IB Biology Extended Essay

Candidate number: 000763-014

OVERSEAS FAMILY SCHOOL (0763)

ASSESSMENT:

Extended Essay

SUBJECT:

Biology

TITLE: Can the seeds of tropical plants with soft coats and a germination period of maximum 2 weeks germinate in winter conditions?

WORD COUNT: 3988

CANDIDATE NAME: Claudia Antoinette Braganza CANDIDATE NUMBER: 000763- (014) EXAM SESSION: May 2012

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ABSTRACT The aim of this essay was to try and answer the question Can the seeds of tropical plants with soft coats and a germination period of maximum 2 weeks germinate in cold and winter conditions? The independent variable in this investigation was temperature, because I manipulated 3 different temperatures (Room Temperature 26oC, cool conditions 3oC and 7oC and winter conditions -12oC) in order to find out about the germination process in tropical seeds when subjected to different environmental conditions. I did this by attempting to control the amount of water given and the oxygen levels the seeds are subjected to; I then placed the seeds in egg trays filled with soil in their different locations for them to start germinating. Of course, I watered them first; I watered them every two days to keep the soil damp. I then recorded the amount of days taken by each seed to germinate judging by the appearance of the first hooked hypocotyl above the soil. The seeds I chose were garden plant seeds, in alphabetical order: Groundnuts, Green Field Peas, Marigold Sierra Yellow, Tomato, Zinnia Dahlia Flora and Zinnia Lilliput. They all germinated epigeally, which meant the hypocotyl emerges above the ground first to mark germination. From the results of my experiment, I could quite safely conclude that these specific seeds had entered into a period of dormancy due to the lack of suitable temperatures in order to germinate. I also suggested that these seeds may have become quiescent because they are ripe seeds that don’t germinate under harsh external conditions until suitable germination requirements for the specific seed has been fulfilled. I termed them as quiescent because compared to their normal germinating conditions, the temperatures I subjected them to were quite harsh.

Word count: 290

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CONTENTS PAGE

1. INTRODUCTION AND HYPOTHESIS

4

2. APPARATUS AND METHODOLOGY

9

3. PICTURE OF EXPERIMENTS

11

4. DATA ANALYSIS

12

5. CONCLUSION AND EVALUATION

17

6. APPENDIX

19

7. WORKS CITED LIST AND BIBLIOGRAPHY

21

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INTRODUCTION AND HYPOTHESIS The aim of this investigation is to find out Can the seeds of tropical plants with soft coats and a germination period of maximum 2 weeks grow in cold and winter conditions? I chose the topic of germination because not much is taught in the IB syllabus about the process physically and chemically except for the factors of germination. My interest in plants stems back to my younger days. My grandmother grew a variety of plants in her garden and I remember watching her plant the seeds in soil and watching them grow over the months and years. Up until Year 6, I just put the explanation down to magic, as most ignorant young children would. One day, my science teacher assigned us to grow our own plants for fun and record the variables and outcomes of the process, to get us used to distinguishing between controlled and manipulated variables. There was no real theory to be learned as a result of this, one could call it an initiation into the world of practical lab work. As the weeks passed, I manipulated different variables such as oxygen, amount of moisture or water and temperature. What I didn’t realize at the time was that the three factors I was manipulating were in fact the three important factors required for germination. So when the time for deciding an EE topic, I immediately knew I wanted to investigate germination in plants in detail. Since I’ve only lived in Southeast Asia, and the weather consists of tropical dry and wet seasons, I decided to investigate germination in tropical plants. I was also interested on whether tropical plants could germinate in cool or winter conditions since they usually do not need a period of dormancy; I wanted to find out exactly what happens and why it happens. So, would cold temperatures induce dormancy in the seeds or slow down the process of germination?

