1. IB Biology Definitions 2009 – 2013/14

2. 2.4.4 Define diffusion. Define diffusion.

3. Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration. Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration.

4. 2.4.4 Define osmosis. Define osmosis.

5. Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration. Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.

6. 3.6.1 Define enzyme. Define enzyme.

7. Enzyme is a globular protein functioning as a biological catalyst in chemical reactions. Enzyme is a globular protein functioning as a biological catalyst in chemical reactions.

8. 3.6.1 Define active site. Define active site.

9. Active site is the site (region) on surface of enzyme to which substrate or substrates bind and which catalyses a chemical reaction involving the substrate. Active site is the site (region) on surface of enzyme to which substrate or substrates bind and which catalyses a chemical reaction involving the substrate.

10. 3.6.4 Define denaturation. Define denaturation.

11. Denaturation is a structural change in a protein that results in the loss (usually permanent) of its biological properties. Refer only to heat and pH as agents. Denaturation is a structural change in a protein that results in the loss (usually permanent) of its biological properties. Refer only to heat and pH as agents.

12. 3.7.1 Define cell respiration. Define cell respiration.

13. Cell respiration is the controlled release of energy from organic compounds in cells to form ATP. Cell respiration is the controlled release of energy from organic compounds in cells to form ATP.

14. 4.1.2 Define gene. Define gene.

15. Gene is a heritable factor that controls a specific characteristic. Gene is a heritable factor that controls a specific characteristic.

16. 4.1.2 Define allele. Define allele.

17. Allele is one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene. Allele is one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene.

18. 4.1.2 Define genome. Define genome.

19. Genome is the whole of the genetic information of an organism. Genome is the whole of the genetic information of an organism.

20. 4.1.3 Define gene mutation. Define gene mutation.

21. Gene mutation is a gene mutation is a change to the base sequence of a gene. Gene mutation is a gene mutation is a change to the base sequence of a gene.

22. 4.2.2 Define homologous chromosomes. Define homologous chromosomes.

23. Homologous chromosomes have the same genes as each other, in the same sequence, but not necessarily the same alleles of those genes. Homologous chromosomes have the same genes as each other, in the same sequence, but not necessarily the same alleles of those genes.

24. 4.3.1 Define genotype. Define genotype.

25. Genotype is the alleles of an organism. Genotype is the alleles of an organism.

26. 4.3.1 Define phenotype. Define phenotype.

27. Phenotype is the characteristics of an organism. Phenotype is the characteristics of an organism.

28. 4.3.1 Define dominant allele. Define dominant allele.

29. Dominant allele is an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state. Dominant allele is an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state.

30. 4.3.1 Define recessive allele. Define recessive allele.

31. Recessive allele is an allele that only has an effect on the phenotype when present in the homozygous state. Recessive allele is an allele that only has an effect on the phenotype when present in the homozygous state.

32. 4.3.1 Define codominant alleles. Define codominant alleles.

33. Codominant alleles is pairs of alleles that both affect the phenotype when present in a heterozygote. (The terms incomplete and partial dominance are no longer used.) Codominant alleles is pairs of alleles that both affect the phenotype when present in a heterozygote. (The terms incomplete and partial dominance are no longer used.)

34. 4.3.1 Define locus. Define locus.

35. Locus is the particular position on homologous chromosomes of a gene. Locus is the particular position on homologous chromosomes of a gene.

36. 4.3.1 Define homozygous. Define homozygous.

37. Homozygous is having two identical alleles of a gene. Homozygous is having two identical alleles of a gene.

38. 4.3.1 Define heterozygous. Define heterozygous.

39. Heterozygous is having two different alleles of a gene. Heterozygous is having two different alleles of a gene.

40. 4.3.1 Define carrier. Define carrier.

41. Carrier is an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele. Carrier is an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele.

42. 4.3.1 Define test cross. Define test cross.

43. Test cross is testing a suspected heterozygote by crossing it with a known homozygous recessive. (The term backcross is no longer used.) Test cross is testing a suspected heterozygote by crossing it with a known homozygous recessive. (The term backcross is no longer used.)

44. 4.3.7 Define sex linkage. Define sex linkage.

45. Sex linkage is the association of a characteristic with gender, because the gene controlling the characteristic is located on a sex chromosome. Sex linkage is the association of a characteristic with gender, because the gene controlling the characteristic is located on a sex chromosome.

46. 4.4.11 Define clone. Define clone.

47. Clone is a group of genetically identical organisms or a group of cells derived from a single parent cell. Clone is a group of genetically identical organisms or a group of cells derived from a single parent cell.

48. 5.1.1 Define species. Define species.

49. Species is a group of organisms that can interbreed and produce fertile offspring. Species is a group of organisms that can interbreed and produce fertile offspring.

50. 5.1.1 Define habitat. Define habitat.

51. Habitat is the environment in which a species normally lives or the location of a living organism. Habitat is the environment in which a species normally lives or the location of a living organism.

52. 5.1.1 Define population. Define population.

53. Population is a group of organisms of the same species who live in the same area at the same time. Population is a group of organisms of the same species who live in the same area at the same time.

54. 5.1.1 Define community. Define community.

