Transport of materialsin the Flowering Plant

2

Contents

QuestionAnswerUptake and transport of waterTranspirationStructure of stomataRoot PressureCohesion-Tension Model of

Water Transport in Xylem

Uptake and transport of - Minerals- Carbon dioxide- Photosynthetic productsModified Plant Food Storage

OrgansModified RootModified StemModified 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 …andplant growth regulators from … to …

5

Materials needed for …

Plants are autotrophic i.e. …

Water, food, minerals, CO2, O2 etc. needed for metabolic reactions e.g. photosynthesis and respiration, growth and reproduction

6

Uptake and transport of water

Water taken in at rootsAbsorbed through root hairs (large surface

area, numerous and no cuticle) by osmosisDiffuses across the cortex from cell to cell

and into the xylemUp the xylem vessels (continuous hollow

pipeline) in the stem and out into the leavesFrom 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 leafCells become less turgidCauses water to move into them from the

xylem vesselsWater 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 stomataOpen by day – higher transpirationClosed at night – transpiration decreasesControlled 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 itTransported in the phloem sieve tubes –

energy required – aka translocationoxygen – 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 rootMay become swollen with starche.g. turnip, carrot, dandelionor sucrose e.g. sugar beet

22

Tap root

23

Modified Stem

Underground stems enlarge with food stores called stem tuberse.g. potato.The ‘eyes’ are budsBuds are only found on stems

24

Stem tuber

25

Modified Leaf

Swollen leaves that store food e.g. onion, tulip, daffodil

These are called bulbsIn 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