cell transport

what is passive transport?

Passive transport is the movement of substances across a cell membrane from high concentration to low concentration without using energy (ATP).

with the concentration gradient

types of passive transport?

Types of Passive Transport 1. Simple Diffusion

• Small molecules move directly through membrane

• Example: oxygen, carbon dioxide

2. Osmosis

• Diffusion of water across a selectively permeable membrane

3. Facilitated Diffusion

• Uses transport proteins/channels

• Still does not require ATP

High concentration → Low concentration

what is active transport

Active transport is the movement of substances across a cell membrane from low concentration to high concentration using energy (ATP).

Key idea

Particles move:

• from low concentration

• to high concentration

This goes against the concentration gradient, so the cell must use energy.

Low concentration→High concentration

what is diffusion?

Diffusion is the movement of particles from an area of high concentration to an area of low concentration until they are evenly spread out.

a type of passive transport

what is dynamic equilibrium?

Dynamic equilibrium is when particles are still moving, but there is no overall change in concentration because they move equally in both directions.

rate of forward = rate of backward

what is Exocytosis?

Exocytosis is the process where a cell removes materials by sending them out in vesicles that fuse with the cell membrane and release contents outside

How it works (simple steps)

1. Materials are packaged into a vesicle inside the cell

2. The vesicle moves to the cell membrane

3. It fuses with the membrane

4. Contents are released outside the cell

what is endocytosis

Endocytosis is the process where a cell brings materials into the cell by surrounding them with the cell membrane and forming a vesicle.

How it works (simple steps)

1. The cell membrane surrounds a substance outside the cell

2. The membrane folds inward

3. A vesicle pinches off inside the cell

4. The material is now inside the cell

what is phagocytosis?

Phagocytosis (“Cell Eating”)

Phagocytosis is a type of endocytosis in which the cell engulfs large solid particles or microorganisms by surrounding them with the plasma membrane to form a vesicle called a phagosome.

Process

1. Cell membrane extends around the particle

2. Membrane encloses it

3. Vesicle forms inside the cell

4. Lysosomes often fuse with the vesicle to digest contents

Functions

• Defense against pathogens

• Removal of dead cells

• Feeding in unicellular organisms

Examples

• White blood cells engulfing bacteria

• Amoeba engulfing food

what is a lysosome?

A lysosome is a membrane-bound organelle that contains digestive enzymes used to break down waste, food particles, bacteria, and old cell parts.

what is pinocytosis?

Pinocytosis (“Cell Drinking”) Definition

Pinocytosis is a type of endocytosis in which the cell takes in extracellular fluid and dissolved substances through small vesicles formed from the plasma membrane.

Process

1. Membrane folds inward

2. Small droplets of fluid are enclosed

3. Vesicles pinch off into the cell

Characteristics

• Non-specific uptake

• Occurs continuously in many cells

Function

• Absorption of nutrients and fluids

what is receptor mediated endocyctosis?

Receptor-Mediated Endocytosis Definition

Receptor-mediated endocytosis is a highly specific type of endocytosis in which molecules bind to membrane receptors before being brought into the cell in vesicles.

Process

1. Specific molecules (ligands) bind to receptors

2. Membrane forms a coated pit

3. Vesicle pinches inward

4. Vesicle enters cell carrying targeted substances

Characteristics

• Highly selective

• Efficient uptake of low-concentration substances

Examples

• Uptake of LDL cholesterol

• Hormone uptake

what is a ligand?

A ligand is a molecule that binds specifically to a receptor protein.

what is osmosis?

Osmosis is the diffusion of water across a selectively permeable membrane from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).

a type of passive transport

what structure is most responsible for maintaining homeostasis in cell

cell membrane maintains homeostasis by controlling what enters and leaves the cell through selective permeability.

explain the structure of the phospholipid bilayer

The phospholipid bilayer consists of two layers of phospholipids with hydrophilic phosphate heads facing outward and hydrophobic fatty acid tails facing inward, forming a selectively permeable cell membrane.

The bilayer maintains homeostasis by controlling:

• Nutrients entering

• Waste leaving

• Water balance

• Ion balance

whhat is turgor pressure?

Turgor pressure is the pressure of water pushing the cell membrane against the cell wall in a plant cell.

How it happens

1. Water enters the plant cell by osmosis

2. The vacuole fills with water

3. The membrane pushes outward against the rigid cell wall

4. Pressure builds up = turgor pressure

how does the phospholipid bilayer work?

• Hydrophilic head (likes water)

• Hydrophobic tails (repel water)

This creates a barrier in the middle that most substances cannot easily cross.

Small, nonpolar molecules can pass through directly:

• Oxygen (O₂)

• Carbon dioxide (CO₂)

They move by diffusion.

High concentration→Low concentration

What cannot pass easily (large molecules)

• Large molecules (glucose)

• Charged ions (Na⁺, K⁺)

These need transport proteins:

• Channel proteins

• Carrier proteins

what is hypotonic?

Hypotonic Solution Meaning

• Outside solution has lower solute concentration

• Outside has more water

What happens

Water moves into the cell by osmosis.

H2O→into cell

• Animal cell may swell or burst

• Plant cell becomes turgid (firm)

what is hypertonic?

Hypertonic Solution Meaning

• Outside solution has higher solute concentration

• Outside has less water

What happens

Water moves out of the cell.

H2O→out of cell

• Animal cell shrinks

• Plant cell becomes plasmolyzed/wilted

what is isotonic

sotonic Solution Meaning

• Equal solute concentration inside and outside

What happens

Water moves equally in both directions.

H2O↔equal movement

Result

• No net water movement

• Cell stays the same size

what is facilated diffusion?

Facilitated diffusion is the movement of substances across a cell membrane from high concentration to low concentration using transport proteins, without using energy (ATP).

• Substance (like glucose or ions) cannot pass through the lipid bilayer directly

• It binds to a channel protein or carrier protein

• Protein helps it cross the membrane

• It moves from high → low concentration

what is a channel protien?

A channel protein is a type of protein found in the cell membrane that acts like a tiny tunnel or doorway. It helps certain substances move in and out of the cell.

helps with facilated diffusion

what is a carrier protien?

A carrier protein is a protein in the cell membrane that helps move substances across the membrane by changing shape.

Unlike a channel protein (which is like a tunnel), a carrier protein grabs the substance and carries it through the membrane.

How it works

1. A specific molecule attaches to the carrier protein

2. The protein changes shape

3. The molecule is released on the other side of the membrane

What carrier proteins transport

• glucose

• amino acids

• some ions

help with facilated diffusion