Transport

Transport in multicellular plants

5.3.3

5.3.3.1

Explain the need for a transport system in plants

Explain what is transported in plants List the components of this system and their

Jobs

Poster

Make an informative A4 poster aimed at GCSE pupils showing– What plants transport and where – The components of the transport system and their

specific jobs– Why plants need a dedicated transport system

5.3.3.2

Explain why plants need a transport system Give an overview of the transport of water in

plants

Why transport?

Plant cells need– Carbon dioxide– Oxygen– Organic nutrients– Inorganic ions – water

For each requirement state what part of the plant the nutrient will come from and where it transported too.

Surface area and the need for transport

Very small organisms can absorb all their required nutrients and gasses through their surface

The larger the animal the smaller the surface area:volume

Therefore the surface is not large enough to provide all the nutrients the organism need

They therefore have specific exchange organs with large surface areas and a transport system

1. What are the exhange organs in plants?

2. What is the transport system?

Transport of water

There are 6 main stages in the transport of water by a plant

1. Water uptake near root tips2. Water enters xylem3. Water moves up xylem4. Water moves from xylem into leaf cells5. Evaporation of water into leaf air spaces6. Transpiration of water vapour through open

stomata

Water potential gradient

Water is at its greatest concentration at the roots

Therefore the water potential is at its greatest

As it travels through the plant it is travelling down its concentration gradient

This is passive transport

Water enters through the roots

The outer layer (epidermis) of root tip cells are drawn out into root hairs

This increases the surface area for osmosis to occur over

The uptake of water by osmosis produces root pressure which drives the transport

Transport through the roots

There are two possible pathways1. Symplast pathway (10%) in which the water travels

through the cytoplasm of the cells. The cytoplasms of all cells in the root are connected by plasmodesmata so no further osmosis occurs until the xylem is reached

2. Apoplast pathway (90%) in which water enter the space between the cell wall and cell membrane. Water can diffuse through the open cell walls without entering any cells. However this stops at the endodermis of the cells where there is a water proof strip (casparian strip) and the water has to enter the cells by osmosis and thus the symplast pathway.

Looking at slides

Look at the slides of the root hairs Save any pictures of good slides Also make labelled diagrams using the

guidance given

5.3.3.3

Look at slides of xylem Explain how water is transported from the root

to the tips of a plant

From the root cells to the xylem

Once the water meets the endodermis of the plant the waxy band of suberin in the casparian strip stops the apoplast pathway

All the water enters the symplast pathway and passes through passage cells and across the endodermis

This allows the plant to control what enters the xylem

Xylem tissue

These are tubes of dead cells which run from the root to the leaves

Water can move at 8m per hour

The differential in water potential drives this movement

Key processes = osmosis and transpiration

Cell types in the xylem (angiosperms)

Vessel elements Tracheids Fibres Parenchyma cells

Xylem vessels

Xylem start off as normal cells

They lay down lignin on the outside of the cell

This makes the cells water impermeable

The cells die leaving only the lignin

This is a long hollow tube

Tracheids

These are also dead cells with lignified walls

They do not have open ends so they don’t make vessels

They do have pits in their walls so water can pass between them

These are the main transport system in primitive plants like ferns and conifers

Flowering plants also have them but use mainly vessels

Fibres and Parenchyma cells

Fibres are elongated cells with lignified walls. They help to support the plant

Parenchyma cells are standard plant cells associated with the xylem tissue

They may store organic molecules or be involved in gaseous exhange

Microscopes

View xs of xylem- draw and save

5.3.3.4

Describe the pathway of water from the xylem to the leaf cells

Link the structure and function of stomata

Movement through leaves

At the leaves the xylem branches into leaf veins

There is one main vein and side veins branch off this.

They deliver water around the leaf

Movement through leaves (cont)

Water can move from xylem into cells by diffusion

It can pass through cells by symplast or apoplast pathways

Stomata

Water can evaporate from cells into air spaces around stomata (sub-stomatal air space)

It can then leave open stomata by diffusion

Guard cells open and close stomata

Stomata are the openings

Guard cells are crescent shaped cells around the opening

When turgid the cells make the stomata open

When water leaves them the guard cells become flaccid and the opening closes

Transpiration drives water transport

Looking at cells

1. Look at pre-prepared slides and make detailed drawings

2. Tear a leaf from distilled water solution and carefully pull off the lower epidermis

3. Wet mount and look for the stomata

4. Repeat with a leaf from a strong sugar solution

Homework

Discuss the importance of stomata to plants with reference to their structure and function.

5.3.3.5

Give examples of the adaptations a plant can have to reduce water loss

List and explain the factors affecting the rate of transpiration

Adaptations to water availability

Plants have to cope with different water availability and develop different adaptations for this

Mesophytes- adequate water Halophytes- salty water Hydrophytes- Freshwater Xerophytes- dry environments

These plants must limit their water loss

Xerophyte adaptations

Look at the plants and develop a table showing the adaptation and how it might help the plant

Adaptation How it works Example

thick cuticle stops uncontrolled evaporation through leaf cells most dicots

small leaf surface area less area for evaporation conifer needles, cactus spines

low stomata density fewer gaps in leaves

  stomata on lower surface of leaf only more humid air on lower surface, so less

evaporation most dicots

shedding leaves in dry/cold season reduce water loss at certain times of year deciduous plants

sunken stomata maintains humid air around stomata marram grass, pine

stomatal hairs maintains humid air around stomata marram grass, couch grass

folded leaves maintains humid air around stomata marram grass,

succulent leaves and stem stores water cacti

extensive roots maximise water uptake cacti

Factors affecting transpiration

Transpiration is affected by Humidity- High humidity reduces the water

potential gradient Light- Light stimulates the stomata to open,

allowing gas exchange for photosynthesis. A by product of this is transpiration

Temperature- a high temp reduces humidity and increases evaporation rate

Air movement- moves evaporated water from the stomata, increasing water potential gradient

Potometer

Use the potometer to find the effect of light/ wind movement on the rate of transpiration

Record all results neatly and write a full conclusion

Evaluate in full Use the simulation of the potometer- complete

activity 1 and 2. Explain the effect of these factors on

transpiration Complete for HWK

5.3.3.5

Draw they structure of phloem and annotate Explain how this is used to transport organic

molecules

Uses of phloem

Sugar is transported in phloem Sugar solution can be up to 30% concentrated Phloem transport is bidirectional- from a source

to a sink.

Structure of phloem

Phloem cells

Sieve-cells are cells with narrow pores all around them. Found in primitive plants

Sieve tube members have sieve plates on the end walls. Found in angiosperms

Companion cells are always found and they control the flow of food though the adjacent sieve cells

Phloem must be living to function They are elongated cells

Homework

Teaching one aspect of phloem in 5 minutes– Loading of sugars– Transport – Unloading– Differences in transport over the seasons– Puncture experiments– Ringing Experiments– Radioactive tracer experiments– Aphid Stylet experiments

5.3.3.8

Compare and contrast the action of phloem and xylem

Draw the structure of vascular bundles in different parts of the plant

Microscopes

Sketch the shape of the vascular bundle in– Roots– Stems– Leaves

Clearly label the xylem vessels and sieve elements in each vascular bundle

Compare and contrast

Using your text book, notes and the laptops produce a large table showing– Similarities – Differences

Between xylem vessels and sieve elements Clearly explain the mechanisms and

importance within this

Homework

Essay- ‘Describe the function of xylem and phloem within the vascular bundle of angiosperms. Your answer should make reference to the structure of these elements’

Use this to help you revise for a test next lesson