1.3 Flashcards
Diffusion
The net movement of particles in fluids from an area of high concentration to an area of low concentration (across the concentration gradient).
Use of diffusion in humans.
- Lungs: oxygen into blood from lungs and carbon dioxide out from blood to lungs during gas exchange.
- Kidneys: waste product urea from cells into blood plasma to be excreted in urine.
Factors that affect rate of diffusion.
- Difference in concentration (concentration gradient).
- Temperature.
- Surface area of membrane.
Single-celled organisms adaptation for substance exchange.
Relatively large surface area to volume ratio allowing transport of molecules in and out of the cell to meet the needs of the organism.
Equations for surface area to volume ratio
- Surface area: number of sides × (length × width)
- Volume: length × width × depth.
Multi-cellular organisms adaptation for substance exchange.
Small surface are to volume ratio - require specialised surfaces and organs for exchanging substances so that sufficient molecules are transported in and out of cells to meet the organism’s needs.
Small intestine adaptations.
- Very long: extends time for nutrient absorption.
- Villi and microvilli: increase surface area for absorption.
- Rich blood supply: maintains concentration gradient.
- One cell thick: short diffusion path.
Lungs adaptations.
- Ventilated: maintains steep diffusion gradient.
- Rich blood supply: maintains concentration gradient.
- Many small spherical alveoli: increase surface area for diffusion.
- Thin alveolus walls: short diffusion path.
Gills adaptations.
- Gills filaments and lamellae: large surface area for absorption.
- Rich blood supply: maintain steep diffusion gradients.
- Thin membrane (GF): short diffusion pathway.
- Countercurrent system: maintain concentration gradient.
Leaves adaptations.
- Thin: short diffusion path.
- Flat: large surface area to volume ratio.
- Many stomata: allows movements of gases in and out of air spaces by diffusion.
- Close cell contact: enables efficient substance exchange from photosynthesis and respiration.
Factors increasing effectiveness of exchange surface.
- Having a large surface area
- Thin membrane, to provide a short diffusion path
- Having an efficient blood supply (in animals).
- Being ventilated (in animals, for gaseous exchange).
Osmosis
Movement of water from a dilute concentration to a concentrated solution through a partially permeable membrane.
Equation for rate of water uptake.
Rate of water uptake = change in mass × (time wanted ÷ time taken for mass change)
Equation for percentage change in mass.
Percentage change in mass = ((end mass - starting mass) ÷ starting mass) × 100
Active transport.
Movements of substance from a more dilute solution to a more concentrated solution (against a concentration gradient), using energy from respiration.
Use of active transport in plants and animals.
- Root hairs: mineral ions absorbed from very dilute solution in soil for healthy growth.
- Bloodstream: sugar molecules absorbed from lower glucose concentration in cells, from the gut, for cellular respiration.
Compare active transport, diffusion and osmosis.
- Only active transport requires energy and moves against a concentration gradient.
- Only osmosis requires a permeable membrane.
- Diffusion transports food molecules, gases (oxygen and carbon dioxide), water and waste products (urea).
- Osmosis transports water only.
- Active transport transports glucose and mineral ions.
