Genetic condition caused by a dominant allele. Someone who is heterozygous for this condition has very restricted growth.
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Acinar cell
A cell from the pancreas. It produces enzymes that are used in digestion.
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Acrosome
An organelle in the head of a sperm that contains digestive enzymes.
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Acrosome reaction
When fertilisation takes place, the membrane surrounding these enzymes bursts. The enzymes digest the follicle cells; they also digest the jelly-like layer surrounding the egg cell allowing the sperm to fuse with the egg membrane.
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Actin
A protein found in many cells. Actin plays an important part in muscle contraction. It is also thought to be involved in cell cleavage.
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Activation energy
Before a chemical reaction can take place, bonds must be broken. This requires energy. This activation energy is provided by heating the substances involved in the reaction. Enzymes lower activation energy needed, so reactions occur at lower temps.
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Active site
The part of an enzyme molecule into which a substrate molecule fits during a chemical reaction. It is like a pocket on the surface of the enzyme and it has a specific shape. Only a substrate molecule with the complementary shape will be able to fit.
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Active transport
A process that involves the movement of substances from where they are in a low concentration to where they are in a higher concentration, against a concentration gradient. Active transport involves carrier proteins and requires energy (ATP)
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Adaptation
Any features of an organism that make it well suited to survive in its environment. Adaptations can be anatomical, physiological or behavioural.
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Adaptive radiation
The way in which a common ancestor may give rise to different species, each occupying a different ecological niche.
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Adenine
One of the nucleotide bases found in nucleic acids. When the two strands of nucleotides which make up a molecule of DNA come together, adenine always pairs with thymine, forming two hydrogen bases.
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Adhesion
A force resulting from attraction between molecules of different substances. In xylem, water molecules adhere to the molecules of lignin and to other substances which make up the walls of the vessel.
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ADP, Adenosine diphosphate
Adenosine diphosphate (ADP) is produced when a phosphate group is removed from ATP. Energy can be transferred from this reaction to do useful work in the cell.
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Adrenaline
A hormone produced by the adrenal glands at times of stress such as when we are angry or frightened. Scientists have shown that there are links between stress, adrenaline and an increased risk of heart disease.
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Aerobic
Aerobic means requiring the presence of oxygen. Aerobic bacteria are bacteria that can only live and multiply in the presence of oxygen. Aerobic respiration is respiration that requires the presence of oxygen.
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Albinism
Genetic condition caused by a recessive allele that results in the nonproduction of pigment.
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Algae
A group of plant-like organisms that include the one-celled organisms that form phytoplankton. Although algae photosynthesise and their cells are surrounded by a cell wall, they are not plants. They belong to a group of organisms called Protoctista.
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Allele
One of the different forms of a particular gene. In humans, a gene codes for the protein that transports chloride ions across the cell surface membrane.
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Allergen
A substance that produces an allergic reaction in a sensitive person. Many different substances can act as allergens. One concern over the widespread use of genetically modified foods is that they may make allergens more widespread.
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Other cards in this set
Card 2
Front
A cell from the pancreas. It produces enzymes that are used in digestion.
Back
Acinar cell
Card 3
Front
An organelle in the head of a sperm that contains digestive enzymes.
Back
Card 4
Front
When fertilisation takes place, the membrane surrounding these enzymes bursts. The enzymes digest the follicle cells; they also digest the jelly-like layer surrounding the egg cell allowing the sperm to fuse with the egg membrane.
Back
Card 5
Front
A protein found in many cells. Actin plays an important part in muscle contraction. It is also thought to be involved in cell cleavage.
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