IB MYP 4-5 Biology-Movement and Transport- Study Notes - New Syllabus
IB MYP 4-5 Biology-Movement and Transport- Study Notes – New syllabus
IB MYP 4-5 Biology-Movement and Transport- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Active and passive transport
- Endocytosis and exocytosis
Movement and Transport: Active and Passive Transport
Why Transport Is Important
Cells constantly exchange substances like nutrients, gases, and waste with their environment. This exchange occurs across the plasma membrane, which is partially permeable allowing certain substances to pass while blocking others. Transport is essential for maintaining homeostasis and cell survival.
Types of Transport
Transport across cell membranes is classified into two main types based on energy usage:
1. Passive Transport
Passive transport does not require energy (ATP). Substances move from a region of high concentration to low concentration – down the concentration gradient.
a. Diffusion
- Movement of molecules from an area of higher concentration to lower concentration.
- Continues until equilibrium is reached.
- Examples: oxygen and carbon dioxide movement in and out of cells.
b. Osmosis
- A special type of diffusion involving only water molecules.
- Water moves from high water potential to low water potential through a partially permeable membrane.
- Important for maintaining water balance in cells.
Results of Osmosis:
– Plasmolysis: Cell shrinks in hypertonic solution
– Lysis: Animal cell bursts in hypotonic solution
– Turgidity: Plant cells swell but do not burst due to rigid cell wall
c. Facilitated Diffusion
- Transport of larger or charged molecules via carrier or channel proteins.
- No energy is used – still a passive process.
- Examples: Glucose transport, ion movement
2. Active Transport
Active transport uses energy (ATP) to move substances against the concentration gradient – from low to high concentration. It involves specific carrier proteins in the membrane.
- Useful for: Absorbing nutrients even when they are in low concentration outside the cell.
- Examples: Glucose absorption in the intestines, ion uptake by root hair cells
Special Bulk Transport Mechanisms
These methods are used for transporting very large molecules or large quantities of substances.
a. Endocytosis
- Cell engulfs material by folding its membrane around it to form a vesicle.
- Phagocytosis: for solids
- Pinocytosis: for liquids
b. Exocytosis
- Opposite of endocytosis vesicles fuse with the membrane and release contents outside the cell.
- Used to remove waste or secrete substances like hormones or enzymes.
Factors Affecting Rate of Transport
| Factor | Effect |
|---|---|
| Surface Area to Volume Ratio | Smaller cells have a larger ratio, making transport more efficient. |
| Temperature | Higher temperature increases kinetic energy, speeding up diffusion. |
| Concentration Gradient | A steeper gradient increases the rate of diffusion. |
Summary
- Transport across membranes is vital for cell survival.
- Passive transport moves substances without energy, while active transport requires ATP.
- Special bulk transport methods help move large particles.
- Rate of transport is affected by surface area, temperature, and concentration gradient.
Endocytosis and Exocytosis
Bulk Transport Across the Membrane
Cells often need to move large molecules or particles that cannot pass through the membrane via diffusion or standard active transport. For this, they use special energy-dependent processes called endocytosis and exocytosis.
1. Endocytosis – Taking in Large Particles
Endocytosis is the process by which a cell engulfs large particles or fluids by folding its plasma membrane inward to form a vesicle. This vesicle traps the material and brings it into the cell.
Types of Endocytosis
- Phagocytosis (“cell eating”): The cell engulfs solid particles like bacteria or debris.
- Pinocytosis (“cell drinking”): The cell takes in liquid droplets or dissolved substances.
Both are active processes and require energy in the form of ATP.
2. Exocytosis – Releasing Substances Out of the Cell
Exocytosis is the reverse of endocytosis. It involves vesicles inside the cell moving to the membrane, fusing with it, and releasing their contents outside the cell.
Functions of Exocytosis
- Removing cellular waste
- Secreting useful substances like:
- Hormones (e.g., insulin)
- Digestive enzymes
- Neurotransmitters
Key Points
- Both endocytosis and exocytosis are types of bulk transport.
- They involve vesicle formation and membrane fusion.
- These processes are active and require ATP.
- They are crucial for:
- Nutrient uptake
- Immune defense (e.g., engulfing pathogens)
- Cell signaling and communication
- Waste removal from the cell