I’m stuck on a Biology question and need an explanation.
Diffusion refers to the movement of molecules from an area of higher to one of lower concentration. It is the result of natural random movement of molecules and hence does not require energy. In the body of an organism, diffusion is a common means of transport. For instance, gases and other solutes diffuse into and out of cells of many organisms. For diffusion to occur, two conditions need to be met. First, there must be a difference in concentration of a substance. Second, the membrane must be permeable to the substance. For example, if the concentration of a substance is higher outside of cells than inside and the cell membrane is permeable to the diffusing molecules, then the substance diffuses into the cells. (If there is equal concentration then substances diffuse in and out).
Cells are able to keep molecules from leaking out or prevent unwanted molecules from coming in by having selectively permeable (or semi-permeable) membranes. Water, gases and other small uncharged molecules are generally able to easily diffuse across. The cell membrane, however, is impermeable to many others, particularly large organic molecules.
This process of water diffusing across a semi-permeable membrane is called osmosis. The net (overall) movement of water across the membrane has a tremendous impact on cells since water is the medium of transport in and out of cells. If the solution outside of cells has a lower solute concentration (hypotonic) and therefore a higher water concentration relative to the solution inside the cell, then net movement of water will diffuse into the cells. The result is an increase in the volume of cytosol that will cause the cell to swell. If the cell does not have a cell wall or some other means of protecting the membrane, it will burst! On the other hand, if the solution outside has a higher solute concentration (hypertonic) and therefore a lower water concentration than inside the cell, then the net movement of water will diffuse out of the cells causing the cell to lose water and shrink. Outside solutions with the same solute concentration as the inside the cell (isotonic) will have a zero net movement of water, and hence, minimal impact.
To review osmosis and learn about real life examples of osmosis, watch
Diffusion of starch and iodine across a membrane
(4 min 29 sec) to view the set up and experiment with results. Focus on the starch solution and ignore the glucose.
Osmosis in potato (DIY experiment)
(1 min 9 sec) which demonstrates the experiment.
Diffusion of starch and iodine across membrane
Enzymes are present in all living tissues because they are critical for chemical reactions. Without enzymes, reactions such as breaking down a sugar molecule would occur too slowly to be useful, perhaps not even in your lifetime. Enzymes are catalysts, which are molecules that speed up chemical reactions. They typically speed up chemical reactions by a very large factor, from 10,000 to 1,000,000 times.
Since enzymes are proteins, they consist of chains of amino acids folded together in a specific 3D shape. If enzymes lose their shape, they lose their ability to bind to their substrates, and their ability to function as a catalyst. This change in the specific 3D shape is called denaturation.
For a review of enzymes, watch“Enzymes” by Amoeba Sisters (5 min 46 sec).
This laboratory will demonstrate the presence of catalase, an enzyme located inside both animal and plant cells, and study its properties. Catalase breaks down toxic hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2). The H2O2 is the substrate for catalase. Water (H2O) and oxygen (O2) are the products. Oxygen (O2) is a gas that creates bubbles that are detectable and an indication that the reaction occurred.
If catalase is present in the cells and functioning, then catalase will break down H2O2 and oxygen gas (O2) will be released.
Test for control condition, catalase enzyme in raw and boiled liver.
Watch “Liver and catalase make-up lab” and follow along with the procedure (only up to 9 min and 30 sec).
*Note: Do not record data for test tube #2 with reused liquid.
Test for catalase enzyme in raw and boiled potato
Watch Catalase Enzymeand following along with procedure (view up to 33 sec. only).
Various pigments are found in leaves. We see these in autumn leaves when the green starts to fade. In some plants like Coleus, the colors can be seen all the time. Pigment colors may be bright orange, yellow, red, purple or green. The green pigment is chlorophyll, a molecule that strongly absorbs light energy and stores it in its chemical form.
Chlorophyll plays a role in photosynthesis, the process that plants use to convert the energy of sunlight into chemical energy in carbohydrates. They do this by using CO2 and H20 as raw materials to manufacture glucose in the presence of light. The glucose can then be transported as sucrose (table sugar) or be stored as starch.
To find out the function of chlorophyll in leaves, the green areas of a leaf will be matched with the location of starch after all the pigments have been extracted. Iodine solution will be used to locate starch in the leaf.
For a review of photosynthesis, watch “Photosynthesis and the Teeny Tiny Pigment Pancakes” by Amoeba Sisters (7 min 45 sec).
If chlorophyll is required in photosynthesis, then we predict that starch (which are products of photosynthesis) will be found in parts of the leaf that contain chlorophyll.
Demonstrate the role of chlorophyll in photosynthesis.
Testing a leaf for starch
Watch Testing a leaf for starch (6 min 25 sec) and follow the procedure below to collect your data.
Starch Detection in Leaves(2 min 34 sec) which follows a similar procedure as listed above. What are the results of starch detection in this experiment?
How do we get our energy? Like fungi, we are heterotrophs, which means we cannot make our own food. Instead, we must get our food from the environment. Fungi do the same. They absorb their food in the form of sugar. Fungi must then convert the stored energy in sugar (ie. glucose) into the usable form of energy in ATP. This process can be carried out with (aerobic) or without (anaerobic) oxygen gas. Fermentation is the process of an organism converting chemical energy from sugar into ATP without oxygen gas. Depending on the type of organism, specific fermentation products are produced. The fungi, Baker’s yeast (Saccharomyces cerevisiae), famously ferments sugars to produce ethanol alcohol in bread, beers, wines and other alcoholic drinks.
The fermentation process is useful in the field of biotechnology. Recombinant DNA technology allows us to insert genes of interest into the yeast plasmid DNA. When the yeast goes through fermentation, it will produce our desired product of interest from the inserted gene. Many products can be manufactured using this method such as foods (ie. cheese, milk, yogurt), pharmaceuticals (drugs), hormones, proteins, vaccines and other products.
In yeast, alcohol is the natural fermentation product and occurs according to this metabolic pathway:
In this exercise, yeast will be allowed to consume sugar containing protein under anaerobic conditions to demonstrate fermentation. We will monitor the release of the endproducts, ethanol alcohol and carbon dioxide (CO2).
To review fermentation, watch Fermentation by Amoeba Sisters (8 min 34 sec).
If yeast is given sugar in the absence of oxygen gas, then they will go through the process of fermentation to produce ethanol, carbon dioxide and ATP.
Watch Fermentation of Yeast & Sugar – The Sci Guys: Science at Home (4 min 17 sec) and follow along with the procedure below.
Note: Human consumption of this experiment’s product is NOT ALLOWED!
Compare the initial reactants in the bottle to the final product (color, transparency):
Record your data from Table 1 for bottle #1 on the graph below. Put time on the X-axis and CO2 released on the Y-axis. Be sure to label your axes.
Next, draw on figure 1 what you predict the data to be for bottle #2 and bottle #3.
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