transport in plants
Why so there a need for transport systems both in plants and animals?
For the delivery of essential substances /nutrients to all parts of the organisms/cells
Can result in growth
Energy
Nutrients
Defence and immunity
To ensure that waste products are removed from cells or body
Urea
Co2
Animals and plants have a small surface area to volume ration therefore they need transport system to ensure that substances get to where they are needed
If you breathe in, the first place the air goes to is the lungs but the oxygen should travel around the body
It would takes hours to get to your fingers and toes if we did not have a good delivery system
Plant transport system comprises of the tissues
Xylem
To transport H20 by osmosis and mineral ions by active transport from roots to all parts of plants
Also gives mechanical and physical support to the plant - due to a substance called lignin
Lignin is a woody, tough, thick, material
Phloem
Tissues that carries amino acids and sucrose to all parts of the plant
X
Individual cells with horizontal cross walls
Plants grow and develop
Cross walls have broken down to form a vessel and tube thus allows h2o to flow through
P
Development of plant
Sieve plates
Cells now have perforations
Identify positions of transport tissue (xylem an phloem)
In dicot roots system and leaves
Task
Draw transverse(cross section) section of
Root
Stem
| Chapter 8 |
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Xylem and phloem
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Plant transport system
All organisms obtain substances somehow
Plants and animals do it differently
Plants from the ground
Mineral ions, water
Carbon dioxide
Branching shapes
In plants
Increases surface area
Relation to volume
Most cells close to surface
Water absorption from roots
Transported to leaves
Transport system called xylem
Mineral ions too
Second transport system
Phloem
Sucrose and amino acids
From leaves and around plan
Xylem
Long drainpipe kind of
Hollow, dead cells
Open tube formed
From roots through stem into every leaf
No nuclei or cytoplasm
Cellulose and lignin cell walls
Lignin is a hard, strong, waterproof substance that forms the walls of xylem vessels
Strong so plant can keep upright
Wood almost lignin entirely
Thick cell walls
Supports xylem vessels
Stop it collapsing inwards
Thin area of wall
Helps movement of water between adjacent xylem vessels
Space in between
Continuous tube
No end walls
Movement for air upwards
Gap where end wall of cell has been lost
Continuous, hollow tube
Function | Feature | Explanation |
Support | The walls of vessels contain lignin |
|
Transport | The cells are dead, with no contents | Water can flow easily through the tube |
| There are no cross walls between dead cells | There is continuous tube for water to flow through, all the way from the roots to the leaves |
| The walls of vessels contain lignin | Lignin is solid and makes sure the vessels stay open and not collapse, allowing water to flow through easily. |
| The diameter of the vessels is between about 15μm and 200μm | This is narrow enough to make sure the column of water inside them does not break; but wide enough to allow a lot of water to flow through. |
Vascular bundles
Xylem and phloem vessels are found close together
Grouped together sort of
Vascular bundles
Roots and stems
Vascular tissue in center
Vascular bundles arranged in a ring
More disorganised in dicots
Found in leaves
Support leaves
Hold leaves flat to capture sunlight
Transport of water
Taking or carrying from one place to another
Water uptake
Root hairs take water from the soil
Tip of roof
Protective cap
Protects growth through soil
Formed by cells in epidermis
No root hairs
Start way behind it
Root hairs don't live long
Damaged by soil
Get replaced
Root hair functions
Absorb water and mineral ions
Water moves into with osmosis
Cytoplasm and cell sap
Quite concentrated
Water in soil is more dilute
Water diffuses into root hair
Down concentration gradient
Through partially permeable membrane
Large surface area
Increases uptake
The pathway of water through a plant
Xylem vessels in the center of root hairs
Water travels up through these vessels
Water travels by osmosis
Through cortex
Tissue of unspecialised cells lying between the epidermis and the vascular tissues of stems and roots
Cell to cell
Seep through space of cells or cell walls
Never entering the cell
Reaches xylem
Transports up root into stem
Water reaching xylem
Moves up
Like a drinking straw
When sucking a straw, you reduce pressure at top
Pressure at the bottom is high
Transpiration
Loss of water vapour from plant
Loss usually takes place in leaves
Leaves open with stomata
Underside
Lower epidermis
Covered with thin film of water
Evaporates from cells into air
Diffuses out of leaf
Mesophyll cells as osmosis
Water is always taken upwards
Xylem vessels
Supply leaf cells
Reduces pressure at the top so that water flows up
Transpiration stream
Transpiration pull
Spongy mesophyll
Important
Helps keep water moving through
Large surface area
Contact with air spaces in leaf
Liquid into mesophyll
Osmosis through xylem
Evaporates from cell walls
Water vapour into interconnecting air spaces
Diffusion out of stomata
Into air surrounding leaf
Greater in leaves with many open stomata
Reduces pressure in vessels
Movement of water from xylem, through mesophyll, into air spaces and removed from upper ends of xylem
Kind of similar to a straw
Because liquid molecules have a tendency to stick to each other
Pressure at the top is less
From high to low pressure
Transpiration pull
Pressure difference
A force produced by the loss of water vapour from a leaf, which reduces the pressure at the top of xylem vessels
Evaporation or excretion of water from the surface of cells in the leaves
Aids drawing water upward from roots to leaves
Measuring transpiration rates
Measuring how much water was taken up is easier than how much water??
Potometer
Water measurer
Different kinds
Transpiration rate determined on how quick a plant takes up water
Conditions that affect transpiration rate
The rate water vapour diffuses is affected by its environment
Higher temperature, quicker wind, transpiration faster
Higher temperature
More kinetic energy
Water evaporates faster
From surface of mesophyll cells
Diffuses out leaf
Windy day
Wind around there contains a lot of water vapour
Diffusion gradient for water vapour
Water vapour diffuses out leaf faster than when a day is still
Humidity
The moisture content in the air
Less water diffuses out the leaves
Not much of a diffusion gradient
Transpiration decreases as humidity increases
High temperature and dry air
Transpiration will happen more quickly
Plants lose water faster
Some plant cells become flaccid
Eventually the leaves will wilt
Translocation of sucrose and amino acids
Translocation - movement of sucrose and amino acids in phloem from sources to sinks
Sources and sinks
Source
Part of a plant that releases sucrose or amino acids, to be transported to other parts
Sink
Part of a plant to which sucrose or amino acids are being transported, and where they are used or stored
During active photosynthesis
Leaves are usually the major sources
Producing sucrose
Roots and flowers are the sinks
Roots change sucrose into starch for easier storage
Flowers use sucrose into fructose
The sweet-tasting sugar in nectar
Sucrose is sometimes later on used to make sweet fruits
During harsh environmental conditions
Could be hot and dry for some countries, other countries could be winter
Plant does not photosynthesise now
The sinks now become the sources
Stored materials convert start into sucrose so it can be transported
