Movement of substances into and out of cells Flashcards
Diffusion
The movement of molecules from a region of higher concentration to a region of lower concentration
Molecules move down a concentration gradient
the movement of molecules is random, but the result of this random movement is the spreading out of molecules until they are at even concentration throughout the available space
Diffusion in living organisms
Molecules move into or out of living cells by diffusion when they cross the cell membrane
The cell membrane is partially permeable, meaning that it allows some molecules to cross, but not others
E.g. smaller molecules can diffuse across the membrane but larger molecules cannot
Diffusion allows living organisms to, e.g.:
gain nutrients in the digestive system
gain oxygen in the lungs
remove waste products in the lungs and kidneys
Osmosis
The movement of water molecules from a region of higher water concentration (a dilute solution) to a region of lower water concentration (a concentrated solution), through a partially permeable membrane
Osmosis is the diffusion of water, as the water is moving down its concentration gradient
Partially permeable membranes prevent the movement of larger molecules, e.g. sugars, but allow the movement of small water molecules
Osmosis in animal cells
Without a cell wall, osmosis can have severe effects on animal cells
In a strong sugar solution (lower water concentration), the cell loses water, becoming crenated (shrivelled)
In distilled water (higher water concentration), the cell gains water, eventually bursting as it lacks a cell wall to maintain structure
Osmosis in plant cells
Due to the cell wall, plant cells are protected from bursting:
In a strong sugar solution (lower water concentration), the cell loses water, the vacuole shrinks, and the cell membrane pulls away from the wall, making the cell flaccid or plasmolysed
In distilled water (higher water concentration), the cell gains water, the vacuole expands, and the membrane pushes against the cell wall, making the cell turgid
Turgid cells provide structural support and prevent wilting in plants
Flaccid
When water has moved out of a plant cell by osmosis. The cell wall is touching the cell membrane but not exerting any force upon it
Turgid
This describes a plant cell which is full of water after water has moved in by osmosis. Plant cells are normally in this state so that they can provide support and shape to the plant.
Active transport
The movement of a substance across a membrane from a low concentration to a high concentration, against the concentration gradient, using energy from respiration
Would plant cells immersed in a dilute solution gain or lose water by osmosis?
Gain water by osmosis
Carrier protein
These proteins are involved in active transport
root hair cells use this method to absorb water from the soil
osmosis
Root hair cells use this method of transport to absorb mineral ions like nitrate and magnesium from the soil.
active transport
Why does a red blood cell burst when placed in water?
A) Dissolved substances diffuse into the cell.
B) Dissolved substances diffuse out of the cell.
C) Water moves into the cell by osmosis.
D) Water moves out of the cell by osmosis.
C
what is plasmolysed
When so much water has left the plant cell by osmosis that the cell membrane peels away from the cell wall.
