Final Internal Assessment that received a high 7 grade with 21/24! Written on the topic of effect of salinity levels of water on transpiration rate.
WARNING: USE FOR REFERENCE ONLY
Investigation on the transpiration rate with different salinity levels of water
Research Question
What is the effect of salinity levels of water (0%, 10%, 20%, 30%, 40%) on the rate of
transpiration(mm/s) of a Nasturtium officinale, calculated by 50mm divided by the time(s)
taken for a plant to uptake 50mm of water?
Aim
To investigate the effect of salinity level of water on the rate of transpiration of a Nasturtium
officinale
Personal engagement
While crossing the Auckland Harbour Bridge on my way home, one day, I remember being
amazed by seeing how a vast number of plants were growing in seawater. Upon further
research, I learnt that the salinity of the ocean fluctuates over time as it goes through a
repetitive process of evaporating – increasing the salinity of water – and “salt sinks” –
decreasing salinity such as via the continuous input of freshwater from rivers. Thus, I
wondered how such fluctuation in seawater salinity impacted the growth of the plants
growing up in seawater. This, coupled with learning transpiration as a vital process for plant
growth in my biology lessons, led me to investigate the relationship between the salinity level
of water and the transpiration rate in my Biology Internal Assessment.
Background research
Water is vital for plants to undergo photosynthesis and growth. Therefore, whenever
transpiration evaporates water vapour at the stomata of the leaves – which are pores on the
underside of the leaf which facilitate gas exchange – this loss of water is replaced by water
transported upwards through the xylem vessel from the roots to the leaves. This flow of water
is referred as the transpiration stream (Graham et al, 2013).
Osmosis is a movement of water from regions with higher water potential (lower solute
concentration) to regions with lower water potential (higher solute concentration) (Allott &
Mindorff, 2014). The process of osmosis is used for the movement of water along the
transpiration stream in plants; the difference of water potential (solute concentration) between
the lower parts of the plant, root cells, and the upper parts of the plant, leaves, facilitates
osmosis and accordingly transportation of water in plants. This is applied also in the case
when the plant cuttings are not rooted, since despite the absence of root cells, there is still a
difference of water potential between the lower parts of the stem and the leaves that
stimulates osmosis (Simon et al, 2018). Therefore, the bigger the difference of water potential
is, between the lower and upper part of the plant cuttings, the faster the osmosis will occur,
and so does transpiration; the smaller the difference is, the slower the osmosis would occur,
as well as the rate of transpiration.
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