55. Community is a group of populations living and interacting with each other in an area. Community is a group of populations living and interacting with each other in an area.

56. 5.1.1 Define ecosystem. Define ecosystem.

57. Ecosystem is a community and its abiotic environment. Ecosystem is a community and its abiotic environment.

58. 5.1.1 Define ecology. Define ecology.

59. Ecology is the study of relationships between living organisms and between organisms and their environment. Ecology is the study of relationships between living organisms and between organisms and their environment.

60. 5.1.6 Define trophic level. Define trophic level.

61. Trophic level is the position that an organism occupies in a food chain or a group of organisms in a community that occupy the same position in food chains. Trophic level is the position that an organism occupies in a food chain or a group of organisms in a community that occupy the same position in food chains.

62. 5.4.1 Define evolution. Define evolution.

63. Evolution is the cumulative change in the heritable characteristics of a population. Evolution is the cumulative change in the heritable characteristics of a population.

64. 6.3.1 Define pathogen. Define pathogen.

65. Pathogen is an organism or virus that causes a disease. Pathogen is an organism or virus that causes a disease.

66. 6.5.4 Define resting potential. Define resting potential.

67. Resting potential is the electrical potential across the plasma membrane of a cell that is not conducting an impulse. Resting potential is the electrical potential across the plasma membrane of a cell that is not conducting an impulse.

68. 6.5.4 Define action potential (depolarization & repolarization). Define action potential (depolarization & repolarization).

69. Action potential is the reversal (depolarization) and restoration (repolarization) of the electrical potential across the plasma membrane of a cell, as an electrical impulse passes along it. Action potential is the reversal (depolarization) and restoration (repolarization) of the electrical potential across the plasma membrane of a cell, as an electrical impulse passes along it.

70. 9.2.5 Define transpiration. Define transpiration.

71. Transpiration is the loss of water vapour from the leaves and stems of plants. Transpiration is the loss of water vapour from the leaves and stems of plants.

72. 10.2.4 Define linkage group. Define linkage group.

73. Linkage group is all the genes that have their loci on the same chromosome. Linkage group is all the genes that have their loci on the same chromosome.

74. 10.3.1 Define polygenic inheritance. Define polygenic inheritance.

75. Polygenic inheritance is a characteristic controlled by more than one gene. Polygenic inheritance is a characteristic controlled by more than one gene. Polygenic inheritance is often due to co-dominant genes. Polygenic inheritance is often due to co-dominant genes. They contribute to continuous variation like the skin colour. They contribute to continuous variation like the skin colour. Other example is grain colour in wheat. Other example is grain colour in wheat.

76. 11.1.3 Define active immunity. Define active immunity.

77. Active immunity is immunity due to the production of antibodies by the organism itself after the bodys defence mechanisms have been stimulated by antigens. Active immunity is immunity due to the production of antibodies by the organism itself after the bodys defence mechanisms have been stimulated by antigens.

78. 11.1.3 Define passive immunity. Define passive immunity.

79. Passive immunity is immunity due to the acquisition of antibodies from another organism in which active immunity has been stimulated, including via the placenta, colostrum, or by injection of antibodies. Passive immunity is immunity due to the acquisition of antibodies from another organism in which active immunity has been stimulated, including via the placenta, colostrum, or by injection of antibodies.

80. 11.3.1 Define excretion. Define excretion.

81. Excretion is the removal from the body of the waste products of metabolic pathways. Excretion is the removal from the body of the waste products of metabolic pathways.

82. 11.3.5 Define osmoregulation. Define osmoregulation.

83. Osmoregulation is the control of the water balance of the blood, tissue or cytoplasm of a living organism. Osmoregulation is the control of the water balance of the blood, tissue or cytoplasm of a living organism.

84. E.1.1 Define the term stimulus in the context of animal behaviour. Define the term stimulus in the context of animal behaviour.

85. A stimulus is a change in the environment (internal or external) that is detected by a receptor and elicits a response. A stimulus is a change in the environment (internal or external) that is detected by a receptor and elicits a response.

86. E.1.1 Define the term response in the context of animal behaviour. Define the term response in the context of animal behaviour.

87. A response is a response to a stimulus, a change in the environment (internal or external) that is detected by a receptor. A response is a response to a stimulus, a change in the environment (internal or external) that is detected by a receptor.

88. E.1.1 Define the term reflex in the context of animal behaviour. Define the term reflex in the context of animal behaviour.

89. A reflex is a rapid, unconscious response to a stimulus. A reflex is a rapid, unconscious response to a stimulus.

90. A.1.1 Define nutrient. Define nutrient.

91. Nutrient is a chemical substance found in foods that is used in the human body. Nutrient is a chemical substance found in foods that is used in the human body.

92. H.6.1 Define partial pressure. Define partial pressure.

93. Partial pressure is the pressures exerted by each of the gases in a mixture of gases. Partial pressure is the pressures exerted by each of the gases in a mixture of gases. The pressure of a gas in a mixture is the same as it would exert if it occupied the same volume alone at the same temperature (Dalton's Law). The pressure of a gas in a mixture is the same as it would exert if it occupied the same volume alone at the same temperature (Dalton's Law).