Transport of materials in the Flowering Plant

2 Contents Question Answer Uptake and transport of water Transpiration Structure of stomata Root Pressure Cohesion-Tension Model of Water Transport in Xylem Uptake and transport of -MineralsMinerals -Carbon dioxideCarbon dioxide -Photosynthetic productsPhotosynthetic products Modified Plant Food Storage Organs Modified Root Modified Stem Modified Leaf

3 Question Why do plants need a transport system?

4 Answer To transport water from … to …, food from … to …, minerals from … to …, gases (? and ?) from … to …and plant growth regulators from … to …

5 Materials needed for … Plants are autotrophic i.e. … Water, food, minerals, CO 2, O 2 etc. needed for metabolic reactions e.g. photosynthesis and respiration, growth and reproduction

6 Uptake and transport of water Water taken in at roots Absorbed through root hairs (large surface area, numerous and no cuticle) by osmosis Diffuses across the cortex from cell to cell and into the xylem Up the xylem vessels (continuous hollow pipeline) in the stem and out into the leaves From the leaves, through the stomata into the atmosphere as water vapour

7 Movement of water through a plant

8 Transpiration is the loss of water vapour from the leaves of a plant Water lost from cells of leaf Cells become less turgid Causes water to move into them from the xylem vessels Water is ‘pulled’ up the stem from the roots

9 Control of Transpiration is by the presence of a waxy cuticle on the leaves and by the opening and closing of the stomata Open by day – higher transpiration Closed at night – transpiration decreases Controlled by changes in the water content of the guard cells

10 Structure of stomata

11 Root Pressure The transport of water up through the xylem is helped by root pressure generated by water entering the root cells by osmosis which pushes the water up the xylem. Does not explain how water gets to the top of tallest plants Water rises as a result of a ‘push’ from below (root pressure) and a ‘pull’ from above (transpiration)

12 Cohesion-Tension Model of Water Transport in Xylem (1/3) = Dixon-Joly Theory. Most acceptable theory - based on cohesive forces of water i.e. the force of attraction between water molecules is great enough to maintain a continuous unbroken column of water and the adhesive forces of water molecules allowing water to ‘stick’ to the walls of the xylem vessels

13 Cohesion-Tension Model of Water Transport in Xylem (2/3) a)leaf cells lose water by evaporation to the atmosphere. b)These cells lose turgidity and draw more water from surrounding cells to try and maintain turgidity. c)This results in the formation of a suction pressure from air spaces to xylem vessels.

14 Cohesion-Tension Model of Water Transport in Xylem (3/3) d)Cells closest to the xylem vessels absorb water from the xylem by osmosis. e)This creates a tension / pull on the water in the xylem and draws the water upwards. f)The water is held at the top of the xylem by the adhesion of water molecules to the xylem wall. Dixon & Joly TCD 1895

15 Cohesion- Tension model

16 Uptake and transport of minerals Minerals are absorbed as ions e.g. magnesium as Mg ++, nitrogen as nitrate, NO3¯ They enter the root hairs dissolved in water by active transport They are transported from the roots to all parts of the plant by the same route as water

17 Uptake and transport of carbon dioxide Carbon dioxide can be obtained directly from respiring cells or enter the leaves by diffusion through the open stomata Needed for …

18 Uptake and transport of photosynthetic products The products are glucose and oxygen. glucose – may be stored as starch in the leaf or transported in the form of sucrose to any part of the plant that needs it Transported in the phloem sieve tubes – energy required – aka translocation oxygen – used in respiration or released through stomata by diffusion

19 Modified Plant Food Storage Organs Many plants store food from the end of one growing season to the beginning of the next in order to complete their life cycle. This is called perennation. The food is stored in perennating organs which can be modified root, stem or leaf.

20 How plants store food to survive the winter

21 Modified Root In some plants e.g. dicots, the first root grows straight down to form the main root of the plant Forms a tap root May become swollen with starch e.g. turnip, carrot, dandelion or sucrose e.g. sugar beet

22 Tap root

23 Modified Stem Underground stems enlarge with food stores called stem tubers e.g. potato. The ‘eyes’ are buds Buds are only found on stems

24 Stem tuber

25 Modified Leaf Swollen leaves that store food e.g. onion, tulip, daffodil These are called bulbs In celery and rhubarb it is the leaf petiole that is modified for food storage Many of these food storage organs are also used in asexual reproduction by the plants.

26 Bulb

27 END