Plant Cell Structure and Membrane Dynamics: Key Concepts for Biology

Plant Cell Types

Different categories of cells in plants, each with specific functions.

Cell Wall

A box-like structure surrounding plant cells, providing support and protection.

Protoplasm

The living content of a cell, including the cytoplasm and organelles.

Organelles

Specialized structures within a cell that perform distinct functions.

Epidermis

The outer layer of cells in plants that serves as a barrier against water loss and pathogens.

Epidermal Gland Cells

Cells that produce substances to protect plants from herbivores.

Green Leaf Cells

Cells that perform photosynthesis by converting sunlight, carbon dioxide, and water into carbohydrates.

Vascular Cells

Cells responsible for the transport of water, minerals, and organic molecules throughout the plant.

Petal Cells

Cells that contain pigments to attract pollinators.

Scent Cells

Cells that produce fragrances to attract pollinators.

Dividing Cell Dimensions

A cube-shaped cell measuring 12µm x 12µm x 12µm.

Epidermal Cell of Lily

Flat, paving stone-shaped cells measuring 45µm x 143µm x 15µm.

Photosynthetic Cell in Leaf of Pear

Short cylinder-shaped cell measuring 7.4µm x 55µm.

Weater-conducting Vessel Cell in Oak

Long cylinder-shaped cell measuring 20µm x 60,000µm.

Fiber Cell in Hemp

Cells that provide structural support and strength to the plant.

Intrinsic Proteins

Proteins that are partially immersed in the lipid bilayer of membranes.

Extrinsic Proteins

Proteins located outside the membrane that interact with the lipid bilayer.

Fluid Mosaic Model

A model describing the structure of cell membranes as a dynamic, fluid-like arrangement of phospholipids and proteins.

Monolayer

A single layer of phospholipids formed when poured onto calm water.

Bilayer

A double layer of phospholipids formed when the lipid layer is agitated.

Domains

Small discrete regions formed by proteins interacting with adjacent proteins in membranes.

Membrane Composition

Biological membranes are composed of proteins and two layers of phospholipid molecules, typically in a ratio of 60% proteins and 40% lipids.

Cell Membrane Function

Regulates the passage of molecules into and out of cells and organelles.

Exocytosis

Vesicles release contents outside the cell, used for removing wastes, debris, proteins, polysaccharides, and mucilage.

Endocytosis

Outer membrane invaginates, then pinches off to form a vesicle, capturing extracellular material, common for algae and microscopic organisms for food uptake.

Selective Permeability

Allows certain substances to pass more easily than others; hydrophobic substances pass through more readily than charged ones.

Facilitated Diffusion

Uses large intrinsic proteins that form hydrophilic channels, helping charged substances cross the membrane without energy.

Active Transport

Involves molecular pumps that bind and transport substances using energy (ATP), allowing cells to accumulate substances against a concentration gradient.

Compartmentalization

Essential for organizing different cellular processes; each membrane-enclosed compartment can specialize in specific functions.

Membrane Fusion

Allows transport of materials within the cell; vesicles fuse with target membranes, contributing to membrane growth.

Plasma Membrane

Outermost boundary of protoplast, selectively permeable, controlling what enters and exits.

Impermeable Membrane

Nothing passes through; no biological membrane is impermeable to everything.

Freely Permeable Membrane

Virtually anything can pass through.

Selectively Permeable Membrane

Certain substances pass through rapidly, others pass through slowly.

Facilitated Diffusion (Definition)

The presence of large intrinsic membrane proteins allows hydrophilic, charged molecules to diffuse through the membrane.

Active Transport (Definition)

Large intrinsic membrane proteins bind a molecule and force it through the membrane, consuming energy in the process.

Glycoproteins

Proteins that have one or more oligosaccharide chains (glycans) covalently attached to them.

Glycolipids

Lipids with a carbohydrate (sugar) molecule attached.

Oligosaccharides

Short-chain sugars, each with about 4-15 sugar residues.

Hydrophobic Substances

Substances that pass through the membrane more readily than charged ones.

Charged Substances

Require assistance to cross the membrane.

Vesicle Lumen

Can carry substances to be processed at the destination.

Giant Cells

Plant cells tend to be larger than animal cells but both types are usually microscopic.

Unusual Cells

Many plant cells die as a necessary part of their development.

Flagella

Sperm cells of plants such as mosses, ferns, and some seed plants that swim.

Nucleolus

Site of ribosome assembly.

Central Vacuole

Stores water, ions, pigments, waste; regulates cell expansion via turgor pressure; has a digestive role breaking down aging organelles.

Tonoplast

The membrane surrounding the central vacuole, impermeable to stored waste.

Eukaryotic Cells

Cells that have a nucleus and membrane-bound organelles, found in plants, animals, fungi, and protists.

Prokaryotic Cells

Simpler cells that do not have a nucleus or membrane-bound organelles, found in Domain Bacteria and Domain Archaea.

Cytoplasm

Everything in protoplasm except the nucleus and vacuole, includes cytosol and all other organelles.

Mitochondria

Site of cellular respiration, converts sugars to ATP, has its own DNA and ribosomes.

Ribosomes

Site of protein synthesis, can be free in cytosol or bound to the endoplasmic reticulum.

Endoplasmic Reticulum (ER)

Double-membrane organelles involved in membrane production and the synthesis of proteins (Rough ER) and lipids (Smooth ER).

Plastids

Double-membrane organelles that contain circular DNA and are primarily responsible for photosynthesis.

Dictyosomes (Golgi Bodies)

'Factories' of plant cells that modify and package vesicle contents and secrete via exocytosis.

Microbodies

Small, single-membrane organelles present in almost all plant cells, including peroxisomes and glyoxysomes.

Cytosol (Hyaloplasm)

Gel-like matrix with water, enzymes, and molecules, containing free ribosomes, microtubules, and microfilaments.

Plasmodesmata

Channels between plant cells that allow cytoplasmic and membrane continuity and enable intercellular communication.

Microtubules

Tubes made of tubulin dimers that form the cytoskeleton, direct organelle movement, and are involved in cell division.

Microfilaments

Made of actin, thinner than microtubules, involved in movement and shape changes.

Chloroplasts

Plastids responsible for photosynthesis, containing grana (stacks of thylakoids).

Amyloplasts

Plastids that store starch.

Chromoplasts

Plastids that contain colored lipids.

Leucoplasts

Colorless plastids involved in lipid synthesis.

Etioplasts

Intermediate form of plastids before chloroplasts in dark-grown tissue.

Proplastids

Plastids of young, rapidly dividing cells.