Chapter 3: Movement in and out of cells.
Diffusion: The net movement of molecules from a region of higher concentration to a lower
concentration down a concentration gradient.
Examples of Diffusion:
Cells (Across Cell Membranes
Oxygen and carbon dioxide diffuse across cell membranes during gas exchange.
Nutrients like glucose and waste products also move by diffusion.
Lungs (Alveoli)
Oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses from the
blood into the alveoli for exhalation.
Factors that affect diffusion:
Distance: Smaller the distance →faster diffusion.
Concentration gradient: A concentration gradient refers to the difference in the concentration
of a substance between two regions. It represents how much the concentration changes from one
area to another.
→Steeper Gradient = Faster Diffusion
→A large difference in concentration between two areas increases the rate of diffusion.
Surface Area: the total area of the outer surface of a three-dimensional object. It measures how
much exposed area an object has.
→Larger Surface Area = Faster Diffusion.
Temperature
→Higher temperature=Faster diffusion.
Osmosis: The movement of water molecules from a higher concentration to a lower
concentration through a partially permeable membrane.
, Osmosis in Plant Cells
Hypotonic Solution (higher water concentration than inside the cell):
Water moves into the cell, causing it to swell. Plant cells have a cell wall that prevents them from
bursting, so they become turgid (firm). This pressure helps support the plant.
Hypertonic Solution (lower water concentration than inside the cell):
Water moves out of the plant cell, causing the cell to shrink (plasmolysis). The cell membrane
pulls away from the cell wall.
Isotonic Solution (equal water concentration inside and outside the cell):
There’s no net movement of water, and the plant cell remains in a balanced state.
Osmosis in Animal Cells
Hypotonic Solution: Water moves into the cell, causing it to swell. If too much water enters, the
cell can burst (lysis), as animal cells don't have a cell wall to contain the pressure.
Hypertonic Solution: Water moves out of the cell, causing it to shrink (crenation). This can
make the cell less effective in its functions.
Isotonic Solution: Water moves in and out at the same rate, maintaining the cell's shape and
function.
Active Transport:
Active transport is the movement of molecules across a cell membrane against their concentration
gradient (from a lower concentration to a higher concentration). This process requires energy in the
form of ATP (adenosine triphosphate) to power the transport proteins involved.
Unlike passive transport (such as diffusion and osmosis), which relies on natural molecular movement,
active transport uses energy to move substances uphill against their gradient.
Key Features of Active Transport:
1. Energy Requirement:
Active transport requires energy because molecules are being moved against the concentration
gradient.
2. Transport Proteins:
Specific proteins, called pumps, help move substances across the membrane. For example, the
sodium-potassium pump actively transports sodium ions out of the cell and potassium ions into
the cell.
3. Movement Against Concentration Gradient:
Molecules move from a region of low concentration to a region of high concentration, which
would not naturally occur without energy.
Examples of Active Transport:
1. Sodium-Potassium Pump (Na⁺/K⁺ Pump)
o Function: Transports 3 sodium ions (Na⁺) out of the cell and 2 potassium ions (K⁺) into
the cell against their concentration gradients.
Diffusion: The net movement of molecules from a region of higher concentration to a lower
concentration down a concentration gradient.
Examples of Diffusion:
Cells (Across Cell Membranes
Oxygen and carbon dioxide diffuse across cell membranes during gas exchange.
Nutrients like glucose and waste products also move by diffusion.
Lungs (Alveoli)
Oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses from the
blood into the alveoli for exhalation.
Factors that affect diffusion:
Distance: Smaller the distance →faster diffusion.
Concentration gradient: A concentration gradient refers to the difference in the concentration
of a substance between two regions. It represents how much the concentration changes from one
area to another.
→Steeper Gradient = Faster Diffusion
→A large difference in concentration between two areas increases the rate of diffusion.
Surface Area: the total area of the outer surface of a three-dimensional object. It measures how
much exposed area an object has.
→Larger Surface Area = Faster Diffusion.
Temperature
→Higher temperature=Faster diffusion.
Osmosis: The movement of water molecules from a higher concentration to a lower
concentration through a partially permeable membrane.
, Osmosis in Plant Cells
Hypotonic Solution (higher water concentration than inside the cell):
Water moves into the cell, causing it to swell. Plant cells have a cell wall that prevents them from
bursting, so they become turgid (firm). This pressure helps support the plant.
Hypertonic Solution (lower water concentration than inside the cell):
Water moves out of the plant cell, causing the cell to shrink (plasmolysis). The cell membrane
pulls away from the cell wall.
Isotonic Solution (equal water concentration inside and outside the cell):
There’s no net movement of water, and the plant cell remains in a balanced state.
Osmosis in Animal Cells
Hypotonic Solution: Water moves into the cell, causing it to swell. If too much water enters, the
cell can burst (lysis), as animal cells don't have a cell wall to contain the pressure.
Hypertonic Solution: Water moves out of the cell, causing it to shrink (crenation). This can
make the cell less effective in its functions.
Isotonic Solution: Water moves in and out at the same rate, maintaining the cell's shape and
function.
Active Transport:
Active transport is the movement of molecules across a cell membrane against their concentration
gradient (from a lower concentration to a higher concentration). This process requires energy in the
form of ATP (adenosine triphosphate) to power the transport proteins involved.
Unlike passive transport (such as diffusion and osmosis), which relies on natural molecular movement,
active transport uses energy to move substances uphill against their gradient.
Key Features of Active Transport:
1. Energy Requirement:
Active transport requires energy because molecules are being moved against the concentration
gradient.
2. Transport Proteins:
Specific proteins, called pumps, help move substances across the membrane. For example, the
sodium-potassium pump actively transports sodium ions out of the cell and potassium ions into
the cell.
3. Movement Against Concentration Gradient:
Molecules move from a region of low concentration to a region of high concentration, which
would not naturally occur without energy.
Examples of Active Transport:
1. Sodium-Potassium Pump (Na⁺/K⁺ Pump)
o Function: Transports 3 sodium ions (Na⁺) out of the cell and 2 potassium ions (K⁺) into
the cell against their concentration gradients.
