Cell Structure, Plant Cells, and Cell Transport: Review Study Notes

Cell Structure and Function

Mitochondria

The mitochondria are membrane-bound organelles known as the "powerhouses" of the cell. They are responsible for producing ATP through cellular respiration.

• Endosymbiotic theory: Proposes that mitochondria originated from free-living prokaryotes that were engulfed by ancestral eukaryotic cells, leading to a symbiotic relationship.

• Maternal DNA: Mitochondria contain their own DNA, which is inherited maternally.

Cytoskeleton

The cytoskeleton provides structural support, facilitates cell movement, and organizes cell components.

• Microfilaments (actin): Thin filaments involved in cell movement and shape changes.

• Microtubules: Hollow tubes that maintain cell shape, enable intracellular transport, and form the spindle during cell division.

• Intermediate filaments: Provide mechanical support for the cell.

• Motor proteins: Such as myosin, kinesin, and dynein, move along cytoskeletal filaments to transport cellular cargo.

Examples of cytoskeletal functions:

• Muscle contraction: Involves actin and myosin filaments sliding past each other.

• Cytoplasmic streaming: Movement of cytoplasm within cells, aiding in distribution of materials.

• Flagella and cilia: Structures composed of microtubules that enable cell movement or move substances across cell surfaces.

• Nuclear lamina: A network of intermediate filaments supporting the nuclear envelope.

Plant Cells

Unique Structures in Plant Cells

• Chloroplasts: Organelles where photosynthesis occurs, containing the pigment chlorophyll.

• Central vacuole: Large organelle that stores water, nutrients, and waste products; helps maintain turgor pressure.

• Cell wall: Rigid outer layer made of cellulose that provides structural support and protection.

• SAV (Surface Area to Volume) ratio in plant cells: Influences the rate of transport of materials into and out of the cell; a higher ratio allows for more efficient exchange.

Cell Transport

Plasma Membrane Structure and Function

• Fluid Mosaic Model: Describes the plasma membrane as a dynamic structure with proteins floating in or on a fluid lipid bilayer.

• Phospholipid bilayer: Composed of two layers of phospholipids with hydrophilic heads facing outward and hydrophobic tails inward.

• Selective permeability: The membrane allows some substances to pass more easily than others.

Transport Mechanisms

• Passive transport: Movement of substances across the membrane without energy input.

  • Diffusion: Movement of molecules from high to low concentration.

  • Osmosis: Diffusion of water across a selectively permeable membrane.

  • Facilitated diffusion: Movement of molecules across membranes via transport proteins.

• Active transport: Movement of substances against their concentration gradient, requiring energy (ATP).

• Transport proteins: Proteins that assist in the movement of substances across the membrane (e.g., channels, carriers, pumps).

Osmosis and Solutions

• Isotonic solution: Solute concentration is equal inside and outside the cell; no net water movement.

• Hypotonic solution: Lower solute concentration outside the cell; water enters the cell, which may cause it to swell.

• Hypertonic solution: Higher solute concentration outside the cell; water leaves the cell, causing it to shrink.

Lab: Cell Lab

• Experiments may include observing osmosis in plant cells, examining cell structures under a microscope, and testing membrane permeability.

Additional info:

• Equation for Osmosis:

$J = -P (C_2 - C_1)$

• Where J is the flux, P is the permeability coefficient, and C_2 - C_1 is the concentration difference across the membrane.