Stimuli and Response Flashcards
What is a taxis?
A simple response whose direction is determined by the direction of the stimulus, therefore the organism will either move towards a favourable stimulus or away from an unfavourable stimulus.
What is a positive taxis?
An organism moving towards a favourable stimulus
What is a negative taxis?
An organism moving away from an unfavourable stimulus.
What is an example of positive phototaxis?
Plants moving towards the light.
What is an example of negative phototaxis?
Earthworms moving away from the light
What is an example of positive chemotaxis?
When some species of bacteria will move towards a region where glucose is more highly concentrated.
What is kinesis?
When an organism responds to a specific stimulus by moving more or moving less but not in a specific direction (the movement is not towards or away from a specific stimulus).
What is the point of kinesis?
The rapid movement usually occurs in order to move an organism into a more favourable or stable environment, so will happen after a dramatic change to the environment.
What is one example of kinesis?
Woodlouse moving towards bodies of water in dry conditions. They move from a more damp area to a dry one, they will move more rapidly in every direction, as this increases their chance of moving into a damp area.
What are the six different types of gene mutation?
Substitution of bases Deletion of bases Addition of bases Duplication of bases Inversion of bases Translocation of bases
What is the definition of a stem cell?
A stem cell is a cell that is able to replicate itself while maintaining an undifferentiated state and is then able to differentiate into mature cell types.
What are the two types of stem cells in humans?
Embryonic and adult
What type of stem cells are embryonic stem cells?
Pluripotent stem cells
What does pluripotent mean?
A pluripotent stem cell can differentiate into many (but not any) type of cell
What type of stem cell are adult stem cells?
Multipotent stem cells
What does multipotent mean?
Multipotent stem cells can differentiate into a limited amount of different types of mature cells (usually just those within the tissue or organ in which they were found)
where are embryonic stem cells found?
give two examples
embryonic stem cells can be taken from spare embryos that are created during IVF.
They can also be taken from the cell removed from an embryo for preimplantation genetic diagnosis at the 8 cell stage of embryo development.
Where are adult stems found? Is this difficult?
They are found in many adult organs (i.e. the brain, the skin etc.), but they are very difficult to harvest.
describe the process of Therapeutic Cloning
- The nucleus of an ovum cell is removed and replaced with a nucleus from the cell of a patient
- The cell is then given a small electric shock to cause it to start dividing
- Once the blastocyst stage, the stem cells can be removed and are cultured to produce genetically identical tissues for the patient.
what is the government’s perspective of therapeutic cloning?
Therapeutic cloning has been allowed by the government, but all embryos must be destroyed after 90 days, to avoid human cloning.
What does totipotent mean?
A totipotent stem cell is capable of giving rise to any cell type.
Name four conditions/situations that stem cell research could aid
- People with parkinson’s disease by replacing faulty brain cells
- People with diabetes by replacing insulin producing tissue in the pancreas
- People with damaged nerves by replacing spinal nerves to allow limbs to work again
- People who need organ transplants
What are the 6 different types of gene mutation?
Substitution of bases Deletion of bases Addition of bases Duplication of bases Inversion of bases Translocation of bases
What happens in substitution of bases mutation?
A nucleotide is replaced by another of a different base.
What are the three situations that can occur due to a substitution of bases mutation?
- the new bases creates a stop codon, causing the polypeptide to be released, meaning that the polypeptide is significantly different and possibly non-functional.
- The new base forms a codon for a different amino acid causing the shape and function of the protein to differ (it could be non-functional)
- A different codon is formed, but it codes for the same amino acid, so has no effect on the polypeptide chain or protein
What is deletion of bases mutation?
What is the effect of deletion of bases mutation?
When a base is deleted, this causes a frame shift as each of the bases have been shifted to the left.
Most triplets will therefore be different and will code for different amino acids, which may result in the production of a non-functional protein.
What is addition of bases mutation?
An extra base is inserted into the sequence, causing the frame to shift to the right.
What are the possible effects of an addition of bases mutation?
If three bases are inserted, creating a new codon, this would not have as much effect on the final polypeptide, but would still result in a different polypeptide (as would be the case if just 1 or 2 new bases were added).
What is duplication of bases mutation?
When one or more bases are repeated. This produces a frame shift to the right.
What is inversion of bases mutation?
When a group of bases becomes separated and then rejoins in the same position in inverse order, which affects the amino acid that is produced.
What occurs in translocation of bases mutation?
A group of bases becomes separated from the DNA sequence on one chromosome and becomes inserted into the DNA of another chromosome.
What is the effect of translocation of bases mutation on the polypeptide chain produced?
