Key Words Flashcards
Activation energy?
Type of word: enzyme action
The minimum amount of energy needed to make a reaction take place. Enzymes provide an alternative pathway with a lower activation energy required for a substrate to change into a product.
Active site?
Type of word: enzyme action
An area on an enzyme molecule where the substrate can bind.
Adhesion?
Water molecules are attracted to surfaces such as the walls of cells, vessels or tubes.
ADP (adenosine DI- phosphate)
A nucleotide consisting of the nitrogenous base, adenine covalently bonded to the pentose sugar ribose, [so forming adenosine] and two phosphate groups forming a short chain. ADP is formed from ATP during energy transfer in cells. The final phosphate group in ATP is removed by hydrolysis to release energy and inorganic phosphate
Alpha Glucose?
A hexose monosaccharide with the formula
C6H1206. An isomer of beta glucose. The - OH
group is below the carbon at position 1.
Alpha Helix?
A type of secondary structure of a protein.
The polypeptide chain is coiled and held in place by hydrogen bonds. Hydrogen bonds form between the oxygen of the -C=0 group
of one amino acid and the hydrogen of the - NH group of an amino acid four places further along the chain.
Amino acids?
Molecules consisting of carbon, hydrogen, nitrogen and oxygen. They are monomers, that when joined together form proteins. Every amino acid has a central carbon atom to which are attached four different chemical groups. The amino [-NH2] group; carboxyl group [-COOH]; hydrogen atom [-H]; R group.
AMYLOPECTIN?
A component of starch. Consists of many alpha glucose molecules joined together in a chain by 1, 4 glycosidic bonds. It has short side branches of alpha glucose attached to the main chain by 1,6 glycosidic bonds.
AMYLOSE?
A component of starch. Consists of many alpha glucose molecules joined together by 1,4 glycosidic bonds. The chain is coiled into a helix.
ANTIPARALLEL?
A term used to describe the opposite arrangement of the two strands of a double helix. The 5’ prime end of one strand aligns with the 3’ end of the other.
ATP [ADENOSINE TRI-PHOSPHATE]?
A nucleotide consisting of the nitrogenous base, adenine covalently bonded to the pentose sugar ribose, [so forming adenosine] and three phosphate groups forming a short chain. ATP is a compound that transfers energy within cells. It is the universal energy currency and used in metabolic processes, muscle contraction; active transport; exocytosis; activation of molecules.
ATP HYDROLASE
An enzyme which catalyses the conversion of ATP and water to ADP, inorganic phosphate and energy. This is a hydrolysis reaction as water is used in the conversion of ATP to ADP
ATP SYNTHASE
An enzyme which catalyses the conversion of ADP and inorganic phosphate into ATP. This is a condensation reaction as water is removed in the process.
BENEDICT’S REAGENT
A blue alkaline solution of copper(II) sulfate. It is used to test for reducing sugars containing an aldehyde functional group (- CHO). When a reducing sugar is heated with Benedict’s reagent, soluble copper (II) sulfate forms as insoluble precipitate of copper(I) oxide.
BETA GLUCOSE
A hexose monosaccharide with the formula C6H12O6. An isomer of alpha glucose. The -OH group is above the carbon at position 1.
BETA PLEATED SHEET
A type of secondary structure of a protein. The polypeptide chain folds in a concertina like way, with hydrogen bonds forming between the oxygen of a -C=O group of one amino acid in one sheet and the hydrogen of the -NH group of an amino acid in an adjacent pleated sheet.
BIURET TES
A chemical test for the presence of amine groups and thus for the presence of proteins. Biuret reagent is added to the unknown substance where a change from blue to purple indicates the presence of proteins.
CATALYST
A substance that increases the rate of a chemical reaction but does not become altered or changed during the reaction, so can be reused
CELL RESPIRATION
Complex sequence of many enzyme controlled reactions that occur in cells and result in the release of energy, that is used to make adenosine triphosphate (ATP).
CELLULOSE
A polymer of beta glucose molecules linked together by 1.4 glycosidic bonds in straight chains. Alternate beta glucose molecules are inverted; -H and -OH groups project above and below the chains. Structural component of plant cell walls.
CHOLESTEROL
Insoluble waxy type of lipid. Consists of four interlocking rings of carbon. A structural component of cell membranes; it is used to make steroid based hormones such as testosterone, oestrogen and progesterone, as well as vitamin D.
COENZYME
A small organic non-protein cofactor. Coenzymes are involved in enzyme catalysed reactions by donating or accepting hydrogen ions or chemical groups such as phosphate groups, between different enzyme catalysed reactions. e.g. NAD; NADP; coenzyme A; FAD
COFACTOR
A non-protein chemical compound that is needed for the biological activity of a protein. e.g. Chloride ions and alpha amylase
COHESION
Water molecules are attracted to each other by hydrogen bonding, allowing the water molecules to flow together.
COLLAGEN
A fibrous structural protein, consisting of three polypeptide chains twisted around each other. Almost every third amino acid in each polypeptide is glycine. Its small size allows the three strands to lie close together. Strength is provided by many hydrogen bonds and covalent bonds between the chains. The chains form a collagen fibril that links with other fibrils to form a collagen fibre. Provides strength in artery walls, tendons, cartilage and bone plus elasticity of the skin.
COMPETITIVE INHIBITION
This occurs when an inhibitor molecule with the same shape as the normal substrate, binds to the active site of an enzyme, blocking access to the substrate. This type of inhibition is reversed by increasing the concentration of the substrate.
COMPLEMENTARY BASE PAIRING
In a DNA molecule, a purine base pairs with a pyrimidine base. Guanine forms three hydrogen bonds with cytosine; adenine forms two hydrogen bonds with thymine.
CONDENSATION REACTION
Two molecules are joined together with a covalent bond. A larger molecule is formed and one molecule of water is released.
CONJUGATED PROTEIN
A globular protein with a prosthetic group such as haem in haemoglobin; cytochromes; phytochromes; lipoproteins.
COVALENT BOND
A strong bond formed when pairs of electrons are shared between non-metal atoms and in compounds formed between non-metals. E.g. glucose C6H12O6
DENATURATION
A change in the tertiary structure of proteins such as enzymes. At high temperatures, hydrogen and ionic bonds which help stabilise the tertiary structure break and the shape of the active site is disrupted. The enzyme can no longer form enzyme-substrate complexes. Thermal denaturation is usually irreversible; denaturation by changes in pH is often reversible.
DISACCHARIDE
A molecule formed by two monosaccharides that join together using a covalent bond called a glycosidic bond. Each glycosidic bond is formed during a condensation reaction with the loss of two hydrogen atoms and one oxygen atom. e.g. sucrose; maltose; lactose.
DISULPHIDE BOND
A covalent bond formed between sulfur atoms of the R groups of two cysteine or methionine or taurine amino acids
DNA
Deoxyribose nucleic acid is a double stranded polymer of nucleotide molecules that carries the information for protein synthesis. Contains the pentose sugar deoxyribose and the bases, adenine, thymine; cytosine and guanine.
DNA HELICASE
An enzyme that breaks the hydrogen bonds between complementary base pairs of DNA. This causes the double strand of DNA to separate into single strands.
