Photosynthesis Flashcards
Two major metabolic pathways for energy conversion in organisms
- Photosynthesis
- Respiration
Metabolism
Any chemical reaction taking place in an organism
Respiration
- Process whereby energy from nutrients is converted into energy
- can be used by the cell in the form of ATP.
ATP
- Adenosine triphosphate
- Energy carrier of the cell
Anabolic vs catabolic metabolic processes
- Anabolic = building-up process e.g. Photosynthesis
- Catabolic = breaking down process e.g. Respiration
Energy is…
The ability to do work or bring about change
First law of energy
Energy can be transformed from one form into another, but it cannot be created or destroyed
Second law of energy
When one form of energy is transformed into another form, some useful energy is always lost as heat
Photosynthesis takes place where?
In the chloroplasts of plants (and photosynthetic bacteria) that contain chlorophyll
Word equation for photosynthesis
(In the presence of light)
(Chlorophyll & enzymes)
Carbon dioxide + water —> glucose + oxygen
Chemical equation for photosynthesis
The process of photosynthesis described in words.
Carbon dioxide reacts with water in the presence of light, chloroplasts and enzymes to form glucose and oxygen.
Requirements for photosynthesis
- Carbon dioxide
- Water
- Light
- Chlorophyll
- Enzymes
Products of photosynthesis
- Glucose
- Oxygen
Plant organs where photosynthesis takes place
- Leaves
- (and to a lesser extent green stems)
How can a scientist establish whether photosynthesis has taken place in a leaf?
- Test the leaf for starch
- Glucose is formed by photosynthesis and this is then stored as starch.
The outline the test for starch
- Boil leaf in water to soften
- Pickle leaf in alcohol to dissolve chlorophyl
- Return leaf to hot water to soften and rince
- Place in petri dish and add iodine solution
- If iodine turns black then starch is present
How and why is a plant de-starched for an experiment?
- Plant is placed in the dark for a period of time
- Plant uses up all stored starch in its leaves
- De-starched plant can now be experimented on, the amount of starch the plants started with is fixed (i.e. none).
A leaf with parts that contain no chloroplasts
Variegated
How to test the requirement of chloroplasts for photosynthesis
- A variegated leaf is exposed to sunlight
- It is then tested for starch
- Where the leaf was green, the iodine turns black
- Where the leaf was cream, the iodine does not change colour
How to test the requirement of light for photosynthesis
- A de-starched plant has a leaf or part of a leaf covered with a material that excludes light (e.g. foil).
- The plant is exposed to sunlight.
- The leaf is tested for starch.
- Where the leaf was uncovered, the iodine turns black
- Where the leaf was covered, the iodine does not change colour
How to test the requirement of carbon dioxide for photosynthesis
- de-starched plants are sealed in a container containing either potassium/sodium hydroxide which removes atmospheric carbon dioxide or sodium bicarbonate which adds atmospheric carbon dioxide.
- The plants are exposed to sunlight.
- Leaves from each container are tested for starch.
- Where the plant was had carbon dioxide, the iodine turns black
Where the plant had carbon dioxide excluded, the iodine does not change colour
Main parts of a chloroplast
- Double membrane
- Fluid matrix inside called the stroma
- Parallel flattened sacs called thylakoids (contains chlorophyll)
- Clusters of thylakoids are called grana
- Grana connected by lamellae
Two-stages of photosynthesis
- Light-dependent phase: requires light to occur
- Light-independent phase: does not require light to occur, only occurs if the light-dependent phase has taken place
Importance of photosynthesis
- Source of food in food chains
- thus all heterotrophs ultimately depend on it for food
- maintain constant global levels of oxygen and carbon dioxide
Factors that affect the rate of photosynthesis
- Temperature
- Levels of carbon dioxide
- Light intensity
- Type/wavelength of light
- Water availability
Effect of carbon dioxide concentration on rate of photosynthesis
Generally:
- Lower carbon dioxide levels decreases rate
- Higher carbon dioxide levels increases rate up to a point, above which the rate decreases again.
Specifically:
- normal levels in atmosphere average about 0,04% carbon dioxide
- An increase of carbon dioxide up to about 0,5% increases rate of photosynthesis.
- however, after 10-15 days the rate decreases
Effect of temperature on rate of photosynthesis
- Optimum temperature generally around 25°C
- Rate of photosynthesis increases from about 10-25°C
- Rate decreases above 25°C as enzymes controlling photosynthesis become denatured.
Effect of light intensity on rate of photosynthesis
- Rate of photosynthesis increases as light intensity increases up to a maximum.
- The maximum rate is less if plant is not at optimum temperature or carbon dioxide concentration (limiting factors)
Explain a limiting factor for photosynthesis
- Photosynthesis rate being limited by one particular factor.
- E.g. Light, water and carbon dioxide could all be available at optimum levels yet it is a cold winters day.
- Thus the temperature will be a limiting factor on the growth of plants.
How can farmers increase the rate of growth of plants in a greenhouse system?
- Increase the amount of any limiting factor affecting the rate of photosynthesis for their crop.
- temperature
- carbon dioxide
- light
- water
How is temperature regulated in a greenhouse system
- greenhouses trap incoming radiation making it warmer
- and this can be regulated
- e.g. with windows or shade netting
How can carbon dioxide be regulated in greenhouse systems?
greenhouses can have extra carbon dioxide introduced
e.g. From respiration/combustion
Bacteria in compost respire increasing the levels
Artificially it can be pumped in from storage units
How can light be increased in greenhouse systems?
- extra lighting on dull/short days
- appropriate wavelength producing bulbs
How can water be regulated in greenhouse systems?
- Irrigation provided when water is limited
- Timers set to water the correct amount
- Nutrients can be added to the water
- Excess water and nutrients can be collected to be recycled
