Comprehensive Notes on Support and Movement
Concept and Need for Support and Movement
Animals and plants exhibit various physical and biochemical activities to sustain life.
Locomotion Difference: A primary distinction is that animals show movement (locomotion) while plants are generally fixed.
Gravity Resistance: Both must support themselves against the force of gravity.
Plant Support Cells:
Collenchymatous cells: Provide support to young/baby plants.
Sclerenchymatous cells: Provide support to adult plants.
Animal Support structures: Muscles, cartilage, and bones provide the framework necessary to move toward food, seek shelter, and escape danger.
Support in Plants
The stem acts as a central support and a supply line between roots and aerial parts.
Parenchyma Cells: Found in the epidermis, cortex, and pith. These cells take in water by osmosis, generating an internal hydrostatic pressure called turgor pressure.
Turgor Pressure Significance: Keeps cells rigid and resistant to bending. If turgidity is lost, herbaceous stems wilt. It is essential for maintaining plant structure.
Mechanical Stress: Terrestrial plants face wind stress. To resist bending, they use specialized tissues:
Vascular Bundles: Contain xylem which is tough and inextensible, acting like steel rods in reinforced concrete.
Ring Arrangement: The circular arrangement of vascular bundles provides effective resistance to wind and weight-bearing capability.
Bundle Caps: In plants like the sunflower, additional sclerenchyma fibers strengthen the vascular bundles.
Specialized Plant Tissues providing Support
Sclerenchyma Cells:
Characteristics: Thick secondary cell walls impregnated with lignin (a hard, organic substance). Most are non-living at maturity.
Fibers (Tracheids): Long, cylindrical cells existing as bundles in xylem or bundle caps.
Sclereids: Shorter than fibers; found in seed coats and nut shells for protection.
Vessels (Tracheae): Long tubular structures joined end-to-end for water conduction in xylem.
Collenchyma Cells:
Characteristics: Possess protoplasts; lack secondary walls. They have angular thickening in primary walls made of pectin and cellulose.
Location: Grouped in strands or cylinders just below the surface of young stems.
Function: Elastic support that elongates with the growth of stems and leaves.
Mechanism of Turgor: Turgor pressure is generated by the high osmotic pressure of the cell vacuole. The tonoplast (vacuole membrane) uses active transport systems to pump ions into the vacuole. This high ionic concentration draws water in, providing mechanical support to soft tissues.
Secondary Growth in Plants
Definition: An increase in plant girth due to the activity of vascular cambium and cork cambium.
Vascular Cambium: A cylinder of dividing cells between primary xylem and phloem. It produces:
Secondary Xylem: Formed on the inner surface; responsible for most thickness increases.
Secondary Phloem: Formed on the outer surface.
Growth Rings: One ring of secondary xylem is typically formed per year. Counting these at the base of the trunk indicates the tree's age.
Wood Types:
Sapwood: The outer, younger portion of secondary xylem active in water conduction.
Heartwood: The inactive, non-conducting inner wood. It accumulates chemicals (resins, oils, gums, tannins) that resist decay and insect attack (e.g., in red cedar and conifers).
Callus Formation: Cambium forms soft parenchymatous tissue (callus) over wounds on stems or roots. It also facilitates the union of branches during budding and grafting.
Commercial Use: The bark of trees like Quercus suber is used to make commercial cork.
Movement in Plants
Types of Movements:
Autonomic Movements: Spontaneous movements due to internal causes.
Paratonic Movements: Movements due to external stimuli.
1. Autonomic Movements
Tactic Movements: Locomotion of an entire cell or organism.
Phototactic: Response to light. Positive example: Passive movement of chloroplasts due to cyclosis to maximize light absorption for fixation.
Chemotactic: Response to chemicals. Example: Sperms of liver-worts, mosses, and ferns moving toward archegonia due to nucleic acids released by the ovum.
Turgor Movements: Due to differential changes in turgor and cell size.
Sleep Movements: Leaves lowering in the evening and raising in the morning (e.g., beans/legumes). Controlled by the pulvinus (swollen petiole base). High turgor on the lower side of the pulvinus raises leaves.
Rapid Movements: Mimosa (sensitive plant) leaflets fold in seconds when touched. This is caused by ions moving out of pulvinus cells, followed by water loss via exosmosis. Recovery takes about 10 minutes.
Growth Movements: Due to unequal growth on two sides of an organ.
Epinasty: Upper surface grows more (buds open).
