Botulinum toxin stops nerve impulse transmission at synapses. Suggest how this may
occur.
[3]
- Botulinum toxin blocks the secretion of acetylcholine from vesicles at the pre-synaptic knob by blocking receptors on post synaptic membrane
- Botulinum inhibits acetylcholine esterase to prevent ACh synthesis so Ach cannot be recycled
- ACh cannot cross the synaptic cleft to bind to receptors
- Therefore, no action potential is generated in the post-synaptic membrane
- Prevents uptake of calcium ions
- Blocks sodium ion channels
(A.I. advice: Botulinum toxin doesn’t compete with acetylcholine at the receptor.
Its main action is to stop ACh being released from the neuron, so there’s less or no ACh available for A.P.
So calling it a “competitive inhibitor of ACh receptors” is technically incorrect, which is why your original answer lost a mark.)
Phenotype is influenced by genetic and environmental factors. Describe one example
of how the environment influences phenotype.
[2]
- Human skin: “Exposure to sunlight increases melanin production, making skin darker.”
- Siamese cats: “Temperature affects fur color. At extremeties, such as ears, tail and paws are much cooler than core body temp, therefore develop darker fur because due to mutation in the tyrosine enzyme, tyrosine more active at producing melanin at lower temp therefore white body and dark extremeties.”
- Plant height: “Plants grown in low light are taller because they elongate to reach light.”
- Hydrangea flowers: “Soil pH affects flower color: acidic soil produces blue flowers, alkaline soil produces pink flowers.”
State three features of the kingdom Plantae, other than being eukaryotic.
[3]
- cellulose cell wall
- large vacuole with liquid cell sap (animals have small vacuole)
- choloroplast/chlorophyll
- multicellular
- differentiated tissues and organs
Cytochrome c is a protein that is found in all living organisms. Analysis of the amino acid sequences of proteins, such as cytochrome c, provides data that taxonomists use
to produce more accurate classifications.
Explain how analysing the amino acid sequences of proteins provides useful data for taxonomists.
[4]
- Taxonomists compare the amino acid sequences of proteins, such as cytochrome c, to look for similarities and differences
- Closely related species have very similar amino acid sequences because their DNA is similar, DNA codes for amino acid sequence of proteins
- Mutations in DNA cause changes in amino acid sequences, so more distantly related species have more differences in their proteins
- By comparing these differences, taxonomists can produce more accurate classifications of species
