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AQA as Biology unit2

Variation Differences between living things
Interspecific variation Variation between species
Intraspecific variation Variation within species (members of the same species differ from each other)
Sampling The process of taking measurements of indviduals which are selected from the popukation of organisms that exists
Genetic differences Are due to different genes that each organism possesses, and arise as a result of mutations, meiosis and fusion of gametes
Environmental influences Effect the way that an organism's genes are expressed, including climatic conditions, soil condition, pH and food availability
Nucleotides Nitrogen containing organic substances that form the basis of the nucleic acids DNA and RNA, made up of a pentose sugar, a phosphate group and organic bases
Mononulceotide A single nucleotide molecule, formed by a condensation reaction between the three components
A pentose sugar A sugar which contains five carbons, such as deoxyribose/ribose
Dinucleotide Two mononulceotides join together by a phosphodiester bond
Polynulceotide A long chain of mononucleotides
Pyrimidine bases Single ring organic bases - cytosine and thymine
Purine bases Double ring organic bases - adenine and guanine
Complementary bases A purine must always bond with a pyrimidine if the 'rungs' of the DNA 'ladder' are to be the same length - adenine always pairs with thymine, and guanine always pairs with cytosine.
DNA (deoxyribonucleic acid) Made up of two antiparallel strands of long polynulceotides that are joined togther by hydrogen bonds between certain bases, twisted to form a double helix. The hereditary material responsible for passing genetic information between cells and generations.
Gene Sections of DNA that contain the coded information for making polypeptides in the form of a specific series of bases alomg the DNA molecule. They determine the nature and development of all organisms.
The triplet code Each amino acid is coded for by three bases
Degenerate The triplet code is degenrate as most amino acids have more than one triplet code
Methionine All sequences start with the same triplet code which codes for the amino acid methionine (if not part of the final polypedtide it is removed later) (separate genes)
Stop Codes Three triplet codes do not code for any amino acid but mark the end of a polypeptide chain
Chromosomes Only visible as distict structures when cells are dividing, consist of two threads (chromatids) joined at a single point (centromere). Contain a single, very long molecule of DNA with many genes along its length.
DNA helicase An enzyme which breaks the hydrogen bonds linking base pairs of DNA, causing the two strands of DNA to unwind and separate during semi-conservative replication
DNA polymerase An enzyme which joins together active nucleotides which are lined up according to complementary bases with an original strand of DNA during semi-conservative replication
Semi Conservative replication The most widely accepted theory of DNA replication - each of the daughter DNA moleules contains one of the original DNA strands, so is half new and half original
Conservative replication A theory suggesting that during DNA replication the parent DNA remains intact and that daughter DNA is built up of completely new molecules. One molecule is made of original material, while the other is entirely new.
Mitosis Nuclear division resulting in two daughter nuclei that have an exact copy of (and therefore the same number of chromosomes as) the DNA of the parent cell. It is a continuous process divided into 4 stages for convienience
Prophase Chromosomes condense and become visible as chromatinm network splits into separate threads/chromosomes. Each chromosome appears as a pair of short, fat chromatids joined at the centromere. Nuclear envelope disintegrates and nucleolus disappears
Metaphase Chromosomes arrange themselves at the centre of the cell and the spindle is formed along the equator. Each centromere is connected to a spindle thread
Anaphase Spindle fibres attached to the chromatids contract and get shorter, meaning wach migrates to an opposite pole of the cell
Telophase The nuclear envelope and nucleolus reform, chromatids reach poles and become indistinct, spindle disintegrates. Cytokinesis occurs where the whole cell splits to form two new cells.
Interphase Occupies most of the cell cycle and is sometimes known as the resting phase as no division takes place. Divided into First growth (proteins produced), Synthesis (DNA replicated), Second growth (organelles grow and divide, energy stores are increased)
Cancer A group of diseases caused by a growth disorder of cells when genes controlling mitosis and the cell cycle are damaged
Tumour A group of abnormal cells which contantly expand in size - can be benign (self contained and won't cause problems in itself) or malignant (cells can break away and cause secondary tumours)
Chemotherapy Disrupts the cell cycle by preventing DNA from replicating (cistplastin) and inhibiting the metaphase stage of mitosis by interfering with spindle formation (vinca alkaloids)
Specialist exchange surfaces Located in specific regions of the organism and required to absorb nutrients and respiratory gases, and remove excretory products. Transport materials between the organism and its environment
Transport system Takes materials from cells to excahnge surfaces and vice versa, and allows materials to be transported to different parts of the organism
Double circulatory system For each complete circuit of the body, blood passes through the heart twice, as pressure is reduced when passing through lung capillaries and needs to be increased in order to maintain high circulation
General structure of blood vessels A tough collagen outer layer (resisting pressure changes), a muscle layer (can contract and control blood flow) and elastic layer (maintains blood pressure by stretch and recoil), an endothelium (smooth - prevent friction, thin-diffusion) and lumen
Arteries Rapidly carry blood away from the heart and into arterioles under high pressure
Arterioles Smaller arteries which control blood flow from arteries into capillaries under lower pressure than arteries
Veins Carry blood from capillaries back to the heart under low pressure
Capillaries Tiny vessels linking arterioles to veins that exchange metabolic materials between blood and body cells. Have a slower flow of blood to allow more time for material exchange.
Created by: Rayrayy



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