Back to AI Flashcard MakerBiology /Biology IB HL - Photosynthesis Key Concepts
What absorbs light and what is done with it?
Light is absorbed by chlorophyll, which convert the radiant energy into chemical energy (ATP)
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Key Terms
Term
Definition
What absorbs light and what is done with it?
Light is absorbed by chlorophyll, which convert the radiant energy into chemical energy (ATP)
Why does photosynthesis increase with light intensity?
As light intensity increases reaction rate will increase, as more chlorophyll are being photo-activated
Does photosynthetic rate increase linearly with light intensity?
At a certain light intensity photosynthetic rate will plateau, as all available chlorophyll are saturated with light
Will different wavelengths have different effects on photosynthesis?
Different wavelengths of light will have different effects on the rate of photosynthesis (e.g. green light is reflected)
What is the role of carbon dioxide?
Carbon dioxide is involved in the fixation of carbon atoms to form organic molecules
Why does photosynthesis increase with CO2 conc?
As carbon dioxide concentration increases reaction rate will increase, as more organic molecules are being produced
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| Term | Definition |
|---|---|
What absorbs light and what is done with it? | Light is absorbed by chlorophyll, which convert the radiant energy into chemical energy (ATP) |
Why does photosynthesis increase with light intensity? | As light intensity increases reaction rate will increase, as more chlorophyll are being photo-activated |
Does photosynthetic rate increase linearly with light intensity? | At a certain light intensity photosynthetic rate will plateau, as all available chlorophyll are saturated with light |
Will different wavelengths have different effects on photosynthesis? | Different wavelengths of light will have different effects on the rate of photosynthesis (e.g. green light is reflected) |
What is the role of carbon dioxide? | Carbon dioxide is involved in the fixation of carbon atoms to form organic molecules |
Why does photosynthesis increase with CO2 conc? | As carbon dioxide concentration increases reaction rate will increase, as more organic molecules are being produced |
Does photosynthetic rate increase linearly with CO2 conc? | At a certain concentration of CO2 photosynthetic rate will plateau, as the enzymes responsible for carbon fixation are saturated |
What two variables can be measured to measure rate of photosynthesis? | Photosynthesis can be measured directly via the uptake of CO2 or production of O2, or indirectly via a change in biomass |
What may be a confounding variable when measuring photosynthesis? | It is important to recognise that these levels may be influenced by the relative amount of cell respiration occurring in the tissue |
How can CO2 uptake be measured? | Measuring CO2 Uptake
Carbon dioxide uptake can be measured by placing leaf tissue in an enclosed space with water
Water free of dissolved carbon dioxide can initially be produced by boiling and cooling water
Carbon dioxide interacts with the water molecules, producing bicarbonate and hydrogen ions, which changes the pH (↑ acidity)
Increased uptake of CO2 by the plant will lower the concentration in solution and increase the alkalinity (measure with probe)
Alternatively, carbon dioxide levels may be monitored via a data logger |
How can O2 production be measured? | Oxygen production can be measured by submerging a plant in an enclosed water-filled space attached to a sealed gas syringe
Any oxygen gas produced will bubble out of solution and can be measured by a change in meniscus level on the syringe
Alternatively, oxygen production could be measured by the time taken for submerged leaf discs to surface
Oxygen levels can also be measured with a data logger if the appropriate probe is available |
How can biomass be measured to measure photosynthesis? | Glucose production can be indirectly measured by a change in the plant’s biomass (weight)
This requires the plant tissue to be completely dehydrated prior to weighing to ensure the change in biomass represents organic matter and not water content
An alternative method for measuring glucose production is to determine the change in starch levels (glucose is stored as starch)
Starch can be identified via iodine staining (turns starch solution purple) and quantitated using a colorimeter |
What is the only significant source of photosynthesis? | Only one significant source of oxygen gas exists in the known universe – biological photosynthesis |
What was done to oxygen before the development of photosynthetic organisms? | Before the evolution of photosynthetic organisms, any free oxygen produced was chemically captured and stored |
When did photosynthetic organisms begin to appear? | Approximately 2.3 billion years ago, photosynthetic organisms began to saturate the environment with oxygen
This led to changes in the Earth’s atmosphere, oceans, rock deposition and biological life |
How did o2 start accumulating in oceans? | Earth’s oceans initially had high levels of dissolved iron (released from the crust by underwater volcanic vents)
When iron reacts with oxygen gas it undergoes a chemical reaction to form an insoluble precipitate (iron oxide)
When the iron in the ocean was completely consumed, oxygen gas started accumulating in the atmosphere |
How did O2 start accumulating in the atmosphere? | For the first 2 billion years after the Earth was formed, its atmosphere was anoxic (oxygen-free)
The current concentration of oxygen gas within the atmosphere is approximately 20% |
How did o2 start accumulating in rocks? | Rock Deposition
The reaction between dissolved iron and oxygen gas created oceanic deposits called banded iron formations (BIFs)
These deposits are not commonly found in oceanic sedimentary rock younger than 1.8 billion years old
This likely reflects the time when oxygen levels caused the near complete consumption of dissolved iron levels
As BIF deposition slowed in oceans, iron rich layers started to form on land due to the rise in atmospheric O2 levels |
How did o2 start accumulating in bio life? | Biological Life
Free oxygen is toxic to obligate anaerobes and an increase in O2 levels may have wiped out many of these species
Conversely, rising O2 levels was a critical determinant to the evolution of aerobically respiring organisms |