DNA POLYMERASE
An enzyme that links free individual DNA nucleotides together by forming phosphodiester bonds. These bonds form between the 3’ hydroxyl group of the end nucleotide to the 5’ phosphate of the nucleotide to be added.
EMULSION TEST
Chemical test for the presence of lipids. Ethanol is added to the lipid sample to dissolve the lipid. The lipid ethanol sample is then added to water to produce a milky/ cloudy suspension.
ENZYME
A globular protein molecule made by cells that acts as a catalyst and increases the rate of a specific chemical reaction
ENZYME-PRODUCT COMPLEX
The complex that forms in the active site after the reaction is complete but before the product or products leave the active site.
ENZYME- SUBSTRATE COMPLEX
The complex which forms when a substrate molecule fits into the active site of an enzyme
ESTER BOND
A covalent bond formed during a condensation reaction between the -OH group of glycerol and the -COOH group of a fatty acid.
FATTY ACID
A molecule with a hydrocarbon chain of varying length, attached to a carboxylic acid [-COOH]
FIBROUS PROTEIN
A protein whose molecules have a relatively long, thin structure that are generally insoluble in water and metabolically inactive. Fibrous proteins such as keratin in hair and nails and collagen in skin, bone and cartilage have structural roles. The blood clotting protein, fibrin is also a fibrous protein.
GLOBULAR PROTEIN
A protein whose molecules fold into a three dimensional spherical shape. They are often water soluble and metabolically active e.g. enzymes; insulin; antibodies; plasma proteins and components of the cytoskeleton.
GLYCEROL
A three carbon alcohol molecule that forms ester bonds with three fatty acids to form a triglyceride.
GLYCOGEN
A branched, insoluble polymer of alpha glucose monomers, linked together by 1,4 and 1,6 glycosidic bonds. Stored as small granules in muscle and liver cells; also found in hyphae of fungi.
GLYCOSIDIC BON
A covalent bond formed when two carbohydrate molecules are joined together by a condensation reaction
HAEMOGLOBIN
A haemoglobin molecule consists of two alpha and two beta polypeptide chains. Each chain is associated with an iron containing haem prosthetic group. Each of the four haem groups can bind to a molecule of oxygen to form oxyhaemoglobin.
HYDROGEN BOND
A weak electrostatic bond between two polarised molecules, both of which have an uneven distribution of electron charge.
HYDROLYSIS
The covalent bond between two molecules is broken with the addition of a water molecule, which separates the two molecules
HYDROPHOBIC INTERACTION
The association between hydrophobic [‘water hating’] R groups of amino acids [e.g. CH3 on alanine] where water is excluded. These hydrophobic interactions help to maintain the tertiary structure of a protein.
INDUCED FIT HYPOTHESIS
The shape of the enzyme’s active site is moulded around the substrate so that the two fit closely together.
IODINE SOLUTION
Iodine dissolved in potassium iodide solution. A yellow-brown solution. Reagent is used to test for the presence of starch. Amylose in starch forms a deep blue complex in the presence of iodine solution. Since amylopectin is highly branched, it binds only a small amount of iodine and produces a paler purple-red colour.
ION
A charged atom or molecule which has lost or gained electrons. In a positively charged ion, the number of electrons is fewer than the number of protons. In a negatively charged ion, the number of electrons is greater than the number of protons.
IONIC BOND
A strong bond resulting from an electrostatic attraction between oppositely charged ions. E.g. Na+ and Cl- forming NaCl.
ISOMER
Molecule containing the same number and types of atoms but the atoms are arranged differently. Examples are α and β glucose.
LATENT HEAT OF VAPORISATION
The energy required to evaporate 1kg of water at its boiling point. Water has a high latent heat of vaporisation due to hydrogen bonding between water molecules. Evaporation of water such as sweat is an effective means of cooling.
LOCK AND KEY HYPOTHESIS
The idea that the enzyme’s active site is complementary in shape to the substrate in the same way as a key [substrate] and a lock [enzyme]
MICROFIBRILS
Bundles of beta glucose chains [in cellulose] held together by hydrogen bonds, which form cross links between adjacent beta glucose chains.
MONOMER
A single smaller molecule that forms the basic unit of polymers. Monomers form covalent bonds with other similar monomers as a result of condensation reactions. The monomers of the following groups are: carbohydrates - hexose sugars; lipids - fatty acids and glycerol; proteins - amino acids; nucleic acids - nucleotides.
MONOSACCHARIDE
A simple small sugar molecule which is sweet tasting and soluble. General formula (CH2O)n where n can be any number from three to seven. e.g. hexoses such as glucose; fructose; pentoses such as ribose; trioses such as glyceraldehyde
NON COMPETITIVE INHIBITION
This occurs when an inhibitor molecule combines with an allosteric site on an enzyme. The tertiary structure of the protein changes, making the active site unable to bind to the normal substrate. This type of inhibition is not reversed by increasing the substrate concentration.
NON REDUCING SUGAR
A sugar that cannot donate electrons from the carbonyl group [C=O] to Cu2+ ions in Benedict’s reagent, so that an insoluble red precipitate of copper (I) oxide is formed. Many disaccharides are non-reducing sugars e.g. sucrose. To detect a non-reducing sugar, the disaccharide must first be hydrolysed into its monosaccharide components by gently boiling with hydrochloric acid.
NON REVERSIBLE INHIBITION
Inhibition that occurs when an inhibitor forms covalent bonds as it combines permanently with an enzyme and completely inactivates it.
NUCLEOTIDE
A monomer of nucleic acids such as RNA and DNA. Each nucleotide consists of three components: a pentose [5 carbon] sugar; phosphate group and a nitrogen containing organic base [cytosine C; thymine T; uracil U; guanine G; adenine A.]
OPTIMUM TEMPERATURE
The temperature at which the rate of an enzyme controlled chemical reaction is at its maximum. Above or below this temperature, the rate is slower. The optimum temperature for an enzyme varies according to the habitat to which an organism is adapted.
ORGANIC NITROGENOUS BASE
A nitrogen-containing organic compound that is a constituent of nucleotides. The five organic bases are Adenine; Thymine; Cytosine, Guanine and Uracil.
PEPTIDE BOND
The bond which forms when two amino acids are joined together by a condensation reaction with the loss of a water molecule [The -OH from the -COOH group of one amino acid combines with a -H from the amino group from the second amino acid].
PHOSPHODIESTER BOND
In the DNA and RNA backbone, this is a covalent linkage formed during a condensation reaction . The phosphodiester bond links a phosphate group to a 3’ carbon and a 5’ carbon in two sugar molecules.
PHOSPHOLIPID
A molecule of glycerol combined with two fatty acids by ester bonds formed during condensation reactions. The third -OH group on glycerol is occupied by a phosphate group. A bilayer of phospholipids forms the basic structure of cell membranes.
PLASTID
Specialised membrane bound organelles found in plant cells e.g. chloroplasts and amyloplasts. Amyloplasts store starch grains.
POLAR MOLECULE
A molecule with an uneven distribution of electrons and hence negative charge. Within a polar molecule there will be regions of delta positive and delta negative charge e.g. water molecule
POLYMER
A large molecule composed of many monomer units joined together by covalent bonds during condensation reactions e.g. proteins; starch; lipids; nucleic acids.
