Plant and Human Support Systems

Support and Movement Overview

• Lecture 1 introduces support systems.
• Lecture 2 covers structure and function of the human skeletal system.
• Lecture 3 is about skeletal muscles.
• Spring lecture discusses neurological control of movement by Dr. Emma Ynell.

Key Concept

• Hollow tubes are structurally stronger when compared to solid tubes of the same mass.

Plant Support

• Support in plants exists at the cellular, tissue, and gross level.

Cellular Support - Turgor Pressure

• Turgor pressure is the pressure exerted by the cell vacuole on the cell wall.
• Wilting is the result of plasmolysis.

Plant Structure

• The shoot system and the root system both play a role in supporting the plant.

Basic Stem Morphology

• Epidermis is the outermost layer of the stem.
• Cortex is the tissue found beneath the epidermis.
• Pith is the central tissue in the stem.
• Vascular bundles consist of xylem and phloem.

Pith - Parenchyma

• Pith is composed of parenchyma cells.
• Parenchyma cells have thin cell walls.
• Vacuole size increase results in an increase in cell size.

Cortex - Collenchyma

• Collenchyma cells have a primary wall with some thickening.
• Collenchyma provides flexibility, which allows bending.

Pith/Cortex Relationship

• Pith and cortex work together.
• Parenchyma presses on collenchyma.
• The relationship between the Pith and Cortex is like a 'Pneumatic Tire'.

Vascular Bundles

• Xylem consists of hollow tubes.
• Apoptosis is a cell wall for water transport.
• Vascular bundles are surrounded by sclerenchyma.
• Sclerenchyma has a thick secondary cell wall.
• Sclerenchyma provides rigidity and elasticity, allowing return to original shape after deformation.

Root System

• Lateral roots primarily absorb water and dissolved minerals.
• Primary root acts as tap root for anchorage and stability.

Skeletal Systems in Animals

• Animals use hydrostatic skeletons, exoskeletons, and endoskeletons as support systems.

Hydrostatic Skeletons

• Earthworms have hydrostatic skeletons.
• A capsule of fluid is surrounded by 2 muscle layers which are circular and longitudinal.
• The fluid filled cavity acts as a rigid column that the muscles act on.
• Contraction of circular muscles elongates and narrows the body.
• Contraction of longitudinal muscles shortens and thickens the body.
• Segmental contraction of muscles and anchorage by bristles drives the body forwards for burrowing.

Exoskeleton

• Mollusks like clams and mussels have exoskeletons.
• Arthropods like insects and crabs have exoskeletons.
• The hard outer surface as protection for the soft tissues acts as armor.
• Arthropods have exoskeletons that offer strength and mobility and allow a site for muscle attachment to create movement
• Arthro = 'joint' and podia = 'foot'
• Chitin is a polysaccharide.
• Exoskeletons are strong and light.
• Exoskeletons have mineralization providing hard, protective armor.
• Exoskeletons are thin and flexible at joints.
• Limitations of exoskeletons include risk of being crushed and the need to molt in order to grow in line of body = molting (ecdysis) which causes a period of potential vulnerability until it hardens.

Endoskeleton - Vertebrates

• Endoskeletons provide a rigid system for muscle contraction and protection of vital organs.
• Endoskeleton structures are cartilaginous or bony.
• Cartilaginous fishes (Chondrichthyes) have endoskeletons.
• Cartilage may be calcified (must be thin), and is efficient and flexible.
• Bony endoskeletons support weight of large animals on land.
• Bony structures provides rigid support against gravity.
• Bony skeletons develop from a cartilaginous skeleton.
• Bony skeletons have levers which can be moved by muscles.
• They are dynamic and respond to physiological loading.

Bone - Gross Structure

• Bones are not solid, having a central (medullary) cavity.
• This reduces weight and adds strength in resisting compression and tension.

Bone - Microscopic Structure

• Bone contains living cells in a mineralized extracellular matrix.
• These are arranged into columns around an artery called osteon.
• Bone matrix comprises circumferential lamellae, osteons, vein, artery, venule, central canal, and perforating canal.

Take Home Message

• Depending on size different types of systems are present to provide efficient and effective support.
• Plants and animals both use hollow tubes as a mechanism of support.