Y3 Bio Topic 2 Flashcards
Define diffusion.
Net movement of particles (atoms, ions, or molecules) from a region of higher concentration to a region of lower concentration, moving down a concentration gradient.
Explain the role of diffusion in living systems.
Diffusion is crucial for processes such as gaseous exchange in lungs and nutrient uptake in root cells, ensuring that substances reach all parts of an organism.
State one key factor that affects the rate of diffusion.
Factors such as the steepness of the concentration gradient, surface area-to-volume ratio, temperature, and distance (e.g. membrane thickness) affect diffusion rates.
Define osmosis.
Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
What is water potential?
Water potential is a measure of the tendency for water to move from one area to another, with pure water set at zero.
Describe what happens when a plant cell is placed in a solution with higher water potential.
Water enters the cell by osmosis, causing the central vacuole to expand and the cell to become turgid; the cell wall prevents rupture.
Describe what happens to an animal cell placed in a solution with higher water potential.
Water enters the cell by osmosis, and because there is no rigid cell wall, the cell may swell and eventually lyse (burst).
Describe plasmolysis.
Plasmolysis occurs when a plant cell is placed in a solution with lower water potential, causing water to exit, the vacuole to shrink, and the cell membrane to pull away from the cell wall.
Define active transport.
Active transport is the energy-consuming process of moving substances against their concentration gradient, from a region of lower concentration to a region of higher concentration.
Why is active transport important?
Active transport allows cells to maintain internal concentrations of substances (e.g. ions, glucose) that differ from those in the surrounding environment, which is critical for processes such as ion uptake by root hairs or nutrient absorption in the intestine.
Give an example of active transport in animal cells.
The sodium-potassium pump, which moves Na+ out and K+ into the cell, is a classic example of active transport.
How many Na+ ions are pumped out compared to K+ ions pumped in by the sodium-potassium pump?
For every 2 K+ ions pumped in, 3 Na+ ions are pumped out.
Define facilitated diffusion.
Facilitated diffusion is the passive movement of molecules across a cell membrane via transport proteins, down their concentration gradient.
What kinds of molecules typically require facilitated diffusion?
Charged ions (e.g. Na+, Ca2+) and large polar molecules (e.g. amino acids, sugars) that cannot easily pass through the lipid bilayer.
List the two types of transport proteins used in facilitated diffusion.
Channel proteins (provide a hydrophilic passage) and carrier proteins (bind the molecule and change conformation to transfer it).
Compare diffusion and facilitated diffusion.
Both are passive processes that move substances down a concentration gradient, but facilitated diffusion requires transport proteins while diffusion does not.
What is the fluid mosaic model of membrane structure?
The fluid mosaic model describes the plasma membrane as a dynamic bilayer of phospholipids with embedded proteins that move laterally, giving the membrane its fluidity and mosaic appearance.
What is the main component of the plasma membrane?
The plasma membrane is primarily composed of a phospholipid bilayer.
How do phospholipids arrange themselves in the bilayer?
The hydrophilic (water-loving) heads face outward toward the aqueous environments, while the hydrophobic (water-repelling) tails face inward.
Name two types of proteins associated with the plasma membrane.
Intrinsic (integral) proteins, which are embedded within the bilayer, and extrinsic (peripheral) proteins, which are loosely attached to the surface.
What function do membrane proteins perform?
Membrane proteins are involved in transport, enzymatic activity, signal transduction, cell-to-cell recognition, and intercellular adhesion.
What is a channel protein and how does it work?
Channel proteins create hydrophilic passages that allow specific molecules or ions to cross the membrane quickly, shielding them from the hydrophobic interior.
What is a carrier protein and how does it work?
A carrier protein binds to a specific molecule, undergoes a conformational change to transport the molecule across the membrane, and then releases it on the other side.
List one function of receptor proteins in the membrane.
Receptor proteins bind chemical messengers (e.g. hormones) and transmit signals into the cell, initiating a response.
What is bulk transport?