POLYNUCLEOTIDE
A chain of nucleotide monomers covalently linked together.
POLYPEPTIDE
A long chain of amino acids joined together by repeated covalent peptide bonds
POLYSACCHARIDE
Large insoluble polymers formed from many monosaccharides that combine by condensation reactions to create long chains. e.g. starch [amylose and amylopectin] ; cellulose; glycogen; chitin.
PRIMARY STRUCTURE
The type, number and sequence of amino acids in an amino acid chain, held together by peptide bonds.
PROSTHETIC GROUP
A non-protein part of a protein molecule that is permanently attached to the molecule and is vital for the normal functioning of the molecule e.g. haem.
PURINE
A group of nitrogen bases which form part of a nucleotide. Purines are double ringed carbon-nitrogen compounds e.g. adenine and guanine
PYRIMIDINE
A group of nitrogen bases which form part of a nucleotide. Pyrimidines are single ringed carbon-nitrogen compounds e.g. cytosine; thymine in DNA and cytosine and uracil in RNA.
QUALITATIVE DATA
Non numerical, descriptive data which can be observed and recorded. e.g. gender; hair colour; language spoken
QUANTITATIVE DATA
Numerical data which can be observed and measured. e.g. body mass; volume; time;
QUATERNARY STRUCTURE
The three dimensional arrangement of two or more polypeptide chains or of a polypeptide and a prosthetic group [non protein component] such as haem, in a protein molecule.
R GROUP
Called a residual group. Consists of a variety of different chemical groups. Each amino acid has a different R group. The 20 naturally occurring amino acids differ only in their R group e.g. glycine has a single hydrogen atom as its R group; alanine has a CH3 R group.
REDUCING SUGAR
A sugar that can donate electrons from the carbonyl group [C=O] to Cu2+ ions in Benedict’s reagent so that an insoluble red precipitate of copper (I) oxide is formed. All monosaccharides are reducing sugar and some disaccharides e.g. maltose; lactose
REVERSIBLE INHIBITION
Inhibition that occurs when an inhibitor molecule temporarily combines with an enzyme. The inhibition is reversed and the enzyme becomes active again, once the inhibitor is no longer attached to the enzyme. Reversible inhibitors can be competitive or non-competitive.
RNA
Ribose nucleic acid is a single stranded polymer of nucleotide molecules containing the pentose sugar ribose and the base uracil instead of thymine. There are three types of RNA [rRNA; mRNA, tRNA] which all have important roles in protein synthesis.
SATURATED FATTY ACID
A fatty acid with a long hydrocarbon chain where only single bonds occurs between adjacent carbon atoms
SEMI CONSERVATIVE REPLICATION
Each new DNA molecule is formed from one parental strand of the original DNA molecule which acts as the template and one strand of new DNA nucleotides
SOLUTE
Dissolved solids, liquids or gases in a liquid [solvent] which can form a solution.
SOLUTION
A liquid [the solvent] with dissolved solids, liquids or gases [solutes].
SPECIFIC HEAT CAPACITY
The energy required to raise the temperature of 1kg of water by 1C. Water has a high specific heat capacity due to the large number of hydrogen bonds between water molecules. Water acts a buffer against sudden temperature changes.
SPECIFICITY
The relationship between an enzyme and the type of substrate molecule with a particular shape that fits into the active site of the enzyme
SURFACE TENSION
Where water molecules meet air, hydrogen bonds tend to pull water molecules back into the body of the water rather than the molecules escaping into the air. The water surface acts like a skin and is often strong enough to support small invertebrates such as pond skaters
TERTIARY STRUCTURE
The structure of a protein molecule resulting from the three dimensional coiling or twisting of the already folded chain of amino acids. The two main types of tertiary structure are globular and fibrous. The tertiary structure is maintained by disulphide bridges; ionic bonds; hydrogen bonds and hydrophobic interactions between different R groups.
TRIGLYCERIDE
A lipid whose molecules are made up of a glycerol molecule combined to three fatty acids.
UNSATURATED FATTY ACID
A fatty acid with a long hydrocarbon chain where there are some double bonds between adjacent carbon atoms
ACTIVE TRANSPORT
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.
ANAPHASE
The centromeres divide and the newly separated chromatids are pulled by their centromeres to opposite poles of the cell. The spindle fibres shorten at both ends so pulling the chromatids apart.
ANTIBODY
A plasma protein known as an immunoglobulin. Synthesised by B cells. Y shaped molecule consisting of four polypeptide chains [two long heavy chains; two short light chains] with two specific identical binding sites in the variable region. Each binding site fits precisely onto a specific antigen.
ANTIGEN
Any part of an organism or substance that is recognised as foreign/non-self by the immune system and stimulates an immune response. Antigens are often proteins on the cell surface membranes or cell walls of invading cells such as microorganisms or abnormal body cells.
ANTIGEN PRESENTING CELL
Macrophages in the lymph nodes engulf pathogens by endocytosis and then ‘cut up’. Antigens from the bacterial or virus surface are incorporated within proteins which then become part of the macrophage cell surface membrane.
ANTIGENIC VARIABILITY
This occurs when pathogens mutate frequently and their antigens change suddenly. Existing vaccines become ineffective
ARTIFICIAL ACTIVE IMMUNITY
This forms the basis of vaccination [immunisation]. The vaccine contains one or more antigens to stimulate an immune response
ARTIFICIAL PASSIVE IMMUNITY
Occurs when antibodies are introduced into individuals from another source. No direct contact with the antigen is required to produce immunity. Antibodies are not replaced when they are broken down and no memory cells are formed so there is no lasting immunity. Examples include anti- venom given to victims of snake bites. People who are likely to have tetanus, diphtheria or rabies are often given antitoxin antibodies by injection as a precaution
ASEXUAL REPRODUCTION
A type of reproduction that does not involve the fusion of sex cells/gametes or a change in the number of chromosomes. Offspring are produced from a single individual and are genetically identical to the parent organism. E.g. vegetative propagation; parthenogenesis; budding; spore formation, fragmentation.
B LYMPHOCYTE
Originate from stem cells in the bone marrow, where they differentiate and mature. B cells spread out through the body’s lymphatic system and during an immune response, they become plasma cells
BINARY FISSION
A form of asexual reproduction in bacteria and some single celled eukaryotes such as Amoeba and Paramecium. During binary fission, the fully grown parent cell divides into two and each half becomes an independent organism.
CALIBRATE
To determine, rectify or mark the graduations of a measuring instrument. e.g. using a stage micrometre to determine the length of each division on an eye piece graticule.
CAPSID
The protein shell of a virus which encloses its genetic material. A lipid envelops with embedded attachment proteins often surround the capsid in some viruses.
CAPSULE
A thick polysaccharide layer which can cover the outer layer of bacterial cell walls. The capsule prevents bacterial desiccation; helps to resist phagocytosis by macrophages and provides protection against bacterial viruses and hydrophobic toxins such as detergents
CARRIER PROTEIN
A protein which spans the plasma membrane. A carrier protein combines with a specific molecule such as glucose, causing the carrier protein to change shape so that the molecule is released to the inside of the membrane.
