Transpiration & Translocation Noadswood Science, 2016

Transpiration & Translocation Wednesday, May 30, 2018 Transpiration & Translocation To explain the transpiration and translocation stream

Precise Learning Students should be able to explain the effect of changing temperature, humidity, air movement and light intensity on the rate of transpiration (measure the rate of transpiration by the uptake of water and investigate the distribution of stomata and guard cells) Students should be able to understand and use simple compound measures such as the rate of transpiration.   Students should be able to: translate information between graphical and numerical form plot and draw appropriate graphs, selecting appropriate scales for axes extract and interpret information from graphs, charts and tables. Students should be able to describe the process of transpiration and translocation, including the structure and function of the stomata. The role of stomata and guard cells are to control gas exchange and water loss.

The Root What are the functions of roots? Absorb water Absorb minerals Anchorage (hold the plant to the ground)

Roots Roots are spread out, helping both absorption of water and minerals and with anchorage… The roots are covered with millions of tiny root hair cells. These have a very large surface area, allowing the roots to absorb large amounts of water and minerals

The Leaf Leaves are designed for one thing – making food via photosynthesis Leaves are broad and flat to capture lots of light Veins carry water to the leaf, and food away to the rest of the plant (veins also support the leaf) Small holes called stomata in the underside of the leaf allow gases in and out

Leaf Components There are specialised parts to a leaf which help with photosynthesis

Epidermal Cells & Waxy Cuticle Cells in the epidermis make wax which covers the leaf surface (especially at the top) which limits water loss and acts as a protective barrier

Palisade Cells These cells are full of chloroplasts (containing chlorophyll) which it where photosynthesis takes place

Spongy Mesophyll This layer is full of air spaces which allows CO2 to reach chloroplasts in the palisade layer

Stomata Stomata are tiny holes which allow CO2 into the leaf (they also allow water to escape) The stomata are pores which open and close automatically controlled by guard cells When there is lots of water they become turgid so the pore opens When there is not much water they become flacid which closes the pore preventing water loss but it also stops CO2 getting in so photosynthesis stops too!

Xylem & Phloem Xylem tubes transport water Phloem tubes transport food

Xylem Xylem tubes are made from dead cells and transport water and minerals from root to stem

Phloem Phloem tubes are made of living tubes and they transport food substances (in both directions) – this is known as translocation

Transpiration Transpiration is the loss of water from a plant

Transpiration Stream Transpiration is the loss of water from a plant, moving from roots to leaves Water from inside a leaf evaporates and diffuses out of the leaf (mainly through stomata) This creates a slight shortage of water in the leaf, so more water is drawn up from the ret of the plant through the xylem vessels to replace it This in turn means more water is drawn up from the roots so there is a constant transpiration stream of water through the plant

Transpiration Issues Transpiration is a side-effect of the way leaves are adapted for photosynthesis They have to have stomata in them so that gases can be exchanged easily As there is more water inside the plant than in the air outside water escapes from the leaves through the stomata via diffusion

Practice Questions What is transported in phloem tubes? Which area of a plant do the phloem tubes transport substances from? Give two substances that are transported in xylem tubes Explain how water is transported from the roots of a plant to its leaves

Answers What is transported in phloem tubes – food substances / dissolved sugars Which area of a plant do the phloem tubes transport substances from – the leaves Give two substances that are transported in xylem tubes – water and mineral ions Explain how water is transported from the roots of a plant to its leaves – water is transported up a plant in the transpiration stream (escaping from stomata in the leaves, being drawn up by xylem and from the roots into the xylem)