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Example structure of a seed (Allott 85)

Germination is defined as the process in which a plant or a fungus emerges from a seed or a spore, respectively, and begins growth (Wikipedia). A seed is a small package produced in a fruit or cone after the union of the pollen from the anther and the ovules in the ovary (Cactus-art.biz). All fully developed seeds will contain an embryo, and most plant species will have foods reserves stored which are wrapped in by the testa. Some plants produce a number of seeds that lack embryos called empty seeds, and they never germinate (Buzzle.com). Most seeds go through a period of quiescence, where no active growth of any kind is recorded; during this time, seeds can be transported to a new location or survive adverse climates until favourable circumstances of growth are met (Wikipedia). Quiescent seeds can be defined as ripe seeds that don’t germinate because of being subject to harsh external environmental conditions which prevent the initiation of metabolic processes and cell growth (Dictionary.com, Wikipedia). Once the favourable conditions are met, the seeds will then begin the process of germination. Essentially, germination is the resuming of growth of the dormant embryonic plant inside the seed. Complex physical and chemical changes begin as the embryo starts to develop into a young shoot and root. Then, the seed sends its first radicle into the soil and its first stem and cotyledon into the sunlight. Mostly, the emergence of a radical marks the end of germination. Page | 5


Seed germination is affected by both internal and external conditions. The most important external conditions are temperature, water, oxygen and at times, light or darkness (Clegg 322-323). Firstly, water is required for germination because mature seeds are extremely dry. They need to take in a significant amount of water that is relative to the dry weight of the seed in order for metabolic processes and growth to resume (Plantphys.info). The seeds would need enough water to moisten them, but not enough to soak. The process of uptake of water is called imbibition and this leads to the swelling and breaking of the testa (Wikipedia). Most plants store a food reserve within the seed, such as proteins, starch and oils, which provide nourishment to the growing embryo. When imbibition occurs, hydrolytic enzymes are activated; they break down the food storage resources and turn them into metabolically useful chemicals (Clegg 323). Of course, they need the second factor oxygen, which must be available for aerobic cell respiration. Some seeds respire anaerobically if oxygen isn’t available but the ethanol produced in anaerobic respiration soon reaches toxic levels. Also, suitable temperatures are needed for germination to occur. The process involves enzyme activity (such as the hydrolytic enzymes) and the activity is too slow at very low or high temperatures (Buzzle.com). Some seeds may remain dormant if temperatures are above or below a particular point, and only germinate during certain times of the year. Lastly, light or darkness can be an environmental trigger for germination to occur. This is a type of physiological dormancy. Most seeds aren’t affected by light or dark, but some need light to enable the process to begin (Wikipedia). The metabolic events during germination are as follows; soon after absorbing water, the plant growth hormone called gibberellin is produced in the cotyledons. Gibberellin stimulates the production of amylase, which then catalyses the breakdown of starch into maltose in the seed’s food reserves. The maltose is then transported to the growth regions of the embryo, including the root and shoot, from the food reserves. This maltose is converted into glucose, either for aerobic respiration or cellular growth (Wikipedia). Some live seeds need more time or specific environmental conditions before they will germinate. They are called dormant seeds. Dormancy-breaking involves changes in membranes, initiated by dormancy-breaking signals, which generally only occurs in hydrated Page | 6


