Unit 3 Exam Questions Flashcards
Describe the function of sodium ion channels in a neurone membrane in response to stimulus.
• allows sodium ions to rapidly diffuse into the neurone
• this brings about depolarisation of the axon and the inside of the neurone becomes positive with respect to the outside
• this brings about the generation of action potential
How does an anaesthetic that blocks the sodium ion channels work
The sodium ions can no longer enter the axon
The threshold is not reached
There is no depolarisation nor action potential along the sensory neurone
How does an anaesthetic that blocks the calcium ion channels in the pre-synaptic membrane of a synapse work
• calcium ions do not diffuse into the synaptic knob
• this prevents the synaptic vesicles from fusing with the presynaptic membrane
• this prevents the neurotransmitter being released into the synaptic cleft
How does the release of more ADH cause a smaller volume if concentrated urine to be produced
• the ADH makes the membranes of the collecting ducts and distal convoluted tubule more permeable to water
• the ADH combines with a receptor
• the vesicles fuse with the membrane on the collecting ducts side which inserts more aquaporins into the membrane
• the water potential of the filtrate is higher than the water potential within the tissue fluid
• water moves into the tissue fluid by osmosis
What is a disadvantage of the total count technique
The death phase cannot be identified
Explain the advantages of collecting results from the whole class
• increases reliability of the mean
• increases the confidence
• allows to identify anomalous results
• allows for the use of a statistical test
Why do muscles use glycogen as an energy store rather than fat
Glycogen does not need a large oxygen supply and does not need to remove a large amount of CO2 or water produced
How are sites selected at random
Lay out a grid and use a random number generator to give coordinates
Why are sites selected at random
• avoid bias
• improve representation of the area
• avoid user generated influence
Why does secondary succession increase the number of plant species
The area is colonised prior to being cleared so seeds, nutrients and humus are already present
It changes the environment and allows other species to grow
What happens to the number of animal species in an area during secondary succession
Increases as there are more habitats, food sources and niches
Why are legumes with rood nodules that contain rhizobium able to survive in soils with low nitrogen levels?
Rhizobium carries out nitrogen fixation where nitrogen gas is converted to ammonium ions which can be used by the plants to make amino acids and proteins and DNA
Why is leghaemoglobin present in the root nodules of leguminous plants
It binds with the oxygen present which gives anaerobic conditions in the root nodule for the rhizobium to fix nitrogen in
Why must rhizobium be in anaerobic conditions
The enzyme nitrogenase which fixes the nitrogen gas is inhibited if oxygen levels are high
Why are trees unable to survive in waterlogged soils
Waterlogged soils lack in oxygen
This means that roots cannot respire aerobically to provide ATP so the active transport of minerals stops and denitrification occurs so there is a lack of nitrate for the trees
