Cell Membrane and Transport

Cell Transport

Intro to Cell Membranes &
Transport

Introduction to Cell Membranes

●

Cell membranes are essential boundaries that separate the cell from
its environment

●

They maintain the cell's internal balance (homeostasis)

●

Made up of a phospholipid bilayer with embedded proteins,
carbohydrates, and cholesterol

Multiple Choice

What happens if cells cannot maintain homeostasis?

• Cells will thrive and grow faster.
• Homeostasis is not essential for cell function.
• Cells will produce more energy than usual.
• Cells may become damaged or die.

Structure of the Cell Membrane

●Phospholipid bilayer - forms flexible barrier

●Hydrophilic heads face outside and inside

●Hydrophobic tails face each other

●Contains proteins, cholesterol, and carbohydrates

●This structure is called the Fluid Mosaic Model

Multiple Choice

What is the purpose of the cell membrane having a phospholipid bilayer?

• To facilitate protein synthesis
• To provide structural support for the cell
• To regulate the movement of things into and out of the cell.

• To store genetic information in the cell.

Membrane Proteins

●Transport proteins - move substances across membrane

●Receptor proteins - receive chemical signals

●Recognition proteins - identify cell type

●Enzyme proteins - catalyze reactions

●Anchor proteins - attach to cytoskeleton

Multiple Choice

What type of proteins identify cell types?

• Structural proteins
• Anchor proteins

• Transport Proteins

• Recognition proteins

Multiple Choice

What is the function of transport proteins?

• Transport proteins help move substances across cell membranes.
• Transport proteins store energy for the cell.
• Transport proteins are involved in DNA replication.
• Transport proteins synthesize hormones in the body.

Multiple Choice

What type of proteins in the cell membrane receive chemical signals?

• Receptors
• Structural proteins
• Transporters
• Enzymes

Role of Cholesterol

●Makes up about 20% of membrane lipids

●Maintains membrane fluidity

●Prevents phospholipids from packing too tightly

●Ratio of cholesterol to phospholipids is crucial for proper function

○The ratio of cholesterol to phospholipids is 1:1.

●Too much or too little affects membrane stability

Multiple Choice

What would happen to the cell membrane if there was not enough cholesterol embedded within in?

• The cell membrane would become rigid and impermeable.
• The cell membrane would gain excessive cholesterol, making it too dense.
• The cell membrane would remain unchanged and stable.
• The cell membrane would become too fluid and unstable, compromising its integrity and function.

Multiple Choice

What is the ratio of cholesterol to phospholipids in the cell membrane?

• 3:1
• 1:2
• 1:1
• 2:1

Multiple Choice

What is the main function of the cholesterol in a cell membrane?

• To maintain membrane fluidity and stability.
• To facilitate the transport of nutrients across the membrane.
• To act as a barrier against toxins.
• To provide energy for cellular processes.

Multiple Choice

True or False: the cholesterol in the cell membrane allows the fatty acid tails of the phospholipids to stick together.

• True
• False

What is Homeostasis?

●

Maintenance of stable internal conditions

●

Cells must regulate:
○Water content

○Temperature

○pH

○Nutrient levels

○Waste removal

Multiple Choice

Why must cells regulate what enters and leaves them?

• To increase cellular size and volume.
• To allow all substances to pass freely.
• To maintain homeostasis and ensure proper cellular function.
• To prevent any interaction with the environment.

Cell Transport Overview

● Two main types:

○

Passive Transport (no energy required)

○

Active Transport (requires energy/ATP)

○

Both types help maintain homeostasis

Passive Transport

● Movement of molecules from high to low concentration
● No energy required
● Types include:

○Simple diffusion

○Facilitated diffusion

○Osmosis

Simple Diffusion

●

Molecules move directly through membrane

●

Follows concentration gradient

●

Examples:
○Oxygen

○Carbon dioxide

○Small nonpolar molecules

Multiple Choice

What is the point of passive transport?

• To transport substances only in one direction.
• The point of passive transport is to facilitate the movement of substances across cell membranes without using energy.
• To create energy for cellular processes.
• To increase energy consumption in cells.

Multiple Choice

How can you easily summarize what simple diffusion is?

• Simple diffusion is the passive movement of molecules across a membrane from high to low concentration.
• Simple diffusion only occurs in liquid environments.
• Simple diffusion is the active transport of molecules against a concentration gradient.
• Simple diffusion requires energy input to occur.

Facilitated Diffusion

● Uses protein channels or carriers

● Helps move larger or charged molecules

● Examples:

○Glucose

○Amino acids

○Ions

Multiple Choice

What part of the cell membrane helps with facilitated diffusion?

