CELLS FUNCTION - PASSIVE & ACTIVE TRANSPORT, OSMOSIS

PASSIVE TRANSPORT - TAKING THE EASY ROAD

While active transport requires energy and work, passive transport does not. There are several different types of this easy movement of molecules. It could be as simple as molecules moving freely such as osmosis or diffusion. You may also see proteins in the cell membranethat act as channels to help the movement along. And of course there is an in-between transport process where very small molecules are able to cross a semi-permeable membrane. 

Sometimes, proteins are used to help move molecules more quickly. It is a process called facilitated diffusion. It could be as simple as bringing in a glucose molecule. Since the cell membrane will not allow glucose to cross by diffusion, helpers are needed. The cell might notice outside fluids rushing by with free glucose molecules. The membrane proteins then grab one molecule and shift their position to bring the molecule into the cell. That's an easy situation of passive transport because the glucose is moving from higher to lower concentration. It's moving down a concentration gradient. If you needed to remove glucose, the cell would require energy. 

LETTING CONCENTRATION DO THE WORK

Sometimes cells are in an area where there is a large concentration difference. For example, oxygen molecule concentrations could be very high outside of the cell and very low inside. Those oxygen molecules are so small that they are able to cross the lipid bilayer and enter the cell. There is no energy needed for this process. In this case, it's good for the cell because cells need oxygen to survive. It can also happen with other molecules that can kill a cell. 

OSMOSIS

Another big example of passive transport is osmosis. This is a water specific process. Usually, cells are in an environment where there is one concentration of ions outside and one inside. Because concentrations like to be the same, the cell can pump ions in an out to stay alive. Osmosis is the movement of water across the membrane. 

For a cell to survive, ion concentrations need to be the same on both sides of the cell membrane. If the cell does not pump out all of its extra ions to even out the concentrations, the water is going to move in. This can be very bad. The cell can swell up and explode. The classic example of this type of swelling happens when red blood cells are placed in water. The water rushes in to the cells, they expand and eventually rupture (POP!). 

    ACTIVITY

CELLS FUNCTION - PHAGOCYTOSIS

PHAGOCYTOSIS - TIME TO EAT!

Simply put, cells need to eat and drink just like you. Phagocytosis is the process of a cell eating. It is one type of endocytosis.  Endocytosis happens when a cell goes out and takes in something.  Phagocytosis is the situation when it gets a solid.  Pinocytosis is the act of grabbing some liquid. The whole cell works during the process. It is not just some membrane proteins taking in a couple of molecules as in active transport. 

Phagocytosis is a cell taking in a large object that it will eventually digest. The classic example is an amoeba eating a bacterium. First, the cell senses the bacterium because of chemicals in the environment. The cell then moves towards the prey. Once contact is made, the amoeba slowly wraps its cell membrane around the object. When the membranes reach out for the prey, they are called pseudopodium. When the cell membrane surrounds the object, the object has actually been sealed in a new vesicle. 

The final step is digestion of the prey. If a cell does not act quickly, the bacterium could begin to reproduce. Lysosomes quickly attach to the vesicle of food and release digestive enzymes. The enzyme action is called an oxidative burst. The food is then broken down and the amoeba absorbs the nutrients. Waste particles remain in the vesicle and can then be sent out of the cell. 

HUNTING FOR DINNER

The ability to hunt down and eat food was a huge accomplishment for cells. Once the process was refined, unicellular organisms became able to eat other objects that were almost as big as they were. They were also able to become independent of processes like diffusion and active transport. Overall, cells could grow faster and larger. That faster growth meant it would take less time for the cell to reproduce. 

CELLS FUNCTIONS - PINOCYTOSIS

PINOCYTOSIS - ONE MORE TIME

Simply put, cells need to eat and drink just like you. Phagocytosis is the process of a cell eating. It is one type of endocytosis.  Endocytosis happens when a cell goes out and takes in something.  Phagocytosis is the situation when it gets a solid.  Pinocytosis is the act of grabbing some liquid. The whole cell works during the process. It is not just some membrane proteins taking in a couple of molecules as in active transport. 

YOU GOTTA HYDRATE

Almost all cells do some form of pinocytosis. The process does not require the cell to go out and hunt down prey as in phagocytosis. It's about taking in drops of fluid that are outside of the cell. All cells need to do that. There are even different styles of pinocytosis. Cells have certain styles depending on what structures they have. 