Hyponasty: Lower surface grows more (buds remain closed).
Nutation: Zig-zag growth of the young stem tip due to alternating growth on opposite sides of the apex.
2. Paratonic Movements
Tropic Movements (Tropos: Turn): Curvature toward or away from stimuli.
Phototropism: Response to light (stems positive, roots negative).
Thigmotropism: Response to touch (e.g., climbing vines coiling around supports).
Chemotropism: Response to chemicals (e.g., fungal hyphae).
Hydrotropism: Response to water (roots positive).
Geotropism: Response to gravity (roots positive, shoots negative).
Nastic Movements: Non-directional responses.
Nyctinasty: Response to external stimuli like light/temp.
Photonasty: Principal stimulus is the photoperiod (flowers opening/closing).
Thermonasty: Intensity of temperature (e.g., tulip flowers closing at night).
Haptonastic: Occurs in response to contact (e.g., Venus flytrap action).
Role of Plant Growth Substances
Auxins (IAA):
Control phototropism by unequal distribution, causing unequal cell enlargement.
Mediate gravitropism: High auxin concentration inhibits root cell growth (curves down) but stimulates stem cell growth (curves up).
Hormonal Ratios: Nastic movements depend on the balance between growth inhibitors (abscisins) and stimulators (gibberellins). Epinasty is linked to auxins; hyponasty to gibberellins.
Support and Movements in Animals
The skeleton is a tough, rigid framework providing protection, shape, and support.
Types of Skeletons:
1. Hydrostatic Skeleton
Found in soft-bodied invertebrates (cnidarians, annelids).
Mechanism: A fluid-filled gastrovascular cavity or coelom acts as support.
Sea Anemone: Constricts circular muscles against fluid in the body cavity to maintain upright stature.
Earthworm: Fluid compartments separated by septa. Circular muscle contraction elongates segments; longitudinal contraction shortens them. Waves of these contractions, aided by setae, move the animal through soil.
2. Exoskeleton
Hardened outer covering secreted by the ectoderm.
Structure:
Epicuticle: Outermost waxy lipoprotein layer; water-impermeable.
Procuticle: Bulk of the skeleton; consists of exocuticle and endocuticle. Made of chitin and proteins.
Modifications: Hardened by sclerotization or calcium carbonate impregnation. Contains joints for movement and sensilla (sensory receptors).
Molluscan Shells: Composed of one or two pieces (e.g., snails, bivalves); grow with the animal.
Arthropod Ecdysis (Moulting): Necessary for growth. Processed in 4 stages:
Enzymes digest endocuticle to separate hypodermis from exoskeleton.
Old exoskeleton splits.
New procuticle and epicuticle are secreted.
New skeleton hardens with calcium carbonate (controlled by the hormone ecdysone).
3. Endoskeleton
Made of bone and cartilage (rigid connective tissues).
Bone: Most rigid; collagen fibers hardened by calcium phosphate.
Compact Bone: Outer dense shell for muscle attachment.
Spongy Bone: Interior, porous, rich in blood vessels; contains bone marrow.
Bony Cells: Osteoblasts (forming), Osteocytes (mature), Osteoclasts (dissolving/remodeling).
Cartilage: Softer, non-vascular; living cells are chondrocytes.
Hyaline: Most abundant; found at movable joints.
Elastic: Bundles of collagen; forms pinnae of ears and epiglottis.
Fibrocartilage: Found in intervertebral discs.
Human Skeleton
1. Axial Skeleton
Skull:
Cranium (8 bones): Parietal and temporal (paired); frontal, occipital, sphenoid, ethmoid (unpaired).
Facial (14 bones): Maxilla, zygomatic, nasal, lacrimal, palatine, inferior concha (paired); mandible and vomer (unpaired).
Vertebral Column: 33 vertebrae with 4 curvatures.
Cervical: 7 (Neck region; includes Atlas and Axis).
Thoracic: 12.
Lumbar: 5.
Pelvic: 9 (Sacrum [5 fused] and Coccyx [4 fused]).
Rib Cage: 12 pairs of ribs articulate with thoracic vertebrae. 10 pairs connect to the sternum; the lower 2 pairs are floating ribs.
2. Appendicular Skeleton
Pectoral Girdle and Forelimb:
Girdle: Scapula, suprascapula, clavicle.
Limb: Humerus, radius, ulna, 8 carpals (wrist), 5 metacarpals (palm), 14 phalanges (fingers).