CELL CYCLE
A sequence of changes during the lifespan of a cell, involving sequences of cell divisions separated by periods of cell growth. The cell cycle has three stages: interphase; nuclear division; cytokinesis. The length of the cell cycle varies for different types of cell e.g. bone marrow cells approx. 18 hours; yeast cells 1.3-3 hours.
CELL FRACTIONATION
The process used to break up cells and isolate their different organelles to study their structure and function.
CELL MEDIATED IMMUNITY
T lymphocytes only respond to antigens that are presented on a body cell, rather than antigens within body fluids.
CELL WALL
This is present in all plant cells and many members of the Protoctista and fungi. In plant cells, the cellulose cell wall consists of microfibrils made from chains of beta glucose monomers, held together by 1,4 glycosidic bonds. Hydrogen bonds occur between adjacent chains. Bundles of microfibrils form fibres embedded in a matrix of pectins and hemicelluloses. The cellulose cell wall provides mechanical strength to prevent the cell from bursting when water enters the cell by osmosis. Collectively cellulose cell walls provide mechanical strength to the whole plant and as cellulose is fully permeable, it allows water to pass along it to enable the movement of water through the plant. The cell walls of fungi are made of a nitrogen containing polysaccharide called chitin.
CENTRIOLE
Centrioles are only found in animal cells and are constructed of microtubules arranged in nine triplets forming a cylinder. Centrioles occur in pairs near to the nucleus in a region called the centrosome. During cell division the centrosome organises spindle fibres [consisting of microtubules] to extend between the centrioles, to separate chromosomes and chromatids.
CHANNEL PROTEIN
These form selective water filled hydrophilic channels across the membrane to allow specific water soluble ions to pass through
CHLOROPLAST
Double membrane bound organelle with its own DNA and 70S ribosomes, found in some plant cells. Photosynthesis occurs in this organelle.
CHOLESTEROL
Cholesterol molecules fit neatly within the phospholipid bilayer of the cell surface membrane. Cholesterol molecules add strength to the membrane; reduce lateral movement of other molecules; make the membrane less fluid at high temperatures and prevent leakage of water and dissolved ions from the cell.
CILIA
Cilia [singular: cilium] are composed of microtubules arranged in a ring of nine pairs surrounding two central microtubules. Unlike flagella, cilia are shorter and are always present in large numbers on the surface of cells. Cilia play a role in the locomotion of protists such as Paramecium. Cilia move liquids across the surface of cells which is turn helps to remove contaminants such as mucus and bacteria in the respiratory tract; cilia play a role in the movement of the secondary oocyte in the oviduct towards the uterus.
CISTERNA
Pleural is cisternae. A series of flattened tubular membranes found in the endoplasmic reticulum and Golgi apparatus.
CLONAL EXPANSION
Small groups of identical B cells and T cells undergo cell division by mitosis to produce effector cells such as plasma cells and memory cells, during an immune response
CLONAL SELECTION
The process during the immune responses when specific clones of B cells and/or T cells interact with antigens displayed on APC’s.
CLONE
A group of genetically identical cells. In the immune response, there are clones of B cells and clones of T cells. Each clone has its own unique cell surface receptor complementary to a specific antigen.
CO-TRANSPORT
The movement of molecules or ions using a concentration gradient which has already been set up by direct active transport e.g. the movement of glucose or amino acids into intestinal epithelial cells along with sodium ions that have been actively transported out by the sodium - potassium pump.
COMMUNICABLE DISEASE
Diseases caused by a pathogen which is transmitted from one host organism to another.
CONSTANT REGION
Consists of a sequence of amino acids which remains the same in all antibodies of the same class. Constant regions bind to receptors on the surface of phagocytes. This helps phagocytes detect pathogens which have been ‘labelled’ by antibodies, prior to pathogen destruction by phagocytosis
CRISTAE
Folding in the inner mitochondrial membrane to provide a large surface area for the attachment of enzymes and other proteins involved in aerobic respiration.
CYTOKINES
Small protein molecules that act as cell signalling compounds. Many of them are involved in stimulating B cells to divide and develop into plasma cells and memory cells. Some T helper cells secrete cytokines that stimulate macrophages to carry out phagocytosis more aggressively. Interleukins are included in the cytokine group.
CYTOKINESIS
In animal cells, the cytoplasm near the equator tucks inwards to divide the cytoplasm. The organelles are shared between the two cells and the Golgi apparatus produces vesicles that form the new section of the plasma membrane
CYTOSKELETON
Located within the cytoplasm and consists of microtubules and microfilaments. The cytoskeleton is responsible for (i) cellular movement using flagella and/or cilia; (ii) intracellular movement so that organelles can move from one part of the cell to another; (iii) supports organelles and provides a scaffolding that strengthens the cell.
CYTOTOXIC T CELL
Type of T cell that kills abnormal cells and body cells that are infected by pathogens, by producing a protein called perforin that makes holes in the cell surface membrane. The cell membrane becomes freely permeable to all substances.
DENDRITIC CELL
A large phagocytic cell with lengthy extensions to give a large surface area to interact with pathogens and with lymphocytes.
DIFFUSION
The net movement of molecules [or ions] from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed. Molecules [or ions] move down a concentration gradient.
DISEASE TRANSMISSION
The transfer of a pathogen from an infected organism to an uninfected organism.
ELISA TEST
Enzyme linked immunosorbent assay’. This is a plate based technique designed to detect and quantify peptides, proteins, antibodies, and hormones in a sample. ELISA can be used to detect HIV and other pathogens which cause TB and hepatitis, as well as in drug and allergen tests. In ELISA, an antigen must be immobilised to a solid surface and then complexed with an antibody, linked to an enzyme. A coloured product is produced. The intensity of the colour is relative to the amount of antigen present.
ENDOCYTOSIS
The process by which cells absorb large quantities of materials by engulfing them. An active process requiring ATP. There are two forms: phagocytosis and pinocytosis.
EUKARYOTE
Cells which have a membrane bound nucleus and organelles such as mitochondria; chloroplasts; RER; Golgi apparatus; 80s ribosomes and linear DNA associated with histones.
EXOCYTOSIS
The reverse of endocytosis. An active process requiring ATP. Secretory vesicles fuse with the cell membrane to release substances from the cell.
EXTRACELLULAR
Within an organism but not inside cells e.g. tissue fluid; blood; lymph
EXTRINSIC PROTEIN
A peripheral globular protein which occurs on one side of the plasma/cell surface membrane.
EYE PIECE GRATICULE
A circular disc fitted into the eyepiece of a microscope, which has a scale marked on it with equal divisions in arbitrary units. The length of each division varies as the objective lens is changed.
FACILITATED DIFFUSION
The movement of charged ions and large polar molecules such as glucose and amino acids, through transmembrane protein channels or protein carrier molecules that span the membrane. A passive process.
FIRST GAP PHASE [G1]
First stage of interphase. The chromosomes are checked for damage. Cell organelles [other than chromosomes ] are replicated
FLACCID
When a plant cell is not turgid but has not yet plasmolysed.
FLAGELLA
Flagella [singular: flagellum] are composed of microtubules arranged in a ring of nine pairs surrounding two central microtubules. Flagella are found in some single cell organisms where they move the cell around e.g. Euglena; Chlamydomonas. A flagellum also forms the tail of motile sperm cells.
