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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

• click on the highlighted area
• read the information
• answer the questions on notebook paper
• turn in
• 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

CHEMICAL REACTIONS - ACIDS/BASES I #9

Acids and Bases Are Everywhere

Every liquid you see will probably have either acidic or basic traits. Water (H₂O) can be both an acid and a base, depending on how you look at it. It can be considered an acid in some reactions and a base in others. Water can even react with itself to form acids and bases. It happens in really small amounts, so it won't change your experiments at all. It goes like this: 

2H₂O --> H₃O⁺ + OH^-

See how the hydrogen ion was transferred? 

Most of the time, the positive and negative ions in distilled water are in equal amounts and cancel each other out. Most water you drink from the tap has other ions in it. Those special ions in solution make something acidic or basic. In your body there are small compounds called amino acids. The name tells you those are acids. In fruits there is something called citric acid. That's an acid too. But what about baking soda? When you put that in water, it creates a basic solution. Vinegar? Acid. 

So what makes an acid or a base? A chemist named Svante Arrhenius came up with a way to define acids and bases in 1887. He saw that when you put molecules into water, sometimes they break down and release an H⁺ (hydrogen) ion. At other times, you find the release of an OH^- (hydroxide) ion. When a hydrogen ion is released, the solution becomes acidic. When a hydroxide ion is released, the solution becomes basic. Those two special ions determine whether you are looking at an acid or a base. For example, vinegar is also called acetic acid. (Okay, that gives away the answer.) If you look at its atoms when it's in water, you will see the molecule CH₃COOH split into CH₃COO^- and H⁺. That hydrogen ion is the reason it is called an acid. Chemists use the word "dissociated" to describe the breakup of a compound. 

Scientists use something called the pH scale to measure how acidic or basic a liquid is. Although there may be many types of ions in a solution, pH focuses on concentrations of hydrogen ions (H⁺) and hydroxide ions (OH^-). The scale measures values from 0 all the way up to 14. Distilled water is 7 (right in the middle). Acids are found between 0 and 7. Bases are from 7 to 14. Most of the liquids you find every day have a pH near 7. They are either a little below or a little above that mark. When you start looking at the pH of chemicals, the numbers can go to the extremes. If you ever go into a chemistry lab, you could find solutions with a pH of 1 and others with a pH of 14. There are also very strong acids with pH values below 1, such as battery acid. Bases with pH values near 14 include drain cleaner and sodium hydroxide (NaOH). Those chemicals are very dangerous.