As there is such a significant effect on the gene expression, so leads to abnormal polypeptides produced in the phenotype.
What health issues can translocation of bases mutation lead to?
Development of certain cancers and reduced fertility.
What are three causes of mutations?
- they can arise randomly/spontaneously during DNA replication
- Exposure to a high energy ionising radiation such as alpha/beta particles as well as short wave radiation such as X rays and UV rays
- exposure to chemicals such as nitrogen dioxide (caused by burning of fossil fuels) and benzopyrene (from tobacco smoke)
What is one possible positive outcome of mutations?
They can help produce genetic diversity, which is necessary for natural selection and speciation.
What are three negative outcomes from mutations?
- They can be harmful
- They can produce organisms that are less well suited to their environment
- If in body cells, mutation can lead to disruption of normal cellular activities, such as cell division, so can then lead to cancer.
What is leaching?
The process by which nutrients are removed from the soil (often by rainwater)
What happens in Leaching?
Rainwater will dissolve any soluble nutrients, such as nitrate ions and carry them deep into the soil, out of the reach of plants. These leached nitrate ions will then make their way into streams, rivers and freshwater lakes.
How can leaching affect humans?
If the river or lake that the dissolved ions end up in is a body of drinking water, these can prevent efficient oxygen transport in babies and has been related to stomach cancer
How can leaching affect the environment?
It can lead to eutrophication
What are the two types of receptors we need to know about in A level bio?
Pressure receptors in the skin and photosensitive receptors in the eyes
What are pacinian corpuscles?
receptors in the skin related to detecting pressure
How do pacinian corpuscles act as transducers?
It converts mechanical energy to electrical energy using chemical compounds
How do pacinian corpuscles work?
The pacinian corpuscle is made up of a lot of capsules surrounding a single nerve cell. Outside this nerve cell is a large amount of positively charged sodium ions (at resting potential). Normally, the sodium channels in the cell membrane are too narrow to allow sodium ions to pass through them. When pressure is applied, the pacinian corpuscle changes shape and allows these positively charged sodium ions to enter the cell. This influx of sodium ions changes the charge of the cell, causing it to depolarized and therefore produce an electrical current.
What is depolarisation?
In a cell or a membrane, the changing of electrical charge.
What are the two types of receptor cells in the eye called?
Rods and Cones
What are rods intended for?
For seeing in the dark.
What are cones intended for?
For seeing in colour
Why are both rod and cone cells transducers?
As they convert light energy to electrical energy via chemical energy.
Why can rod cells still function despite them receiving so little light in the dark?
Because many rod cells share a single sensory neuron. Therefore, the small amount of light energy from each of the different rod cells is combined to create an impulse along the neuron. Therefore the threshold value is more easily exceeded with multiple rod cells than if there was one rod cell.
How do rod cells convert light energy to electrical impulse?
All rod cells contain a pigment called rhodopsin. This is broken down by light into opsins which then create an electrical impulse.
What is saltatory conduction?
When the nerve impulse jumps between the nodes of ranvier instead of running through the whole axon.
How does the myelin sheath relate to the speed of an impulse through an axon?
Myelinated axons carry electrical energy quicker as the action potential jumps from one node of ranvier to the other, over the myelin sheath.
How fast does an impulse travel through a myelinated axon?
90m/s
How fast does an impulse travel through an unmyelinated axon?
30m/s
What are two factors that affect the speed of action potential?
Diameter of the axon and temperature
How does the diameter of the axon effect the speed of the nerve impulse?
The greater the diameter of the axon the faster the impulse, as there is more mass to carry the impulse at one time.
How does the temperature of a neuron affect the speed of the neuron?
At a higher temperature, there is a faster rate of diffusion of sodium ions into the axon, which therefore increases the speed of the impulse. The temperature also increases, which would increase the productivity of enzymes related to making ATP, so the rate of active transport of ions in and out of the axon would be faster, so the nerve impulse would be faster.
What is the refractory period?
A period of time after the axon has been depolarised where the channel proteins reclose, so no new action potential can be created.
How/in what way does the impulse travel along the neuron?
In one way, from the cell body along the axon to the terminals.
What is the “all or nothing” theory of neural impulses?
Action potential only occurs if a stimulus reaches a threshold value. If this threshold is not reached, there will be no action potential. Therefore, the axon either completely fires (all) or doesn’t at all (nothing) depending on whether the threshold is met.
How can we detect the size of a stimulus using a neuron?
By the magnitude/number of impulses. A larger stimulus will reach the threshold more times/will create a larger potential so either larger or multiple impulses are generated.
what sort of ion channels are in the presynaptic neuron?
