All the definitions for unit 1

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Achondroplasia Genetic condition caused by a dominant allele.
Someone who is heterozygous for this condition has very restricted
Activation energy Before a chemical reaction can take place, bonds
must be broken. This requires energy. This activation energy is normally
provided by heating the substances involved in the reaction. Enzymes
reduce the amount of activation energy necessary, so reactions in living
organisms can take place at relatively low temperatures.
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 into this active site.
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; in other words, it involves the movement of substances
against a concentration gradient. Active transport involves the use of
specific carrier proteins in cell membranes. It also requires energy in
the form of ATP.
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. The atoms of the two
bases are arranged in such a way that two hydrogen bonds form
between them.
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.
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
Albinism Genetic condition caused by a recessive allele that results in
the non-production of pigment.
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. We all have this gene, the CF gene. The CF gene
has two alternative forms or alleles. The normal allele, F, produces a
functioning protein. The other allele, f, produces a protein which is very
slightly different and does not function. If a person has two copies of the
f allele, he or she will have cystic fibrosis.
Alveolus, Alveoli One of the tiny air sacs in the lungs where gas
exchange takes place. The alveoli are lined by a layer of cells known as

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These cells are very thin and this helps to ensure
efficient diffusion of oxygen from the alveoli into the blood and of
carbon dioxide from the blood into the alveoli. The total surface area of
all the alveoli in the lungs is very large. This large surface area also helps
to ensure efficient diffusion.
Amino acid The basic unit or monomer from which proteins are
formed. There are twenty different amino acids which may be linked by
condensation to form proteins.…read more

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Aneurysm A weakening of the wall of an artery, which results in a
balloon-like swelling. The condition is obviously very serious but in some
cases it is possible to repair the damaged artery surgically.
Angina Pain in the chest that occurs when the heart muscle does not
receive enough oxygen-rich blood. During exercise heart muscle requires
more oxygen because its rate of respiration is higher. If the coronary
arteries cannot supply enough oxygenated blood, the heart muscle
respires anaerobically.…read more

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Most of the ATP in a cell is produced from ADP and phosphate
using energy transferred during the process of respiration. When ATP is
broken down, ADP and phosphate are produced and a small amount of
energy is made available. This energy may be used: in active transport;
to synthesise large molecules such as proteins from smaller ones such as
amino acids; and for movement in cells such as sperm and muscle cells.…read more

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This increases the surface area on which lipid-digesting
enzymes act.
Blood clot When a wound occurs, a protein in the blood called
fibrinogen is converted to fibrin. Fibrin forms a mesh of protein fibres
over the surface of the wound. This mesh traps red blood cells to form a
blood clot. Blood clots may form inside arteries in people with
cardiovascular disease. This may lead to the artery becoming blocked,
a condition known as thrombosis.…read more

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Carcinogen A substance which will cause cancer. Many organic
substances, such as those found in the tar in cigarette smoke, are
carcinogens. They damage DNA. Cells in which the DNA is damaged may
become cancerous. This is more likely when there is an inherited
tendency to develop cancer.
Cardiac cycle One complete cycle of the heart as it fills with and then
pumps blood. During systole, cardiac muscle contracts and the heart
pumps blood out through the aorta and pulmonary arteries.…read more

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These bonds hold the cellulose
molecules together in bundles called microfibrils.
CFTR protein The channel protein whosemalfunctioning causes cystic
Channel protein A protein that spans a membrane and is involved in
the transport of molecules across the membrane.
Cholesterol A type of lipid, which plays an important part in the body.
It is an component of cell membranes and is a precursor, which is
converted into other important substances such as bile salts, and
steroid hormones such as testosterone and progesterone.…read more

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Columnar epithelium Epithelial cells are cells that form the outer
surface of many animals. They also line cavities inside organs. Epithelial
cells differ in shape. Columnar epithelial cells are, as their name suggests,
tall and thin, and line the small intestine and the airways of the lungs.
Complementary base pairing, Complementary The nucleotide bases
in nucleic acids always pair in a particular way. Adenine always pairs
with thymine in DNA and with uracil in RNA. Cytosine always pairs with
guanine.…read more

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Cytoplasm The cytoplasm is a jelly-like fluid surrounded by the cell
surface membrane. Ions, sugars and amino acids are dissolved in
cytoplasm, and large molecules are suspended. It also contains a
network of proteins, which help to give the cell its shape. Organelles
such as mitochondria are suspended in the cytoplasm.
Cytosine One of the nucleotide bases found in nucleic acids. When the
two strands of nucleotides which make up a molecule of DNA come
together, cytosine always pairs with guanine.…read more

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diffuses into a cell down a diffusion gradient.
Digestion, Digest The process in which the large insoluble molecules
which make up an organism's food are broken down by enzymes to
smaller soluble molecules. Mammals such as humans have specialised
Dipeptide A molecule that is made up of two amino acids joined by a
peptide bond.
Disaccharide A carbohydrate that is made up of two sugar units or
monosaccharides. Maltose is a disaccharide. It is made of two
molecules of glucose joined by condensation.…read more



this is so useful!! do you have any more notes, on the second unit/paper 2??

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