Edexcel A level Biology with 100% correct questions and and answers

Molecular phylogeny It compares the structure of a particular molecule from different organisms to discover their degree of evolutionary relation. Somatic cell A cell in an organism which isn't a gamete. DNA Deoxyribose nucleic acid. Carries the genetic information for cells and some viruses. mRNA Messenger ribose nucleic acid (single stranded). The product of transcription. Speciation The process through which a species is created Sympatric Due to reproductive isolation. Allopatric Due to geographical isolation Niche The role an an organism in an ecosystem. Habitat The natural environment in which a species lives. Biodiversity The diversity of plant and animal life in a particular habitat Ecosystem Organisms and their interactions with biotic and abiotic factors. Carpentered world hypothesis People who live in a world with many straight lines and right angles tend to interpret obtuse and acute angles as right angles. Muller-Lyer Illusion An illusion where a man could be pointing at two different objects, but depth cues let us know it is the object in the foreground he is pointing to. Inhibitory synapse These are synapses that make it less likely that an action potential will happen in the post synaptic membrane. Auxins Plant hormones that stimulate growth by causing cells to elongate. Indoleacetic acid (IAA) A specific type of auxin. Summation When the effect of multiple impulses adds up. Spatial summation Summation from many impulses from different neurons. Temporal summation Summation from multiple consecutive impulses from a single neuron. Excitatory synapse These synapses make the postsynaptic membranes more permeable to sodium ions. Synapse Where two neurones meet. Synaptic cleft The gap in a synapse. Nodes of Ranvier These are gaps in the myelin sheath where depolarisation can occur. Saltatory conduction This is the conduction of an impulse by 'jumping' between the nodes of ranvier. Depolarisation When the polarisation across the cell membrane is reversed, making the inside of the axon positive and the outside negative. Hyperpolarisation When the potential difference in the cell is more negative than the resting potential due to excess potassium ions moving out since the membrane is now highly permeable. Voltage-dependent gated channels These are channels which open due to changes in the voltage across the membrane. Positive feedback When one change leads to further change with the same effect. Repolarisation When the cell returns to having a resting potential of -70mV after spiking to about +40mV. Action potential The change in voltage from +40 to -70mV that occurs during repolarisation. Resting potential The potential difference inside the axon when it is at rest. Approx -70mV. Photoreceptors Light receptors. Antagonistic muscles Muscle pairs arranged to work against each other to move a joint. Reflex arc A simple nerve pathway responsible for reflexes. Reflex An involuntary, rapid response to a stimuli. Sensory neuron A neuron which carries impulses from sensory cells to the CNS. Relay neuron These neurons are mostly found within the CNS and they connect neurones together. Myelin sheath The fatty insulating layer made up of schwann cells that wraps around the axon to protect and speed up the impulse. Motor neurone A neuron with the cell body situated in the CNS, with axons that extend out to the effectors (muscles and glands) Dendrites These conduct impulses towards the cell body. Axon This conducts an impulse away from the cell body. Rods Rods are cells in the retina which detect light and dark. Cones Cones are cells in the retina which detect colour. Rhodopsin The purplish pigment in the rod cells which absorbs light and chemically changes. It is stored in the flattened vesicles on the outer segments of the rod cells. Hippocampus Where long term memory is stored. Corpus callosum White matter made up mainly of axons. It provides connections between the cortex and other brian structures. It also forms connections between the two hemispheres of the brain. Basal Ganglia A collection of neurones deep in each hemisphere which select and initiate stored programs for movement. Medulla oblongata Controls breathing, heart rate and blood pressure. Pituitary gland Gland that controls other glands and regulates growth rate, reproduction, and metabolism Cerebellum This is responsible for balance and co-ordinating movement by receiving information from the motor cortex, muscles and joints. Midbrain This relays information (including visual information from the eyes and auditory from the ears) to the cerebral hemispheres. Pons A part of the brainstem located between the medulla and midbrain. Occipital lobe This is concerned with processing visual information from the eyes, e.g. shape, colour, perspective. Parietal lobe This is concernred with orientation, sensation, calculation, some types of recognition and memory. Frontal lobe This is concerned wth high reasoning, personality, forming associations and ideas. It includes the primary motor cortex which stores information on how to carry out movements. Temporal lobe This is concerned with processing auditory information, e.g. hearing, speech. Also involved in memory. Cortex This is the grey folded matter around the brain. Thalamus This routes all the sensory information to the correct part of the brain, via the white matter. Hypothalamus This is below the thalamus and contains the thermoregulatory centre. It is responsible for homeostasis of body temperature, water in the body, sleep, thirst and hunger. It is also directly connected to the pituitary gland. Neural plasticity The ability for neurones to change in structure and function. Apoptosis Programmed cell death. Sarcomere ... Acrosome reaction Enzymes released by the acrosome digest the zona pellucida. Cortical reaction Release of enzymes by the cortical granules which cause the zona pellucida to thicken. Homeostasis Maintenance of internal body conditions within an appropriate range. Semi conservative replication DNA replication which creates two DNA molecules, with half of each being the old DNA. tidal volume The volume of air that moves in and out of the lungs during a normal breath. Spirometry procedure to measure lung capacity using a spirometer. Macrophage ... T killer cells ... HIV ... Tuberculosis ... T helper cells ... B helper cells ... Antigen presenting cells Cells which display the antigens of the foreign cells on their surface for other cells to recognise. Antibody ... Preimplantation genetic diagnosis (PGD) ... Chorionic villus sampling ... Amniocentesis A large needle is used to extract amniotic fluid, which Single Nucleotide Polymorphisms A type of genetic variation, which is one difference in a nucleotide. Candidate Gene A gene that is likely to cause a disease. Drug targets Molecules which can be altered by the binding of a drug. Non invasive pre-natal diagnosis Happens