B3.1.1 Dissolved substances Flashcards
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.
