate; it is a high-energy molecule used for energy storage by organisms. In plant cells, ATP is produced in the cristae of mitochondria and chloroplasts.

cell membrane - the thin layer of protein and fat that surrounds the cell, but is inside the cell wall. The cell membrane is semipermeable, allowing some substances to pass into the cell and blocking others.

cell wall - a thick, rigid membrane that surrounds a plant cell. This layer of cellulose fiber gives the cell most of its support and structure. The cell wall also bonds with other cell walls to form the structure of the plant.

centrosome - (also called the "microtubule organizing center") a small body located near the nucleus - it has a dense center and radiating tubules. The centrosomes is where microtubules are made. During cell division (mitosis), the centrosome divides and the two parts move to opposite sides of the dividing cell. Unlike the centrosomes in animal cells, plant cell centrosomes do not have centrioles.

chlorophyll - chlorophyll is a molecule that can use light energy from sunlight to turn water and carbon dioxide gas into sugar and oxygen (this process is called photosynthesis). Chlorophyll is magnesium based and is usually green.

chloroplast - an elongated or disc-shaped organelle containing chlorophyll. Photosynthesis (in which energy from sunlight is converted into chemical energy - food) takes place in the chloroplasts.

christae - (singular crista) the multiply-folded inner membrane of a cell's mitochondrion that are finger-like projections. The walls of the cristae are the site of the cell's energy production (it is where ATP is generated).

cytoplasm - the jellylike material outside the cell nucleus in which the organelles are located.

Golgi body - (also called the golgi apparatus or golgi complex) a flattened, layered, sac-like organelle that looks like a stack of pancakes and is located near the nucleus. The golgi body packages proteins and carbohydrates into membrane-bound vesicles for "export" from the cell.

granum - (plural grana) A stack of thylakoid disks within the chloroplast is called a granum.

mitochondrion - spherical to rod-shaped organelles with a double membrane. The inner membrane is infolded many times, forming a series of projections (called cristae). The mitochondrion converts the energy stored in glucose into ATP (adenosine triphosphate) for the cell.

nuclear membrane - the membrane that surrounds the nucleus.

nucleolus - an organelle within the nucleus - it is where ribosomal RNA is produced.

nucleus - spherical body containing many organelles, including the nucleolus. The nucleus controls many of the functions of the cell (by controlling protein synthesis) and contains DNA (in chromosomes). The nucleus is surrounded by the nuclear membrane

photosynthesis - a process in which plants convert sunlight, water, and carbon dioxide into food energy (sugars and starches), oxygen and water. Chlorophyll or closely-related pigments (substances that color the plant) are essential to the photosynthetic process.

ribosome - small organelles composed of RNA-rich cytoplasmic granules that are sites of protein synthesis.

rough endoplasmic reticulum - (rough ER) a vast system of interconnected, membranous, infolded and convoluted sacks that are located in the cell's cytoplasm (the ER is continuous with the outer nuclear membrane). Rough ER is covered with ribosomes that give it a rough appearance. Rough ER transport materials through the cell and produces proteins in sacks called cisternae (which are sent to the Golgi body, or inserted into the cell membrane).

smooth endoplasmic reticulum - (smooth ER) a vast system of interconnected, membranous, infolded and convoluted tubes that are located in the cell's cytoplasm (the ER is continuous with the outer nuclear membrane). The space within the ER is called the ER lumen. Smooth ER transport materials through the cell. It contains enzymes and produces and digests lipids (fats) and membrane proteins; smooth ER buds off from rough ER, moving the newly-made proteins and lipids to the Golgi body and membranes

stroma - part of the chloroplasts in plant cells, located within the inner membrane of chloroplasts, between the grana.

thylakoid disk - thylakoid disks are disk-shaped membrane structures in chloroplasts that contain chlorophyll. Chloroplasts are made up of stacks of thylakoid disks; a stack of thylakoid disks is called a granum. Photosynthesis (the production of ATP molecules from sunlight) takes place on thylakoid disks.

vacuole - a large, membrane-bound space within a plant cell that is filled with fluid. Most plant cells have a single vacuole that takes up much of the cell. It helps maintain the shape of the cell.

ANIMAL & PLANT CELL - ACTIVITIES

ANIMAL & PLANT CELLS ORGANELLES - ACTIVITY  #1

CELL ORGANELLES - ACTIVITY #2

animal cell - interactive

LAB EXPERIMENT VARIABLES - ASSIGNMENT

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• read the information
• answer the questions on notebook paper
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• IDENTIFY VARIABLES IN SCIENCE EXPERIMENTS  

SCIENCE WORLD MAGAZINE - [12/9]

SCIENCE WORLD 

2/17/2014

SCIENCE WORLD (12/9)