Calcium channel ions
What happens when an action potential reaches the presynaptic cell?
Calcium ion channels open, which allows an influx of calcium ions. These in turn break down the vesicles containing the neurotransmitters, which allows them to be released when the meet the membrane of the presynaptic cell.
What happens when an excitatory neurotransmitter reaches the postsynaptic cell?
Sodium channels open. This leads to the postsynaptic cell becoming depolarised and creating a potential.
What two organelles does the presynaptic cell contain??
Mitochondria and Smooth endoplasmic reticulum
How are the two organelles used in the presynaptic cell?
After neurotransmitters are broken down, ATP from the mitochondria is used to recombine the parts to reform the neurotransmitter. The neurotransmitter is made in the smooth endoplasmic reticulum.
What does unidirectionality mean?
It refers to how synapses can only travel in one direction- from the presynaptic to the postsynaptic cell.
What does summation mean?
Low frequency action potentials often produce insufficient amounts of neurotransmitters to trigger a new action potential. They can be added up together, in summation, to reach the threshold.
What is spatial summation?
When a number of different neurons together release enough neurotransmitter to exceed the threshold value to create a potential.
What is temporal summation?
When the same neuron repeatedly receives neurotransmitters and is depolarised, therefore reaching the threshold through repetition
What are histones?
They are basic proteins that associate with DNA in the nucleus and help condense it into chromatin. DNA coils around histones.
What are transcription factors?
Where do they occur?
They are molecules that help RNA polymerase bind to the template DNA strand. Each transpositional factor will bind to a specific sequence on the DNA and stimulate transcription.
Only in Eukaryotic cells.
What hormone can act as an activator of transcription factors?
Oestrogen
How does oestrogen activate transcription factors?
Oestrogen will bind to a transcription factor in the cytoplasm. This binding causes the transcription factor to change shape. The transcriptor then enters the nucleus through a nucleic pore. The transcription factor then binds to the DNA at a specific point due to its new shape.
How does coiling of the histones relate to transcription?
When DNA is loosely coiled around the histone the DNA is more accessible to transcription factors. When DNA is tightly coiled/packed, it is inaccessible to to transcription factors and therefore can’t be transcribed.
What happens in the acetylation of histones and how does this affect transcription?
An acetyl group is added to the histone. This lessens the attraction of the DNA to the histone. This makes the DNA less tightly wrapped around the histone so is therefore more accessible to transcription factors, so the gene is expressed.
What occurs in deacetylation/ decreased acetylation?
The addition of an acetyl group causes the histone to be more attracted to the phosphate group in the DNA, causing the DNA to more tightly coil/close around the gene, causing it to not be expressed.
What occurs in methylation?
A methyl group is added to a cytosine base and therefore inhibits transcription.
What are the two ways methylation affect transcription?
1- By attracting proteins that induce deacetylation of the DNA strand, causing the DNA to be more tightly wrapped around the histone, so the DNA is not transcribed.
2- It prevents the binding of transcriptional factors, which prevents transcription.
What is Heterochromatin?
A tightly packed, dense form of chromatin which deeply winds in DNA.
What is Euchromatin?
A lightly packed form of chromatin that has loosely coiled DNA.
What is small interfering RNA?
A type of RNA that destroys mRNA before translation so therefore protein synthesis can not occur.
What is the process by which siRNA inhibits gene expression?
An enzyme cuts double stranded RNA into small sections called siRNA. One of the two siRNA strands combines with an enzyme which then go to the mRNA strand and binds to complementary bases. The enzyme then cuts the mRNA into small sections. This means the mRNA can not be translated and the genes can not be expressed.
What are muscle fibres made up of?
Myofibrils
What are myofibrils made up of?
Small units called sarcomeres.
What are sarcomeres made up of?
two proteins- actin and myosin
What are the differences between the I band and the A band?
The I band is lighter as it only contains actin and contains the Z disk, while the A band contains both myosin and actin so is therefore darker in appearance, but does contain the H zone, which is lighter as it contains only myosin.
What occurs in contraction?
Myosin interacts with actin to create a cross bridge.
How does action potential travel from the postsynaptic cell to the sarcoplasmic reticulum?
Via T tubules
What occurs when action potential reaches the sarcoplasmic reticulum?
Calcium ion channels open and calcium diffuses into the sarcoplasm.
How do calcium ions interact with tropomyosin and how does this relate to myosin?
The calcium ions bind to tropomyosin. This causes the tropomyosin protein to move and unveil the myosin binding site. This allows for myosin to attach to the actin protein and form the myosin-actin crossbridge.