FLUID MOSAIC MODEL
The structure of the plasma membrane. Consists of a dynamic phospholipid bilayer, scattered with moving transmembrane and peripheral globular proteins. Glycolipids, glycoproteins and cholesterol molecules are also scattered throughout.
GLYCOLIPID
Short branching carbohydrate chain is covalently bonded to a phospholipid in the membrane. Glycolipids act as recognition sites, help to maintain membrane stability and help cells attach to one another to form tissues.
GLYCOPROTEIN
An extrinsic globular protein in the membrane which has a short branching carbohydrate chain attached. Glycoproteins act as recognition sites and cell-surface receptors e.g. for hormones and neurotransmitters.
GOLGI APPARATUS
Consists of a series of unconnected flattened membranous sacs called cisternae and Golgi vesicles. The functions of the Golgi apparatus are to (i) modify proteins and lipids from the RER and prepare them for secretion. (ii) produce secretory enzymes (iii) form lysosomes
GRANUM
A stack of thylakoid membranes, containing chlorophyll pigments which absorb light energy during cyclic and non-cyclic photophosphorylation.
HELPER T CELL
Type of T cell that coordinates an immune response by stimulating the responses of B cells and cytotoxic T cells by producing chemical signals such as interleukins.
HERD IMMUNITY
Known as population immunity. When sufficient numbers in a population are immune to an infectious disease, either through vaccination or exposure to the pathogen, these people provide a barrier to further pathogen transmission to those individuals who are not vaccinated or have low functioning immune systems.
HOMOGENATION
The process used to break open cells to release the organelles from the cell. The process uses a blender/homogeniser and cold, isotonic buffered solution.
HUMORAL IMMUNITY
B lymphocytes produce specific antibodies in response to specific antigens present on the surface of a pathogen, foreign cell, toxin, damaged or abnormal cell circulating in the blood and tissue fluid
HYDROPHILIC
Polar; ‘water-loving’.
HYDROPHOBIC
Non-polar; ‘water-hating’.
INTERPHASE
A period of considerable cellular activity within the cell cycle when the cell is not dividing. Consists of G1 phase, when cell organelles except chromosomes replicate; S phase when DNA is replicated; G2 phase when DNA is checked for errors.
INTRACELLULAR
Within a cell
INTRINSIC PROTEIN
A transmembrane globular protein which spans the membrane and is exposed at both surfaces.
INVAGINATION
Folding in of the plasma membrane to form a pocket
LASER SCANNING COFOCAL MICROSCOPE
Based on a conventional optical microscopy and used to enhance optical resolution. Cells are stained with fluorescent dyes. A thick section of tissue or small living organism is scanned with a laser beam, which is reflected by the dyes to produce a computerised 3D image
LYSOSOMES
Membrane bound vesicles, which lack an internal structure, produced by the Golgi apparatus. They contain a variety of digestive enzymes which can break down proteins, carbohydrates, lipids and nucleic acids. Lysosomes hydrolyse material ingested by phagocytosis; break down damaged and/or dead cells and organelles [autolysis]; release enzymes by exocytosis to destroy material around the cell.
LYSOZYME
A type of enzyme presents in lysosomes. Lysozymes hydrolyse the cell walls of ingested bacterial once lysosomes have fused with phagosomes during phagocytosis.
MACROPHAGE
A large long lived phagocytic cell that remains in tissues. Macrophages process pathogens and present antigens to T lymphocytes.
MAGNIFICATION
The ability of a lens to enlarge the size of an object. Calculated by dividing the image size by the real size of the object.
MATRIX
The interior solution in the mitochondria. It contains lipids, and enzymes involved in the Krebs cycle. Mitochondrial DNA and 70S ribosomes allow the production of some mitochondrial proteins.
MEMORY CELL
Lymphocytes which develop during the primary immune response and retain the ability to antibodies quickly when an antigen enters the body on a second, or subsequent occasion.
METAPHASE
Spindle fibres of microtubules form and the centromere of each chromosome attaches to the equator of the spindle.
MICROMETER μm
An SI unit of measurement which is one thousandth of a millimeter
MICROTUBULES
Microtubules are small tubular structures in the cytoplasm, composed of the polymer tubulin, a globular protein that is arranged in spirals. Microtubules form part of the cytoskeleton, which provides structure and support in eukaryotic cells.
MICROVILLI
Finger like projections of the cell surface membrane, about 0.6μm in length. Often described as a ‘brush border’. Used to increase the surface area of the cell surface membrane.
MITOCHONDRION
Mitochondria [pleural]. Double membrane bound organelle with its own DNA and 70S ribosomes, found in most eukaryotic cells. Site of aerobic respiration e.g. the Krebs cycle and oxidative phosphorylation.
MITOSIS
Cell division which produces two identical daughter cells with the same number of chromosomes as the parent cell. Important in growth, replacement and repair of cells; asexual reproduction; production of stem cells; tumours.
MONOCLONAL ANTIBODY
A single type of antibody produced by a clone of plasma cells, which have originated from a specific B lymphocyte. Monoclonal antibodies have uses in medical diagnosis e.g. prostate cancer; pregnancy testing and therapeutic drug treatment for cancer
MONOCYTE
A larger cell than a neutrophil that circulates in the blood and leaves to remain as a long lived macrophage in tissues such as the lungs.
MUREIN
A polymer of sugars and amino acids used to produce a mesh like layer which forms bacterial cell walls. Otherwise known as peptidoglycan.
NANOMETER nm
An SI unit of measurement which is one thousandth of a micrometer
NATURAL ACTIVE IMMUNITY
Results from an individual becoming infected with a pathogen under normal natural circumstances. The body produces its own antibodies and may continue to do so for many years.
NATURAL PASSIVE IMMUNITY
This occurs when antibodies cross the placenta during pregnancy and when a young child is breast fed by its mother. No direct contact with the antigen is required to produce immunity. Antibodies are not replaced when they are broken down and no memory cells are formed so there is no lasting immunity.
NEUTROPHIL
A short lived phagocytic cell produced in the bone marrow that circulates in the blood. They have lobed nuclei and granular cytoplasm.
NON- COMMUNICABLE DISEASE
Diseases not caused by pathogens and have numerous causes e.g. Genetic; degenerative; deficiency and lifestyle.
NUCLEOLUS
A darkly stained region within the nucleus, responsible for the manufacture of ribosomal RNA and hence ribosomes.
NUCLEUS
Present in eukaryotic cells and consists of chromatin. Chromatin is a complex of DNA and histone proteins. DNA, provides the template for making RNA. The nucleus indirectly controls the activities of the cell. Chromatin exists in two forms: lighter, less condensed euchromatin and darker, more condensed heterochromatin.
ORGAN
A collection of tissues combined and coordinated together to perform a specific function e.g. heart; leaf; stomach.
ORGAN SYSTEM
A collection of organs which work together as a single unit, to perform specific functions more efficiently e.g. digestive system to digest and process food; respiratory system for breathing and Organisms Exchange Substances with Their Environment.
ORGANELLE
A specialised part of a cell that performs a particular function.
OSMOSIS
The diffusion of water molecules from a region of high water potential to a region of lower water potential across a partially permeable membrane.
PATHOGEN
A disease causing organism; many are microorganisms such as viruses, bacteria, fungi and Protoctista.
