A2 Human Biology Unit 12

Text questions

P246/Q1

The part of the brain, which interprets images on your retina, cannot cope with a lack of image.
Therefore your brain fills in the "blind area" with what is immediately around it (i.e. the colour of
the image produced nearest to it).

P248/Q2

As a result of a Pacinian corpuscle springing into this "O" shape all the Na+ gates which were pressed to open before (when pressure was applied) are now "pressed" to close.

P248/Q3

Air/conjunctiva-cornea, cornea/aqueous humour, aqueous humour/lens, lens/vitreous humour (light will be refracted at the border between two media of different densities).

P252/Q4

Neurotransmitter released by the rods has an inhibitory effect on relay cells.

P252/Q5

If you look to one side of a star (rather than directly at it), visual acuity of the retina will be improved. This change results from the image being focused on the cone cells rather than rod cells.

P253/Q6

Deficiency of vitamin A → insufficient amount of retinal produced → vision adversely affected.

P254/Q7

Actin filaments arranged in a regular hexagonal pattern;

Pattern A = A-band pattern B = H-zone pattern C = I-band

P256/Q8

The width of A-band stays the same; the width of I-band decreases.

P258/Q9

Role of Ca²⁺ and ATP during the contraction of myofibril:

Ca2+	ATP
When stimulation by the nervous system stops: Ca²⁺ taken up by sarcoplasmic reticulum → cross bridges will not reform after myosin head has detached from its actin → muscle will relax	ATP is involved in a cyclical process of ATP hydrolysis, attachment of myosin heads to receptor sites on actin, change of angle of myosin head & detachment of myosin heads from receptor sites on actin.

P259/Q10

Breast meat/muscle = fast muscle (: poor blood capillary supply, muscle cells lack myoglobin), hence light in colour. Leg meat = slow muscle (: rich blood capillary supply, their sarcoplasm is packed with myoglobin), hence dark in colour. Function of this muscle: postural endurance.

Assignment

P262/Q1	a)	Aerobic respiration
	b)	Many mitochondria + cytochrome pigments (Electron Transport Chain).
P262/Q2		Fast muscles contain a store of many glycogen granules, because ATP required for their movement is produced from glycolysis. This is to enable fast muscles to produce ATP for immediate use. The function of slow muscles is postural endurance. ATP produced from glucose via aerobic respiration, hence no need for glycogen.
P262/Q3		Fast muscle (: large diameter of fibres, high amount of sarcoplasmic reticulum, high ATP-ase activity: ATP → ADP + energy) are well adapted for rapid, powerful contractions necessary in jumping/throwing sport events.
P262/Q4	a)	Affinity of myoglobin for oxygen is higher than that of haemoglobin. As a result myoglobin is fully saturated with O2 at a much lower partial pressure than haemoglobin.
	b)	% saturation of myoglobin with O2 is high: there is a reserve of O2 in myoglobin available for slow muscle fibres for aerobic respiration as ATP is used up during their contraction.
P262/Q5		Dense/good nerve supply to fast muscle fibres (= many neuromuscular junctions) will cause a higher number of synoptic vesicles containing ACh to release their contents across the synoptic cleft onto sarcolemma (motor end plate). As a result, more muscle fibres will contract → faster muscle contractions (important in fencing, boxing, etc.)

Examinations

P263/Q1	a)	During vigorous exercise, stored ATP is used within 10 seconds. Phosphocreatine stored in muscle cells is used to generate more ATP: ADP ~~~~> ATP Phosphocreatine ~~~~~~~~~~~~> creatine
	b)	(i) Fast muscle fibres depend mainly on glycolysis for the production of ATP. Large amounts of glycogen in fast muscle fibres will provide the necessary glycogen; (ii) Glucose and oxygen supplied to slow muscle fibres via capillaries;
P263/Q2	a)	(i) H-zone: only myosin A-band: mostly myosin + some actin (ii) H-zone shortens when the muscle contracts;
	b)	Many mitochondria present → aerobic respiration produces a lot of ATP → sustained muscle contraction over long period of time possible.
P264/Q3	a)	Cone cells
	b)	The image of the object would be focused on the rod cells, which detect shape but cannot detect colour.
	c)	(i) There are 3 sorts of cone cells: Cells sensitive to red light Cells sensitive to green light Cells sensitive to blue light Purple light is a mixture of red and blue light. If cone cells sensitive to red & blue light are both stimulated, then the purple colour will be detected by the vision centre in the brain. (ii) The purple line would be aligned with the blue line (drawn, as instructed in the question, below the horizontal line).