Week 6 Lab 6 Cell Structure and Function

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Dec 6, 2023

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Note: All your answers to questions must be in Red or other color (not including blue) for easier grading. Points will be deducted if you do not distinguish your answers. Lab 6. Cell Structure and Function Objectives:  Distinguish between eukaryotic and prokaryotic cells.  Describe the structure and function of plant and animal cells.  Define the following terms: diffusion, osmosis, equilibrium, tonicity, turgor pressure, plasmolysis.  Describe what drives simple diffusion (why do the molecules move?).  List the factors that may affect the speed of simple diffusion.  List which molecules, in general, can freely diffuse across the plasma membrane of a cell.  Describe what drives osmosis (why do water molecules move?).  Explain why water moves out of a cell when the cell is placed in a hypertonic solution.  Explain why water moves into a cell when the cell is placed in a hypotonic solution.  Describe what physically happens to a cell if water leaves the cell.  Describe what physically happens to a cell if water enters the cell. Vocabulary:  Cell theory  Plasma membrane  Cytosol  Plasma membrane  Chromosomes  Ribosomes  Prokaryotic cells (Prokaryotes)  Eukaryotic cells (Eukaryotes)  Central Vacuole  Cell wall  Lignin  Chloroplast  Chlorophyll  Centrosome  Lysosomes  Diffusion

 Osmosis  Solute  Isotonic  Hypertonic  Hypotonic  Turgor Pressure  Plasmolysis Introduction: Cell theory states that the cell is the fundamental unit of life. However, cells vary significantly in size, shape, structure, and function. At the simplest level of construction, all cells possess a few fundamental components. These include cytosol (a gel-like substance composed of water and dissolved chemicals needed for growth), which is contained within a plasma membrane (also called a cell membrane or cytoplasmic membrane); one or more chromosomes (condensed DNA and proteins), which contain the genetic blueprints of the cell; and ribosomes , organelles used for the synthesis of proteins. Beyond these basic components, cells can vary greatly between organisms, and even within the same multicellular organism. The two ( main type or categories of cells are) largest categories of cells— prokaryotic cells ( ex: bacteria; usually smaller & simpler ) and eukaryotic cells (ex: plant & animal cells; bigger than prokaryotic & more complicated b/c there are more organelles inside of them) —are defined by major differences in several cell structures. In this exercise, you will examine the semipermeable nature of the cell membrane (aka, plasma membrane). The cell membrane controls what enters and exits the cell, and therefore serves a very important cellular function. You will also explore the concept of tonicity, which refers to the solute concentration of a solution, and its inherent ability to influence the rate and direction of osmosis.

Prokaryotic Cells: Prokaryotic cells are cells without a nucleus. The DNA in prokaryotic cells is in the cytoplasm rather than enclosed within a nuclear membrane. Prokaryotic cells are found in single-celled organisms, such as bacteria, like the one shown in Figure 1 . Organisms with prokaryotic cells are called prokaryotes . They were the first type of organisms to evolve and are still the most common organisms today. Bacteria are described in the following video: https://youtu.be/TDoGrbpJJ14 Figure 1: This diagram shows the structure of a typical prokaryotic cell, a bacterium. Like other prokaryotic cells, this bacterial cell lacks a nucleus but has other cell parts, including a plasma membrane, cytoplasm, ribosomes, and DNA. Identify each of these parts in the diagram.

