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IGCSE Unit 8 TRANSPORT IN PLANTS 2015-16

Updated to follow Mary and Geoff Jones Cambridge IGCSE Biology Coursebook 3rd edition. Follows Co-ordinated sciences syllabus
by

Blanca Peris

on 27 February 2016

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Transcript of IGCSE Unit 8 TRANSPORT IN PLANTS 2015-16

CHAPTER 8 TRANSPORT IN PLANTS
Water evaporates from the leaves causing a kind of "suction" that pulls the water up the stem
Water travels up the stem through the xylem vessels. This flow is called
TRANSPIRATION STREAM.
Transpiration is the evaporation of
water vapour
from the leaves.
Importance of transpiration:
on a hot day trees may draw up hundreds of liters of water from the soil and most of it will evaporate in the leaves.
It is thought that this evaporation may help to cool the leaves in a very sunny day.
The role of the stomata: they help to control the balance between loss of water vapour and uptake of carbon dioxide.
They also react to water stress: if the leaf is losing water by transpiration faster than it is being taken up by the root they start to close to delay the wilting.
FACTORS AFFECTING THE RATE OF TRANSPIRATION
1. LIGHT INTENSITY:
In hot and cold climates, plants may suffer from water shortage. How?
Adaptations to arid conditions
1. Deciduos trees: they lose every evaporation surface when water may be unavailable.
2. Evergreen trees such as pines have small needle-like leaves reducing water lost.
3. Cacti are adapted to hot and dry conditions by having no leaves and their stem makes photosynthesis offering a small surface area for evaporation, their stomata are closed during the day, they store water in their tissues (succulent).
8.3 TRANSPIRATION
Mineral salts from the soils are carried to the leaves in the xylem vessels. Water and salts move always upwards.
QUESTIONS 8.6-8.9
p.99
8.2 UPTAKE OF WATER AND SALTS
Questions p 63
8.5 TRANSPORT OF GASES
Gases will move in and out of a plant by DIFFUSION (Definition?)
5 ABSORPTION BY LEAVES
Leaves absorb substances if they are sprayed on to them. Mineral ions in solution can be absorbed through the cuticle or the stomata. This can be used as fertilizer (FOLIAR FEEDING)

Some insecticides are systemic, they enter in the plant when the leaves absorb and translocates them. They have to be broken down to harmless molecules by the plant before they are used in human consumption.
THE END
2. HUMIDITY:
3. AIR MOVEMENTS:
4. TEMPERATURE:

light intensity the rate of transpiration.

In humid air rate

wind speed transpiration rate

Warm air rate
The phloem sap has
SUCROSE
and
amino acids
.
Transports water and salts in 1 direction.
Xylem
The cell walls are thickened with
lignin
which makes it strong and impermeable.
Transports food substances wherever they are needed.
Phloem
They are alive and have perforations in the end walls to allow the pass of substances.
8.1 PLANT TRANSPORT SYSTEMS
Why do plants need a transport system?
REQUIREMENTS
CO
2
WATER
MINERAL IONS
It simply diffuses as the branching shapes make every cell close to the surface.
Absorbed from the ground
Absorbed by the roots and needs to be transported to the leaves in the XYLEM.
PHLOEM: a second transport system for sucrose and amino acids from the leaves to places that need them
Its cells join end to end (cell walls disappear) forming elongated tubes called
vessels.
Food cannot enter in the cells and they die. Vessels contain no cytoplasm or nuclei
The cells form elongated tubes called
sieve tube elements
.
The cells lose their nuclei.
Vascular bundles (p. 95-96)
A group of xylem vessels and phloem tubes.
They have different positions. We can see them in transverse sections:
Transverse section of a root
Transverse section of a stem
They help to support the plant.
Are vascular bundles found in leaves?
QUESTIONS 8.1-8.5 p96
PATHWAY OF WATER
SALTS
: are taken by active transport (HOW?)
Water enters in plants through their root hair cells by
osmosis
.
FUNCTION: absorb water and minerals (ions) from the soil.
SPECIALISED CELLS: their structure provide a large surface area.
Osmosis: their cytoplasm is concentrated compared to the soil so water diffuses into them down its concentration gradient.
2. Then moves through the root CORTEX cells until the XYLEM.
1. Water enters a root hair cell.
4. Finally it reaches the mesophyll cells in the leaf.
3. It goes inside xylem vessels up the stem.
Thousands of leaves evaporate water like this and draw water to replace it from the xylem vessels.
The root cap protects the root as it grows through the soil
8.1 PLANT TRANSPORT SYSTEMS
Xylem
Phloem
Vascular bundles
8.2 UPTAKE OF WATER AND SALTS
8.3 TRANSPIRATION
Factors affecting transpiration
8.4 TRANSPORT OF MANUFACTURED FOOD
TRANSPORT IN PLANTS
Mineral ions are in low concentration in the soil. Always lower than in the root hair cell.
Special carrier proteins in the root hair cell carry the mineral ions against their concentration gradient.
During daylight stomata are open allowing water vapour to diffuse out so, although the effect is not direct:
If the air is very humid it has a lot of water vapour and it can accept little more so transpiration slows down.
In still air the region round a transpiring leaf will have a lot of water vapour so transpiration slows down.
Warm air can hold more water vapour so transpiration is quicker than in cold air. Kinetic energy of water molecules increases and they diffuse faster.
Roots obtain oxygen from air spaces in the soil.
In woody plants gases pass through small openings in the bark called
LENTICELS
.
In leaves and green stems gases enter and leave through the
stomata
.
End of Chapter Questions
Page 103
8.4 TRANSPORT OF MANUFACTURED FOOD
The movement goes from regions of production (or
sources
) to regions of storage or use (or
sinks
).
Its movement is called
TRANSLOCATION
and can be upwards or downwards.
This creates a water potential gradient in the xylem, drawing cohesive water molecules up the plant.
Transpiration produces a tension (pull) from above.
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