Movement and Support in Animals

Exam-style Questions

1. The diagram shows the appearance of a sarcomere from a relaxed muscle fibril, as seen with a light microscope.

a) Use your knowledge of the sliding filament hypothesis to explain the appearance of each of the bands P, Q and R.

b) Draw a similar diagram to show the appearance of the sarcomere when the fibril is contracted.

(Marks available: 4)

Answer

Answer outline and marking scheme for question: 1

Give yourself marks for mentioning any of the points below:

a) P - Actin.

Q - Actin + Myosin.

R - Myosin.

(3 marks)

b) Diagram with narrower P region and no/very thin R region.

(1 mark)

(Marks available: 4)

2. The drawing shows some of the main flight muscles of a locust.

a) What name is used to describe the action of a pair of muscles such as A and B?

b) Explain how the action of muscles A and B brings about movement of the wing.

(Marks available: 3)

Answer

Answer outline and marking scheme for question: 2

Give yourself marks for mentioning any of the points below:

a) Antagonistic.

(1 mark)

b) Muscle A contracts, pulls wing down.

Muscle B contracts, pulls wing up.

(2 marks)

(Marks available: 3)

3. Complete the table below (showing the differences between the three muscle types):

Muscle Type

Skeletal

Cardiac

Smooth

Function

 (a)

 (b)

 (c)

Cell

 (d)

 (e)

(f) 

Control of Contraction

 (g)

 (h)

(i)

Speed of contraction

 (j)

 (k)

(l)

(Marks available: 4)

Answer

Answer outline and marking scheme for question: 3

Muscle Type

Skeletal

Cardiac

Smooth

Function

Locomotion

Pumping blood through heart

Lines blood vessels

Cell

Striated

Specialised striated

Unstriated

Control of Contraction

Voluntary

Involuntary

Involuntary

Speed of contraction

Rapid

Intermediate

Slow

(Marks available: 4)

Muscles and Movement

Movement is made more flexible with joints. Here, ligaments hold bones together. They limit the movement thus preventing dislocation. The joints move due to the force of muscles acting on them.

Muscles and Movement

Muscles are attached to bones by tendons that are made of collagen fibres. When a muscle contracts, the tendon and its attached bone are pulled towards the contracting muscle.

Many joints work due to the action of antagonistic muscles; one set causes the joint to move one way, the other set causes it to return. When one muscle in the pair is contracting, the other is relaxing (not stretching). An example of this arrangement is the elbow joint controlled by the biceps and triceps muscle.

There are three types of muscle, skeletal, cardiac and smooth...

  Skeletal: Cardiac: Smooth:
Function: Locomotion Pumping blood through heart Line blood vessels, digestive tract (peristalsis), uterus, etc.
Cells: Striated Specialised striated Unstriated
Control of contraction: Voluntary - conscious Involuntary Involuntary
Arrangement: Regular arrangement so the muscle contracts in one direction Cells branch and interconnect allows efficient transfer of impulses so brings about simultaneous contraction No regular arrangement (different cells can contract in different directions)
Speed of contraction: Rapid Intermediate Slow
Length of time contracted: Short Intermediate Can remain contracted for a relatively long time

Each muscle is called a fibre. Each fibre made up of a bundle of myofibrils.

Each myofibril is made of myofilaments - actin and myosin.

A muscle fibre:

A muscle fibre

The myofilaments are arranged so that each myosin is surrounded by 6 actins:

Myofilaments

The actin, being thinner, shows up under a microscope as a light band. The myosin, being thicker, shows up as a dark band.

Actin:

It consists of 2 threads wrapped around each other. At each twist there is a binding site for myosin. In a relaxed state, a molecule called tropomyosin covers these sites.

Actin

Myosin:

The filament consists of many myosin molecules. Each molecule has a tail and a double globular head.

Myosin

The head attaches to the myosin binding sites on the actin where the actin and myosin filaments overlap.

These attachments are called cross-bridges. The heads contain ATPase enzyme which releases energy from ATP to power muscle contraction.

Contraction occurs when an impulses from a motor neurone reaches the synapse at the junction with the muscle. If it is stronger than a threshold stimulus (see Nervous and Hormonal Control Learn It) contraction will occur.