Read entire magazine

CLASS DISCUSSION

2/20/2014

CHEMISTRY UNIT - ASSIGNMENTS

1/27-WHY DON'T OIL & WATER MIX - VIDEO

1/13 -ELEMENTS, COMPOUNDS, MIXTURES - pp

1/9- SCIENCE NEWS - STUDENT PROJECT

1/8-MIXTURES  #13

• IMPURE SUBSTANCES - pp

1/7-SALTS  #12

1/7-CRYSTALS  #11

1/6-ACIDS & BASES  #10

• ACIDS & BASES - ACTIVITY

1/6-NAMING COMPOUNDS  #9

• NAMING COMPOUNDS - pp

1/6-COMPOUND & MIXTURE REVIEW - CLOZE  #8

2/5-CHEMICAL REACTIONS - ACIDS/BASES II  #10

• ACID/BASE QUIZ

2/5-CHEMICAL REACTIONS - ACIDS/BASES I   #9

2/4-CHEMICAL REACTIONS - CATALYST  #8

2/4-CHEMICAL REACTIONS - EQUILIBRIUM II  #7

• EQUILIBRIUM - QUIZ

2/4-CHEMICAL REACTIONS - EQUILIBRIUM I  #6

2/4-CHEMICAL REACTIONS - THERMODYNAMICS  #5

• THERMODYNAMICS - QUIZ

2/4- CHEMISTRY QUIZS

• COMPOUNDS & MIXTURES QUIZ

• PHYSICAL & CHEMICAL CHANGES - QUIZ

CHEMICAL REACTIONS - STOICHIOMETRY  #4

2/3-CHEMICAL REACTIONS - MEASURING REACTION RATES  #3

2/3-CHEMICAL REACTIONS - RATE OF REACTION  #2

• CHEMICAL REACTIONS RATE - QUIZ

2/3-ENDOTHERMIC & EXOTHERMIC

• ENDOTHERMIC & EXOTHERMIC - QUIZ

CHEMICAL REACTIONS - ACIDS/BASES II #10

Names to Know

Let's look at the whole picture now. There is a scale for acids and bases just like everything else. Here are a couple of definitions you should know: 

Acid:   A solution that has an excess of H⁺ ions. It comes from the Latin word acidus, which means "sharp" or "sour". 
Base:   A solution that has an excess of OH^- ions. Another word for base is alkali.
Aqueous:   A solution that is mainly water. Think about the word aquarium. AQUA means water. 
Strong Acid:   An acid that has a very low pH (0-4).
Strong Base:   A base that has a very high pH (10-14). 
Weak Acid:   An acid that only partially ionizes in an aqueous solution. This means that not every molecule breaks apart. Weak acids usually have a pH close to 7 (3-6). 
Weak Base:   A base that only partially ionizes in an aqueous solution. This means that not every molecule breaks apart. Weak bases usually have a pH close to 7 (8-10). 
Neutral:   A solution that has a pH of 7. It is neither acidic nor basic. 

More Ideas About Acids and Bases

We told you about that guy Arrhenius and his ideas about concentrations of hydrogen and hydroxide ions. You're also going to learn about Brønsted-Lowry ideas. These two chemists from Denmark and England looked at acids as donors and bases as acceptors. What were they donating and accepting? Hydrogen ions. It's a lot like the first definition we gave, where an acid breaks up and releases/donates a hydrogen ion. This newer definition is a little bit more detailed. Scientists used the new definition to describe more bases, such as ammonia (NH₃). Since bases are proton acceptors, when ammonia was seen accepting an H+ and creating an ammonium ion (NH₄⁺), it could be labeled as a base. You didn't have to worry about hydroxide ions anymore. If it got the H+ from a water molecule, then the water (H₂O) was the proton donor. Does that mean the water was the acid in this situation? Yes. 

A chemist named Lewis offered a third way to look at acids and bases. Instead of looking at hydrogen ions, he looked at pairs of electrons (remember our pictures with dot structures in Atoms and Elements?). In Lewis' view, acids accept pairs of electrons and bases donate pairs of electrons. We know that both of these descriptions of acids and bases use completely opposite terms, but the idea is the same. Hydrogen ions still want to accept two electrons to form a bond. Bases want to give them up. Overall, Lewis' definition was able to classify even more compounds as acids or bases. 

What Really Happens

What really happens in those solutions? It gets a little tricky here. Let's look at the breakup of molecules in aqueous (water-based) solutions one more time for good measure. Acids are compounds that dissociate (break) into hydrogen (H+) ions and another compound when placed in an aqueous solution. Remember that acetic acid example? Bases are compounds that break up into hydroxide (OH^-) ions and another compound when placed in an aqueous solution. We'll talk about baking soda in a few paragraphs. 

Let's change the wording a bit. If you have an ionic/electrovalent compound and you put it in water, it will break apart into two ions. If one of those ions is H⁺, the solution is acidic. The strong acid hydrogen chloride (HCl) is one example. If one of the ions is OH^-, the solution is basic. An example of a strong base is sodium hydroxide (NaOH). There are other ions that make acidic and basic solutions, but we won't be talking about them here. 

That pH scale we talked about is actually a measure of the number of H⁺ ions in a solution. If there are a lot of H⁺ ions, the pH is very low. If there are a lot of OH^- ions compared to the number of H⁺ ions, the pH is high. 

Think about this idea for a second: Why would a liquid with high levels of NaOH be very basic, yet dangerous at the same time? The Na-OH bond breaks in solution and you have sodium ions (positive) and hydroxide ions (negative). The sodium ions don't really pose a danger in solution, but there are a huge number of hydroxide ions in solution compared to the hydrogen ions that might be floating around as H₃O⁺ (a hydronium ion).All of those excess OH^- ions make the pH super high, and the solution will readily react with many compounds. The same thing happens on a less dangerous scale when you add baking soda to water. During the dissociation, OH^- ions and carbonic acid are released in the solution. The number of OH^- ions is greater than the number of H₃O⁺ions (H⁺ and H₂O), and the pH increases. It's just not as strong a difference as in sodium hydroxide. 

That's basically it.

ACID/BASE QUIZ