Animal Biology - GRE Subject Test: Biology

Antibodies are part of the adaptive immune response, which means that they are formed later in an infection. Because both recognition sites have the same structure, they are responsive to only one type of antigen. They are located on the outside of B cells, and can be released freely into the plasma by plasma cells.

Placental crossing is done mainly by IgG antibodies. These fast-acting antibodies provide temporary immunity for the fetus until it is able to have its own immune system produce sufficient antibody amounts.

Antibodies are produced by the adaptive immune system and to antigens presented by a pathogen. The antibody-antigen complex is then detected by cytotoxic T-cells, which destroy the infected cell. The antibodies are created by B-lymphocytes, which can differentiate when exposed to a specific pathogen. Differentiated B-lymphocytes known as plasma cells are responsible for the mass production of certain antibodies.

Macrophages are derived from monocytes and serve as phagocytes in the innate immune response. Basophils are also part of the innate immune response and, along with mast cells, produce histamine to initiate the inflammatory response.

Acquired immunity is developed in the body following a previously encountered infection. The innate immunity is, by definition, always present in the body and is used to attack all general forms of infection.

The granulocyte cells are considered part of innate immunity and help mediate the immune response against foreign pathogens. These cells include basophils, neutrophils, eosinophils, mast cells, and macrophages (which are differentiated from monocytes).

The adaptive immune response involves the production of antibodies against specific target antigens. Plasma cells are an integral part of the adaptive response and secrete large volumes of antibodies in response to a secondary infection by a previously encountered pathogen. T-cells and B-cells are also part of the adaptive response.

The five types of leukocytes are: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Three of these (neutrophils, eosinophils, and basophils) contain granules, tiny sacs containing enzymes which can lyse microorganisms. The other two leukocytes (lymphocytes and monocytes) do not contain these granules.

There are many types of white blood cells with distinct functions in the body. Neutrophils and monocytes are phagocytes that engulf bacteria. B-lymphocytes produce one type of antibody. Basophils are the least common of the leukocytes, and release histamine during inflammation.

Before a B-lymphocyte can proliferate and differentiate, it must present its antigen to a helper T-cell. If the helper T-cell recognizes the antigen as foreign, it will activate the B-lymphocytes, and cause them to differentiate into plasma cells and memory B-cells.

T and B cells are both part of the adaptive immune response. This means that they are typically made to handle very specific pathogens that may be encountered in the body. Before they are released into circulation, both must undergo negative selection, which makes sure that they do not respond to natural peptides that they encounter in the body. Failure of this step to take place can result in autoimmune diseases.

Many of the modulations of the immune response are controlled by helper T cells. In order to change the type of antibody secreted by a B cell, helper T cells need to interact with them via a number of cytokines. The types of cytokines secreted by helper T cells will tell the B cells which antibodies to start secreting.

The type of blood a person has not only tells us which antibodies they create, but also which blood type can be given in the event of a transfusion. A person with type A blood has A antigens on his red blood cells. As a result, the person does not make A antibodies; these would bind to the A antigens and initiate an autoimmune response.

Because the person does not make the B antigen, there are B antibodies in the body. This means that the person cannot be given type B blood. B type blood cells would be targeted by the antibodies present in the body, causing an autoimmune reaction against the foreign blood. Since type O blood does not have any surface antigens, this blood type can be given to anybody. No antibodies will react with type O blood.

B cells play numerous integral roles in the immune response against foreign pathogens (viruses, bacteria, and fungi), including forming transient microenvironments called germinal centers, where they produce long-lived plasma cells that are high affinity for specific antigen and memory B cells. They also serve as antigen-presenting cells and producers of cytokines and chemokines; However, B cells are not able to produce extracellular traps, which primarily are composed of DNA and work to trap pathogens. Neutrophils produce extracellular traps.

