B3. Movement into and out of cells Flashcards
What is diffusion?
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of random movement of particles.
Does diffusion require energy?
No
Give three examples of diffusion in living organisms.
Oxygen diffusing from alveoli into blood capillaries in the lungs.
Carbon dioxide diffusing out of cells into the bloodstream.
Glucose diffusing from the small intestine into blood capillaries during digestion.
What factors affect the rate of diffusion?
Concentration gradient: The steeper the gradient, the faster the diffusion.
Temperature: Higher temperature increases particle kinetic energy and diffusion rate.
Surface area: Larger surface area increases diffusion.
Distance: Shorter diffusion distances allow faster diffusion.
Size of molecules: Smaller molecules diffuse faster than larger ones.
What is 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 a partially permeable membrane?
A membrane that allows small molecules like water to pass through but restricts larger molecules (like sugars or proteins).
How does osmosis affect plant cells in pure water?
Water enters the cell by osmosis, the vacuole swells, and the cell becomes turgid (firm), which supports the plant.
What happens to a plant cell placed in a concentrated sugar or salt solution?
Water leaves the cell by osmosis, causing the cytoplasm and membrane to pull away from the cell wall — the cell becomes plasmolysed.
What happens to animal cells in pure water?
Water enters by osmosis; because animal cells lack a cell wall, they may swell and burst (this is called lysis).
What is active transport?
Active transport is the movement of substances against a concentration gradient, from an area of lower concentration to an area of higher concentration, using energy from respiration (ATP).
Give two examples of active transport in living organisms.
Root hair cells actively transport mineral ions (e.g., nitrate ions) from the soil into the root.
Uptake of glucose by epithelial cells in the villi of the small intestine.
Why is active transport important for root hair cells?
So that plants can absorb essential minerals like nitrates and phosphates from the soil, even if these are in low concentrations, for making proteins and other vital molecules.
Why does active transport require mitochondria?
Active transport requires energy in the form of ATP. Mitochondria carry out aerobic respiration to produce ATP for the transport proteins in the cell membrane.
How are cells adapted for active transport?
They have many mitochondria to provide ATP.
They have special carrier proteins in their membranes that pump substances across.
