I–L
11.1 A–D
 
11.2 E–H
 
11.3 I–L
 
 
11.4 M–P
 
11.5 Q–T
 
11.6 U–Z
 
I–L
I
imprinting
Instinctual behavior in which social bonds are formed during early development. Typically used with the example of a newly hatched bird or other animal identifying and treating the first moving object it sees as its mother.
incomplete dominance
Occurs when two different alleles of the same gene are both partially expressed in a heterozygote. The resulting phenotype is intermediate between the homozygous phenotypes of the two alleles. Color in a four o’clock flower is an example of incomplete dominance.
independent assortment
Mendel’s conclusion that during gamete formation, the segregation of one pair of genes has no influence over the segregation of another pair of hereditary units. Two different traits will thus be inherited independently of each other. This law holds true, except for linked genes. It is often called Mendel’s second law.
inheritance of acquired traits
A crucial, and incorrect, aspect of Lamarck’s theory of evolution. Lamarck believed that the traits a parent acquired during its lifetime would be passed on to its offspring.
instincts
Behavior that is hardwired into the brain of an organism; behavior that does not have to be learned.
insulin
Hormone secreted by the pancreas that reduces blood sugar levels. A lack of insulin can result in diabetes.
interphase
The phase of the eukaryotic cell cycle in which the cell prepares for division, primarily by replicating its DNA. After interphase, the cell enters mitosis.
intertidal zone
The most shallow zone in a marine habitat. Periodically dry or wet with the changing tides. Algae, sponges, mollusks, starfish, and crabs inhabit this zone. Also called the littoral zone.
ion
An atom or molecule that has lost or gained an electron and consequently has a positive or negative charge.
isotonic
A situation in which the concentration of solutes in a solution is equivalent to what it contains. There is no concentration gradient in isotonic solutions and no net flow of solutes or water.
K
karyotype
A photograph of the chromosomes from an individual cell, usually lined up in homologous pairs, according to size. Missing, extra, or abnormal chromosomes can then be easily identified, aiding in the diagnosis of genetic disorders.
kidney
The organ of blood filtration in humans. The functional unit of the kidney is the nephron.
kingdom
The broadest category of biological taxonomy.
Krebs cycle
A metabolic pathway in aerobic organisms in which acetyl-CoA combines with oxaloacetic acid to form citric acid. For this reason, the Krebs cycle is also known as the citric acid cycle. The cycle produces energy in the forms of ATP, NADH, and FADH2.
L
Lamarckism
An evolutionary theory (proved false by Darwin) stating that species change over time by the use and disuse of structures and the inheritance of acquired traits.
learned behavior
Behavior that an organism picks up over the course of its life. Three types of learned behavior are habituation, conditioning, and associative learning.
Leeuwenhoek, Antonie van
Dutch clothing salesman (1632–1723) who made the first observations of bacteria and protozoa using single-lens microscopes of his own design.
ligament
Connective tissue between bones.
linked genes
Genes that are located close together on the same chromosome. Linked genes will not undergo independent assortment during gamete formation, constituting an exception to the law of independent assortment. Crossing-over will disrupt the linkage of two genes on the same chromosome if they are far enough apart.
lymphatic system
A means of returning blood fluid, lymph, that has escaped from capillaries back into the bloodstream. Defended against foreign bodies by lymphocytes.
lymphocyte
White blood cell that is specialized to kill specific invading bacteria. Three types of lymphocytes work in coordination: B cells, helper T cells, and killer T cells.
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