Naive B cells (and most other immune cell subtypes) need more than one signal to become activated. They normally need B cell receptor signaling (signal 1), costimulation by other receptors (signal 2), and cytokines/chemokines (signal 3). This system is necessary in order to prevent aberrant activation of lymphocytes (safeguard against autoimmunity).

In regards to the other statements, there are numerous autoreactive B cells at any given time due to the stochastic nature of VDJ recombination and germinal center reactions. Therefore, tolerance mechanisms and checkpoints are incredibly important to keep these cells in check; central and peripheral tolerance are equally important. Self-nuclear reactive B cells and T cells are both necessary and critical in autoimmune pathogenesis. Female sex hormones are definitely believed to contribute greatly to autoimmune disease pathogenesis (e.g. estrogen). Over 75% of autoimmune patients are women.

The left atrium receives blood from the pulmonary veins, which carry blood that was freshly oxygenated from the lungs to the heart. The partial pressure of oxygen is always highest soon after oxygenation, thus blood returning from the lungs would have a high partial pressure.

The superior and inferior vena cavae return deoxygenated blood from the body to the heart, and would have very low oxygen partial pressures. The right atrium receives this deoxygenated blood from the vena cavae and transfers it to the right ventricle. From the ventricle, the deoxygenated blood is transported to the lungs via the pulmonary arteries. It only becomes oxygenated again after reaching the lungs, and then returns to the heart through the pulmonary veins.

We know that systemic arteries carry oxygenated blood away from the heart and that these vessels pass through tissues, allowing oxygen to diffuse into the tissues and carbon dioxide to diffuse out into the bloodstream. We also know that veins carry blood back to the heart, which by this time is oxygen-poor due to its gas exchange with the tissues of the body. The partial pressure of oxygen in veins must be lower than it is in arteries, since the veins carry deoxygenated blood.

The remaining statements regarding gas exchange are true.

During inspiration, the lungs expand as the diaphragm contracts and internal intercostal muscles relax. As the volume of the thoracic cavity increases, its pressure decreases. This creates a pressure gradient, driving air from an area of high pressure (the environment) into the area of low pressure (the lungs).

When you are not breathing, your respiratory system cannot perform its function. Unwanted gases, such as carbon dioxide, cannot be removed from the system and necessary gases, such as oxygen, cannot enter the system. This causes a buildup of carbon dioxide in the body, which leads to acidosis. Carbon dioxide is converted to carbonic acid via carbonic anhydrase. This carbonic acid builds in the blood, lowering its pH.

Hemoglobin is the main oxygen carrier in the human body. Each hemoglobin protein is able to carry four oxygen molecules. As the hemoglobin travels through the blood vessels of the body, the oxygen is released to tissues and used in the electron transport chain.

If oxygen is unable to bind to hemoglobin, our bodies cannot carry the needed oxygen to the tissues of the body. This can occur when carbon monoxide displaces oxygen from hemoglobin.

This question requires a basic understanding of general chemistry and/or general physics. Remember that gas will only move from an area of high pressure to low pressure; thus, if air is moving out of the lungs, the pressure inside of the lungs must be greater than the pressure outside of the lungs. The point at which air does not move in or out of the lungs is a signal that the pressure of the gas inside of the lungs is equal to that of atmospheric pressure.

In a biological sense, remember that the diaphragm contracts to cause inhalation, which results from negative or decreased pressure in the lungs. When the diaphragm relaxes, the pressure in the lungs must increase again. The increase in pressure forces the air out of the lungs and back into the atmospheric environment.

Oxygen is taken up from the blood by all cells to be used in ATP production. The process of cellular respiration (energy production) creates carbon dioxide as a waste product, which, if accumulated, can cause the blood to become dangerously acidic. Gases in the lungs diffuse passively into or out of the air entirely based on where the concentration is lowest. Thus, oxygen levels in the blood must be lower in concentration than those in the lungs in order for oxygen to enter the blood, and carbon dioxide levels in the blood must be higher than those in the lungs order for carbon dioxide to exit.