The control center of a cell is the _____.
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Over time, people’s perceptions of cell structure have shifted dramatically. Cells were once thought to be mere membranous sacs containing fluid and a few floating particles, according to early biologists. Cells are infinitely more complex than this, according to today’s biologists.
In the human body, cells come in a range of sizes, shapes, and forms. The definition of a “generalized cell” is introduced for descriptive purposes. It incorporates characteristics from all cell types. A cell is made up of three parts: the cell membrane, the nucleus, and the cytoplasm, which sits between the two. The cytoplasm contains complex arrangements of fine fibers as well as hundreds, if not thousands, of tiny but distinct structures known as organelles.
A cell (Plasma) membrane covers every cell in the body. The cell membrane is responsible for separating extracellular and intracellular material. It preserves the integrity of a cell and regulates the movement of materials into and out of it. For the required exchange, all materials inside a cell must have access to the cell membrane (the cell’s boundary).
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Now that you know that all cells are surrounded by the plasma membrane, you can take a look inside a prototypical human cell to learn about its internal components and functions. The plasma membrane, nucleus, and cytoplasm are the three primary regions of animal cells. The nucleus is a central organelle in a cell that houses the cell’s DNA (Figure 3.6). The cytosol and organelles are two components of the cytoplasm. The fluid medium required for biochemical reactions is provided by cytosol, a jelly-like substance found within the cell. An organelle (also known as a “small organ”) is one of many types of membrane-enclosed bodies found in cells, each with its own function. The many different cellular organelles work together to keep the cell safe and performing all of its essential functions, just as the various bodily organs work together in harmony to perform all of a human’s functions.
The nucleus (Figure 3.7) is the largest and most visible organelle in a cell. Since it stores all of the genetic instructions for producing proteins, the nucleus is usually referred to as the cell’s control center. Some cells in the body, such as muscle cells, are multinucleated, which means they have more than one nucleus. Nuclei are absent in certain cells, such as mammalian red blood cells (RBCs). When RBCs mature, they eject their nuclei to make room for the vast number of hemoglobin molecules that transport oxygen across the body. RBCs have a short life span without nuclei, so the body must continually create new ones.
The cell cycle (and cancer) [updated]
What contribution did Anton van Leeuwnhoek make to cell theory?
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Under a microscope, he was the first to see living cells. In 1675, he saw a swarm of single-celled species moving about in pond water. He referred to them as “animalcules.”
Based on whether or not they have a nucleus, all cells can be classified into one of two groups.
Prokaryotic (bacteria without a nucleus) and Eukaryotic (bacteria with a nucleus) (all other types of life except the two kingdoms of bacteria)
When it comes to magnification and resolution, what’s the difference?
Magnification refers to how much larger a picture appears in a microscope, while resolution refers to how fine you can see objects. High magnification is useless if the resolution is poor.
True or False: “Active and passive transport work together to keep substances on both sides of the cell membrane in balance. FALSE (While passive transport is capable of doing so, active transport is rarely capable of doing so.) Active transport typically carries contaminants from low-concentration areas to high-concentration areas, resulting in a higher concentration on one side of the membrane and a lower concentration on the other. This is the polar opposite of going toward equal concentrations on both sides of the membrane, also known as equilibrium.)
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When you compare the animal and plant cells on the previous pages, you’ll find that many of the cell parts are strikingly similar. Cell organelles in paramecia, petunias, and primates have similar appearances and perform similar functions (see table 4.2 on pages 88-89).
If you traveled deep enough into the interior of one of your cells, you will finally arrive at the cell’s heart. The nucleus can be located there, cradled inside a network of fine filaments like a ball in a basket (figure 4.8). The nucleus is the cell’s command and control center, directing all of the cell’s activities. It also houses the genetic archive, which houses the hereditary data.
The nucleus is made up of a double membrane known as the nuclear envelope that covers a fluid-filled interior that houses the chromosomes. Individual nuclear pores can be seen spreading through the two membrane layers of the envelope in cross section. The pore is packed with protein, which helps to regulate pore entry.