The Cell Organelles


 

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Click on the labels in the illustration above to learn more about the cell organelles.


Cell Organelle Information - You will need to know both the structure and function of the organelles in a cell. Make sure you know the difference in organelles found in plant and animal cells.


Nucleus

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Function
The nucleus is the control center of a cell as such it is the most important part of the cell. The control arises from the genetic information stored in the nucleus. Genes are made of the nucleic acid DNA. Hundreds of genes are linked together into enormous molecules called chromosomes (chromatin). Genes can be switched on or off and are indirectly responsible for making proteins which do the work of the cell.

Structure

The nucleus is a large roundish organelle. It is bounded by a double membrane which has numerous pores. Inside the nucleus are chromosomes and a dark region called a nucleolus which makes ribosomes. (Ribosomes are necessary for protein synthesis.)
 

 


Plasma membrane

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Function
The plasma membrane is also a vital component of cellular control. Its responsibility is to restrict what can enter or leave the cell. This process is called homeostasis.

Structure

The plasma membrane is made up of a bilayer of phospholipids. Many specialized proteins are found floating in the bilayer and are necessary for homeostasis. Because the lipid bilayer is fluid numerous pores or openings are created as the phospholipids swirl about. This makes the membrane selectively permeable to small molecules. Large molecules rarely make it through these pores.

 


Cell Wall

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Function
Plants have cell walls which are located outside the plasma membrane. Animal cells lack cell walls. The cell wall gives the plant strength and allows plants cells to fill with water creating an internal pressure called turgor pressure.

Structure

Cell walls are a strong collection of laminated fibers. Each fiber contains hundreds of strands of cellulose. Cellulose, as you should recall, is a macromolecule composed of glucose monomers (subunits).

 


Endoplasmic Reticulum

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Function
This folded membrane forms sacs to store proteins or other substances. It creates a vast surface area where the manufacture of proteins and new membranes can take place.

Structure

Endoplasmic reticulum is a folded mass of membranes made of the same phospholipids found in the plasma membrane. There are two types of ER smooth (without ribosomes) and rough (with ribosomes)

 


Ribosomes

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Function
Ribosomes are responsible for protein synthesis

Structure

Cells normally have millions of ribosomes, each ribosome has two parts which come together during protein synthesis. A ribosome is made of numerous proteins and RNA.

 


Golgi complex

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Function
The Golgi complex takes proteins made by the endoplasmic reticulum and exports them out of the cell as needed. It is able to keep dangerous proteins from damaging the cell which made them. It is like a packaging department ready to deliver the protein products made in the cell.

Structure

The Golgi complex looks like a stack of pancakes made of membranes with smaller vacuoles or vesicles on either side of the main structure.
 

 


Lysosome

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Function
Lysosomes are only needed by animal cells. They help break down and remove old worn out cell parts. They are also involved in the digestion of food particles brought into the cell through infoldings in the plasma membrane

Structure

A membrane bound sac lysosomes are a small vacuoles or vesicles in the cytoplasm filled with digestive enzymes. They bud off from the Golgi complex and fuse with food vacuoles

 


Vacuole

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Function
Vacuoles are generally used to store cell products or protect the rest of the cell from invading microorganisms. The large central vacuole of plant cells is a special case. It is used to store water and cellular wastes and helps maintain the necessary internal pressure of plants called turgor pressure.

Structure

 Vacuoles are membrane bound sacs with little or no internal structure.

 


Mitochondria

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Function
Mitochondria found in both plants and animals are called the power houses of the cell. They convert the energy in the bonds of glucose and oxygen to readily available energy in the form of ATP. This process is called aerobic respiration.

Structure

Mitochondria are oval, sometimes branching organelles which have a double membrane. The pair of membranes create two compartments one of which is used to store hydrogen ions. This gives mitochondria an electrical potential like a miniature battery. The inner membrane of mitochondria is highly folded. The rod-like folds are called a cristae.
 

 


Chloroplasts

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Function
Chloroplasts are large organelles found in plants cells which are responsible for photosynthesis. Plants use photosynthesis to convert water and carbon dioxide into glucose. Chloroplasts are green because of the pigment chlorophyll. Plants can store other pigments in organelles similar to chloroplasts. Tomatoes have plastids which store a red pigment.

Structure

Chloroplasts are a double membrane organelles. Like mitochondria two compartments are formed one of which stores hydrogen ions. The inner membranes of chloroplasts are called thylakoids. The thylakoids often form coin-like stacks called grana.


Cytoskeleton

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Function
The cytoskeleton provides support and movement for a cell and its organelles. Organelles can be from place to place in a cell by attaching to microtubule track ways. The various shapes of cells are controlled by the cytoskeleton. Microtubules are involved in cell division.

Structure

The cytoskeleton is made of a network of protein fibers, filaments, and tubules. They attach to special proteins on the interior surface of the plasma membrane forming a semisolid region called a gel.

 


Cilia and Flagella

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Function
Cilia and flagella are used primarily by animal cells for movement. Flagella are larger single versions of cilia. Cilia are short but numerous compared to flagella.

Structure

Each cilia (or flagella) is a circular series of 9 pairs of microtubules (often containing an additional central pair of tubules) surrounded by a long slender sheath of plasma membrane.
 

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