plant nutrition & transport
TRANSCRIPT
-
7/28/2019 Plant Nutrition & Transport
1/21
Plant Nutrition & Transport
-
7/28/2019 Plant Nutrition & Transport
2/21
Definitions
Transpiration
Loss of water vapour from the leaves
through the stomata by di f fus ion
Translocation
Movement of sucrose and amino acids
from regions of production or of storage toregions of use for respiration or growth
-
7/28/2019 Plant Nutrition & Transport
3/21
The Process of Photosynthesis
Green plants take in carbon dioxide through their leaves. Thishappens by diffusion.
Water is absorbed through plants roots by osmosis andtransported through the xylem vessels
Chloroplasts, containing chlorophyll, are responsible for
trapping light energy This energy is used to break up water molecules and then to
bond hydrogen and carbon dioxide to form glucose
Glucose is usually changed to sucrose for transport around
the plant, or starch for storage. Oxygen is released as a waste product, or used by the plant
for respiration.
-
7/28/2019 Plant Nutrition & Transport
4/21
Testing a leaf for Starch the Process
Stage Reason Safety PointsBoil the leaf in water To kill the leaf this
makes it permeable
Danger of scalding
Boil the leaf in ethanol To decolourise the leaf
chlorophyll dissolves in
ethanol
No naked flames
ethanol is highly
flammable
Rinse the leaf in water Boiling the leaf in
ethanol makes it brittle
the water softens it
Spread the leaf out on a
white tile
So that the results are
easy to see
Add iodine solution to
the leaf
To test for the presence
of starch
Avoid skin contact with
iodine solution
-
7/28/2019 Plant Nutrition & Transport
5/21
Factors needed for Photosynthesis Experiments can be used to find out what factors are needed for
photosynthesis
First the plant is destarched. This involves leaving the plant in thedark for 48 hours
The plant uses up all the stores of starch in its leaves
One plant is exposed to all conditions needed this is the control
Another plant is deprived of one condition
After a few hours the starch test is carried out on the control andtest plant/leaf
When tested only the parts of the plant that contain chlorophyll willcontain starch
The carbon dioxide around a plant can be controlled by keeping theplant in a sealed container with carbon dioxide absorber such assodium hydroxide pellets.
The control plant would be in an identical container, without carbondioxide absorber
-
7/28/2019 Plant Nutrition & Transport
6/21
Ext only
Effects of light intensity &
Carbon Dioxide concentration on
photosynthesis As light intensity increases, so does the rate ofphotosynthesis (graph page 32)
The light intensity (I) is related to the distance
(d) between the lamp and the plant (I = 1/d2) As the lamp is moved closer, the light intensity
increases.
The photosynthetic rate cannot be increased
indefinitely; a point is reached where all thechloroplasts cannot trap any more light
Also if there is a limiting factor (such as carbondioxide) the rate of photosynthesis becomes
limited.
-
7/28/2019 Plant Nutrition & Transport
7/21
Ext only Use of carbon dioxide enrichment,
optimum light and optimum temperatures in
greenhouse systems Greenhouses are used in some countries to control
conditions for plant growth, especially when growingconditions outside are not ideal. The glass helps trapheat inside, and atmospheric conditions can be
controlled. Atmospheric air only contains 0.04% Carbon dioxide,
so it can easily become a factor that limits the rate ofphotosynthesis. A greenhouse is a closed system, so
the content of the air in it can be controlled. Forexample, the amount of carbon dioxide can beincreased by burning fossil fuels in the greenhouse, orreleasing pure carbon dioxide from a gas cylinder
If lighting is not optimum artificial lights are used
-
7/28/2019 Plant Nutrition & Transport
8/21
Leaf Structure
-
7/28/2019 Plant Nutrition & Transport
9/21
Leaf StructurePart of a Leaf Details
Cuticle Made of wax, waterproofing the leaf. It is secreted by cells of the upper
epidermis
Upper
Epidermis
These cells are thin and transparent to allow light to pass through. No
chloroplasts are present. They act as a barrier to disease organisms.
Palisade
mesophyll
Main region for photosynthesis. Cells are columnar (quite long) and packed
with chloroplasts to trap light energy. They receive carbon dioxide by diffusion
from air spaces in the spongy mesophyll
Spongy
mesophyll
Cells are more spherical and loosely packed. They contain chloroplasts, but not
as many as in palisade cells. Air spaces between cells allow gaseous exchange
carbon dioxide to the cells oxygen from the cells during photosynthesis
Vascular bundle This is a leaf vein, made up ofxylem and phloem. Xylem vessels bring water
and minerals to the leaf. Phloem vessels transport sugars and amino acids away
(this is called translocation)
Lower
epidermis
Acts as a protective layer. Stomata are present to regulate the loss of water
vapour (this is called transpiration). Site of gaseous exchange into and out of
the leaf.
Stomata Each stoma is surrounded by a pair of guard cells. These can control whether
the stoma is open or closed. Water vapour passes out during transpiration.
Carbon dioxide diffuses in and oxygen diffuses out during photosynthesis.
-
7/28/2019 Plant Nutrition & Transport
10/21
Importance of nitrate and
magnesium ions
Nitrate ions
are needed to synthesise (build up) proteins
Remember that all proteins contain the element nitrogen
To build proteins, plants first make amino acids
Each amino acid is formed by combining sugars, made
during photosynthesis, with nitrate
The amino acids are made into long chains by bonding
them together
The proteins are used to make cytoplasm and enzymes Magnesium ions are needed to make chlorophyll. Each
chlorophyll molecule contains one magnesium atom.