Eukaryotic Cells In nature, the relationship between form and function is apparent at all levels, including the level of the cell, and this will become clear as we explore eukaryotic cells. The principle “form follows function” is found in many contexts. For example, birds and fish have streamlined bodies that allow them to move quickly through the medium in which they live, be it air or water. It means that, in general, one can deduce the function of a structure by looking at its form, because the two are matched. A eukaryotic cell is a cell that has a membrane-bound nucleus and other membrane-bound compartments or sacs, called organelles, which have specialized functions. The word eukaryotic means “true kernel” or “true nucleus,” alluding to the presence of the membrane-bound nucleus in these cells. The word “organelle” means “little organ,” and, as already mentioned, organelles have specialized cellular functions, just as the organs of your body have specialized functions. Plant Cells are squarish rectangular in size in shape b/c it contains a cell wall to maintain the cell shape. Main difference btwn the animal & plant cell, are 3 structures: plasma membrane, chromosome, & ribosomes. Plant cells resemble other eukaryotic cells in many ways. For example, they are enclosed by a plasma membrane and have a nucleus and other membrane-bound organelles. A typical plant cell is represented by the diagram in Figure 2b .

Figure 2. Plant cells (b) have all the same structures as animal cells (a), plus some additional structures. Structures found in plant cells, but not animal cells include a large central vacuole, cell wall, and chloroplasts.  The large central vacuole is surrounded by its own membrane and contains water and dissolved substances. Its primary role is to maintain pressure against the inside of the cell wall, giving the cell shape and helping to support the plant.  The cell wall is located outside the cell membrane. It consists mainly of cellulose and may also contain lignin , which makes it more rigid. The cell wall shapes, supports, and protects the cell. It prevents the cell from absorbing too much water and bursting. It also keeps large, damaging molecules out of the cell.  Chloroplasts contain the green pigment chlorophyll and carry out photosynthesis. Chromoplasts make and store other pigments. They give flower petals their bright colors. Animal Cells are circular-ish sometimes similar shape but closely related to a circle & organelles you see here are also found on the plant cell. Main difference btwn the animal & plant cell, are 3 structures: plasma membrane, chromosome, & ribosomes. At this point, you know that each eukaryotic cell has a plasma membrane, cytoplasm, a nucleus, ribosomes, mitochondria, peroxisomes, and in some, vacuoles, but there are some striking differences between animal and plant cells. While both animal and plant cells have microtubule organizing centers (MTOCs), animal cells also have centrioles associated with the MTOC: a complex called the centrosome. A typical plant cell is represented by the diagram in Figure 2a . Animal cells each have a centrosome and lysosomes, whereas plant cells do not.  The centrosome (the organelle where all microtubules originate) replicates itself before a cell divides, and the centrioles appear to have some role in pulling the duplicated chromosomes to opposite ends of the dividing cell.  In addition to their role as the digestive component and organelle- recycling facility of animal cells, lysosomes are considered to be parts of the endomembrane system. Lysosomes also use their hydrolytic enzymes to destroy pathogens (disease-causing organisms) that might enter the cell. Diffusion

Diffusion is defined as the net movement of molecules or ions from a region of high concentration to a region of lower concentration. Diffusion continues until a state of equilibrium is reached, which means that the molecules are randomly distributed throughout the system. Diffusion is considered a form of passive transport because no energy is required in the process. Diffusion can occur in a gas, a liquid, or a solid medium. Diffusion also occurs across the selectively permeable membranes of cells. Osmosis Osmosis is a special case of diffusion in which water molecules pass through a selectively permeable membrane, but larger molecules do not. Osmosis proceeds from a region of high water concentration, across a semi- permeable membrane, to a region of lower water concentration until equilibrium is reached. A solute is a solid substance , such as salt or sugar that is dissolved in a solvent. Water is usually the solvent in living systems. A typical animal cell contains a salt concentration of 0.9%. A solution of equal solute concentration is referred to as isotonic . A cell placed in an isotonic environment will experience movement of water inside and outside the cell, but there will be no change in the biology of the cell. A hypertonic solution contains a high solute concentration with respect to cells. For example, a solution containing 10% salt is hypertonic. When a cell is placed in a hypertonic environment, there is a net movement of water to the outside of the cell (from the higher water environment inside the cell). The cell shrinks in response . A solution of low solute concentration is referred to as hypotonic . A solution containing 0.5% salt is hypotonic with respect to the cell. When a cell is placed in a hypotonic environment, there is a net movement of water into the cell. The cell swells in response .

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