Author: philcolls76@outlook.com
Last saved by: Gemma Archibald
Document comments: Created by the \'abHTML to RTF .Net\'bb 5.5.2.4

Muscles homework 3 – Twitch fibres. 		NAME:

Action plan following completion

Q1. Slow and fast skeletal muscles both contain slow and fast muscle fibres but in different proportions. The proportion can be determined by observing stained sections of muscle under a microscope. The stain used reacts with an ATPase enzyme. Muscle fibres containing a lot of this ATPase stain brown. Fibres containing little ATPase stain yellow.
The diagram shows stained muscle fibres in a section taken from a muscle.

(a)     Both slow and fast muscle fibres contain ATPase.
Explain why.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(b)     The tissue in the diagram came from muscle with a high proportion of brown-staining fibres. Was the tissue removed from slow or fast skeletal muscle?
Explain your answer.
........................................................................................................................
........................................................................................................................
........................................................................................................................
(1)

(c)     The muscle tissue in the diagram had been stained for viewing with a microscope.
What is the evidence that it had been stained for viewing with an optical (light) microscope? Explain your answer.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)(Total 5 marks)
Q2.  It is believed that each person is born with a certain percentage of slow and fast muscle fibres in their skeletal muscles. Most people have about 50% slow fibres and 50% fast fibres.
A sports scientist wondered if these percentages could change over time depending on the type of sport in which a person was involved. He knew from previous investigations that:
•        the number of mitochondria within a fibre can change
•        the diameter of a fibre can change
•        the number of muscle fibres in a skeletal muscle remains constant over time.
He determined the mean percentages of slow and fast fibres in skeletal muscles of different types of athletes.  His results are shown in the graph below in the form in which he presented them.

(a)     (i)      In which type of athlete would the sports scientist expect to find muscle fibres with the highest number of mitochondria?
...............................................................................................................
(1)
(ii)     Explain the reason for your choice of athlete.
...............................................................................................................
...............................................................................................................
............................................................................................................... (2)
(b)     The leg muscles of long-distance cyclists are usually larger than the leg muscles of non-athletes.
Suggest why.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................(3)
(c)     A reader of the sports scientist’s results stated that ‘the results show that regular weightlifting changes your proportion of slow and fast skeletal muscle fibres.’
Do you agree with this statement? Explain your answer.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
...................................................................................................................(2)(Total 8 marks)
Q3. The diagram shows part of a myofibril from a relaxed muscle fibre.
 
(a)     When the muscle fibre contracts, which of the A band, I band and H zone
(i)      remain unchanged in length,
.............................................................................................................(1)
(ii)     decrease in length?
.............................................................................................................(1)
(b)     Explain what caused the decrease in length in part (a)(ii).
......................................................................................................................
......................................................................................................................
......................................................................................................................(2)
(c)     The whole muscle fibre is 30 mm long when relaxed. Each sarcomere is 2.25 µm long when contracted. Use the scale given on the diagram to calculate the length of the contracted muscle fibre in millimetres.

Length of contracted fibre = ...................................... mm       (2)
(d)     The table gives some properties of the two different types of muscle fibre found in skeletal muscle.
(i)      Complete the table by writing the words ‘high’ or ‘low’ for the remaining three properties of each type of muscle fibre.
 
| Type of muscle fibre
| Type 1 | Type 2
Speed of contraction | high | low
Force generated | high | low
Activity of the enzymes of glycolysis | high | low
Number of mitochondria | |
Activity of Krebs cycle enzymes | |
Rate of fatigue | |
(3)
(ii)     The myosin-ATPase of type 1 muscle fibres has a faster rate of reaction than that in type 2 fibres. Use your knowledge of the mechanism of muscle contraction to explain how this will help type 1 muscle fibres to contract faster than type 2.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
............................................................................................................. (4)
    (iii)  	The blood leaving an active muscle with a high percentage of type 1 muscle fibres contained a higher concentration of lactate than that leaving a muscle with a high percentage of type 2 muscle fibres. Explain why.
.............................................................................................................
.............................................................................................................
......................................................................................................... (2)  (Total 15 mark)