Plant need chlorophyll to trap light to provide energy
during photosynthesis
-
7/28/2019 Plant Nutrition & Transport
11/21
Nitrogen Fertilisers
Use
To increase crop yields. Intensive farming(repeatedly using the same land for crops) removes
nitrates from the soil. These need to be replaced to
prevent a drop in yield. Nitrates can be replaced in
three ways: Applying animal manure
Crop rotation growing leguminous plants such as
peas, beans and clover every 2 or 3 years; these plants
develop root nodules containing nitrogen-fixing
bacteria, and the roots are ploughed into the soil,
boosting nitrate levels
Adding artificial fertilisers such as ammonium nitrate
-
7/28/2019 Plant Nutrition & Transport
12/21
Nitrogen Fertilisers
Dangers of overuse Wilting and death of plants. Applying too much
nitrogen fertiliser can result in water being drawn out
of the plant roots by osmosis. The plants wilt and
may die.
Eutrophication this is the destruction of life in
nearby rivers or lakes.
-
7/28/2019 Plant Nutrition & Transport
13/21
Flowchart of overuse - Dangers of
overuse
LeachingNitrates are soluble they can be leached out of the soil by heavy
rainfall and are carried into the nearest water system such as a river
Rapid algal growth
The presence of extra nitrates promotes growth of water plants (algae)
Death of algae
Surface algal growth blocks light for algae below as the surface algae
grow more quickly they also die
Decay by bacteria
As the algae die, they are decomposed by bacteria the bacteria
respire aerobically, using up oxygen
Death of aquatic animals
Fish and other aquatic animals die from lack of oxygen
-
7/28/2019 Plant Nutrition & Transport
14/21
Ext only Effects of nitrate ion & magnesium ion
deficiencies on plant growth
Nitrate ion deficiency If the plant has a nitrate ion deficiency it will not be able to
make proteins, so growth will slow down
The stem becomes weak, lower leaves become yellow and
die, while upper leaves turn pale greenMagnesium ion deficiency
If the plant has a magnesium ion deficiency it will not be able
to make a chlorophyll
Leaves turn yellow from the bottom of the stem upwards.Plant growth will suffer because it will have reduced
photosynthesis
Yellowing of leaves due to lack of magnesium ions is called
chlorosis
-
7/28/2019 Plant Nutrition & Transport
15/21
Transport in Plants
Root Hair Cells These form on young roots to increase the surface
area of the root for absorption of water and mineral
ions, as well as providing anchorage for the plant
The cell extension (the hair) increases the surface
area of the cell to make it more efficient in absorbing
materials
http://www.bbc.co.uk/schools/ks3bitesize/science/images/plant_root_cell.gif -
7/28/2019 Plant Nutrition & Transport
16/21
Passage of water through
root, stem & leaf
Water passes through the cells of the root byosmosis, reaching the xylem vessels in the centre
When the water reaches the xylem it travels up these
vessels, through the stem to the leaves
Mature xylem cells have no cell contents, so they act
like open-ended tubes allowing free movement of
water through them
In the leaves, water passes out of the xylem vesselsinto the surrounding cells
Mineral ions are also transported through the xylem
-
7/28/2019 Plant Nutrition & Transport
17/21
Transpiration
Transpiration is the loss of water vapour from a leaf Water in the leaf cells forms a thin layer on their
surfaces
The water evaporates into the air spaces in the
spongy mesophyll
This creates a high concentration of water molecules
They diffuse out of the leaf into the surrounding air,
through the stomata, by diffusion
-
7/28/2019 Plant Nutrition & Transport
18/21
Factors affecting the transpiration rate
Factor ExplanationIncrease in temperature Increases the kinetic (movement) energy
of water molecules, so they diffuse
faster
Increase in air movement, e.g.
Wind
Removes water molecules as they pass
out of the leaf, maintaining a steep
concentration gradient for diffusion
Decrease in humidity Results in a lower concentration of
water molecules outside the leaf,
making a steeper concentration gradientof diffusion
Increase in light intensity Stomata open to allow gas exchange for
photosynthesis, so water vapour can
diffuse out of the leaf
-
7/28/2019 Plant Nutrition & Transport
19/21
How wilting occurs
Young plants stems and leaves rely on their
cells being turgid to keep them rigid
If the amount of water lost from the leaves of
a plant is greater than the amount taken into
the roots, the plant will have a water shortage
Cells become flaccid if they lack water, and
they will no longer press against each other
Stems and leaves loose their rigidity, and wilt
-
7/28/2019 Plant Nutrition & Transport
20/21
Ext only Mechanism of water uptake
Water enters root hair cells by osmosis. Thishappens when the water potential in the soilsurrounding the root is higher than in the cell
As the water enters the cell, its water potentialbecomes higher than in the cell next to it, e.g. Inthe cortex.
So, the water moves by osmosis, into the next
cell. The process is repeated until water reachesthe xylem. Water also passes from cell to cellalong the cell walls
-
7/28/2019 Plant Nutrition & Transport
21/21
Ext only Mechanism of water
movement through a plant
Water vapour evaporating from a leaf creates akind of suction, as water molecules are attractedto each other.
So, more water is drawn into the leaf from thexylem
This creates a transpiration stream, pulling waterup from the root
Xylem vessels act like tiny tubes-drawing waterup the stem by capillary action. Roots alsoproduce a root pressure, forcing water up xylemvessels