Ap Bio Essay 1983

1983 State the conclusion reached by Mendel in his work on the inheritance of characteristics. Explain how the followlng deviates from these conclusions a. Autosomallinkage b. Sex-Jinked (X-/inked) inheritance c. Polygenic (multiple-gene) inherItance

2. Describe the fluid-mosaic model of a plasma membrane. Discuss the role of the membrane in the movement of materials through it by each of the following processes. a. Active transport b. Passive transport 1.

The fluid-mosaic model of a plasma membrane describes the bilayer of phospholipids in cellular membranes. This bilayer consists of two layers of phospholipids with the tails facing inward toward each other and the heads facing to the outside of the membranes.

2.

The term “fluid” relates to the observation that the components of the membrane, like the phospholipids and proteins, are constantly moving. This is basically explaining that the membrane is not solid or stable, but is always flowing and changing.

3.

The term “mosaic” explains that membranes are made of many different types of molecules including proteins, phospholipids, glycoproteins, and glycolipids. Just like a mosaic painting, plasma membranes are made of various compounds with different sizes and functions.

4.

The plasma membrane of cells regulates the movement of all compounds into and out of the cell. In all types of transport involving the cell, this selective permeable membrane controls everything that can enter and exit the cell.

5.

Certain small compounds lacking a charge like O2, N2, H2O, and CO2 can easily pass through the phospholipid bilayer. These can move through passive transport.

6.

Other compounds larger than water or that have a charge like glucose, sucrose, H+, K+, or Na+ cannot move through the membrane easily. These can move through active transport.

7.

Active transport is the process of moving particles across the membrane against the concentration gradient. This means that the particles are being transported from a low-concentration to a high-

concentration. This type of transport that works like a water pump requires energy input from a source like ATP. 8.

Passive transport does the exact opposite. With a desire to reach equilibrium, particles move from where there is a high-concentration to a low-concentration. When equilibrium is reached (when there are equal amounts of the compound on both sides of the membrane), transport does not stop, but continues at an equal rate in both directions.

9.

This flow of particles that occurs to reach equilibrium is analogous to the movement of particles of a scent when a bottle of perfume is sprayed. The particles flow away from each other to spread out evenly across a room.

10.

The role of many proteins that reside in the membranes is to function as enzymes and provide a channel for active transport. Like those of an anabolic reaction, the enzymes require energy to accomplish their task.

11.

This is seen in the sodium potassium pump that keeps a low concentration of sodium ions (Na+) and high concentration of potassium ions (K+) within the cell. It pumps three sodium ions out of the cell for every two potassium ions transported in. This pump in the plasma membrane is necessary in the nervous system by maintaining the resting potential.

12.

After some chemical reactions, the waste products must be moved out of the cell against the concentration gradient. Active transport is required to pump these compounds out of the cell using energy. This occurs through exocytosis where the waste products are transported in small sacs with structures similar to that of the plasma membrane’s phospholipids bilayer.

13.

Endocytosis is used to take things into the cell through a process similar to exocytosis. It uses the same type of sacs used in exocytosis that are made out of sections of the plasma membrane.

14. When food particles too large to be taken in through passive transport require entrance to the cell, a type of endocytosis occurs. This is called phagocytosis and is a very common method of eating in single-cell organisms like amoebas. The plasma membrane engulfs the pieces of food and creates a small sac made of its phospholipid bilayer to transport it through the cell. 15.

Smaller particles, commonly liquids, enter the cell through the same method as phagocytosis, but on a smaller scale. The active transport of small particles such as liquids into the cell is pinocytosis. These particles may not be able to enter the cell because of their charge.

16.

In all of the above types of active transport like endocytosis and exocytosis, the sacs the particles travel by are actually small pieces of the plasma membrane. In exocytosis, a section of the membrane is actually replaced as the waste products are released from the cell. Endocytosis removes some phospholipids from the plasma membrane that permits them to enter the selective permeable membrane.

17. Passive transport is usually discussed as two different types of transport. Diffusion and osmosis occur in very similar situations, but vary in the particular compound they transport. 18. Generally the compounds that travel via passive transport are smaller compounds that are greatly concentrated inside or outside of the cell and need to even out. This type of transport occurs naturally and does not require ATP to proceed. 19.

Diffusion is the movement of ions or molecules from regions of higher concentration to regions of lower concentration. These molecules can be anything as long as they are not too large or have a great charge.

20. The particles that are transported through the plasma membrane during passive transport are called the solutes. The substance that they move in (very commonly water—the universal solvent) is called the solvent. 21. Osmosis is the movement of water, and only water, from a region of high concentration to regions of low concentration. Because water is such an important compound to all cells, osmosis is considered its own type of passive transport. 22. Commonly related to blood cells, osmosis greatly controls the size of cells. As more water enters the cell, the size of the cell can drastically increase or decrease immensely if water exits the cell. 23.

In an isotonic solution, the cell is in equilibrium regarding water and is considered flaccid. Especially important to red blood cells, this is the idea state of cell size and condition.

24. Hypertonic solutions exist when the supply of water outside the cell is very limited. In the fashion of passive transport, water flows out of the cell through the plasma membrane and causes the cell to shrivel up, usually killing the cell. 25. The exact opposite of hypertonic is a hypotonic solution where massive amounts of water are present outside the cell. To reach equilibrium, water rushes into the cell causing the cell to swell, and, in some cases, burst. 26. Due to the charges of the different parts of the phospholipids, the heads, the outer portion of the membrane, are hydrophilic, water-loving. The tails, on the other hand, are hydrophobic, water-fearing. 27.

During cellular respiration, massive amounts of ATP are produced from passive transport. During Chemiosmosis (another type of diffusion), energy is extracted from hydrogen ions that pass through the plasma membrane of a mitochondrion. Protein channels in the membrane act as enzymes to extract energy from this process.