BIOLOGY
YEAR 2
QUARTER 2
2020
Plant physiology
SUMMARY OF THE COURSE PLANT PHYSIOLOGYNWI-BB069B
ELISE REUVEKAMP
,Content
Day 1: Water and transport..................................................................................................................... 2
Water transport................................................................................................................................... 3
Day 2: Nutrients....................................................................................................................................... 9
Day 3: Photosynthesis ........................................................................................................................... 15
Light reaction..................................................................................................................................... 16
Dark reaction ..................................................................................................................................... 19
Cell walls and growth ........................................................................................................................ 21
Day 4: Introduction and shape .............................................................................................................. 22
Plant, cell, signalling and gene expressions (Introduction) ............................................................... 22
The general principle of signal transduction: .................................................................................... 23
Patterning (Shape)............................................................................................................................. 25
Auxin as morphogen (Shape) ............................................................................................................ 26
Day 5: Shape and Growth ...................................................................................................................... 28
Auxin signal transduction (Shape) ..................................................................................................... 28
Meristematic growth (Growth) ......................................................................................................... 30
Growth and auxin (Growth) .............................................................................................................. 31
Growth and gibberellin (Growth) ...................................................................................................... 32
Day 6: Adaptation .................................................................................................................................. 36
Light as signal for development (Adaptation) ................................................................................... 36
Photo- and gravitropism (Adaptation) .............................................................................................. 39
Salt inhibits growth (Adaptation) ...................................................................................................... 40
Adaptations to inundation/flooding (Adaptation) ............................................................................ 41
,Day 1: Water and transport
Water is essential for most plant functions:
- It provides firmness of the plant and enables growth
- Acts as a solvent
- Enables transport in the plant
Water has a very high consumption, which is necessary due to the loss of water when CO2 is taken
up from the air. The stomata open and CO2 is taken up, but the water is lost as suction allows
transport of water from the roots to the leaves. This suction is also necessary, so that the water is
distributed all over the plant.
- The plant keeps the water content in balance, as small
decreases in water content leads to high amounts of
stress.
Higher water availability leads to higher primary production
in agriculture and natural ecosystems. This is because plants
can take up more nutrients along with the water and therefore
photosynthesize better, since they can keep their stomata
open to take up CO2.
- More water → stomata open → more CO2 → more photosynthesis
- Less water → less transpiration → less CO2 → less photosynthesis
- Tropical → temperate → savanna → desert
Water is a very suitable solvent and transport medium due to characteristic physical properties:
1. It has high polarity → ions and polar molecules dissolve easily
2. It can form H-bridges → adhesion and cohesion forces contribute to attraction between
molecules and thus allows the transporting function of water.
Adhesion = is the attraction force between different molecules
Cohesion = is the attraction force between molecules of the same substances
Xylem and phloem form the vascular bundle transporting water, nutrients and carbohydrates in the
plant.
- Xylem → transports water and nutrients
from the roots through the rest of the
plant
- Phloem → transports carbohydrates
from the leaves to the rest of the plant
The epidermis is the outermost layer of the plant,
it provides a barrier to infection from
environmental pathogens and regulates the
amount of water released from the body into the
atmosphere through trans-epidermal water loss.
The cortex transports materials into the central cylinder of the root through diffusion and stores food
in the form of starch.
, The endodermis, regulates the water and other substances that get into the plant. It is a single layer
of cells that border the cortex. It allows what gets into the vascular core.
Water transport
Water transport in plants will always follow the water potential: the potential energy of water or its
ability to perform mechanical work. It evaluates the tendency of water to move from one place to
another.
Water will always move towards a more negative water potential. A low water potential implies
that the concentration of water and the driving force to move from one area to another is low.
The water potential depends on three factors; osmotic potential, hydrostatic pressure and
gravitational potential. The formula is expressed as follows:
(Pa = J/m3 = N/m2)
- Osmotic potential (Ψs) = the pressure that results from osmosis, water moves from
hypotonic to hypertonic solutions (or low osmolarity (<dissolved particles) → high osmolarity
(>dissolved particles)
Ψs = 0, no dissolved particles
Ψs < 0, the more negative the osmotic potential the more solvents present
o Ψs = - (n/V) · R ·T
➢ n= amount of dissolved particles (be mindful of salts)
➢ V= volume of solution (m3)
➢ R= gas constant (8.314K/mol)
➢ T= temperature (K) → not a big effect, as it is in Kelvin
- Hydrostatic pressure (Ψp) = physical pressure resulting from turgor or tension caused by
cohesion of the rising water in a vessel (pulling force)
Ψp < 0, pulling force that forces the water to go out of the cell
Ψp > 0, pushing force that forces the water to go into the cell
- Gravitational potential (Ψg) = pressure exerted by the position of the water column in the
field of gravity (when looking at small distances the effect of gravitational pressure is
negligible)
Ψg > 0, the water has a gravitational pressure pushing it downwards
➔ In whole plants (especially trees) gravity can potentially be a very important component.
o Ψg = ρw · g · h
➢ ρw is the density of the liquid (in kg m-3) = 0.998 · 103
kg m-3 for water.
➢ g is gravitational acceleration = 9.8 m s-2
➢ h is height (in m, really big values are needed for this
factor to make a significant difference in the potential)
Turgor = the pressure exerted by the cell wall on the plant cell.
- Turgor pressure is low, when the volume of the cell decreases due to water loss
- Turgor pressure is high, when the volume of the cell increases due to water uptake
When the water uptake and evaporation are un balanced, turgor loss will happen quickly →
shrinkage of the cell. Pure water in an open beaker at an atmospheric pressure of 1 atm has a
potential of zero: Ψs = 0 MPa, Ψp = 0 MPa, Ψg = 0 MPa.