seeds (Wikipedia). Some factors that affect seed dormancy include the presence of abscisic acid, which inhibits germination, and gibberellin, which ends seed dormancy (Clegg 323). Dormancy occurs to seeds that have undergone incomplete seed development, which causes the embryo to be immature, and this is overcome in time. It also occurs in seeds with an impervious testa which is eventually made permeable either by abrasion with coarse soil or by action of microorganisms. Seeds that have a requirement for pre-chilling under moist conditions before they can germinate also have a dormancy period. For this investigation, I decided to use dicotyledonous seeds because they are the most commonly found ones in Singapore. There are two types of dicot germination: epigeal germination, where the hypocotyl (section of shoot below cotyledon) elongates and forms a hook, and once it reaches the surface it will straighten and pull the cotyledons and shoot tip of growing seedlings into the air whereas hypogeal germination means that the epicotyl (section of shoot below cotyledon) elongates and forms the hook while the cotyledons stay underground where they eventually decompose (Theseedsite.co.uk). For control, all the seeds I chose germinated epigeally, although groundnuts are an intermediate between epigeal and hypogeal germination, but first germinated epigeally so it is mostly controlled. Specifically, I decided to choose garden plants and vegetables because they take a shorter time for germination. In lieu of my time limits, this was the best choice in order to ensure multiple trials are possible. The seeds that I chose were, in alphabetical order: Groundnuts (Peanut variety), Marigold Sierra Yellow, Tomato, Green Field Peas, Zinnia Dahlia Flora and Zinnia Lilliput. I chose 4 different temperatures to be manipulated: room temperature (26oC), cool conditions (3oC and 7oC) and winter conditions (-12oC). The seeds that will be tested at 7oC will also be put at room temperature afterward to make a conclusive assumption on whether tropical seeds have a period of dormancy. To make this decision, I will judge by seeing if the seeds germinate at room temperature after being left in cool conditions. It may also help to decide whether some of the seeds can be classified as truly tropical as the sources claim. This decision is made by seeing if the seeds germinate in cool conditions and winter conditions, which they are not supposed to do if they are truly tropical seeds. Usually, germination has first started when the first radicle pushes through the soil; however for this investigation, the emergence of the first hooked hypocotyl will mark Page | 7


germination. This is because the seed will be covered in soil, and if the soil is disturbed frequently to check whether the radicle has emerged it will cause anomalies. I conducted this experiment entirely in my house so that I never missed any of the signs of germination, and because it is easier to monitor. I hypothesize that the seeds will have double the normal time taken for germination when subjected to cool and winter conditions. Usually, tropical plants don’t have any period of dormancy and so it will be interesting to know if these specific seeds have that mechanism.

I.e. Cool conditions (3oC) and Winter conditions (-12oC)

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APPARATUS AND METHODOLOGY MATERIALS 1) Horti-brand seeds (Groundnut, Marigold, Tomato, Field pea, Lilliput and Dahlia) x1 pack each 2) Soil (Horti Seed & Potting Mix, J Arthur Bower’s Seed & Cutting Compost) x1 pack 3) Empty egg tray (preferably different colours for easy distinguishing) 4) Digital refrigerator

x1

5) Toothpicks and labels

x24

6) Pen

x1

7) Teaspoon

x2

x4

METHOD 1) Prepare all the materials. The seeds have been treated appropriately so no imbibition is needed prior to planting the seeds. 2) Place out the four egg trays. If they are not different colours, make sure to label them with their temperatures. Label 6 of the burrow sections with one seed name. 3) Using a teaspoon, first scoop out one spoon of soil. Even the soil out using the back of the spoon. Do these to all 6 burrow sections in all the egg trays. 4) Take out 3 seeds from the groundnut packet and push them into the individually labelled soil until they are fully covered. Do this to the other 3 egg trays. 5) Scoop out another teaspoon and spread evenly on top of the seeds. Repeat for the other 3 egg trays. 6) Repeat step 4 for all the other seeds (Marigold, Tomato, Field pea, Lilliput and Dahlia). Do this to all 4 trays. 7) Repeat step 5 for all 4 egg trays. 8) Take the other teaspoon, place 2 spoons of water into all of the seeds covered in soil. Remember that the soil should never be wet, only damp, but not dry either. Wait 15 minutes for the water to be fully absorbed before placing the trays in their respective conditions. 9) Place the tray in room temperature (26oC) near a windowsill but position it away from direct contact with sunlight. Direct contact may speed up germination too much. Page | 9


10) Place the tray in cool conditions inside the main refrigerator. Set the temperature to 3oC. 11) Place the other tray in cool conditions inside the chiller. Set the temperature to 7oC. 12) Place the tray in winter conditions inside the freezer or other area in which temperature can be adjusted. Set the temperature to -12oC. 13) Now, check periodically every 2 days and remember that the coiled hypocotyl marks germination. Water the seeds every 2 days when the soil starts showing signs of being dry; remember that the soil must always be damp.

