Y2 Key Words Flashcards
Photo ionisation
When chlorophyll absorbs light, causing electrons to be excited and emitted
Chemio osmotic theory
The movement of H+ ions (protons) across a membrane results in ATP synthase catalysing the production of ATP by the condensation of ADP and inorganic phosphate (Pi)
Dehydrogenase enzymes
Enzymes that catalyses an oxidation-reduction reaction, e.g., oxidation of reduced NAD at the start of the electron transfer chain
Tropism
A directional growth response of a plant to an external stimulus
Taxis
A directional response to a stimulus, e.g. movement towards or away from a stimulus
Kinesis
A non-directional responses to a stimulus, e.g. an increase or decrease in the frequency of changes in direction of movement
Pacinian corpuscle
A cell adapted to detect pressure changes
Receptor
A cell adapted to detect specific changes in the external or internal environment.
Generator potential
The change in potential difference across the cell-surface membrane of a receptor as a result of a stimulus.
Visual acuity
The clarity of vision. In other words, the ability to distinguish between objects.
Purkyne fibres
Cells in the walls of the ventricles which carry electrical impulses from the base of the heart up the walls of the ventricles, causing them to contract
Myogenic
Nervous stimulation originating in the muscle tissue (rather than from neurones)
Chemoreceptors
Receptor cells which are sensitive to specific chemicals
Pressure receptors
Receptor cells which are sensitive to changes in pressure
Resting potential
The voltage across the cell-surface membrane of a neurone which is at ‘rest’. It is approx.. -70mV
Depolarisation
A change in resting potential of a neurone resulting from an influx of Na+ into the neurone
Action potential
The momentary positive potential difference across the surface membrane of a neurone following its depolarisation
Refractory period
The period of time during which no new action potentials can be produced. This is the result of the Na+ voltage-gated channels not opening
All or nothing principle
A threshold value must be reached in order for an action potential to occur. And all action potentials are the same size
Cholinergic synapse
A synapse is the junction between two neurones. In a cholinergic synapse, the neurotransmitter released between the two is always acetylcholine.
Saltatory conduction
When the action potential jumps from one node of Ranvier to the next. Depolarisation (and repolarisation) only occurs at the nodes of Ranvier.
Excitatory synapse
A synapse at which the neurotransmitter binds to ligand gated Na+ channels, resulting in Na+ moving into the post-synaptic neurone. So the post-synaptic neurone becomes more positive.
Inhibitory synapse
A synapse at which the neurotransmitter binds to ligand gated Cl- channels or ligand gated K+ channels, resulting in either Cl- moving in or K+ moving out. So the post-synaptic neurone becomes more negative.
Neuromuscular junction
A synapse between a motor neurone and a muscle. Different neurotransmitters can be released at different neuromuscular junctions.
Antagonist muscle pairs
Muscles which oppose the action of each other. When one muscle contracts, the other muscle relaxes
Muscle fibre
This is a muscle cell. It contains many myofibrils
Myofibril
Comprised of actin and myosin filaments
Sarcolemma
The cell-surface membrane of a muscle fibre
T tubules
Invaginations of the sarcolemma deep into the muscle fibre
Sarcoplasmic reticulum
e Specialised organelle in a muscle fibre which acts as a reservoir of Ca2+ ions
Actin
A fibrous protein which has a binding sites for myosin heads to attach. Actin is pulled towards the centre of the sarcomere during contraction.
Myosin
A fibrous protein with ‘heads’ which bind to the binding sites on actin filaments pulling the actin towards the centre of the sarcomere during contraction.
Tropomyosin
A protein which is wrapped around an actin filament. It is moved in the presence of Ca2+ so that the myosin-head-binding sites on the actin are exposed, allowing myosin to bind and contraction to take place.
Phosphocreatine
A metabolite found in muscle cells that allows ATP to be produced by substrate-level phosphorylation
Homeostasis
The maintenance of the internal environment within restricted limits
Negative feedback
The process that occurs when a change from the normal level is detected and initiates a response which acts against the change, returning the system to its original (normal) level (i.e. the set point)
(this can include causing the corrective measures to be turned off)
OR
where a change triggers a response which reduces the effect of
a change
Positive feedback
The process that occurs when a change from the normal level is detected and initiates a response which acts with the change, causing the system to deviate further from its original (normal) level (i.e. the set point)]
OR
where a change triggers a response which increases the effect
of a change
Glycogenesis
The formation of glycogen from glucose
Glycogenolysis
The hydrolysis of glycogen to form glucose
Gluconeogenesis
The formation of glucose from amino acids or fatty acids
Insulin
A hormone produced by the beta cells in the islets of Langerhans in the pancreas.
It binds to receptors on target cells causing more glucose channel proteins to become embedded in the cell-surface membrane, so the permeability of the cell to glucose increases. Insulin also activates enzymes which convert glucose to glycogen and in adipose cells convert glucose to triglycerides.