• Lipid bilayer
• Nucleus
• Transport proteins (channel and carrier proteins)
• Ribosomes

Osmosis

● Movement of water across membrane

● Water moves from high to low concentration

● Critical for cell volume regulation

● Affected by solute concentration

Multiple Choice

Why is osmosis vital in cells?

• Osmosis is vital in cells because it regulates water balance, maintains turgor pressure, and supports nutrient transport.
• Osmosis is a process that occurs only in animal cells.
• Osmosis helps in the production of energy in cells.
• Osmosis is only important for plant cells.

Solution Types

●Isotonic - equal solute concentration

●Hypotonic - lower solute concentration outside

●Hypertonic - higher solute concentration outside

Effects of Different Solutions

●Isotonic - cell maintains normal size

●Hypotonic - cell swells (may burst)

●Hypertonic - cell shrinks (plasmolysis)

Multiple Choice

What would happen to a red blood cell if it was placed in a 5% salt solution?

• The red blood cell will swell and burst.
• The red blood cell will shrink due to water loss.
• The red blood cell will remain unchanged.
• The red blood cell will become more flexible.

Multiple Choice

Why would a cell burst when placed in a hypotonic solution?

• A cell bursts when it is placed in a neutral solution with no water movement.
• A cell bursts because it is too small to hold any water.
• A cell bursts in a hypertonic solution due to dehydration.
• A cell bursts in a hypotonic solution due to excess water influx causing internal pressure to exceed membrane capacity.

Active Transport

● Moves substances against concentration gradient
● Requires energy (ATP)
● Examples:

○

Sodium-potassium pump

○

Calcium pumps

○

Proton pumps

Multiple Choice

Why does active transport require energy?

• Active transport requires energy to move substances against their concentration gradient.
• Active transport does not require energy.
• Active transport is a passive process that occurs naturally.
• Active transport moves substances with the concentration gradient.

Endocytosis

● Cell "eating"

● Types:

○Phagocytosis (cell eating)

○Pinocytosis (cell drinking)

○Receptor-mediated endocytosis

○Requires energy

Exocytosis

●

Cell "spitting out"

●

Vesicles fuse with membrane

●

Releases contents to exterior

●

Important for:

○Waste removal

○Hormone secretion

○Neurotransmitter release

Cell Membrane Selectivity

●

Selective permeability

●

Controls what enters and exits

●

Based on:
○Size

○Charge

○Chemical properties

○Cell needs

Multiple Choice

What type of molecules pass through the cell membrane easily?

• Large, polar molecules
• Ions and charged particles
• Water molecules
• Small, nonpolar molecules

Review Key Concepts

●Cell membrane structure and components

●Passive vs. active transport

●Role of proteins and cholesterol

●Importance of homeostasis

●Types of solutions and their effects

●Endocytosis and exocytosis

Multiple Choice

Living things must maintain _______ by controlling what enters and leaves the cell.

• stability
• equilibrium
• balance
• homeostasis

Multiple Select

The cell membrane is a _________ structure.

• fluid mosaic
• rigid layer
• bilayer

• single layer

Multiple Choice

A phospholipid is made up of ______ parts.

• two
• four
• five
• three

Multiple Choice

The three parts of a phospholipid are: phosphate head, _______ backbone, and two fatty acid tails.

• sugar
• amino acid
• nucleotide
• glycerol

Multiple Choice

The head of a phospholipid is _______, meaning it loves water.

• hydrophilic
• nonpolar
• lipophilic
• hydrophobic

Multiple Choice

The fatty acid tails of a phospholipid are ________, meaning they hate water.

• hydrophobic
• amphipathic
• lipophilic
• hydrophilic

Multiple Choice

The ability for a phospholipid to turn on its side, swim through the tails, and pop back into the structure is called _______________.

• flip-flop movement
• transverse diffusion
• fluid mosaic model

Multiple Choice

Proteins determine which particles can pass through the membrane, serve as enzymes, and ______.

• cell signaling/act as markers

• cell structure
• energy production
• genetic information

Multiple Choice

The ratio of cholesterol to phospholipids is ______.

• 1:2
• 3:2
• 2:1
• 1:1

Multiple Choice

The cholesterol tends to make the lipid bilayer less fluid, prevents the tails from sticking, makes the bilayer more stable, and ____________ of water soluble solutions.

• increases fluidity
• promotes solubility
• reduces permeability
• enhances permeability

Multiple Choice

If your cell membrane has 72 phospholipids, how many cholesterol molecules are there embedded?

• 72

• 30
• 42

• 27