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PICTURE OF EXPERIMENT READY TO GO

Temperature i.e. 3oC Label containing seed name i.e. Tomato

Soil i.e. JAB Seed and Cutting Compost

Egg tray

Seed i.e. Groundnut

Toothpick

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Candidate number: 000763-014 DATA ANALYSIS

First, I will analyze the results of the seeds sown in room temperature i.e. normal conditions, in order to understand the results of the seeds sown in cool conditions and winter conditions. All the seeds sown in room temperature germinated within the germination period prescribed on the packet. This means that the factors of germination have been successfully met. Since the seeds have been treated, initial imbibition was not required in order for the seeds to start their metabolic processes. The right conditions for each seed differed slightly, but they all needed the three factors of germination in order to start the process. For example, groundnuts had to be sown deeper (1 inch) than the other seeds (6mm) to allow sufficient room for the first radicle to grasp the soil. Other than that, it required enough water to dampen the soil every two days and oxygen was provided in the air, as well as the temperature being in the right range. This information is displayed below:

Mean germination time in 26oC (days) 16 14 12 10 Days 8 6 4 2 0

Mean germination time in 26oC (days)

Plants

When I first did some practice runs before the real trials, I found that the seeds had to be watered every two days in order for the soil to stay continuously damp. At first, I watered the seeds every day to stay safe; however, the soil then became too wet and soon enough, maggots started appearing. After this, I then tried watering the seeds every 3 days since watering every day lead to stagnation of water and every two days seemed too soon at the time. I observed that by the 3rd day, the soil was too dry, which led me to conclude that maybe 2 days was the right time. When I tested this out, it turned out to be just right and the seeds germinated within the time period estimated on the packet. Oxygen was in Page | 12


the air already; however, I had to make sure the air-conditioning was not turned on to ensure that the air was not artificially cooled and the temperature wouldn’t be affected. Actual Germination Temperature (oC) 18 21-27 21-27 21-30 21-27 21-26

Seed Groundnut Marigold Tomato Field peas Dahlia Lilliput

Table of Actual Germination Temperatures (Various sources)

The seeds in the cool and winter conditions never germinated at all. This showed how important temperature was for a seed to germinate, even though other factors were provided in the right conditions. The table above shows the actual temperature needed by each seed to germinate, provided that oxygen and water is provided as needed. Oxygen was one factor I couldn’t completely control, so this may be one of the many reasons behind the seed not germinating. This result was a surprise as I thought that by continuing to provide water as needed, the seeds would just take longer to germinate. Since those seeds didn’t germinate, there must be a number of factors that would have influenced them. After absorbing water, the plant growth hormone gibberellin is produced; by watering the seeds before I put them into their respective conditions, it can be assumed that gibberellin would have started to be produced by the seed before the temperature had set in. Once this happened, the seed would have sensed that not all the right conditions were provided in order for the germination process to occur, probably 10 minutes after being put into cool and winter conditions. At this point in time, since the right conditions hadn’t been met yet, the seed would have started producing abscisic acid, which would inhibit germination in the seed. Gibberellin is now not being produced, which induces the seed into a period of dormancy. After gibberellin is produced, it stimulates the production of amylase to break down the starch in the food reserves to maltose so that it can be transported to the root and tip of the seed to start growth. However, the gibberellin that may have been initially produced would have been stopped immaturely and no germination would take place since Page | 13


