New News Biology #24

Transport In Plants

Translocation = transport of sugar within the plant

Because the sugar is made in the leafs through photosynthesis, but it is needed throughout the plant, so the sugar needs to be transported by a clever mass transport system, the phloem tubes

The phloem tubes: these tubes are made up of living cells, and cell sap flows through pores within the cells. A marvelous feature is that cell sap can flow both up & down the plant

The cell sap: its actually a fancy name for the mixture of water & sugar within plants, and the sugar within it can be used up by the cells or stored up for use later

Transpiration = evaporation of water from leaves

Here’s an interesting question: ‘How does water move UP the plant if the plant doesn’t have a pump?’ Well it is done by the evaporation of water through another kind of tube, the xylem tube

The xylem tube: unlike the phloem tubes, these tubes are made up of dead cells (meaning they don’t have ends), and are used to transport water & mineral ions. It is strengthened by a material known as ‘lignin’

Rate of transpiration are determined by these factors:

Temperature: warmer temperatures = a higher rate of transpiration, because more water is likely to evaporate, dragging up the chain of water up the xylem tube

Air Flow: higher rate of airflow = higher rate of transpiration, as the concentration gradient is kept high

Light Intensity: brighter light = higher rate of transpiration, due to the fact that more stoma are opened for photosynthesis

Humidity: higher humidity = lower rate of transpiration, because the concentration gradient is lowered