AQA A2  (Module 6) Human Biology

 

ANSWERS TO IN-CHAPTER QUESTIONS

 

Unit 12: Receptors and Effectors

 

 

 

 

COMPARE YOUR ANSWER WITH THE SUGGESTED RESPONSE GIVEN BELOW: RETURN YOUR MARKED SCRIPT TO YOUR TUTOR

IF YOU ARE UNCLEAR OR UNCERTAIN ABOUT ANY ASPECT OFTHIS CHAPTER IT IS ESSENTIAL THAT YOU ARRANGE FOR EXTRA TUTOR HELP AND GUIDANCE

 

 

 

Q1.   

The blind spot on the Retina has no rod or cone cells; so no (image) impulse is transmitted to the brain.  Each eye has a different area of vision missing.  The fusion of messages from both eyes enables the brain to fill in the “gap” in the picture.

 

Q2.   

This corrects the deformation of the capsule that is pressing on the sensitive nerve endings at the centre of the pacinian corpuscle.  The stretched nerve membrane now returns to its original shape shutting the gates of the sodium channel proteins.  The nerve membrane goes into the refractory period since an action potential was previously generated.  This enables the person to feel the pressure has been released.

 

Q3.   

Air ® cornea

Cornea ® aqueous humour

Aqueous humour ® lens

Lens ® vitreous humour

 

Q4.   

Excitatory.

 

Q5.   

The light is more likely to impinge on the rods of the area around fovea.  You can see more stars on a dark night out of the “corners” of your eyes.  In dim light only rods are activated, so colour vision is lost as well as acuity.

 

Q6.   

Poor vision in dim light conditions; insufficient retinal to combine with opsin to form rhodopsin which is needed for the rod cells to work.

 

Q7.   

a)     Actin in the protein present in actin filaments, which are much thinner than myosin filaments.  Therefore actin filaments cause lighter striations.  Actin filaments are attached to plates called Z lines.  The myosin and actin filaments slide over each other so that their overlap increases during muscle contraction.

b)     A = A Band
B = H Zone
C = I Band.

 

Q8.   

The A Band stays the same.  The I Band all but disappears, i.e. it narrows, as the filaments slide one another, i.e. they interdigitate.  Interlocking figners is a good analogy – pushing them together shortens the distance they span.

 

Q9.   

The actin potential spreads down the membranes of the T-tubules.  This causes the membranes of the nearby sarcoplasmic reticulum to become more permeable and Ca2+ ions diffuse out rapidly.  The Ca2+ ions reach the actin filaments in the myofibrils, unblocking the binding sites and causing contraction, i.e. actomyosin cross bridges form.  The Ca2+ ions attach to troponin, which causes the tropomyosin to change position, unblocking the binding site, i.e. the cross bridges can form.  No energy is needed.  This is what causes rigor mortis after death.

 

The ATP is needed to break the links between the actin and myosin so allowing the sliding filament cycle of muscle contraction to be repeated.  This occurs late after death therefore the body relaxes.

 

Q10.         

Breast meat of turkey is light in colour as it is fast twitch muscle.  They contain relatively little myoglobin.  They allow fast muscle contraction.  Predators possess many fast fibres for fast reactions to capture prey.

 

Leg meat is dark as it is slow twitch muscle, which is suited to long-term slow contractions.  They contain much more myoglobin.  They consume less fuel than fast muscle.