3.2 Photosynthesis - Affecting Factors Flashcards
Factors that affect photosynthesis- temperature
Biochemical processes are regulated by enzymes.
Enzymes are a kind of protein.
Enzymes have an optimum temperature at which they work best.
Above or below the optimum temperature the rate of biochemical process slows.
Plant growth has an optimal temperature, differs with different plants.
Generally between 20C and 30c lower for shade and marine plants.
Increase in temp> increased metabolic rate to optimum level.
Above threshold temps> enzyme systems deactivated.
Factors that affect photosynthesis.
Light Quality
Light can be measured in lux and as irradiance (watts oer meter squared.
Photosynthetically Active Radiation is in the region of 400 and 700nm.
A plant must receive sufficient light to enable photosynthesis to compensate for depletion of carbohydrates by respiration.
Below light compensation point, plant is losing, not gaining, carbohydrates.
Light quality refers to its wavelength.
Light compensation point
Point on light curve where the rate if photosynthesis exactly matches the rate of respiration> plant growth is optimized at this point.
Light saturation point
If light intensity becomes too great the rate if oxygen production tails off > further increase of light striking leaf does not increase rate of photosynthesis any further.
Light wavelengths
The quality of light refers to its wavelength.
Growth under green light (499-759nm) is slower than growth under red light (650 - 700mn)
Growth under high red and far red light is often more branching than that grown under other light conditions.
This is important when growing plants under artificial lights.
Nutrients essential for chlorophyll formation
Nitrogen
Magnesium
Iron
Water and photosynthesis to
Ware is essential to plant health, it is necessary for tissue and enzyme activity.
Wilted leaves cannot photosynthesise efficiently.
Water stress causes stomata to close.
Closed stomata cause shortage of carbon dioxide.
Plants that live in arid conditions have adaptations to avoid losing too much water vapor from open stomata eg.stomata open at night. Carbon dioxide intake is carried out and then stored until it can be used in photosynthesis.
Carbon dioxide levels and indoor growing environments
When carbon dioxide levels are below 150ppm photosynthesis stops.
Best range for most plants lies between 1000 and 1500ppm.
Supplementation of carbon dioxide may be necessary - carbon dioxide enrichment.
Above 5000ppm there is no advantage for photosynthesis but it is risky for greenhouse workers.
Environmental factors that limit or prevent entry if carbon dioxide into the leaf.
Wind speed, when wind speed is high the rate of transpiration may exceed the plants ability to absorb water.
Stomata may close.
Photosynthesis will halt as long as the stomata are closed.
When relatively humiliating outside the leaf is high the efficiency of diffusion through the stomata and this will influence the amount of carbon dioxide to leaf for photosynthesis.
Carbon dioxide - entry into leaf.
Stomata in leaf is the primary center if gas exchange.
When stomata are open carbon dioxide enters through diffusion as concentration of carbon dioxide is lower inside photosynthsising leaf than outside.
Once inside the leaf carbon dioxide is fairly soluble in water.
Therefore, it dissolves on the walls of leaf cells and diffuses through the cytoplasm to the chloroplasts.
Reasons for supplementary and replacement lighting and photoperiodic lighting.
Extending the day length.
Producing stronger crop during low light periods.
To trigger some photoperiodic response.
Producing a crop for a specific event eg, Valentine’s Day crop of roses.
Photoperiodic lighting - use of night break lighting or light breaks is more commonly used to shorten night length and cyclic lighting - not a factor photosynthesis.
