Transport in plants Flashcards
How does osmosis occur in plant cells?
The plant cell swells up and then the cytoplasm pushes against the wall. A plant cell that has developed an internal pressure like this is called turgid.
When does a plant cell lose water by osmosis?
The cell is placed in a concentrated sucrose solution that has a lower water potential than the cell contents, it will lose water by osmosis.
The cell decreases in volume and the cytoplasm no longer pushes against the cell wall. In this state, the cell is called flaccid.
Whats a plasmolyzed cell?
When cell contents shrink so much that the membrane and cytoplasm split away from the cell wall and gaps appear between the wall and the membrane.
Why does osmosis occur in plant cells?
If a plant cell is placed in water or a dilute solution, the contents of the cell have a lower water potential than the external solution, so the cell will absorb water by osmosis.
Whats turgor?
The force within the cell that pushes the plasma membrane against the cell wall.
How do roots uptake water?
Around the tips of the plants roots, there are tiny root hairs which are the main sites of water absorption.
The long, thin outer projection of the root hair cell penetrates the soil, reaching the soil water.
The water in the soil has some solutes dissolved in it, such as mineral ions, but their concentrations is lower than the concentrations of solutes inside the root hair cell.
The soil water therefore has a higher water potential than the inside of the cell. This allows water to enter the root hair cell by osmosis.
Water travels up the root by the xylem.
Whats transpiration in planst?
A process that involves loss of water vapor through the stomata of plants. This cools down the plant when the weather is very hot.
What happens in transpiration?
The vapor escapes from the stomata below the lamina of the leaf. Water leaves the cells of the leaf mesophyll and evaporates into the air spaces between the spongy mesophyll cells. The water cells then diffuse out through the stomatal pores.
Whats the transpiration stream?
Transpiration causes water to be “pulled up” the xylem in the stem and roots in a continuous flow known as the transpiration stream.
Whats the xylem?
A vascular tissue that allows substances to move from certain parts of the plant to the others. Its responsible for distributing water and minerals taken by the roots. Xylem contains dead cells arranged end to end forming continuous vessels.
Whats phloem?
A vascular tissue that allows substances to move from certain parts of the plant to the others. consists of living cells at all stages of development. Tubes in the phloem are formed by cells arranged end to end but have cell walls, and retain their cytoplasm.
Whats the structure of a young stem?
In a young stem, xylem and phloem are grouped together in vascular bundles.
In the root the vascular tissue is in the central core.
In older stems the vascular tissue grows to form complete rings around the stem.
Whats stomatal transpiration?
Most of the transpiration takes place through the stomata. In stomatal transpiration, water vapor moves through the stomata of a leaf. Water absorbed by the roots rises through the stem and reaches the tissues of the leaves via veins, where a large number of spongy mesophyll cells in the leaf have their surfaces exposed to the intercellular spaces. The surfaces of the cells give out some of the water which forms a thing film, the water from this film evaporates and the vapor formed saturates in the intercellular spaces. This vapor then diffuses into the other connecting intercellular spaces and finally reaches substomatal space from where it escapes out through the stomata.
How do the stomata open?
During day time, as a result of photosynthesis, concentration of CO2 rises leading to osmotic uptake of water by the guard cells to swell. Since the wall of guard cells towards stomatal opening is thick while the outer convex wall is thin, inflow of water in the guard cells causes them to bulge outwards thus widening the stomatal opening.
How do stomata close?
When the osmotic pressure of the guard cells lower, the water leaves these cells due to exosmosis and moves to the neighboring epidermal cells having a cell sap of a higher concentration. The guard cells become flaccid and shrink and the stomatal aperture closes.