YEAR 2
QUARTER 2
2020
Plant physiology
SUMMARY OF THE COURSE PLANT PHYSIOLOGYNWI-BB069B
ELISE REUVEKAMP
,Content
Day 1: Water and transport..................................................................................................................... 2
Water transport................................................................................................................................... 3
Day 2: Nutrients....................................................................................................................................... 9
Day 3: Photosynthesis ........................................................................................................................... 15
Light reaction..................................................................................................................................... 16
Dark reaction ..................................................................................................................................... 19
Cell walls and growth ........................................................................................................................ 21
Day 4: Introduction and shape .............................................................................................................. 22
Plant, cell, signalling and gene expressions (Introduction) ............................................................... 22
The general principle of signal transduction: .................................................................................... 23
Patterning (Shape)............................................................................................................................. 25
Auxin as morphogen (Shape) ............................................................................................................ 26
Day 5: Shape and Growth ...................................................................................................................... 28
Auxin signal transduction (Shape) ..................................................................................................... 28
Meristematic growth (Growth) ......................................................................................................... 30
Growth and auxin (Growth) .............................................................................................................. 31
Growth and gibberellin (Growth) ...................................................................................................... 32
Day 6: Adaptation .................................................................................................................................. 36
Light as signal for development (Adaptation) ................................................................................... 36
Photo- and gravitropism (Adaptation) .............................................................................................. 39
Salt inhibits growth (Adaptation) ...................................................................................................... 40
Adaptations to inundation/flooding (Adaptation) ............................................................................ 41
,Day 1: Water and transport
Water is essential for most plant functions:
- It provides firmness of the plant and enables growth
- Acts as a solvent
- Enables transport in the plant
Water has a very high consumption, which is necessary due to the loss of water when CO2 is taken
up from the air. The stomata open and CO2 is taken up, but the water is lost as suction allows
transport of water from the roots to the leaves. This suction is also necessary, so that the water is
distributed all over the plant.
- The plant keeps the water content in balance, as small
decreases in water content leads to high amounts of
stress.
Higher water availability leads to higher primary production
in agriculture and natural ecosystems. This is because plants
can take up more nutrients along with the water and therefore
photosynthesize better, since they can keep their stomata
open to take up CO2.
- More water → stomata open → more CO2 → more photosynthesis
- Less water → less transpiration → less CO2 → less photosynthesis
- Tropical → temperate → savanna → desert
Water is a very suitable solvent and transport medium due to characteristic physical properties:
1. It has high polarity → ions and polar molecules dissolve easily
2. It can form H-bridges → adhesion and cohesion forces contribute to attraction between
molecules and thus allows the transporting function of water.
Adhesion = is the attraction force between different molecules
Cohesion = is the attraction force between molecules of the same substances
Xylem and phloem form the vascular bundle transporting water, nutrients and carbohydrates in the
plant.
- Xylem → transports water and nutrients
from the roots through the rest of the
plant
- Phloem → transports carbohydrates
from the leaves to the rest of the plant
The epidermis is the outermost layer of the plant,
it provides a barrier to infection from
environmental pathogens and regulates the
amount of water released from the body into the
atmosphere through trans-epidermal water loss.
The cortex transports materials into the central cylinder of the root through diffusion and stores food
in the form of starch.
, The endodermis, regulates the water and other substances that get into the plant. It is a single layer
of cells that border the cortex. It allows what gets into the vascular core.
Water transport
Water transport in plants will always follow the water potential: the potential energy of water or its
ability to perform mechanical work. It evaluates the tendency of water to move from one place to
another.
Water will always move towards a more negative water potential. A low water potential implies
that the concentration of water and the driving force to move from one area to another is low.
The water potential depends on three factors; osmotic potential, hydrostatic pressure and
gravitational potential. The formula is expressed as follows:
(Pa = J/m3 = N/m2)
- Osmotic potential (Ψs) = the pressure that results from osmosis, water moves from
hypotonic to hypertonic solutions (or low osmolarity (<dissolved particles) → high osmolarity
(>dissolved particles)
Ψs = 0, no dissolved particles
Ψs < 0, the more negative the osmotic potential the more solvents present
o Ψs = - (n/V) · R ·T
➢ n= amount of dissolved particles (be mindful of salts)
➢ V= volume of solution (m3)
➢ R= gas constant (8.314K/mol)
➢ T= temperature (K) → not a big effect, as it is in Kelvin
- Hydrostatic pressure (Ψp) = physical pressure resulting from turgor or tension caused by
cohesion of the rising water in a vessel (pulling force)
Ψp < 0, pulling force that forces the water to go out of the cell
Ψp > 0, pushing force that forces the water to go into the cell
- Gravitational potential (Ψg) = pressure exerted by the position of the water column in the
field of gravity (when looking at small distances the effect of gravitational pressure is
negligible)
Ψg > 0, the water has a gravitational pressure pushing it downwards
➔ In whole plants (especially trees) gravity can potentially be a very important component.
o Ψg = ρw · g · h
➢ ρw is the density of the liquid (in kg m-3) = 0.998 · 103
kg m-3 for water.
➢ g is gravitational acceleration = 9.8 m s-2
➢ h is height (in m, really big values are needed for this
factor to make a significant difference in the potential)
Turgor = the pressure exerted by the cell wall on the plant cell.
- Turgor pressure is low, when the volume of the cell decreases due to water loss
- Turgor pressure is high, when the volume of the cell increases due to water uptake
When the water uptake and evaporation are un balanced, turgor loss will happen quickly →
shrinkage of the cell. Pure water in an open beaker at an atmospheric pressure of 1 atm has a
potential of zero: Ψs = 0 MPa, Ψp = 0 MPa, Ψg = 0 MPa.