Basic pinocytosis involves a cell taking in very small drops of extracellular fluids. Many organelles pinch off vesicles into the cytosol. Pinocytosis sees the cell membrane wrap around a drop and pinch it off into the cell. The molecules inside of the newly created vesicles can then be digested or absorbed into the cytosol. 

Pinocytosis is a process that is happening all of the time. An amoeba may form the vesicles easily as it moves along. A cell with many microvilli (like in your intestine) is constantly pinching off little vesicles filled with fluid. Those types of cells never move so they need to be more efficient. 

CELLS FUNCTIONS - INTRO

Looking at Cell Functions

All cells have a purpose. If they don't do anything productive, they are not needed anymore. In the big picture, a cell's purpose is much more important than acting as small organizational pieces. They had their purpose long before they started working together in groups and building more advanced organisms. When alone, a cell's main purpose is to survive. 

Even if you were a single cell, you would have a purpose. You would have to survive. You would be moving around (probably in a liquid) and just trying to stay alive. You would have all of your pieces inside of you. If you were missing a piece you needed to survive, you would die. Scientists call those pieces organelles.  Organelles are groups of complex molecules that help a cell survive. 

All Cells are not Created Equal

In the same way that cells survive in different ways; all cells have different types and amounts of organelles. The larger a cell becomes the more organelles it will need. It makes sense if you think about it. If you are a big cell, you will need to eat more than a little cell. You will also need to convert that food into energy. A larger cell would need to eat more and may wind up having more mitochondria to process that food into energy. 

While they might have a purpose, more advanced cells have a difficult time surviving on their own. A cell from your brain could not survive in a Petri dish for long. It doesn't have the right pieces to live on its own. It does have the ability to transmit electrical systems around your body. An amoeba could survive in a dish forever, thrive, and reproduce. On the other hand, that amoeba will never help you transmit electrical impulses. The brain cell is far more advanced and has specific abilities and organelles. Simpler cells have a better chance of surviving on their own while complex cells can accomplish tasks that are more advanced. 

CELLS FUNCTIONS - MITOSIS

Mitosis - When Cells Split Apart
Eventually cells need to duplicate. There are two main methods of replication, mitosis and meiosis. This tutorial will talk about mitosis. 

The big idea to remember is that mitosis is the simple duplication of a cell and all of its parts. 
It duplicates its DNA and the two new cells (daughter cells) have the same pieces and genetic code. Two identical copies come from one original. Start with one; get two that are the same. You get the idea. 

Beyond the idea that two identical cells are created, there are certain steps in the process. 
There are five (5) basic phases in the life-cycle of a cell. You should remember the term PMATI (pronounced PeeMahtEee). PMATI is the acronym for the phases of a cell's existence. It breaks down to. 

PROPHASE - METAPHASE - ANAPHASE - TELOPHASE - INTERPHASE

We suppose it would be good to know what happens during those phases. Always remember - PMATI! 

The Phases

Prophase: A cell gets the idea that it is time to divide. First, it has to get everything ready. You need to duplicate DNA, get certain pieces in the right position (centrioles), and generally prepare the cell for the process of mitotic division. 

Metaphase: Now all of the pieces are aligning themselves for the big split. TheDNA lines up along a central axis and the centrioles send out specialized tubules that connect to the DNA. The DNA (chromatin) has now condensed into chromosomes. Two strands of a chromosome are connected at the center with something called a centromere. The tubules actually connect to the centromere, not the DNA. 

Anaphase: Here we go! The separation begins. Half of the chromosomes are pulled to one side of the cell; half go the other way. When the chromosomes get to the side of the cell, it's time to move on to telophase. 

Telophase: Now the division is finishing up. This is the time when the cell membrane closes in and splits the cell into two pieces. You have two separate cells each with half of the original DNA. 

Interphase: This is the normal state of a cell. We suppose that when it comes to cell division, you could call this the resting state. It's just going about its daily business of surviving and making sure it has all of the nutrients and energy it needs. It is also getting ready for another division that will happen one day. It is duplicating its nucleic acids, so when it's time for prophase again, all the pieces are there. 










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MITOSIS

MITOSIS

MITOSIS