Glucagon
A hormone produced by the alpha cells in the Islets of Langerhans in the pancreas.
It binds to receptors on target cells and activates enzymes which cause glycogenolysis and gluconeogenesis to take place.
Type I diabetes
An autoimmune disease in which the body kills the beta cells of the pancreas so insulin can no longer be produced.
Type II diabetes
Insulin-independent diabetes. Usually caused by either abnormal insulin receptors or a lack of insulin receptors.
Osmoregulation
Maintaining a constant water potential in the fluids of an organism.
Genotype
The genetic constitution of an organism
Phenotype
L
The expression of the genotype and its interaction with the environment
Dominant allele
The allele of a gene that is expressed in the phenotype, even in the presence of an alternative allele
Recessive allele
The allele of a gene that is only expressed in the phenotype if there is another identical allele present
Codominant alleles
Both alleles of a gene are expressed in the phenotype of a heterozygote
Homozygous
When an individual contains two identical alleles of a gene
Heterozygous
When an individual contains two different alleles of a gene
Sex linkage
When a gene is found on the X or Y chromosome
Autosomal linkage
Genes which are found on the same chromosome are said to be linked. This makes the alleles of these genes more likely to be inherited together
Epistasis
The interaction of different genes
Population
A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
Gene pool
All the alleles of all the genes in a population
Hardy weinburg principle
Predicts that allele frequencies will not change from one generation to the next, as long as certain assumptions are met.
Hardy weinburg equation
An equation that can be used to calculate the frequency of alleles of a gene, genotypes and phenotypes in a population
Stabilising selection
Selection that favours phenotypes at, or near, the mean of the population range.
This preserves the characteristics of a population
Directional selection
Selection that favours phenotypes that are away from the mean of the population range.
Extreme phenotypes have a selective advantage.
This changes the characteristics of the population over time.
Disruptive selection
Selection that favours both the extreme phenotypes and selects against the individuals with average phenotypes. This changes the characteristics of the population over time.
Evolution
A change in allele frequencies in a population
Reproductive separation
When individuals do not (or cannot) reproduce to form fertile offspring
Allopatric speciation
When new species evolve from a single ancestral species as a result of a physical separation between individuals of the original population.
Sympatric speciation
When a new species evolves from a single ancestral species within the same geographic location.
Genetic drift
Change in the frequency of an allele or genotype as a result of chance
Addition mutation
One or more bases are added to a gene
Deletion mutation
One or more bases are removed from a gene
Substitution mutation
One or more bases are substituted within a gene
Inversion mutation
A chromosome mutation in which a section of the chromosome is reversed.
Duplication mutation
A chromosome mutation in which a section of the chromosome is duplicated
Translocation mutation
A chromosome mutation in which a section of one chromosome is removed and becomes attached to a different, non-homologous chromosome.
Mutagenic agent
An agent which makes mutations more likely to occur.
Frame shift
When an addition or deletion of bases occurs such that the reading frame of the gene changes from that point on
Degenerate nature of genetic code
Some amino acids are coded for by more than one base triplet
Totipotent cells
Undifferentiated cells which have the ability to divide continuously and mature into any type of body cell
Cell specialisation
A process which causes cells to become modified (through the expression of specific genes) so that they are adapted to carry out a particular function.
Pluripotent cells
Can divide in unlimited numbers cells and have the ability to give rise to several cell types
Multi potent cells
Cells which have the ability to divide and give rise to a limited number of cell types (fewer than pluripotent cells)
Unipotent cells
Cells which can only divide to form one type of cell
Induced pluripotent stem cells
Pluripotent cells which are produced by treating unipotent cells with specific protein transcription factors
Transcription factor
A Transcription factor binds to a gene
• At a specific DNA sequence in the promoter;
• Stimulates RNA polymerase to attach and transcribe the
gene (or can prevent transcription)
Epigenetics
The study of heritable changes in gene function that do not involve changes to their base sequences
Methylation of DNA
The addition of methyl groups to DNA bases, usually to switch off a gene.
Acetylation of histones
The addition of acetyl groups to a histone protein, affecting the transcription of a gene.
RNAi
RNA molecules (such as siRNA or microRNA) which inhibit gene expression by ‘neutralising’ specific mRNA molecules so that translation cannot take place. They bind to complementary mRNA sequences either preventing the mRNA from attaching to the ribosome or enabling enzymes to break up the mRNA
Benign tumour
A mass of dividing cells which do not break away and invade neighbouring tissue (i.e, do not metastasise)
Malignant tumour
A mass of cells which divide uncontrollably and can metastasise, invading other tissues
Tumour suppressor gene
A gene which codes for a protein that prevents cell division.
Oncogenes
A gene which codes for a protein that results in uncontrollable cell division
Proto oncogenes
A gene which codes for a protein that stimulates cell division or controls cell differentiation