PHAGOCYTOSIS
The uptake of solid material into cells. Pseudopodia project from the cell, surround the solid material e.g. microbe, to encapsulate the material into a phagocytic vesicle/ vacuole. ‘Cell eating’.
PHAGOSOME
A phagocytic vesicle containing the engulfed pathogen.
PILI
Short, thin hair like structures composed of protein, which are present on the surface of many bacteria and archaea. Pili have a role in movement, adherence to cell surfaces and in the formation of conjugation tubes, which allow exchange of genetic material between bacterial cells.
PINOCYTOSIS
Method by which small particles and liquids are taken into cells. The plasma membrane invaginates to form very small vesicles. ‘Cell drinking’.
PLASMA CELL
An activated B cell that makes and releases antibodies during the immune response.
PLASMODESMATA
Gaps in plant cell walls through which cytoplasmic strands connect the protoplast of one cell with an adjacent cell.
PLASMOLYSIS
The shrinking of the cytoplasm away from the cell wall of a plant cell, when water is lost due to osmosis when the water potential of the surrounding solution is lower than the cell
PRIMARY IMMUNE RESPONSE
The production of antibodies for the first time by plasma cells, following exposure to a foreign antigen
PROKARYOTE
Cells with no membrane bound nucleus or membrane organelles. Cell wall made of murein; circular DNA not associated with proteins; additional circular DNA plasmids may be present; ribosomes are smaller [70s]. Mucilaginous capsule may be present.
PROPHASE
DNA undergoes supercoiling and chromosomes are visible as two sister chromatids held together by a centromere. The nucleolus has disappeared and the nuclear membrane has broken down.
PROTOPLASM
The part of a cell contained within the plasma membrane; the nucleus and the cytoplasm [excluding large vacuoles].
PSEUDOPODIA
Protrusions of the cell membrane which resemble ‘false feet’. Formed during phagocytosis. Pseudopodia extend and surround large particles or microbes, to seal them into a vesicle.
RESOLUTION
The ability of a microscope to distinguish two adjacent points as separate from each other.
RETROVIRUS
A virus such as HIV, with single stranded RNA. When a retrovirus invades a host cell, it uses its enzyme reverse transcriptase to make DNA from an RNA template
REVERSE TRANSCRIPTASE
An enzyme which catalyses the conversion of RNA into DNA
RIBOSOME
A ribosome consists of a large and small subunit, containing ribonucleic acid [rRNA] and protein. Ribosomes are the site of protein synthesis and are located in the cytosol of eukaryotic and prokaryotic cells, as well as on RER in eukaryotic cells. Ribosomes in eukaryotic cells are larger and referred to 80s as opposed to 70s ribosomes in prokaryotes
ROUGH ENDOPLASMIC RETICULUM
An elaborate three dimensional series of sheet like membranes which are continuous with the outer nuclear envelope, which form a system of flattened cisternae. RER has ribosomes present on the outer surfaces of the cisternae to produce proteins destined for transport and secretion. RER provides a large surface area for protein and glycoprotein synthesis as well as a pathway for the transport of materials especially proteins to the Golgi apparatus for further processing.
SCANNING
ELECTRON MICROSCOPE
A focussed beam of electrons is passed across the surface of the specimen to produce a three dimensional view of the surface. Maximum magnification is x100 000 and maximum resolution is 10nm.
SECOND GAP PHASE [G2]
DNA is checked for damage that may have occurred during replication. The cycle may be delayed to repair the DNA.
SECONDARY IMMUNE RESPONSE
The production of antibodies by memory cells, following a second or subsequent exposure to the original antigen. Response is quicker, more antibody molecules are produced and the response lasts for longer
SMOOTH ENDOPLASMIC RETICULUM
SER lacks ribosomes on its surface and is often more tubular in appearance. Its functions are to (i) synthesise, store and transport lipids and phospholipids (ii) synthesise steroids such as cholesterol and reproductive hormones. (iii) synthesise, store and transport carbohydrates; (iv) detoxify lipid soluble drugs.
STAGE MICROMETER
This is used to calibrate the scale on the eye piece graticule for each objective lens used. The micrometer slide has a scale engraved into it, calibrated in known divisions e.g. 0.1mm
STROMA
The colourless thick fluid which surrounds the grana in the chloroplasts. The light independent stage or Calvin cycle takes place in the stroma. Starch grains are also present in the stroma.
SYNTHETIC PHASE [S]
DNA undergoes semi-conservative replication. A check is made that all chromosomes have replicated. If they have not, the cell cycle is stopped.
T LYMPHOCYTE
Type of white blood cell which originates in bone marrow but matures in the thymus gland. When T cells respond during an immune response, they do not make and release antibodies.
TELOPHASE
The spindle fibres disintegrate and new nuclear membranes form around each group of chromosomes. New nucleoli form in each daughter nucleus
THYLAKOIDS
A complex arrangement of internal membranes which are grouped into stacks called grana [singular: granum], joined by intergranal lamellae. Chlorophyll pigments which absorb light energy, are located on the thylakoid membranes.
TISSUE
A collection of similar cells which perform a specific function e.g. epithelial tissue; xylem.
TRANSMISSION ELECTRON MICROSCOPE
A beam of electrons focussed by electromagnets pass through ultra-thin dead tissue samples. Capable of a maximum magnification of x500 000 and a resolution of 0.2nm.
TURGID
The protoplast of a plant cell is pushed against the cellulose cell wall when water enters the cell by osmosis. When the pressure of the protoplast equals the resistive force of wall pressure, no further water enters the cell and the cell is described as fully turgid.
ULTRACENTRI- FUGATION
Process which follows homogenisation. Fragments in the filtered homogenate are spun at different speeds in a centrifuge to separate different types of organelles from each other.
VACCINE
A biological preparation that produces artificial active immunity. A vaccine often contains a weakened or dead form of the pathogen, its toxin or one of its’ surface proteins.
VACUOLE
A membrane bound organelle found in plant and fungal cells/hyphae. Functions include: providing structural support in stems; leaves and flowers; growth and cell expansion in germinating seeds; isolation of toxic or waste materials; maintenance of an acidic internal pH.
VARIABLE REGION
Antigen binding site on an antibody/immunoglobulin
VIRUS
Acellular non-living particles which are smaller than bacteria, between 20-300nm. Consist of DNA or RNA enclosed within a protein coat called a capsid.
WATER POTENTIAL
This is represented by the Greek letter psi [ψ] and is measured in units of pressure, usually kilopascals [kPa]. It is measure of the relative tendency of water to move from one area to another. Water moves from a higher water potential to a lower water potential. Pure water has a water potential of zero at 25oC and 100kPa. The more solute added to water, the lower [or more negative] the water potential
ABSORPTION
The movement of digested food molecules across the wall of the small intestine/ ileum into the blood or lymph.
ADHESION
Water molecules stick to the walls of xylem vessels. This helps to maintain the column of water in position even when transpiration is not taking place e.g. at night. Without adhesion, the force of gravity could cause the water column to drop.
ALVEOLI
[singular alveolus]. Known as air sacs. Arranged in groups at the end of the smallest bronchioles. The alveoli are lined with a single layer of epithelium [which acts as a gas exchange surface] but there is also an extracellular matrix of collagen and elastic fibres between the alveoli. The elastic fibres allow the alveoli to expand during inspiration and recoil during expiration.
