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
