Human Bio Exam 2

Why is being small an advantage to a cell?

• Small cells have less genetic material.
• Smaller cells can store more energy than larger cells.
• Being small increases the risk of damage from external factors.
• Increases surface area-to-volume ratio for efficient nutrient exchange and waste removal.

Structure of a Plasma Membrane

• Phospholipid bilayer, Lipid tails, Cholesterol, Proteins, and Carbohydrate chain

• Phospholipid layer, nonpolar region, polar region, amino acids

• Carbohydrate chains, glucose, citric acid cycle

• Bilipid tails, cholesterol, proteins, amino acids, and carbohydrate chains

Structure of a Plasma Membrane: Phospholipid Bilayer

• Provides membrane stiffness and stability.

•  Hydrophobic; allow passage of small lipid molecules, O₂, and CO₂.

• • Act as gateways, receptors, and structural support.

• Hydrophilic heads face water; hydrophobic tails face inward

Structure of the Plasma Membrane: Lipid Tails

• Lipid tails are found in the cytoplasm and do not interact with the plasma membrane.
• Lipid tails are charged and repel water molecules in the plasma membrane.
• Lipid tails are hydrophilic and form the outer layer of the phospholipid bilayer.
• Hydrophobic; allow passage of small lipid molecules, O₂, and CO₂.

Structure of the Plasma Membrane: Cholesterol

• Cholesterol decreases the permeability of the plasma membrane.
•  Cholesterol provides membrane stiffness and stability.

• Cholesterol is only found in plant cell membranes.
• Cholesterol acts as a barrier to all substances in the plasma membrane.

Structure of the Plasma Membrane: Proteins

• Proteins are absent in the plasma membrane structure.
• Proteins act as gateways, receptors, and structural support.

• Only peripheral proteins are involved in membrane functions.
• The plasma membrane is composed solely of lipids.

Structure of the Plasma Membrane: Carbohydrate Chain

• Carbohydrate chains are attached to proteins and lipids on the extracellular side of the plasma membrane.
• Carbohydrate chains are not associated with proteins or lipids in the plasma membrane.
• Carbohydrate chains are found only on the intracellular side of the plasma membrane.
• Carbohydrate chains are primarily responsible for the transport of molecules across the plasma membrane.

Passive Transport

• Movement of molecules across the membrane without energy.

• Movement of substances against their concentration gradient.

• Allows accumulation of necessary molecules or expulsion of unwanted ones.

•  Vesicles fuse with the membrane to release substances outside the cell.

Three Passive Transport Methods

• Diffusion, Osmosis Facilitated Diffusion

• Exocytosis, Endocytosis, Vesicles

• Lipid layer, protein channels, facilitated transport

• Lipid tails, cholesterol, carbohydrate

Passive Transport Method: Diffusion

• 1. Diffusion transport larger molecules across the membrane.

• The movement of molecules from one region to another due to random motion.

• Diffusion facilitates through extracellular, bonding with molecules in the intracellular.

• 1. Diffusion through protein channels – Specific molecules pass based on size, shape, or charge.