Uncategorized Questions

The human retina contains three types of cone cells:• cone cells sensitive to red light• cone cells sensitive to green light• cone cells sensitive to blue light.Staring at a white card causes all three types of cone cells to be stimulated.A student investigated the duration of afterimages using red squares and purple squares. Hisresults are shown in the table.Suggest a null hypothesis for this investigation.

The blink reflex is caused by stimulation of receptors in the eye or eyelid.Suggest two types of stimuli to which these receptors might respond.

When the heart beats, both ventricles contract at the same time.Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN.

The blink reflex can be stopped by drugs which prevent the opening of sodium ion channelproteins in the axons of motor neurones.Suggest how these drugs affect the passage of nerve impulses along the axons.

Using the results in the table above, calculate the percentage decrease in mean pulse ratewhen lying down compared with when standing.

In humans, resting blink rate varies widely from 8 to 24 blinks per minute.This variation could result in the investigations into effect of stimulation on blink rateproducing means that are not significantly different. Explain why.

The membrane potential at Q was the same whether medium or heavy pressure wasapplied to the finger tip. Explain why.

The cone density is highest on the fovea in the centre of the retina. In a human fovea thereare 150 000 cones per mm2. The diameter of a human fovea is 1.4 mm.Calculate the number of cones on the human fovea.The formula for calculating the area of a circle is πr2

A biologist investigated the stimulation of a Pacinian corpuscle in the skin of a fingertip.She used microelectrodes to measure the maximum membrane potential of a Pacinian corpuscleand its sensory neurone when different pressures were applied to the fingertip.The figure below shows the Pacinian corpuscle, its sensory neurone and the position of themicroelectrodes.Explain how the resting potential of -70 mV is maintained in the sensory neurone when nopressure is applied.

The retinas in the eyes of humans and birds have cone cells that absorb light of differentwavelengths.A scientist recorded the absorption of light of different wavelengths by different types of humancone cells. Her results are shown in Figure 1. Each curve shows the absorption of light by onetype of cone cell.Human colour vision has been explained by the trichromatic theory, meaning that it is based onthree colours.(a) Explain how the evidence from Figure 1 supports this theory.

The student did not carry out repeats. He was still able to carry out a statistical test.Explain why.

Scientists investigated the effect of humidity on the movement of the insect, Tenebrio molitor.The insects were placed in choice chambers with one side kept at 100% humidity and the otherside kept at 30% humidity.The insects were used one at a time and the path the insect followed recorded on paper.What type of behaviour was shown by the insect in Figure 1?Give evidence from Figure 1 to support your answer.

Suggest the conditions that the researcher used when obtaining her data for 0 seconds.

ATP is an energy source used in many cell processes. Give two ways in which ATP is asuitable energy source for cells to use.

The blink reflex involves synapses. Below is a diagram of a synapse.Identify A, B and C.

Suggest and explain two reasons why there is a high frequency of the E280A mutation inYaramul (lines 13-15).1. Isolated so inbreeding / low genetic diversity / small gene pool; 2. Allele inherited (through generations) from (common) ancestor;

Calculate the actual distance between points A and B. Give your answer inmicrometres (μm).

Alzheimer's disease (AD) is a non-reversible brain disorder that develops over anumber of years. At the start of 2014 the number of Americans with AD wasestimated to be 5.4 million. Every 30 seconds another person in Americadevelops AD.5 In the brain of a person with AD there is a lower concentration of acetylcholine.This affects communication between nerve cells and initially results in memoryloss and confusion. Some of the symptoms of AD that are associated withcommunication between nerve cells are reduced by taking the drug donepezil.Donepezil inhibits the enzyme acetylcholinesterase.10 A gene mutation called E280A found on chromosome 14 causes early-onset ADat a mean age of 49 years. The age at which the E280A mutation is expressedto cause AD varies.Yaramul is a town in a historically isolated region of the Andes Mountains. Thepopulation of this town has the highest frequency of the E280A mutation in the15 world. The origin of the E280A mutation in this population has been traced backto a common ancestor in the 17th century. Natural selection has not reducedthe frequency of the E280A mutation in the population.This autosomal dominant mutation involves a change in triplet 280 from GAA toGCA. Scientists analysed chromosome 14 from 102 individuals from Yaramul.20 They recorded a sample size of 204 and detected 75 E280A mutations but only74 potential AD cases. The scientists identified individuals with the mutation bywhole genome sequencing. They had decided that a DNA probe would not be asuitable method to detect the E280A mutation.Assuming no one with AD died in 2014, calculate the annual percentage increase in ADcases in America for 2014 (lines 2-4).

A student reading the researcher's report concluded that the difference between the resultsfor 30 seconds and 45 seconds was significant. Do you agree with his conclusion? Explainyour answer.

The presynaptic knob contains actin filaments and myosin molecules.The myosin molecules can attach to mitochondria and move them towards the presynapticmembrane, as shown in the diagram.Use your knowledge of how myosin and actin interact to suggest how the myosin moleculemoves the mitochondrion towards the presynaptic membrane.Do not include the roles of calcium ions and tropomyosin in your answer.