AMYLASE
A type of carbohydrase enzyme which breaks down starch to maltose
AORTA
The main artery which divides into three above the heart. Aorta carries oxygenated blood from the left ventricle under high pressure to all parts of the body except the lungs.
APOPLAST PATHWAY
The movement of water through the cell walls of plant cells. The cell walls are readily permeable and the pathway offers little resistance to the flow of water.
ARTERIOLE
As blood flows further from the heart, arteries branch into smaller blood vessels called arterioles. Arterioles regulate blood flow. They have a relatively thicker layer of smooth muscle than arteries and when this contracts it narrows the arteriole and restricts blood flow. The smooth muscle is controlled by the autonomic nervous system. Arterioles have a relatively thinner layer of elastic tissue because blood pressure is lower.
ARTERY
A blood vessel which usually carries oxygenated blood away from the heart. They have a narrow lumen and blood is under high pressure. The outer tunica adventitia/externa of collagen is relatively thinner in arteries than veins. Arteries have a thick tunica media of smooth muscle and elastic tissue and a thin smooth inner lining [endothelium] which reduces friction to allow blood to flow freely. The overall thickness of the artery wall is greater than in veins, to resist the vessel bursting under pressure.
ATRIUM
[pleural atria]. A top thin walled chamber of the heart. The right atrium receives deoxygenated blood from the superior and inferior vena cava. The left atrium receives oxygenated blood from the pulmonary veins.
BICUSPID VALVE
The valve between the left atrium and left ventricle. Sometimes known as the left atrioventricular valve.
BILE SALTS
One of the primary components of bile, produced by the liver and stored in the gall bladder. Aid the absorption of fat soluble vitamins i.e. A, D, E and K . Bile salts emulsify lipids into tiny droplets called micelles. This increases the surface area of the lipids to speed up the action of lipases.
BOHR EFFECT
A decrease in pH and an increase in carbon dioxide concentration lowers the affinity of haemoglobin for oxygen. The oxygen dissociation curve for haemoglobin shifts to the right at any given partial pressure of oxygen.
BREATHING RATE
The number of breaths per minute [a breath is taking air in and breathing it out]
BRONCHIOLES
These are numerous, thin, narrow branches of the bronchi. They do not have cartilage rings. The walls are lined with smooth muscle so that larger bronchioles can control the flow of air in and out of the alveoli [air sacs]. Smaller bronchioles have no goblet cells or cilia on their epithelium.
BRONCHUS
[plural bronchi]. Bronchi are two divisions of the trachea, each leading to one lung. They are similar in structure to the trachea although they have a smaller diameter and thinner walls. The bronchi have complete rings of cartilage to support them.
BUCCAL CAVITY
Known as the oral cavity or mouth in animal anatomy
CAPILLARY
Small, numerous blood vessels responsible for the exchange of materials with cells. They have a small narrow lumen which slows blood flow to enable a longer time for materials to be exchanged. There are spaces [intercellular junctions] between endothelial cells to allow white blood cells to escape to combat infections within tissues.
CARBOHYDRASE
A type of enzyme which breaks down carbohydrates ultimately to monosaccharides by hydrolysis.
CARDIAC CYCLE
The contraction and relaxation of heart muscle in a regular cycle. The cycle consists of sequences of systole followed by diastole. The atria contract followed by the ventricles and then there is a short period of relaxation before the cycle starts again.
CARDIAC OUTP
The volume of blood pumped by one ventricle of the heart in one minute. It is usually measured in dm3 min-1.
Cardiac output = heart rate x stroke volume
CARTILAGE
A form of connective tissue that provides strengthening and support. It is composed of cells surrounded by a matrix of complex polysaccharides and amino groups. Cartilage is resistant to tension and compression. It is not as strong as bone but is more flexible than bone.
CASPARIAN STRIP
A continuous band which goes around the wall of endodermal cells in the root. It is made of suberin, a waxy, waterproof substance.
CHITIN
A large structural polysaccharide made from chains of modified glucose. Chitin is found in the exoskeletons of insects, as rings around the outside of insect tracheae and in the hyphal walls of many fungi species.
CHYLOMICRON
Special particles adapted for the transport of lipids through epithelial cells of the ileum. They are formed when triglycerides associate with cholesterol and lipoproteins in the endoplasmic reticulum and Golgi apparatus
CILIATED EPITHELIUM
A layer of cells which forms a covering or lining which possess tiny hairs or cilia on its surface. The cilia of ciliated epithelium beat constantly to remove mucus towards the top of the trachea.
CLOSED CIRCULATORY SYSTEM
A circulatory system in which blood circulates entirely within blood vessels.
COHESION
Water molecules are polar and form hydrogen bonds between one another and hence tend to stick together. Cohesion forces help to maintain a continuous column of water in xylem vessels.
COLLAGEN
A structural fibrous protein which on boiling yields gelatine. Found in skin, tendons; cartilage; teeth and the walls of blood vessels. A collagen molecule consists of three polypeptide chains in the shape of a helix, wound around each other to form a three stranded ‘rope’. Collagen has a high tensile strength.
COLON
The longest part of the large intestine, which is connected to the small intestine at one end and the anus at the other. Responsible for the reabsorption of water and some electrolytes from partially digested food.
COMPANION CELL
A cell closely associated with a phloem sieve tube element, directly linked via many plasmodesmata. Companion cells appear to regulate the activity of sieve tube elements and play a role in the loading and unloading of sucrose.
CORONARY ARTERY
Blood vessel which supplies oxygenated blood to cardiac muscle.
CORONARY VEIN
Blood vessel which returns deoxygenated blood from heart muscle [myocardium] to the right atrium.
COUNTERCURRENT FLOW
The flow of blood through the gill lamellae is in the opposite direction to the flow of water over the gills. This maintains a steep diffusion gradient between the water and the blood, so maximising the oxygen that can be extracted from water.
DEOXY- HAEMOGLOBIN
The form of haemoglobin without oxygen.
DIASTOLE
The period of time when the heart muscle is relaxed.
DIGESTION
The breakdown of large complex insoluble food molecules into simpler, smaller, soluble ones. The process can occur mechanically e.g. in the mouth using teeth, and chemically using hydrolytic enzymes.
DIPEPTIDASES
Enzymes which break/hydrolyse the peptide bond between two amino acids of a dipeptide. Dipeptidases are membrane bound and part of the cell surface membrane of the epithelial cells of the ileum.
DOUBLE CIRCULATORY SYSTEM
Blood passes through the heart twice during each circuit of the body.
EGESTION
The act or process of removing undigested or waste material from a cell or organism e.g. defaecation
ELASTIC FIBRES
These are found in all lung tissues, including the alveoli. As expiration is a passive process, elastic fibres provide elasticity to enable recoil of the lungs during expiration
EMULSIFICATION
The process of splitting lipids [fats and oils] into tiny droplets called micelles, by bile salts.
ENDOPEPTIDASE
Enzymes which break/hydrolyse peptide bonds between amino acids in the central part of a protein molecule, forming a series of shorter peptide chains.
