The movement of particles of solute from a region of high solute concentration to a region of lower solute concentration until the solute is evenly spread out.
Examples of Diffusion
CO2 and urea out of cells
O2 and soluble food particles into cells
Food through the gut wall
CO2 and O2 through the wall of the alveolus
CO2 into the leaves of plants and O2 out of the leaves of plants
Osmosis
The movement of water from a region of higher water concentration to a region of lower water concentration, through a selectively permeable membrane (s.p.m.).
Examples of osmosis:
water into root cells
in the loop of Henle
the gills of fish
Water concentration describes the concentration of water in a sample:
Pure water has the highest possible water concentration
As solute is added the water concentration goes down
The words hypertonic, isotonic and hypotonic describe the water concentration of two solutions separated by a selectively permeable membrane such as visking tubing or a cell membrane.
Hypertonic -the solution with the lower water concentration
Hypotonic – the solution with the higher water concentration
Isotonic – two solutions with the same water concentration
Osmosis in Animal Cells
In osmosis in animal cells the red blood cell is generally used as an example
in the animation opposite it begins with a red blood cell in an isotonic solution.
By clicking on the buttons it is possible to change the concentration of the bathing solution to:
hypotonic:
the water concentration outside the cell is now higher than inside
more water molecules flow into the cell than flow out
the cell swells and bursts
hypertonic:
Osmosis in Plant Cells
the water concentration outside the cell is now lower than inside
more water molecules flow out the cell than flow in
the cell shrivels up
Plasmolysis – The state of a plant cell in a hypertonic solution, the cell shrinks.
Turgid – Plant cells in a hypotonic solution, the cell swells against the cell wall and the cell is rigid and firm
Flaccid – Plant cells in a hypertonic solution, the cell shrinks away from the cell wall and the cell is limp.
a chemical that causes a chemical reaction to occur, or speeds up a chemical reaction without itself being changed itself.
Substrate(s) + enzyme product(s)
The do this by lowering the activation energy for the reaction (the energy required to start a reaction(
Enzyme.
A biological catalyst
enzymes are proteins
they operate best at an optimum pH and temperature
Enzymes are denatured (destroyed) at high temperatures:
The shape of an enzyme is essential to the way it works, heating destroys the shape of a protein thereby destroying the ability of the enzyme to cause catalysis.
Most human proteins denature at a temperature around 65º
enzymes are specific to the reaction they catalyse (they catalyse one and only one reaction):
For example amylase turns starch into maltose, it has no effect on protein or fat
active site
the place on an enzyme where the substrate(s) binds
lock and key
the concept that enzymes operate by substrates fitting into a shape defined by the active site of the enzyme
A change in the enzyme then carries out the reaction on the substrates
Synthesis reactions – make more complex molecules out of simpler substrates
Glucose-1-phosphate + potato phosphorylase starch
Degradation reactions – break more complex molecules into simpler products
•
Amylase
Starch maltose
•
Pepsin
Proteins large peptides (chains of amino acids from protein digestion)
Respiration is a chemical process, occurring in the mitochondria in the cytoplasm of all living cells, which breaks down sugar to provide energy for the cell
Aerobic respiration requires the presence of oxygen
Anaerobic respiration does not require oxygen
Glucose is a source of energy in the cell
The chemical that transports and transfers energy in the cell is called ATP (adenosine triphosphate).
During respiration sugar is broken down into CO2 and water
During Respiration the energy compound ATP is made from ADP and inorganic phosphate molecules (Pi)
ADP + Pi + energy from respiration ATP
Where energy is required within the cell the reverse reaction takes place
ATP ADP + Pi + energy·
Some heat is lost as waste during respiration.
Stages of respiration
Glycolysis·
requires glucose as an energy source
Glucose is broken downinto 2 molecules of pyruvic acid
The pyruvic acid is broken down aerobically or anaerobically
2 molecules of ATP are generated in this stage.
Aerobic Breakdown
Only happens in the presence of oxygen:
Pyruvic acid enters the aerobic respiration system
CO2 is generated as waste
Hydrogen is given energy
It is passed on to a hydrogen acceptor molecule
It is then called a reduced hydrogen acceptor
Hydrogen is passed into another chemical system
The waste hydrogen is reacted with the oxygen to make water
The energy from the hydrogen is used to turn 36 molecules of ADP into 36 molecules of ATP
Giving a total of 38 molecules of ATP for aerobic respiration
Anaerobic Breakdown
In the absence of oxygen pyruvic acid is changed to:
Lactic acid in mammals
Alcohol (ethanol) and carbon dioxide in plants and fungi (such as yeast)
No further energy is produced
Giving a total of 2 molecules of ATP for anaerobic respiration.
Lactic acid in muscles leads to fatigue:
The reaction in animals is reversible – once oxygen is available the lactic acid is converted back to pyruvic acid.
The reaction in plants leading to alcohol is not reversible.