Pelvic Girdle and Hindlimb:
Girdle: Two coxal bones, each formed by the fusion of ilium, ischium, and pubis.
Limb: Femur (proximal), patella (kneecap), tibia and fibula (parallel bones), 7 tarsals (ankle), 5 metatarsals, 14 phalanges (toes).
Joints
Mobility Classification:
Immovable: No movement allowed.
Slightly Movable: Minimal movement.
Freely Movable: Includes Hinge and Ball and Socket joints.
Structural Classification:
Fibrous: Held by short collagen fibers (e.g., skull, teeth in jaw).
Cartilaginous: Hyaline or fibrous cartilage (e.g., vertebrae, pubic symphysis).
Synovial: Contains fluid-filled cavity, fibrous capsule, and synovial membrane. Ligaments hold bones together.
Hinge Joint: Moves in two directions (elbow, knee).
Ball and Socket Joint: Moves in several directions (hip, shoulder).
Skeletal Deformities and Repair
Genetic Causes: Cleft palate (maxilla/palatine failure to fuse), Microcephaly (small skull), Osteoarthritis.
Hormonal Causes: Osteoporosis (reduced bone mass, common in aged women with low estrogen). Treated with Estrogen Replacement Therapy (ERT).
Nutritional Causes:
Osteomalacia: Inadequate mineralization causing soft bones.
Rickets: Childhood disease; bowed legs due to Vitamin D or Calcium deficiency.
Disc Slip: Herniation of the nucleus pulposus through the annulus fibrosus, causing nerve pain.
Sciatica: Stabbing pain along the sciatic nerve due to injury or disc slip.
Fracture Repair:
Reduction: Closed (manual) or Open (surgery/pins).
Healing Phases:
Hematoma Formation: Blood clot, cell death, swelling.
Soft Callus Formation: (3-4 weeks) Capillaries clear debris; fibroblasts/osteoblasts build tissue.
Bony Callus Formation: (2-3 months) Hard bony union formed.
Remodeling: Excess material removed; bone resembles original shape.
Muscles and Myofilaments
Three Muscle Types:
Smooth: Visceral, non-striated, single nucleus, spindle-shaped, involuntary (e.g., digestive tract).
Cardiac: Striated, branched, single nucleus, involuntary (heart mass).
Skeletal: Striated, multinucleated, cylindrical, voluntary (attached to bones via tendons).
Ultrastructure of Skeletal Muscle:
Sarcomere: Segment between two Z-lines; the unit of contraction.
A-band: Dark, anisotropic, contains H-zone (bisected by M-line).
I-band: Light, isotropic, bisected by Z-line.
Myofilaments:
Thick Filaments (): Composed of myosin with globular heads (cross bridges).
Thin Filaments (): Composed of actin molecules, tropomyosin, and troponin (3 polypeptide complex).
Sliding Filament Model: During contraction, actin slides past myosin. I-band shortens, H-zone disappears, Z-lines move closer.
Contraction Control:
Nerve impulse reaches neuromuscular junction.
T-system (T-tubules) carries impulse to Sarcoplasmic Reticulum (SR).
SR releases .
binds to troponin, displacing tropomyosin and exposing binding sites on actin.
Myosin heads attach, hydrolyzing ATP for power stroke.
Rigor Mortis: After death, ATP depletion prevents cross bridge detachment, causing stiffness.
Energy: ATP from aerobic glucose breakdown or creatine phosphate. Anaerobic breakdown produces lactic acid, causing muscle fatigue.
Muscle Disorders and Locomotion Modes
Tetany: Low blood Calcium; leads to excitability, twitches, and spasms.
Tetanus: Infectious disease caused by Clostridium tetani; causes persistent painful spasms (lock jaw).
Cramps: Tetanic contraction due to low blood sugar, electrolyte depletion, or dehydration.
Muscle Arrangement:
Antagonism: Pair of muscles working oppositely (e.g., Biceps [flexor] and Triceps [extensor]).
Biceps Brachii: Arises from scapula (origin) and inserts into radius (insertion).
Locomotion in Mammals:
Plantigrade: Walking on soles/wrists (Man, bears).
Digitigrade: Walking on digits (Rabbits, rodents).
Unguligrade: Walking on tips of toes/hoofs (Deer, goats).
Locomotion in Air: Birds use passive flight (gliding as aerofoils) or active flight (flapping). Pectoral muscles attach to the massive keel of the sternum.