2.9 (Photosynthesis) Flashcards
What is photosynthesis?
Photosynthesis is a metabolic pathway. Carbon dioxide and along with water is used to produce carbohydrates. Oxygen is released as a waste gas.
What is the chemical equation for photosynthesis?
6CO₂ + 6H₂O ——— C₆H₁₂O₆ + 6O₂
Outline photosynthesis (according to chemical equation).
- Carbon is ‘fixed’ from carbon dioxide and used to produce to glucose.
- Water is split: the hydrogen is used to help in the production of glucose, but the oxygen is excreted as a waste gas.
- Light energy is transferred to chemical energy stored in the glucose molecule
- Used in respiration, stored as starch or used to build cell walls as cellulose
Define photolysis.
Splitting of water molecules
What are light dependent reactions?
Uses light energy to produce ATP and to split water, making H⁺ ions
What are light independent reactions?
Uses ATP and H⁺ ions to ‘fix’ CO₂, making glucose
What polysaccharide molecules are found in plants and what are their uses (2)?
- Starch: a chemical store of energy
* Cellulose: builds up the plant cell wall
Outline the electromagnetic spectrum.
- All radiation has a frequency and wavelength
- Waves with a low frequency are more spaced out, so have a longer wavelength and vice versa
- High frequency radiation has many waves per unit of time, therefore lots of energy
- Only a small part of the electromagnetic spectrum is visible to our eyes
- Low frequency radiation is low in energy, too low to be used in most organisms
- The pigments in photosynthetic organisms absorb wavelengths of light that contain energy appropriate for photolysis
- Gives rise to action and absorption spectra
Why does a leaf look green?
- Chlorophyll is the main photosynthetic pigment
- Blue and red wavelengths are absorbed
- Green light is reflected
Do all plants have the same action/absorption spectrum?
No, some plants have accessory pigments which allow them to take advantage of the green wavelengths of light.
How does light intensity affect the rate of photosynthesis?
- When light intensity is increased, the rate of photosyntheis increase, therefore it is the limiting factor at low levels
- At high levels of light intensity, further increases have no effect on the rate of photosynthesis, therefore another factor is limiting photosynthesis
How does CO₂ concentration affect the rate of photosynthesis?
- CO₂ is a substrate for the metabolic pathway hence the relationship is similar to how enzymes reactions are limited by substrate concentration
- At low concentrations it is the limiting factor, however at high concentrations it is not
How does temperature affect the rate of photosynthesis?
- Increases in temperature give molecules more kinetic energy causing substrates to collide with active sites more frequently, this increases the rate of photosynthesis
- As the temperature approaches the optimum the enzymes begin to denature (active site changes to become non-functional) causing the rate of photosynthesis to increase more slowly and eventually peak
- After the optimum temperature enzymes denature rapidly causing a fast decrease in the rate of photosynthesis as temperature increases further
How is the rate of photosynthesis measured (formula)?
Rate = change/time
How can each of the limiting factors of photosynthesis be investigated?
- CO₂ uptake:
Placing the plant in a closed space with water.
CO2 reacts with the water producing bicarbonate and hydrogen ions, which increases the acidity of the solution. Increased CO2 uptake -> increased pH -> increased rate of photosynthesis - Oxygen production:
Aquatic plants can submerged in water in a closed space with a gas syringe attached. Alternatively gas volume can be measured by displacing water in an inverted measuring cylinder or by simply counting bubbles.
Oxygen probes can be used with terrestrial plants kept in closed environments to measure increases in oxygen concentration - Change in biomass:
Glucose production can be (indirectly) measured by a change in a plant’s dry biomass.
starch levels in a plant (glucose is stored as starch)
can be identified by staining with iodine solution, this can be quantitated using a colorimeter
