B3.3 Muscle and motility (year 6)

Question 1

Example of a sessile and motile organism

Answer 1

Sessile: Venus flytrap
- Sessile organisms cannot move from place to place, but can still respond to environmental stimuli
- waits for insect to crawl/fly inside its “trap” a pair of leaves with short and sturdy trigger hairs.
- within a second of hairs being triggered, leaves close around the prey. Internal portion of leaves secretes enzymes to digest the insect

Motile: Brown-throated three-toed sloth
- organism that can move from place to place
- Tree dwelling and herbivorous
- have 3 long toes adapted to hang from branches, but these adaptations make it very hard to move on the ground

Question 2

Describe how a sarcomere contracts by the sliding of actin and myosin

Answer 2

Sacromeres are placed along myofibrils, and are attached to each other end to end. When one saarcomere contracts, all sarrcomeres in the same muscle contract.

Sarcomeres are made if myosin and actin
- Upon contraction, myosin remains stationary and the 2 sides of the actin move towards the centre of the sarcomere.
- the myosin has moveable heads that interact with the actin to accomplish this, using ATP.

Question 3

Describe the role of titin and antagonistic muscles in muscle relaxation

Answer 3

Muscles the accomplish opposite movements are antagonisitc.
- titin is a protein that helps in muscle relaxation, having multiple folds that allow it to act as a spring
- when sarcomeres shorten during contraction, the 2 sides of each sarcomere move towards the centre = spring-like tension in titin created that is released when muscle relaxes.
- titin also holds myosin fibres in place in the sarcomere and prevents muscle fibres overstretching

• as a muscle can only exert a force upon contraction, antagonistic muscles are needed to accomplish opposite movements.

Question 4

Describe the structure and function of motor units in skeletal muscle

Answer 4

neuromuscular junctions:
- a synapse where a chemical message from the brain (by electrical impulse) is sent into the muscle tissue to stimulate a contraction

Motor fibres:
- control movement by contraction
- are part of a motor unit along with a motor neuron

Motor neurons:
- neurons that carry chemical message to muscle tissue
- has a set no. of muscle fibres that it controls
- if low intensity is needed, a relatively low no. of motor neurons are activated.

Question 5

Diff btwn arthropods and vertebrates in terms of skeletal structure

Answer 5

Arthropods have exoskeletons made of chitin. As the skeleton is on the outside, the muscle attachement points are inside the hollow skeleton

Vertebrates have an endoskeleton made of bones, muscles are attached at the bones at various points to allow the movements characteristic of that animal.

Question 6

Role of skeletons in movement/muscle contraction

Answer 6

• Many individual bones/segments act as levers to maximise efficiency for a variety of movements.
• these levers lower the force necessary to accomplish work
• arthropods with their exoskeletons often take full advantage of leverage, having jointed body parts, with antagonisitc muscle pairs attached.

Question 7

Describe synovial joints and their adaptations + example

Answer 7

Synovial joints are when 2 bones need to move against each other, allowing for a wide range of motion

• e.g. the head of a FEMUR forms a ball that fits into a rounded socket in the PELVIS = ball-and-socket joint

Adaptations:
- Cartilage, a smooth protective connective tissue that covers both bones to avoid bone on bone contact
- Synovial fluid acts as a lubricant to reduce friction
- Ligaments are tough and fibrous to hold the bones in place but allow a range of motion
- Tendons are connective tissue that connects the muscles of the synovial joint to their appropriate bones
- Muscle tissues contract and relax to enable (antagonistic) movement

Question 8

Example of antagonistic muscle action to facilitate internal body movements

Answer 8

Intercostal muscles lie btwn each pair of ribs, using the ribs as their origin and insertion points.
- the angle of the internal intercostal muscles are almost oppposite to those of the external intercostal muscles, even though both sets use the attachment of the ribs to the vertebrae as the fulcrum point
- When external intercostal muscles contract, the rib cage is pulled upwards and out (inspiration)
- When antagonisitic internal intercostal musles contract, the ribcage moves down and inwards (expiration)
- When the external intercostal muscles contract, the expansion of the ribcage results in the stretching of the internal intercostal muscles, streching the titin fibres in each sarcomere, creating potential energy for the contraction of the internal intercostal muscles. Vice versa for expiration

Question 9

Describe the needs for locomotion (5) + 1 example of each

Answer 9

Foraging for food (honey bee)
Escape danger (flying fish)
Search for mate (loggerhead sea turtle)
Migration (arctic tern)
Dispersal (hoary bat)

Question 10

Adaptations for swimming in marine animals

Answer 10

e.g. dolphins:
Streamlining = move through viscous water with ease

Limbs to flippers = steering

tail adapted to form a fluke = allows for up-and-down movement for propulsion

Change to the airways = exchange air at periodic intervals with a minimum of the body leaving the water

Can stay underwater for several minutes w/o breathing to make deep dives

Can seal blowhole tightly btwn breaths to that water does not enter airway

Retained mammalian characteristics e.g. being endothermic, producing milk for young, advanced 2-sided circulatory system