B3.1.1 Dissolved substances Flashcards
(24 cards)
Give 2 ways dissolved substances move.
Diffusion and active transport.
What is diffusion?
When particles of a substance move from an area where they are in high concentration to an area of low concentration.
What does diffusion allow?
Dissolved substances to move in or out of cells.
What is active transport?
Moves dissolved molecules from low concentration to high concentration, against a concentration gradient.
What does active transport require?
Energy from respiration.
What is a protein carrier?
A protein that is responsible for transporting specific substances through the cell membrane.
Give an example of active transport.
Root hair cells
Give an example of diffusion.
Gas exchange in the lungs.
What is a partially permeable membrane?
Allows small, soluble molecules such as water to pass through it freely but prevents larger molecules.
What will happen if a cell has a more dilute (more water) solution inside it surrounding it?
The cell loses water by osmosis.
- Animal cell shrivels up
- Plant cell becomes flacid
What will happen if a cell has a more concentrated (less water) solution inside it surrounding it?
The cell gains water by osmosis.
- Animal cell swells and bursts
- Plant cell becomes turgid / firm
What will happen if a cell has the same concentration solution inside it as its surroundings?
There is no net movement of water and so the cell remains the same.
What does active transport allow?
Cells to absorb ions from very dilute solutions.
Describe the only circumstances in which diffusion works efficiently.
If the distance over which the substances have to diffuse is small and the organism has a large surface area compared to its volume.
Small organisms
What is an exchange surface?
A specially adapted surface across which substances can be exchanged efficiently.
Give 2 properties of an exchange surface.
Having a large surface area
Being thin, to provide a short diffusion path
Give 2 ways animals can increase the effectiveness of exchange surfaces.
Having an efficient blood supply
Being well ventilated (gaseous exchange)
What are villi?
Folds within the wall of the small intestine across which digested food molecules are exchanged between the gut and the bloodstream by active transport and diffusion.
What increases the difficulty of exchanging materials?
The size and complexity of an organism.
Give 2 examples of specialised exchanged surfaces in humans.
- Villi
- Alveoli
What do most soft drinks contain?
- Water
- Sugar
- Ions
What do sport drinks contain?
Water, sugar and mineral ions at levels which are most effective at replacing what is lost during sweating.
What happens if water and ions are not replaced after sweating?
The ion / water balance of the body is disturbed and the cells do not work as efficiently.
Why is drinking water not enough after extended periods of exercise?
Because water is only able to rehydrate the body and does not replace the lost ions and glucose.
