Lil' Plant Cell

Create a visual representation/model (ie. graph or diagram) to make predictions about the exchange of molecules between an organism and its environment, the use of these molecules (ie. CHNOPS and incorporation into carbohydrates, proteins, lipids, nucleic acids, membrane structure, genetic information, etc.), and consequences to the organism if these molecules cannot be obtained.

Take a plant cell and put it in an isotonic solution. Take an animal cell and put it in the same isotonic solution. Which one is happier? The animal cell! [Take a look at ‘-tonic’ under Ch 7 yo understand why] With this in mind, understand that the plant cell is somewhat soft and limp because it is not in the ideal state of absorbing water and water soluble molecules, such as carbohydrates. The plant cell is not retaining the full amount of molecules it needs to be efficient at providing energy and structure to the whole plant. If this continues, and the solution changes to become a hypertonic solution, there will be no water retained in the plant cell, and it will become very limp and quite squishy. As a result, it will have a hard time creating energy and providing structure to the plant. If all plant cells end up like this within a plant, the plant may rot and die from lack of water.

Endo- and Exo- -cytosis

Describe the processes of endocytosis and exocytosis. Propose a model illustrating each process.

Endocytosis is the process of a cell taking in macromolecules by forming a vesicle around the substance with its own cell membrane. Exocytosis is the expulsion of material as a vesicle within a cell travels outwards and fuses with the membrane, opening up and ejecting the substances it was carrying.

http://ibbiology.wikifoundry.com/page/Explain+how+vesicles+transport+materials+within+a+cell

Active Transport

Describe active transport. Propose a model illustrating this process.

Active transport is the opposite of passive transport, in the way that active uses ATP to transfer material through a membrane whereas passive does not. This is the movement against the concentration gradient. Because substances are moving against the grain, they need extra help, an extra push. Proteins studded throughout the membrane facilitate this process. This is an important process because it helps cells work towards equilibrium, even when the surrounding environment is not the proper tonicity for a cell to maintain equilibrium. Please see ‘Glucose and Na+/K+ Transport’ under Ch 7 for an explanation of the sodium-potassium pump which is depicted below.

http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ce/m3/s5/

Glucose and Na+/K+ Transport

Explain how membrane proteins play a role in facilitated diffusion of charged and polar molecules in general and in relation to the specific molecules below.

Glucose transport: These transport proteins are integral membrane proteins that allow glucose to pass through the hydrophobic [glucose is a hydrophilic polar molecule] regions of a cell membrane by creating a polar pathway for the molecule to pass through.

Na+/K+ transport: The sodium-potassium pump is activated by ATP and pumps two K+ ions into the cell as three Na+ ions leave the cell. The following link will take you to a very helpful and informative animation that is followed up with a mini quiz.

http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

Passive Transport

Describe passive transport and explain its role in cellular systems

Passive transport is the movement of substances across a membrane without the expenditure of energy. Diffusion, facilitated diffusion, filtration, and osmosis are examples of passive transport. In cellular systems this is a very important action, because all ATP created by a cell is very precious, the more it can reserve and use for other purposes, the better. Essential substances such as lipids, water, oxygen, and small monosaccharides can pass through via passive transport and give the cell the materials it needs, without causing it to work overtime for it. Water, for example, is a very important substance in all cells. [See ‘-tonic’ under Ch 7 for more details on the importance of water in cells] Because water can diffuse in and out of cells passively, a cell is able to maintain its internal environment without exerting too much energy.

-tonic

Explain the terms: hypotonic, hypertonic or isotonic in relationship to the internal environments of cells. Illustrate each environment with a model and explain which environment is best for plant and animal cells. Justify and explain your model with evidence.

Hypotonic - Cells expand in this environment, because there is less solute outside the cell than there is inside. In an attempt to reach equilibrium, the fluid outside the cell will enter the cell to even out the solute-to-volume ration. This causes cells to swell because there is more fluid within the cell than there usually would be, there is more volume. This can cause animal cells to burst, [lysed] as they do not have cell walls to provide a hard casing. Plant cells love hypotonic solutions because they are able to fill up their vacuoles and internal environments with water and other substances. This gives plants structure and rigidity [turgid].

Hypertonic Solution - Cells shrivel up in this environment, because there is more solute outside the cell than there is inside. In an attempt to reach equilibrium, the fluid within the cell will exit and flow outside, to even out the solute-to-solution ratio. This causes cells the shrivel up because there the fluid that once gave the cell structure is now gone. In animal cells, this is called a shriveled cell. In plant cells, this is called a plasmolyzed cell.

Isotonic - Cells are at a normal state, the amount of solute outside and inside the cell is even. Animal cells and plant cells are both gaining and losing water in this state. This is the ideal state for animal cells; a constant exchange with the environment. But, this is not the ideal state for plant cells. Plant cells do not want to have a constant exchange of water, they want to retain water. If they are unable to retain water, plants will be limp.

Mastering Biology | Pearson; Campbell Biology