Any bacteria which has a long flagella that is used for movement. The term is used by immunologists and serologists as a form of classification.

2. H band
Definition:

The H band is an area within muscle tissue which is light when stained and consists only of myosin fibers (and no actin fibers). The H band is at the center of each muscle sarcomere.

3. H strand (heavy strand)
Definition:

The strand of a double-stranded DNA molecule that is more buoyant than the other and floats at the top of a column when the dsDNA is denatured and put in an equilibrium centrifuge.

4. H substance
Definition:

A polysaccharide precursor molecule which is used to make the antigens on the surface of human blood cells that are classified in the ABO blood group system.

5. H-RAS
Definition:

A point-mutated proto-oncogene that is found in melanomas and in carcinomas of colon, lung and pancreatic tissue.

6. H2 histocompatibility
Definition:

The ability of a tissue to be grafted from a donor to a host, without the host's immune system attacking the grafted tissue. The chances of H2 histocompatibility is determined by how well the tissue proteins (cell surface glycoproteins in the tissue, to be specific) match between donor and host.

7. habit
Author: Mirrored from Jim Croft's Flora of Australia
Definition:

The growth form of a plant, comprising its size, shape, texture and orientation.

8. habitat
Author:
Definition:

1. The physical location or type of environment in which an organism or biological population lives or occurs.
2. The place occupied by an organism, population, or community. It is the physical part of the community structure in which an organism finds its home, and includes the sum total of all the environmental conditions present in the specific place occupied by an organism . Often a habitat is defined to include a whole community of organisms.

9. habitat component (habitat attribute)
Author:
Definition:

A single element (e.g., velocity, depth, cover, etc.) of the habitat or environment in which a fish or other aquatic species or population may live or occur.

10. habitat type
Author:
Definition:

A land or aquatic unit, consisting of an aggregation of habitats having equivalent structure, function, and responses to disturbance.

11. habituation
Definition:

The tendency of some neurons to require either a stronger nerve signal or a longer recharge period before it can fire again, if it has been triggered recently.

12. hadron
Definition:

Any of over 100 elementary particles that are the building blocks of atomic particles such as protons and neutrons.

13. hairpin loop
Definition:

An area where single-stranded DNA or RNA has folded back on itself and nucleotides from the two separate segments have base paired, so that the resulting structure appears as the name describes.

14. Haldane's evolutionary unit
Definition:

A unit of measurement, given in darwins, which measures the increase in body size of a chronospecies over evolutionary time.

15. Haldane's rule (Haldane's law)
Definition:

If one of the two sexes is missing, sterile, or rare in a population of first-generation hybrids between two different species, then that sex is the heterogametic sex (has two different sex chromosomes, such as XY as opposed to XX).

16. Haldane, J.B.S.
Definition:

J.B.S. Haldane was born in 1892, died in 1964. He was a British geneticist and author who wrote many works of popular science.

17. half life
Definition:

The time it takes one half of a given material (such as a radioactive isotope or a pesticide) to decay or disappear.

18. half register
Definition:

A misalignment between two identical sets of repeating units of nucleotides within two copies of the same chromosome (one set of repeating units per copy of the chromosome), where repeating unit "A" from one set is inappropriately aligned with repeating unit "B" on the other set, so that "ABABAB" on one set would be aligned with "BABABA" on the other set instead of the correct "ABABAB" with "ABABAB".

19. half-a-Gram stain
Definition:

A lab technique used to detect the presence of members from the bacterial family Legionellaceae in samples of sputum.

20. half-inferior
Author: Mirrored from Jim Croft's Flora of Australia
Definition:

Of an ovary, partly below and partly above the level of attachment of the perianth and stamens.

21. half-life
Definition:

1. The period of time required for half of the quantity of a radioactive substance to decay, to transform into a different substance (which may also be radioactive), to disintegrate, or to be eliminated from a biological system or ecological system.
2. The period of time required for half of the reactants involved in a chemical reaction to turn into products or be otherwise affected by the reaction.

22. half-tetrad analysis
Definition:

The analysis of tetrad chromosomes (a pair of homologous chromosomes, thus four total chromosomes) after recombination when only half of the tetrad (two of the four chromosomes) can be analyzed.

23. halite
Definition:

Salt (sodium chloride) found in mineral form.

24. hallucinations
Author: Guo Li
Definition:

Hallucinations are sensory perceptions based on no real stimuli.

25. hallucinogen
Definition:

A chemical substance which causes hallucinations and other thought disturbances by acting on the central nervous system.

26. halo blight (halo spot)
Definition:

Halo blight is a fatal plant disease which attacks legumes and is caused by the bacteria Pseumonas phaseolicola. The plant develops yellow-ringed, water-soaked spots, then withers and dies without rotting.