Bulk transport is the process by which cells move large molecules or large quantities of substances into or out of the cell via vesicles.
Define exocytosis.
Exocytosis is the process by which a cell expels materials in vesicles by fusing them with the plasma membrane.
List one example of exocytosis in the human body.
Secretion of hormones by endocrine cells or release of neurotransmitters by neurons.
Define endocytosis.
Endocytosis is the process by which cells engulf external substances by invaginating the plasma membrane to form vesicles.
Name the three types of endocytosis.
Phagocytosis (ingestion of large particles), pinocytosis (ingestion of fluids), and receptor-mediated endocytosis (selective uptake via receptor binding).
What is phagocytosis?
Phagocytosis is a type of endocytosis where solid particles, such as bacteria, are engulfed by cells (commonly performed by white blood cells).
What is pinocytosis?
Pinocytosis is a non-selective form of endocytosis where cells take in extracellular fluid and dissolved substances.
Describe receptor-mediated endocytosis.
In receptor-mediated endocytosis, molecules bind to specific receptors on the cell surface, triggering the formation of vesicles to internalize the bound substances.
How does temperature affect passive transport?
Higher temperatures increase the kinetic energy of molecules, thereby increasing the rate of passive transport.
How does surface area-to-volume ratio affect the rate of diffusion?
Cells or organisms with a larger surface area-to-volume ratio have a higher rate of diffusion, enabling faster exchange of substances.
What is the significance of concentration gradient in passive transport?
A steeper concentration gradient results in a faster rate of passive transport.
How does active transport differ from passive transport?
Active transport requires energy to move substances against their concentration gradient, whereas passive transport does not require energy.
What role does the cell membrane play in substance movement?
The cell membrane acts as a selectively permeable barrier, controlling the entry and exit of substances to maintain internal homeostasis.
What experimental technique supported the fluid mosaic model?
The freeze fracture technique, which splits the membrane to reveal embedded proteins, supports the fluid mosaic model.
How do cholesterol molecules affect membrane fluidity?
Cholesterol molecules help stabilize the membrane and modulate its fluidity by preventing the phospholipids from packing too tightly.
What are the key differences between diffusion, osmosis, and active transport?
Diffusion involves the net movement of any particles down a concentration gradient; osmosis specifically involves water movement across a partially permeable membrane; active transport moves substances against a gradient using energy.
How does facilitated diffusion differ from simple diffusion?
Facilitated diffusion relies on specific transport proteins to move substances across the membrane, whereas simple diffusion occurs directly through the lipid bilayer.
What is crenation?
Crenation is the shrinking of animal cells (especially red blood cells) when placed in a hypertonic solution, causing spikes to appear on the cell surface.
What is the effect of a hypotonic solution on a plant cell?
In a hypotonic solution, water enters the plant cell, making it turgid; the rigid cell wall prevents it from bursting.
What is the effect of a hypertonic solution on a plant cell?
In a hypertonic solution, water leaves the plant cell, causing plasmolysis where the cell membrane detaches from the cell wall.
Why is bulk transport necessary for cells?
Bulk transport allows cells to move large molecules (like proteins and polysaccharides) that cannot pass through the membrane via individual transport proteins.
Provide an example of active transport in plant cells.
Absorption of dissolved mineral ions by root hair cells is an example of active transport.
What percentage of water in a cell is typically found in the cytoplasm?
Approximately 90% of a cell’s composition is water, which is essential for the function of cellular enzymes and metabolic reactions.
How does the energy cost of active transport compare to passive transport?
Active transport consumes energy (ATP) while passive transport processes, such as diffusion and osmosis, do not require energy.
What is the statistical significance of surface area-to-volume ratio in small versus large cells?
Smaller cells have a high surface area-to-volume ratio, which facilitates rapid exchange of substances, while larger cells have a lower ratio that may limit transport rates.
How does the fluidity of the membrane impact cellular function?
Increased membrane fluidity enhances the movement of proteins and lipids, which is essential for processes such as signal transduction, endocytosis, and exocytosis.
