Exam (elaborations)
BOT2603 Plant physiology, Water Relations and Plant nutrition
Consists of 26 pages of questions and answers from unit 1 to 6.
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Exam preparation Unit 1-6Unit 1(Bot2603)
Hydrogen bonding: chemical bond that happens between a hydrogen and a highly
electronegative atom such as N, O, or F. They have strong intermolecular forces. The bond
strength of hydrogen ranges from 4kJ to 50kJ per mole.
• Specific heat: this refers to the amount of heat a substance can store before it changes
temperature. The specific heat for water is 4.184J.g-1C-1
• Thermal conductivity: this refers to how heat is spread across a substance or object from
the point of application.
• Heat of fusion: this refers to the amount of energy it requires to change a solid to a liquids.
For H2O it is 335 J.g-1 at 0C̊
• Heat of vaporisation: Energy it requires to change liquid to a gas/vapour. Water it is 44KJ
mol-1 at 25 C̊
• Solvent properties of water: this means that water is able to dissolve several substances in
it. Due to water being a polar molecule and having partially positive and negative charges it
can easily dissolve other polar molecules and ions. Water also forms hydration shells around
the solute which its being dissolved. This is basically a clustered of water molecules that
form around the solute and prevent recombination of other solute or crystal structures from
being formed.
• Cohesion and adhesion properties: Cohesion refers to the intermolecular forces between
the same molecules (between water molecules). Adhesion refers to the attraction between
one substance and other substance. (Between water molecules and the side of the container
the water is in)
• Bulk flow: this refers to the flow of solutes due to external pressures being added. Such as
hydrostatic pressure created due to gravity. For example, some of the movement of water
from through the xylem and to the rest of the plant. It can also occur in the phloem with the
transport of larger solutes.
Diffusion: This refers to the movement of molecules from an area of high concentration to a
area of lower concentration. For example, when plants absorb carbon dioxide.
• Fick’s law: This law showcases all the variables that affect the rate of diffusion. The rate of
diffusion is directly proportional to the surface area and concentration difference and
inversely proportional to the thickness of the membrane.
• Osmosis: is the movement of water through diffusion hence from a area of high
concentration to an area of lower concertation through a semi permeable membrane.
• Membrane permeability: refer to the ability of a membrane to allow the flow of
substances through it.
, • Chemical potential: is the free energy per mole of a substance. Measuring the capacity of
a substance to react or move. Osmosis can only occur when there is a difference in chemical
potential across a selective permeable membrane.
• Water potential: this indicates how water will flow, which is from an area of high water
potential to an area of low water potential. The formula of water potential is the pressure
potential plus the solute potential. The solute potential refers to the osmotic potential of
the substance and pressure potential refers to the physical hydrostatic pressure in the cells.
• Plasmolysis: refers to the protoplast in the cell shrinking away from the cell wall. Hence
there is decrease in turgor pressure and the plant appears to be wilting. Occurs in a
hypertonic solution.
incipient plasmolysis: refer to the start of plasmolysis when the water starts to flow out of
the cell. And the protoplast pulls away from the cell wall.
• The configuration (structure) of the water molecule
Bent molecule consisting of 2 hydrogens and one oxygen.
Oxygen is highly electronegative
Hence it is bonded to hydrogen forming a polar molecule
Oxygen becomes partially negatively charged and hydrogen is partially positive.
• The hydrogen bond: key to the properties of water. Also study figure 1.1 (p 2).
Hydration shells: which is important for water as a solvent.
Bound water: tightly and orientated water molecules which cushions proteins.
The hydrogen bonds means that water can bond will several groups such as alcohols,
aminos, carbonyl groups.
• The comparison between water and other molecules of similar molecular mass (table 1.1,
p 2)
• The physical phase of water at physiological temperatures
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