Cell Sructure

The cell is the basic unit of life.  The following is a glossary of animal cell terms.  All cells are surrounded by a cell membrane.  The cell membrane is semipermeable, allowing some substances to pass into the cell and blocking others.  It is composed of a double layer of phospholipids and embedded proteins.  Color and label the cell membrane tan.  Plant cells have an additional layer surrounding them called the cell wall.  The cell wall is made of nonliving material called cellulose.  Color and label the cell wall brown.  The centrosome (also called the “microtubule organizing center”) is a small body located near the nucleus.  The centrosome 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.  Only animal cells have centrosomes.  Color and label the centrioles purple.  Microtubules are shaped like soda straws and give the nucleus and cell its shape.  Label the microtubules inside the nucleus.

One theory of the origins of cells states that the first life on earth consisted of several types of tiny protocells, cell-like organisms. These organisms were able to survive and reproduce in a very limited environment because of their simplicity. Over time, some of these protocells came together and shared their specialization in a symbiotic relationship. These colonies of protocells eventually became the cells we know today. All living things are made up of cells. Cells are the smallest working units of all living things. All cells come from preexisting cells through cell division.

Picture 1.example of cells

2.2  Types Of Cell

                        Prokaryotes cells with no nucleus or organelles with membranes. Bacteria and blue-green bacteria are prokaryotic cells. Do not have structures surrounded by membrane Few internal structures One-celled organisms,Bacteria.

Picture 3. Procaryotic cell

                        Eukaryotes cells that contain a nucleus and organelles surrounded by a membrane. The cells of protozoa, algae, fungi, plants, and animals are eukaryotic cells. Contain organelles surrounded by membranesMost living organisms.

Picture 2. Eukaryotic Cells

2.3  Cells Organells

  1. Cell Membrane

A complex barrier of lipid molecules separating the cell from its external environment. These molecules can move apart to allow larger particles to move in or out of the cell. The “selectively permeable” cell membrane regulates what passes into and out of the cell. Some substances, like water, move freely through the cell membrane by a process known as osmosis. In osmosis, particles move easily from an area of high concentration to an area of low concentration by molecular motion only.Cells can push particles in the opposite direction, from low concentration to high, but it will take energy from the cell to do this.

Picture 4. Cell membrane

  1. Cytoplasm

A thick, aqueous solution of salts surrounding the organelles inside the cell membrane. Nutrients and minerals spread through the cytoplasm to all parts of the cell. The constant motion of this gel-like substance is called cytoplasmic streaming. Gel-like mixture.Surrounded by cell membrane.Contains hereditary material.

 

  1. Nucleus

The structure inside the cell that directs cell activities. Contains the DNA of a cell. Directs cell activities. Separated from cytoplasm by nuclear membrane.

  1. Cell wall

On the outside of some cells, bacteria and plants, this structure functions for support and protection. There are pores in the cell wall allowing substances to come in contact with the cell membrane.

  • Types of cell walls :
  1. Primary cell wall – formed during cell growth, it is composed of parallel layers of cellulose and pectin. This structure allows the cell to expand as it grows. While it does provide support, it is not nearly as strong as the secondary cell wall.
  2. Secondary cell wall – formed after cell growth stops, it is composed of interwoven cellulose and lignin fibers. This structure is very strong, but does not give. It gives plants their “woody” characteristic.
    1. Ribosome

The sites of protein synthesis in a cell. These small, spherical structures are the most numerous organells in almost all cells. Some ribosomes produce protein to be used within the cell and some produce protein that is “exported” to other parts of an organism.

Picture 5. Ribosom

  1. Endoplasmic reticulum

A membrane system of folded sacs and tunnels in the cytoplasm. Rough “ER” is covered with ribosomes. It is common in cells that export proteins and directs the proteins flow. Smooth “ER” as few or no ribosomes. It functions as a pathway for molecules to follow. Smooth type: lacks ribosomes. Rough type (pictured): ribosomes embedded in surface.

Picture 6. RE

Rough endoplasmic reticulum (rough ER) is 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.  Color and label the rough ER violet.  Rough ER transports materials through the cell and produces proteins in sacks called cistern which are sent to the Golgi body, or inserted into the cell membrane.  The Golgi apparatus or Golgi complex is a flattened, layered, sac-like organelle that looks like a stack of pancakes.  The Golgi body modifies & packages proteins and carbohydrates into membrane-bound vesicles for “export” from the cell.  Color and label the Golgi export vesicles red.  Smooth ER does NOT have ribosomes on its surface.  It makes proteins and lipids that will be exported by the cell.  It also controls the Calcium level in muscles and detoxifies poisons, alcohol, and drugs.

  1. Golgi Apparatus

A stack of membranes or sacs that acts to prepare substances for export from the cell. Once the Golgi apparatus has enclosed the final product in a vesicle, or pouch, the product is sent through the cell membrane.

Picture 7. Golgi Aparatus

  1. Mitochondria

Respiration centers of a cell. Large organelles scattered through most cells, they are most numerous in cells that use a lot of energy like liver and muscle cells. Produces energy through chemical reactions – breaking down fats & carbohydrates. Controls level of water and other materials in cell. Recycles and decomposes proteins, fats, and carbohydrates.

Picture 8. Mitochondria

  1. Lysosome

Digestive centers of a cell. They produce many different types of enzymes and digest things from food particles to a cell’s own worn out parts. Digestive ‘plant’ for proteins, fats, and carbohydrates. Transports undigested material to cell membrane for removal. Cell breaks down if lysosome explodes.

Picture 9. Lysosome

  1. Vacuole

Most common in plant cells, they are storage sites within a cell. Membrane-bound sacsfor storage, digestion, and waste removalContains water solutionHelp plants maintain shape.

Picture 10. Vacuoles

2.4      Size of living things

The smallest known living thing on Earth is a bacteria in the genus Coxiella. These bacteria are about 8 millionths of an inch (0.2 micrometers) in diameter. Their small size means these bacteria contain only 100 million to 120 million atoms. While this may seem like a large number, keep in mind that the human body has over 5 Billion cells. It is believed that fewer atoms would be unable to build the structures needed to store information and carry out the metabolic processes needed for life.

The largest known animal is the blue whale, Balaenoptera musculus. It is known to reach lengths over 100 feet (30+ meters) and weigh 120 tons. The chart below indicates that all animal cells are about 10 micrometers in diameter. This means that the cells of a blue whale and a human are essentially the same size.

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