2.1 Osmosis And Plant Transport Flashcards
What is osmosis
Osmosis is the movement of water molecules from a dilute solution to a more concentrated solution, through a selectively permeable membrane
What is a dilute solution ?
A dilute solution contains less solute molecules
What is a concentrated solution?
A concentrated contains more solute molecules
What is a selectively permeable membrane?
A selectively permeable membrane is a membrane which allows some molecules through but not others
What molecules cannot move across a selectively permeable membrane?
Larger molecules cannot move across a selectively permeable membrane
How do water molecules move across the selectively permeable membrane
Water molecules move across the membrane from a dilute solution to a concentrated solution.
Why does water move across the membrane?
Water moves to balance the solute concentration on both sides of the membrane
When a solution is dilute what does this mean in terms of water
There is more water in a dilute solution
When a solution is concentrated what does this mean in terms in terms of water
There is less water and more solute molecules
When does osmosis stop ?
Osmosis continues until the solute is at the same concentration on both sides of the membrane or until further water movement becomes limited by the cell wall (plant cells only)
What happens when water enters a plant cell ?
- Water flows into the cell from a more dilute solution outside the cell, to a more concentrated solution inside the cell sap
- Vacuole fills with water and increases in size
- Pushing the cytoplasm backwards against the cell wall
- Cell membrane pushed against the cell wall
- Cell wall stretches slightly and cell becomes turgid
What does the force of the cell membrane pushing against the stiff cell wall do ?
It increases the pressure in the cell making it firm or turgid.
What does the turgor pressure do ?
- The turgor pressure stops too much water from entering the cell so that it cannot burst.
- It gives the plant cells support and keeps non-woody plants upright.
What happens if there is a shortage of water in the plant cell and what is this described as?
- Plant cells cannot remain turgid and wilting occurs.
- Cells that are not turgid are described as being flaccid or plasmolysed
What happens if a plat cell loses too much water by osmosis?
A condition called plasmolysis occurs and the cell is unlikely to survive
What happens in a plasmolysed plant cell ?
- The water flows from the more dilute solution inside the cell sap to the more concentrated solution outside the cell
- Vacuole loses water and decreases in size
- Cytoplasm shrinks
- The cell membrane pulls away from the cell wall
- cell wall becomes soft/flaccid
- Cell becomes plasmolysed
Cell membranes let through small molecules like ?
Oxygen and water
The movement of molecules from a high to low concentration is ?
Diffusion
What is diffusion?
The movement of molecules from a high to low concentration
What 4 things do plants use water for ?
- Supply water to leaves for Photosynthesis
- To transport minerals and dissolved nutrients round the plant in specialised vascular tissue called xylem (water) and phloem (food)
- To provide support to the cells by filling them with water due to osmosis and making them turgid
- For transpiration
Where can water only enter through in a plant ?
Water can only enter a plant through the root hair cell which have a large surface area to allow greater uptake of water
How does water move through the plant ?
Water moves through the plant and is pulled from the roots up the stem to the leaves the process of evaporation
What is the equation to remember the processes of water up take of a plant
Water uptake by a plant (root hair cells) = water used for photosynthesis (leaves, mostly palisade ) + water used for support/turgor (stem) + water lost in transpiration (goes out through stomata in the leaves)
What are plants that live in areas where water is limited called ?
Xerophytes
