transport transport in multicellular plants 5.3.3
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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
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