4.1.3 Transport in cells Flashcards
What is diffusion?
The spreading out of particles from an area of higher concentration to an area of lower concentration.
What types of substances move by diffusion?
Gases (oxygen and carbon dioxide in gas exchange) and waste products (urea into blood plasma).
What factors affect the rate of diffusion?
Concentration gradient, temperature, surface area of the membrane.
Why do single-celled organisms have a high surface area to volume ratio?
To allow sufficient transport of molecules to meet their needs.
How is the effectiveness of an exchange surface increased?
Large surface area, thin membrane (short diffusion path), efficient blood supply (in animals), ventilation for gaseous exchange (in animals).
How are different organs adapted for material exchange?
Small intestine – villi increase surface area, lungs – alveoli provide a large surface area, fish gills – thin membranes with good blood supply, plant roots – root hairs increase surface area, leaves – stomata allow gas exchange.
What is osmosis?
The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
What practical is used to study osmosis?
Investigating the effect of different concentrations of salt or sugar solutions on the mass of plant tissue.
What calculations are needed for osmosis experiments?
Rate of water uptake, percentage gain/loss of mass, graph plotting and interpretation.
What is active transport?
The movement of substances from a more dilute solution to a more concentrated solution, requiring energy from respiration.
Where does active transport occur in plants?
In root hair cells to absorb mineral ions from the soil.
Where does active transport occur in animals?
In the gut to absorb sugar molecules into the blood for respiration.
How do diffusion, osmosis, and active transport differ?
Diffusion: Moves substances from high to low concentration, no energy needed. Osmosis: Diffusion of water across a membrane, no energy needed. Active transport: Moves substances against the concentration gradient, requires energy.