27. Halococcus
Definition:

Halococcus is a genus of gram-negative, non-motile, spherical, red or orange bacteria which grows in very high concentrations of salt (NaCl) and can be found in salted fish and meats. Halococcus belongs to the family Halobacteriaceae.

28. haloperidol (Haldol)
Definition:

This antipsychotic drug is used to treat schizophrenia and manic psychosis; it is sometimes used to treat Gilles de la Tourette's syndrome.

29. halophile
Definition:

Any organism that lives or thrives in a salty environment.

30. halophyte
Definition:

A plant (such as salt marsh grass) that can tolerate or thrives in a salty environment.

31. halotolerant
Author: Mirrored from Tsute Chen's Glossary of Microbiology
Definition:

An organism capable of growing in the presence of sodium chloride (salt) but not requiring it.

32. halotolerant (haloxene)
Definition:

Halotolerant describes an organism which is able to grow in environments with high concentrations of salt (though it doesn't necessarily prefer high salt environments).

33. hamartoma
Definition:

A benign (noncancerous) tumor which is made up of tissues normally found in the area that it is in, but in an unusual mixture. This type of tumor results from a developmental anomaly of embryonic cells.

34. hamster test (hamster zona-free ovum test, HZFO test, sperm penetration assay, SPA)
Author: Fertilitext
Definition:

The hamster test is a test of the ability of a man's sperm to penetrate a hamster egg stripped of its outer membrane, the zona pellucida.

35. hamstring
Author: Guo Li
Definition:

The hamstring is a group of three large fusiform femoral muscles (semitendinosus, semimembranosus, and long head of biceps femoris) on the back part of the thigh. They serve as:

• extensors of the thigh at the hip joint
• flexors of the leg at the knee joint

36. Hantavirus
Definition:

A virus in the family Bunyaviridae that causes a type of hemorrhagic fever. It is thought that humans catch the disease mainly from infected rodents, either through direct contact with the animals or by inhaling or ingesting dust that contains their dried urine.

37. hantavirus pulmonary syndrome
Author: Guo Li
Definition:

Hantavirus pulmonary syndrome is characterized by the infection of one type of hantavirus called the Muerto Canyon virus (which is prevalent in the southwestern US and is carried by rodents such as mice). It presents as a nonspecific febrile illness followed by rapid development of shock-like state and ARDS.

38. haploid
Definition:

A single set of chromosomes (half the full set of genetic material), present in the egg and sperm cells of animals and in the egg and pollen cells of plants. Human beings have 23 chromosomes in their reproductive cells. Compare diploid.

39. haploid number
Definition:

The haploid number is the total number of chromosomes in a single set, such as would be found in a gamete or a haploid somatic cell (such as in fungus or gametophyte plants). In humans, the haploid number would be 23.

40. haploidiploidy
Definition:

Haploidiploidy is a genetic system in which one sex of the species (usually the male) is haploid (has only one set of chromosomes) and develops from eggs which have not been fertilized by sperm, and the other sex (usually the female) is diploid (has two sets of chromosomes) and develops from fertilized eggs. An example species is the honeybee.

41. haploidization
Definition:

Haploidization is the process of creating a haploid cell from a diploid cell by progressively losing chromosomes through nondisjunction (they fail to separate equally into the daughter cells during mitosis).

42. haplomitosis
Definition:

Haplomitosis is a form of cell division which certain flagellates (a group of protozoans with flagella) undergo. It involves the separation of the genetic material in the nucleus into two groups.

43. haplophyte
Author: Mirrored from Dave Sutton's Aquatic Plant Glossary
Definition:

Having the number of chromosomes characteristic of the gametes for the organism.

44. haplotype
Definition:

1. A combination of alleles (for different genes) which are located closely together on the same chromosome and which tend to be inherited together.
2. A group of alloantigens which are produced by the same allele or a group of closely related genes.

45. hapten
Definition:

A small molecule which is not by itself an immunogen (can cause an immune response), but has at least one element of an antigen and can combine with an antibody or another larger carrier molecule to become immunogenic.

46. hapteron
Author: Mirrored from Dave Sutton's Aquatic Plant Glossary
Definition:

A holdfast, a specialized root-like projection that functions to anchor a plant.

47. haptoglobin
Definition:

An acid glycoprotein found in blood plasma which, when it binds to free hemoglobin in the blood (i.e. not within a red blood cell), cannot be filtered and eliminated from the body by the kidneys. People with hemolytic disorders (diseases that involve the destruction of red blood cells) have low serum levels of haptoglobin (the normal range is 0.5 - 3.2 g/L).

48. haptotropism (adj. haptotropic)
Definition:

An orientation response of an organism to stimulation by touch.

49. hard palate
Author: Guo Li
Defin