The interior layers of a leaf: palisade layer, spongy mesophyll, which allows oxygen, carbon dioxide, and water vapor to exchange between cells and the atmosphere; and stomata, through which gases enter and exit the leaf.
Antibodies do not destroy antigens. Instead, they mark them for T cell destruction by binding to them.
Antibodies do not destroy antigens. Instead, they mark them for T cell destruction by binding to them.
An antigen is a substance on the surface of a cell that identifies the cell as a pathogen
The main function of B cells is to recognize specific antigens and produce specific antibodies.
Pathogens can cause infected cells to produce a protein called "interferon." This substance causes nearby uninfected cells to produce enzymes that block the reproduction of pathogens.
Cytotoxic T cells, also called "killer T cells," attack dangerous cells by producing a protein that bursts the cell membrane.
Lymph is transported through lymph vessels. Special structures called "lymph nodes" filter lymph and store white blood cells. When the body is fighting an infection, white blood cells are produced in great numbers.
Important structures in the lymphatic system include the tonsils, thymus gland, and the spleen. The spleen is very important because it removes worn-out red blood cells, platelets, bacteria, and other things from the blood.
Phagocytes are leukocytes that engulf unwanted cells and pathogens in a nonspecific manner.
Macrophages are the largest leukocytes, and lymphocytes are leukocytes involved in specific defense activities.
T cells are lymphocytes that seek and destroy pathogens. There are several types of T cells.
When the body is fighting an infection, white blood cells are produced in great numbers.
The theory of continental drift states that the present-day continents were joined together in a supercontinent called Pangaea. Over time, the continents drifted away from each other to their present-day positions.
When birds eat, food passes from the mouth to an enlarged part of the esophagus called the crop. Here food is stored and softened, then passes to the gizzard, then travels to the intestine where nutrients are absorbed.
Light energy travels as an electromagnetic wave, and as a stream of moving particles called photons.
When light passes through a prism, the glass slows the light down. Different colors in white light have different wavelengths. Each wavelength is refracted a different amount, causing them to separate into different colors in the process of dispersion.
The placenta is a structure that enables the exchange of vital nutrients, oxygen, carbon dioxide, and wastes between the mother and the embryo.
A skeleton is the body's framework.
The chemical structure of the first carbohydrate is simpler than the second carbohydrate, which is a complex carbohydrate. Complex carbohydrates are broken down slowly by the body and release sugars into the blood stream over a longer period of time.