What follows is the Sliding Filament Hypothesis:

  1. Acetylcholine, a neurotransmitter substance, is released into the synapse, diffuses across and attaches to specific receptors on the sarcolemma (the outer membrane of the muscle fibre).
  2. The muscle sarcolemma is depolarised.
  3. Depolarisation spreads along the fibre.
  4. This causes calcium to be released from the sarcoplasmic reticulum into the sarcoplasm.
  5. Calcium displaces tropomyosin, thus uncovering the myosin binding sites on the actin filaments.
  6. ATP attached to the myosin heads cause them to flex and attach to the actin in the overlapping areas.
  7. ATP is hydrolysed to ADP + P. The energy released causes the heads to alter their angle to their tails. This pulls the actin filament past the myosin filament.

The cross-bridges detach and reattach, this time further along the actin filament.

 

The areas of overlap therefore lengthen and the light bands shorten. The sarcomere becomes relatively short. The shortening of sacromeres along the length of the muscle is the cause of contraction.

Bones

Locomotion is generally brought about by a system of muscles in conjugation with a skeleton. The skeleton may be an endoskeleton, an exoskeleton or a hydrostatic skeleton. The support system will be adapted to methods of locomotion for a particular animal (e.g, flying, swimming, climbing, and walking).

It consists of bone, cartilage, tendons and ligaments. Its functions are:

  • Support.
  • Protection of soft tissue.
  • Movement - a point of attachment for muscles.
  • Production of red blood cells and some white blood cells.
  • A source (sink) for calcium and phosphate.

Cartilage is firm but elastic. Cartilage cells are called chondrocytes. They secrete a hard, rubbery matrix around themselves.

They also secrete collagen fibres that become embedded in the matrix to strengthen it. The cells themselves live in small cavities in the matrix called lacunae.

No blood vessels, nerves or lymph vessels run through cartilage so the cells rely on diffusion for any nutrients and oxygen.

The central portion of a bone contains marrow. This may be yellow (a fat store) or red (the site of red blood cell and some white cell production). The marrow is surrounded by compact bone that withstands forces in a downward direction.

The head of the bone may have spongy bone between the compact bone and the marrow. Spongy bone also runs down the length of most bones other than the long bones of the arms and legs. This can withstand forces from many directions. This arrangement allows bones to be strong yet light.

Bone is also made up of a matrix and lacunae inhabited by cells, osteocytes, which secrete the matrix.

It has many blood vessels through it, as the rate of diffusion would be too low to keep the cells alive. The matrix is like that of cartilage but it contains a complex calcium phosphate mineral that makes the bone hard and strong. It is prevented from being brittle by collagen.

Between the lacunae are small channels (canaliculi). These contain more osteocytes. Capillaries and nerves run through other channels called Haversian canals.

Copyright S-cool

Other cells, osteoclasts, dissolve bone with acid that they produce, and then osteocytes lay down new bone. This allows the bone to change shape if necessary and it keeps the bone tissue relatively young.

S-Cool Revision Summary

Locomotion is generally brought about by a system of muscles in conjugation with a skeleton. The skeleton may be an endoskeleton, an exoskeleton or a hydrostatic skeleton. The support system will be adapted to methods of locomotion for a particular animal (e.g, flying, swimming, climbing, and walking).

It consists of bone, cartilage, tendons and ligaments.

Its functions are:

Support.

Protection of soft tissue.

Movement - a point of attachment for muscles.

Production of red blood cells and some white blood cells.

A source (sink) for calcium and phosphate.

Cartilage is firm but elastic. Cartilage cells are called chondrocytes. They secrete a hard, rubbery matrix around themselves.

They also secrete collagen fibres that become embedded in the matrix to strengthen it. The cells themselves live in small cavities in the matrix called lacunae.

Movement is made more flexible with joints. Here, ligaments hold bones together. They limit the movement thus preventing dislocation. The joints move due to the force of muscles acting on them.

Muscles are attached to bones by tendons that are made of collagen fibres. When a muscle contracts, the tendon and its attached bone are pulled towards the contracting muscle.

Each muscle is called a fibre. Each fibre made up of a bundle of myofibrils.

Each myofibril is made of myofilaments - actin and myosin.

The myofilaments are arranged so that each myosin is surrounded by 6 actins.

Actin: consists of 2 threads wrapped around each other. At each twist there is a binding site for myosin. In a relaxed state, a molecule called tropomyosin covers these sites.

Myosin: the filament consists of many myosin molecules. Each molecule has a tail and a double globular head.

Contraction occurs when an impulses from a motor neurone reaches the synapse at the junction with the muscle. If it is stronger than a threshold stimulus contraction will occur.

Syndicate content