Plant Physiology

• Algae are not plants; they lack a vascular system.
• In plants, cells form tissues, tissues form organs, and organs form an organism within an ecosystem.
• Plant cell walls are made of cellulose.
• Osmotic pressure is important in plant cells.
• Plants are multicellular, terrestrial, and photosynthetic organisms.
  • Multicellularity allows for differentiated cells with various functions.
  • Terrestrial plants adapted to cope with very dry air.
  • Photosynthesis converts solar energy into chemical energy.

Plant Physiology

• Abaxial refers to the underside of a plant.
• Adaxial refers to the top of a plant.
• Plant functions are broadly distributed throughout the plant.
• Gas exchange occurs through stomata.
• Energy assimilation occurs in photosynthetic tissues.
• Nutrients are transported through vascular tissues.
• Light perception is facilitated by light receptors.
• Water and nutrient uptake occurs through the root.
• Signals control and coordinate plant function through vascular tissues.
• Support is provided by the cell wall and hydrostatic pressure.
• Control leads to regulation, resulting in a response.
  • Control and regulation can be differentiated by their mode of action within a system.
  • Control enables a system to respond to external perturbations.

Plant Cell Assembly

• Plants are assembled from cells.
• The plasma membrane acts as a barrier, maintains the internal environment, and exhibits selective permeability due to its phospholipid bilayer.
  • It's permeable to water and gases but impermeable to ions and larger molecules.
• The cell wall provides structure and support, preventing unwanted organisms from entering.
  • Only some prokaryotes have cell walls.
• Chloroplasts and mitochondria are organelles that belong to the endomembrane system.
• Oxygenic photosynthesis produces oxygen, while anoxygenic photosynthesis does not.
• Photosynthetic eukaryotes have complex cell structures with organelles, while photosynthetic prokaryotes have simple structures without complex organelles.
• Pectin contributes to cell adhesion and hydration.
• Lignin provides secondary support for extra strength and waterproofing.
• Cell walls maintain cell shape and prevent bursting in hypotonic solutions.
  • They also offer mechanical support for the plant to stand up.
  • Communication occurs through plasmodesmata.
  • The cell wall facilitates turgor pressure, exerted by the cytoplasm and vacuole against the cell wall.
  • The cell wall resists excessive expansion when water enters, maintaining turgor pressure.
  • Transport can also be regulated by the cell wall.

Osmotic Pressure

• Osmotic pressure (π = CRT) is the pressure required to prevent water movement across a semi-permeable membrane due to osmosis.
  • High osmotic pressure causes stomata to open.
  • Low osmotic pressure causes stomata to close and become flaccid.
• Osmosis is the movement of water molecules from a low solute concentration.
• In a hypotonic environment, water enters, increasing turgor pressure.
  • Low outside solute concentration, high inside.
• In a hypertonic environment, water exits, causing shrinkage (plasmolysis) where the cell membrane pulls away from the wall.
  • High outside solute concentration, low inside, but is reversible.
• In an isotonic environment, there is no net water movement as the cell membrane is stable.
• Growth is an increase in plant or organ dimensions over time but it is irreversible.
• Plant cells move water by osmosis and pressure.
• Development consists of identifiable events resulting in qualitative and quantitative changes in plant structure.
  • Plants can adjust their organ number and size.
  • This process includes embryogenesis and organogenesis.
• Morphogenesis is the study of the origin and development of physical form which determines external structure of plants.
  • Anatomy determines morphogenesis.

Cell Primary Wall

• The cell wall consists of interwoven cellulose microfibers.
• Cell walls exhibit heterogeneity and diversity.
• Between primary and secondary cell walls lies the middle lamella, a glue-like layer made of calcium and pectin.
• Glucose forms cellulose microfibrils, which then form fibrils, constructing the cell wall and ultimately the plant cell.
• Hydrogen bonds connect cellulose and hemicellulose.
• Pectins are joined by ionic bonds.
• Water is incompressible.
• Once stretched, cell walls cannot revert to their original size and shape, leading to the addition of new cell wall components.
• Growth occurs perpendicular to the microfibrils but can be random if the microfibrils are arranged randomly.
• Cellulose, proteins, and other components contribute to cell wall structure.

Function of Cell Wall

• Regulates cell growth
• Constrains turgor pressure
• Determines shape, protects from pathogens by Signalling, cell-to-cell communication
• After cell division, the middle lamella forms first, followed by the primary cell wall.
  • Secondary cell walls form when the cell stops growing.
• Cellulose microfibrils form outside the cell with a special enzyme complex, bound in the plasma membrane.
• Pectins come from golgi bodies.
• Cell walls are composed of different carbohydrates to increase resistance against pathogens.
• Tip growth occurs at an isolated part of the cell, while diffused growth occurs throughout the entire cell.
• Isotropic cellulose microfibrils are randomly oriented, while anisotropic cellulose microfibrils are transverse.
• When an object is pulled, there is a certain threshold after which it is irreversible
  • It is Visco-elastic so when it expands, it original shape
• As water comes in more material are deposited
• Turgor pressure must exceed a yield threshold for cell expansion to occur.
  • As pressure increases, the cell wall stretches, allowing growth.
  • This is until no new growth occurs
• When at the stable point = rate of water uptake == rate of cell expansion
  • Means: balanced forces when pressure pushing outward in equilibrium with cell wall resistance
  • Controlled growth allows the cell to expand that a steady rate without rapid changes
  • Equilibrium is reached but there is just eough to maintain growth without over or under growing,
• 1cm from the root tip is were the active cell division happens for differentiation

Cell Division and Meristems

• Regions/zones of active cell division
• Three events: cell division, cellenlargemt, cellular differentiation
• Primary meristems: for embryo development
• Secondary meristems: increase in girth post germination
• Indeterminate: continuously divides andreplenished = it is immortal
• Determinate: an certain size it stops anddies .
• Differentiation: cells develop into specialized cell
• acquision and development
• Communication ○ Symplastically: occurs in plasmodesmata and cell to cellthrough cytoplasm -ongdistance ○ Applastically: thtought walls and extracellular spaceds pid and passive movements
• Auxins can only be from the tip of the plant and downwards
• Protein Kinaves are for signals
• Signals are Temporal and spacial; basedon its position. -Auxim transport occur through flux protein carries
• Plant devlopment, stress response are aregulated by plant horomones