What You Need to Know about Cells for the GED Science Test - dummies

What You Need to Know about Cells for the GED Science Test

By Murray Shukyn, Achim K. Krull

Cells will be covered on the GED Science test. Among living things, a cell is the smallest, but the body of information that surrounds it is huge. Check out the following for the vocabulary you should recognize and understand and information to make it all clearer. Remember that you need a general knowledge of the subject but a good understanding of the words.

Passing the life test

Cells are the most basic form of life, which leads to the question: What exactly is life? Something is considered to be living only if it has the following characteristics:

  • Adaptation: The ability to adjust to a changing external environment.

  • Growth: The ability to increase in size in all or some of its parts, not just acquiring more matter.

  • Homeostasis: The ability to regulate its own internal environment to maintain a cell or body at a relatively constant state.

  • Metabolism: The transfer of energy by consumption of matter or chemicals or through photosynthesis.

  • Organization: Being composed of one or more cells.

  • Reproduction: The ability to reproduce either sexually or asexually (without sex).

  • Response to stimuli: The ability to react to external stimuli, including light, sound, and heat. Responses may vary from the most basic chemical response of a single-cell organism to motion resulting from the perception of a complex sensory system.

Viruses straddle the line between living and nonliving organisms. Because they require a host cell to reproduce (instead of cell division), don’t grow, and don’t have energy metabolism or produce waste products, many scientists consider them nonliving organisms that deserve a class of their own — infectious agents.

Viruses are not included in the classification of living organisms because

  • (A) they’re too small.

  • (B) they infect other organisms.

  • (C) they can’t reproduce without a host cell.

  • (D) they rely on other organisms for their survival.

Viruses aren’t considered to be living organisms because they lack many of the properties shared by living organisms, such as the ability to reproduce through cell division, to metabolize energy, to grow, and to produce waste products.

Understanding cell theory

Cell theory is one of the principle theories in modern biology and was made possible by the invention of the microscope. According to cell theory,

  • All known living things are comprised of cells.

  • The cell is the structural and functional unit of all living things.

  • All cells come from other cells through the process of cell division.

  • Cells contain the hereditary information that’s passed from one cell to another when the cell divides.

Multicellular (many celled) organisms have various levels of organization within them. Although individual cells may perform specific functions, they also work together for the good of the entire organism and become dependent on one another.

Multicellular organisms have the following five levels of organization, ranging from simplest to most complex:

  • Cells are the basic unit in living organisms.

  • Tissue is composed of similar structural and functional cells working together for a specific purpose.

  • Organs are composed of tissues working together.

  • Organ systems are two or more organs working in concert to perform a specific function.

  • Organisms are composed of organ systems. An organism is an entire entity capable of all basic life processes.

Which of the following is not one of the main principles of cell theory?

  • (A) To exist, a cell must be a part of a larger organism.

  • (B) Cells are the basic units that comprise all living things.

  • (C) All cells are created through the process of cell division.

  • (D) Every living thing is composed of cells.

Choice (A) is the correct answer. Some microscopic organisms consist of a single cell. All the other choice are principles of cell theory.

Recognizing cell parts

Although cells are tiny, they’re comprised of even tinier parts. The following list should help you pick the parts out of a lineup:

  • Cytoplasm: The fluid membrane that holds and supports all of a cell’s components.

  • Endoplasmic reticulum (ER): An extensive network of sac-like structures that synthesize proteins and lipids and assist in folding and transporting manufactured proteins.

  • Golgi body (Golgi apparatus): Layers of membrane-bound structures that modify, sort, and package complex molecules (macromolecules) to be used within the cell or to be secreted by the cell.

  • Lysosome: Cube-shaped structures that contain enzymes to help break down cell waste and prepare it for excretion. These structures are found only in animal cells.

  • Vacuoles: Plant cells’ equivalent to lysosomes.

  • Membrane (wall): The protein layer that surrounds the cell, giving it form and protecting it from its external environment. The membrane is selectively permeable to allow food and other desirables into the cell, while keeping harmful matter outside. (Permeable means water or gas can pass through it, like a coffee filter.)

  • Mitochondrion: Commonly described as the cell’s “power plants,” the mitochondrion is a membrane-enclosed structure where cell respiration occurs. The activity of mitochondrion within a cell and the number of mitochondria determine the cell’s metabolism.

  • Chloroplast: Plant cells’ equivalent to the mitochondrion. Chloroplasts capture light energy and convert it into free energy within the cell.

  • Nucleus: The part of a cell that contains its DNA and controls reproduction.

  • Organelles: Any of the many subunits within a cell, including ribosomes, mitochondria, and lysosomes.

  • Ribosome: Components within a cell that form proteins from amino acids.

    Cell parts.