Plant Cell Structure and Function

Plant Cell Structure and Function

• Plant cells are the basic building blocks of plant structure, playing critical roles in processes like gas exchange, water transport, photosynthesis, and ion transport.

• Plant structure and function are interconnected, with structure enabling function.

Plant Body Plan

• Seed plants have a consistent body plan with three primary organs: leaves (photosynthesis), stems (support), and roots (anchorage, water/mineral uptake).

• Leaf attachment occurs at nodes, with internodes being the stem sections between successive nodes. The shoot is the stem combined with its leaves.

• Two main seed plant categories are gymnosperms (naked seeds), exemplified by conifers (pine, fir, etc) and angiosperms (enclosed seeds) which are the dominant flowering plants.

• Plant growth occurs in specialized cell division zones called meristems, particularly apical meristems at shoot and root tips, and axillary buds.

Plant Cell Walls

• Plant cells differ from animals in being surrounded by rigid cell walls that facilitate vertical plant growth and support.

• Cell growth is restricted by adjacent cells interconnected via the middle lamella.

• There are two types of cell walls: primary (thinner, young growing cells) and secondary (thicker, stronger, and often lignified, for support).

Biological Membranes

• Plant membranes are phospholipid bilayers containing proteins.

• Phospholipids are amphipathic, meaning they have both hydrophilic (polar) and hydrophobic (nonpolar) regions. Plant membranes use unsaturated fatty acids to maintain fluidity under variable temperatures.

• Membrane proteins (integral, peripheral, and anchored) are responsible for selective traffic across the membrane and performing other vital cell processes.

The Nucleus

• The plant nucleus is the primary site for genetic material storage and regulation.

• Plant genomes vary significantly in size, with some being larger than others.

• DNA is organized into chromatin, a complex with proteins.

• Nucleosomes are fundamental packaging units in which DNA is coiled around histone proteins.

• The nucleus contains the nucleolus, a site for ribosome synthesis containing rRNA genes.

The Cytoplasm

• The endoplasmic reticulum (ER) is an extensive internal membrane network consisting of smooth and rough forms.

• Smooth ER is involved in lipid synthesis and membrane assembly.

• Rough ER plays a crucial role in protein synthesis and secretion for extracellular use and vacuoles.

Golgi Apparatus

• The Golgi apparatus, or Golgi body, is a stack of cisternae (flattened membrane sacs) involved in post-translational processing of proteins and the synthesis of polysaccharides.

• Plants may have hundreds of Golgi bodies distributed throughout the cytoplasm.

• Glycoproteins experience further modifications to get targeted to their correct location.

Central Vacuole

• The central vacuole is a large, water-filled compartment in mature plant cells, contributing substantially to cell volume.

• The vacuole is enclosed by the tonoplast, managing the contents within the vacuole.

• Both water and solutes are present in the vacuole.

Other Structures

• Protein bodies store proteins.

• Lytic vacuoles have enzymes for hydrolysis of macromolecules.