Transport Flashcards
Phloem
A plant transport tissue made of cells arranged end to end. They have cellulose cell walls and cytoplasm. The cytoplasm connects each cell together creating a sieve tube. It has no nucleus and is controlled by companion cells living next to the sieve tube.
Sieve plate (phloem)
The end of each cell is formed by a cross-section of cellulose with holes.
Sieve tube (phloem)
Living cytoplasm extend through the holes of the sieve plate and link with the next cell, forming the tube.
The sieve tube transports the products of photosynthesis from leaves to other parts of the plant. Sugar is taken to the roots and converted into starch for storage. Sugars for energy or amino acids for building proteins are carried to growing points in the plant.
Xylem
Transports water and minerals throughout the plant.
Structure of the xylem
Contains dead cells arranged end to end, forming a continuous vessel. The xylem has no cytoplasm. Water passes through the lumen (hollow space). The walls are made of lignin.
The xylem vessels begin as living cells with cytoplasm and cellulose cell walls. As they develop, they elongate and the cell walls are made of lignin. The cells die, forming lumen. Lignification makes them able to carry water up. Lignin is impermeable to water.
Root Hair cell
Main site of water absorption by the roots, the hairs increase the surface area of the root epidermis. Each hair is a specialized cell. The RHC penetrates between soil particles, reaching the soil water, containing dissolved solutes. Soil water has a higher water potential than inside the cell. Water enters the RHC by osmosis. Water moves from the RHC to the root cortex. A water potential gradient is kept going by water taken up by the xylem in the middle of the root.
Transpiration
Loss of water vapor, from the mesophyll cells, causes water to be pulled up the xylem in the stem and roots in a continuous flow (transpiration flow).
Transpiration function
Supplies water for leaf cells to carry out photosynthesis.
Carries mineral ions dissolved in water.
Provides water to keep the plant cells turgid.
Allows evaporation from the leaf surface, which cools the leaf (similar to humans sweating).
Rate of transpiration - 4 main factors
Light intensity
Temperature
Humidity
Wind speed
Rate of transpiration - Light intensity
The rate increases in light, because the stomata opens so that the lead can photosynthesize.
Rate of transpiration - Temperature
High temp increases the rate by increasing the rate of evaporation of water from mesophyll cells.
Rate of transpiration - Humidity
This reduces the diffusion gradient between the air spaces in the leaf and the external air. The rate of transpiration decreases in humid air and increases in dry air.
Rate of transpiration - Wind speed
The rate increases with faster air movements across the surface of the leaf. The moving air removes water vapor left near the stomata.
