Transport Mechanism of Plant Cells

• Active flight


  • Requires wings that develop enough lift to overcome the downward force of gravity
• Flying animals


  • Have adaptations that reduce body mass
• Adaptations in birds


  • No urinary bladder or teeth
  • Relatively large bones with air-filled regions
• Locomotion on land


  • Requires an animal to support itself and move against gravity
  • Diverse adaptations have evolved in vertebrates
• Walking, running, hopping, or crawling on land

  • Maintaining balance is a prerequisite
  • Crawling animals must exert energy to overcome friction
  • Air poses relatively little resistance
• Endoskeleton


  Hard internal skeleton, buried in soft tissue
• Organisms with endoskeletons


  • Ranging from sponges to mammals
• Mammalian skeleton


  • Has more than 200 bones
  • Some bones are connected at joints by ligaments that allow freedom of movement
• Types of joints


  • Ball-and-socket
  • Hinge
  • Pivot
• Exoskeleton


  Hard encasement deposited on the surface of an animal
• Arthropod exoskeleton


  • Jointed, called a cuticle, can be both strong and flexible
  • Chitin is often found in arthropod cuticle
• Hydrostatic skeleton


  Consists of fluid held under pressure in a closed body compartment
• Organisms with hydrostatic skeletons


  • Cnidarians, flatworms, nematodes, and annelids
• Peristalsis


  A type of movement produced by rhythmic waves of muscle contractions from front to back
• Types of skeletal systems

  • Hydrostatic skeletons
  • Exoskeletons
  • Endoskeletons
• Skeletal systems


  • Transform muscle contraction into locomotion
  • Skeletal muscles are attached in antagonistic pairs, the actions of which are coordinated by the nervous system
  • The skeleton provides a rigid structure to which muscles attach
• Cardiac muscle


  Found only in the heart, consists of striated cells electrically connected by intercalated disks, can generate action potentials without neural input
• Smooth muscle


  Found mainly in walls of hollow organs such as those of the digestive tract, contractions are relatively slow and may be initiated by the muscles themselves or caused by stimulation from neurons in the autonomic nervous system
• Types of skeletal muscle fibers

  • Slow oxidative
  • Fast oxidative
  • Fast glycolytic
• Slow-twitch fibers


  • Contract more slowly but sustain longer contractions, are all oxidative
• Fast-twitch fibers


  • Contract more rapidly but sustain shorter contractions, can be either glycolytic or oxidative
• Oxidative fibers


  • Rely mostly on aerobic respiration to generate ATP, have many mitochondria, a rich blood supply, and a large amount of myoglobin
• Glycolytic fibers


  • Use glycolysis as their primary source of ATP, have less myoglobin than oxidative fibers and tire more easily
• Myoglobin


  A protein that binds oxygen more tightly than hemoglobin does
• Poultry and fish


  • Light meat is composed of glycolytic fibers, while dark meat is composed of oxidative fibers
• The theoretical yield of ATP from glucose is 36
• Twitch


  Results from a single action potential in a motor neuron
• Summation


  More rapidly delivered action potentials produce a graded contraction
• Tetanus


  A state of smooth and sustained contraction produced when motor neurons deliver a volley of action potentials
• Nervous control of muscle tension

  • Contraction of a whole muscle is graded, which means that the extent and strength of its contraction can be voluntarily altered
  • Two basic mechanisms: varying the number of fibers that contract, and varying the rate at which fibers are stimulated
• Motor unit


  Consists of a single motor neuron and all the muscle fibers it controls, produces an action potential that results in all muscle fibers within the motor unit to contract
• Tropomyosin and troponin complex


  Bind to actin strands on thin filaments when a muscle fiber is at rest, preventing actin and myosin from interacting
• Calcium ions (Ca2+)


  Bind to the troponin complex and expose the myosin-binding sites, allowing muscle fiber contraction
• Sliding-filament model of muscle contraction

  1. Thin (actin) and thick (myosin) filaments slide past each other longitudinally

  2. The "head" of a myosin molecule binds to an actin filament, forming a cross-bridge and pulling the thin filament toward the center of the sarcomere

  3. Glycolysis and aerobic respiration generate the ATP needed to sustain muscle contraction
• Vertebrate skeletal muscle


  Also called striated muscle because of the light and dark bands, moves bones and the body, bundle of long fibers running parallel to the length of the muscle
• Sarcomere


  The functional unit of a muscle, bordered by Z lines, made up of myofibrils
• Animals


  Multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers. Most are mobile and use traits like strength, speed, toxins, or camouflage to detect, capture, and eat other organisms.
• Nutritional Mode


  Heterotrophs that ingest their food
• Cell Structure and Specialization of Animals

  • Multicellular eukaryotes
  • Lack cell walls
  • Held together by structural proteins like collagen
  • Nervous tissue and muscle tissue are unique, defining characteristics
• Tissues


  Groups of similar cells that act as a functional unit