Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The cell envelope in prokaryotes is a chemically complex three-layered structure consisting of the outermost glycocalyx, followed by the cell wall and then the plasma membrane.
Bacteria are classified into Gram-positive and Gram-negative based on the differences in their cell envelopes and the manner in which they respond to the staining procedure developed by Christian Gram using .
The glycocalyx differs in composition and thickness; it can be a loose sheath called the slime layer or a thick and tough layer called the capsule.
The Fluid Mosaic Model, proposed by Singer and Nicolson (1972), describes the plasma membrane as a 'quasi-fluid' where lipids and integral proteins are arranged in a mosaic fashion.
The plasma membrane is composed of a lipid bilayer, mainly , with proteins and carbohydrates interspersed. The polar heads face outwards and the hydrophobic tails face inwards to ensure the non-polar tail of saturated hydrocarbons is protected from the aqueous environment.
Membrane proteins are classified as peripheral (on the surface) or integral (partially or totally buried in the membrane). In human erythrocytes, the membrane has approximately protein and lipids.
The cell wall is a non-living rigid structure that forms an outer covering for the plasma membrane of fungi and plants. It provides shape, protection from mechanical damage, and helps in cell-to-cell interaction.
The plant cell wall is composed of , , , and proteins. Algae have cell walls made of , , , and minerals like .
The middle lamella is a layer mainly composed of () which holds or glues the different neighboring cells together.
📐Formulae
💡Examples
Problem 1:
A researcher observes a plant cell and notices a layer that disappears as the cell matures and the secondary wall is formed. Identify this layer and its primary component.
Solution:
The layer is the Primary Cell Wall.
Explanation:
In a young plant cell, the primary wall is capable of growth. As the cell matures, this capability diminishes and the secondary wall is formed on the inner (towards membrane) side of the cell. The primary wall is mainly composed of fibers.
Problem 2:
Explain the significance of the hydrophobic nature of the lipid tails in the thick plasma membrane.
Solution:
Protection of saturated hydrocarbons from the aqueous environment.
Explanation:
The plasma membrane lipids are arranged in a bilayer. The hydrophobic tails of the are sequestered in the interior of the membrane to avoid contact with in the intra- and extra-cellular fluids.
Problem 3:
What is the specific function of plasmodesmata in the cell wall structure?
Solution:
Cytoplasmic bridge between cells.
Explanation:
The cell wall and middle lamellae may be traversed by which connect the cytoplasm of neighboring cells, allowing for the transport of molecules and communication.