ENDOTHELIAL CELL
Collectively these form a single cell layer which lines all blood vessels. Signals from endothelial cells organise the growth and development of connective tissue containing collagen, that forms the surrounding layers in the tunica externa/blood vessel wall.
EXOPEPTIDASE
Enzymes which break/hydrolyse peptide bonds on the terminal amino acid of the shorter peptide molecules formed by endopeptidases. The action of exopeptidases produces dipeptides and individual amino acids.
EXPIRATION
An alternative word for ‘breathing out’. Largely a passive process. The internal intercostal muscles contract and the rib cage moves down and inwards. The diaphragm muscles relax and the diaphragm is pushed up again by the contents of the abdomen.
EXTERNAL INTERCOSTAL MUSCLE
Muscle which lies between the ribs. External intercostal muscles contract during inspiration to move the rib cage upwards and outward. During expiration, the external intercostal muscles relax
GILL FILAMENT
Gills are the gas exchange organs of bony fish. Each gill is made up of a series of stacked membranes which protrude from the gill arch. Gill filaments increase the surface area of each gill for gas exchange.
GILL LAMELLA
Sometimes called a gill plate. Each gill lamella occurs at right angles on a gill filament. Gill lamellae increase the surface area of each gill filament for gas exchange.
GOBLET CELL
These cells line the trachea, bronchi and larger bronchioles. Goblet cells are located between ciliated cells of the epithelium. Goblet cells secrete mucus.
HAEMOGLOBIN
A globular protein found in erythrocytes/ red blood cells. Consists of four polypeptide chains, each associated with a haem group containing an Fe2+ ion. Each Fe2+ ion can combine with a single oxygen molecule [O2] to form oxyhaemoglobin. Haemoglobin carries oxygen from the lungs to body tissues and returns carbon dioxide from the tissues back to the lungs
HEART RATE
The number of times the heart beats in one minute. Measured as beats per minute.
HYDROPHYTE
Plants which are adapted to live in fresh water [with leaves floating on the surface or beneath the surface].
HYDROSTATIC PRESSURE
The pressure exerted by a fluid. A pressure is created by the pumping action of the heart at the arterial end of capillaries which tends to force fluid out of the plasma into the intercellular spaces to form tissue fluid.
ILEUM
The longest part of the small intestine. Contains crypts of Lieberkühn which secrete the maltase; sucrase; exopeptidases; endopeptidases. The inner walls are folded into villi to give a large surface area for absorption. The surface area is further increased by microvilli on the epithelial cells of each villus.
INSPIRATION
An alternative word for ‘breathing in’. An active process involving the contraction of the external intercostal muscles to move the rib cage up and outwards, whilst the muscles of the diaphragm contract causing it to flatten
INTERNAL INTERCOSTAL MUSCLE
Muscle which lies between the ribs. Internal intercostal muscles relax during inspiration. During expiration, the internal intercostal muscles contract to move the rib cage down and inwards.
ISOTOPE
Two or more forms of the same element with the same number of protons but different numbers of neutrons in their nuclei. Isotopes differ in their relative atomic mass and physical properties. Many isotopes are radioactive and used in tracer experiments in living tissues.
LACTASE
An enzyme which hydrolyses the single glycosidic bond in a lactose molecule. This hydrolysis produces the monosaccharides, glucose and galactose.
LACTEAL
Capillary like structures found in the lymphatic system.
LARGE INTESTINE
Absorbs water [by osmosis], minerals and vitamins. Faeces are stored in the rectum and egested through the anus.
LIPASE
A type of enzyme produced in the pancreas which hydrolyses the ester bond found in triglycerides to form fatty acids and monoglycerides. A monoglyceride is a glycerol molecule with a single fatty acid attached.
LYMPHATIC SYSTEM
An extensive network of lymph vessels and lymph nodes throughout the body which carry fluid called lymph. The system works closely with the cardiovascular system and plays a role in the immune response; collection and return of fluid/proteins to the blood; absorption of chylomicrons.
MALTASE
An enzyme which is part of the cell surface membranes of the epithelial cells lining the ileum. Often referred as a ‘membrane bound disaccharides’. Maltase hydrolyses maltose into alpha glucose.
MASS FLOW HYPOTHESIS
The current model of translocation in phloem. Divided into three phases: 1. Transfer of sucrose into sieve tube elements from photosynthesising tissue. 2. Bulk movement of sucrose through sieve tube elements 3. Transfer of sucrose from sieve tube elements into storage or other sink cells.
MICELLE
Tiny spheres of bile salts surrounding long chain fatty acids and monoglycerides.
OESOPHAGUS
Another name for the gullet. A tube which carries food from the mouth to the stomach.
ONCOTIC PRESSURE
A form of osmotic pressure exerted by blood proteins e.g. albumin that tends to pull water from the tissue fluid into the blood plasma.
OPERCULUM
A flap of tissue that covers the gills in bony fish.
OXYGEN DISSOCIATION CURVE
A graph which shows the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen.
OXYGEN UPTAKE
The volume of oxygen consumed by the subject. The spirometer removes carbon dioxide from the re-breathed air, therefore the volume of air gradually decreases as oxygen is extracted from it. The change in volume on the spirometer trace, is a measure of oxygen uptake.
OXYHAEMOGLOBIN
The form of haemoglobin combined with oxygen.
PALISADE MESOPHYLL
A layer of columnar cells rich in chloroplasts found beneath the upper epidermis of a leaf
PLASMODESMA
[plural: plasmodesmata]. A microscopic channel through plant cell walls, connecting the cytoplasm of two cells. These are lined with plasma membrane. Sieve tube elements and companion cells are connected by plasmodesmata, to allow transport of molecules during translocation.
POTOMETER
Used to measure the rate of water uptake in a cut plant shoot. It is assumed that the rate of water uptake is directly proportional to the rate of water loss by transpiration.
PULMONARY ARTERY
This transfers deoxygenated blood from the right ventricle to the lungs for gas exchange.
PULMONARY VEINS
These transfer oxygenated blood from the lungs to the left atrium of the heart.
RECTUM
The final section of the large intestine. Faeces are stored here before periodically being removed through the anus.
RESIDUAL VOLUME
The volume of air that remains in the lungs after maximum forceful expiration. It is the volume of air that cannot be expelled and keeps the alveoli open at all times.
ROOT PRESSURE
A force that drives water upwards in xylem vessels. It is primarily generated by osmotic pressure in root cells and can be demonstrated by exudation of fluid in a cut stem, just above soil level.
SEMI LUNAR VALVE
A valve which occurs at the base of the aorta and pulmonary artery to prevent backflow of blood into the ventricles. Alternative names include the aortic valve and the pulmonary valve.
SIEVE TUBE ELEMENTS
Living cells which form continuous tubes within phloem tissue. Each sieve tube element is associated with a companion cell. Sieve tube elements have no nucleus, few organelles and very little cytoplasm to aid their ability to transport assimilates such as sucrose, amino acids and mineral ions.
SINK
An area of a plant above or below photosynthesising leaves where sucrose is taken out of the phloem e.g. developing potato tuber; nectary; meristems.
SMOOTH MUSCLE
This is found in the trachea, bronchi and the larger bronchioles. It maintains the tone of the airways and also allows expansion in conditions when extra oxygen is needed e.g. during exercise.