there wouldn’t be any food resources supplied. Hydrolytic enzymes are produced and work when the temperature is in the right range; the enzymes may have been produced since enough water had been soaked in for the 15-minute interval before placing the seeds in their respective places, but enzymes denature at very high temperatures and work very slowly at very low temperatures. Once the seed had sensed that the temperature was below its working range, the enzymes’ activity would have slowed down significantly because of the lack of optimum temperature. I assume that the seeds entered into a period of dormancy because of the lack of the factors stated above. It is quite a rare occurrence for tropical plants to have periods of dormancy since the all factors needed for germination are in ample supply all year long, except probably during the wet and monsoon seasons. To break this dormancy, the seed would need to be hydrated before dormancy-breaking signals induce changes in the membrane. At the same time, gibberellin would need to be produced to promote seed germination while abscisic acid, which inhibits germination, would need to be stopped producing. However it is quite an assumption to make without further analysis, which is why the experiment done at 7oC and then put into room temperature should be analyzed first. This test was done to see if the seeds truly had entered into dormancy periods when tested in the lower temperatures. There were two seeds that germinated in this temperature: field peas and marigold, and I will consider them anomalies. The sources I have consulted state that these seeds are tropical; however, one site states that field peas can be grown in temperatures as low as 10oC. Though, since only one site can vouch for this, I will continue on the knowledge that they germinate between temperatures of 21-30oC. It is very interesting that field peas can germinate even in 7 oC, but once the temperature was lowered to 3oC there was no sign of germination. In accordance with my hypothesis however, it did take double the time it took for the seeds to germinate in room temperature. An explanation that is relevant is that field peas are also grown in temperate zones like the Upper Midwest states of Wisconsin and Minnesota in USA. Although known to be cultivated extensively in the tropical regions of Southwest Asia in countries like India and Page | 14


China, the fact that they can be successfully grown in temperate zones too can mean an evolutionary adaptation to lower temperatures than in the tropical region. Over the time has led to a gradual separation of types: those grown for vegetable use, those grown for seed and fodder, and the edible podded types which have evolved most recently (green with yellow tinge used in this experiment). It is during this time that the field pea would have evolved and changed its adaptations in accordance with the changing climates it was put in. As for the marigold, all sources that were actively sought state that it germinates between the temperatures of 21-27oC, therefore making this result a surprise on my part. The specific species that I chose is the Tagetes erecta which is native to countries in the tropics such as Thailand and specific states in India that don’t have a winter season. The temperatures in these areas rarely reach temperatures as low as 21 oC so it should have been impossible for the marigold seeds to germinate in temperatures of 7 oC. Common sources state however that marigold is known to be a tough plant, germinating even in temperatures as high as 35oC. This explanation can be owed to the fact that Tagetes erecta is known in English as African marigold, which explains the extreme adaptability of this plant. It was also brought to France, a country with moderately cold temperatures, and the dwarf species Tagetes patula evolved; during the travelling between different climates, there must have been an evolution of the species along the way that made the marigold such a flexible plant. In colder temperatures, it can be said that marigold do not grow as magnificently tall as their counterparts in the normal germinating and growing temperatures of 21-27oC. The other seeds -which are the groundnut, tomato, dahlia and lilliput seeds- did not show any signs of germination when they were put into room temperature after being subjected to 7oC. This set of results disproves my hypothesis completely as it shows that tropical seeds may indeed have the dormancy mechanism within them. The hydrolytic enzymes produced during the germination process would not be working at their optimum temperature thereby slowing down the process significantly. However, this still doesn’t mean that the process may have been completely stopped until appropriate temperatures for the seeds to germinate are provided; therefore it is necessary to classify when exactly can the seeds can be assumed to have gone into a dormancy period. I would say that this Page | 15


assumption would be valid to make after triple the time taken for the seeds to germinate under normal conditions. This is why I put the seeds in room temperature after subjecting them to 7oC for an extra week to legitimize my deduction as much as possible. I also assume that these seeds specifically, could be classified as quiescent seeds. A period of quiescence is when no active growth is recorded, and during this time the seeds can survive harsh environmental conditions and can be transported to an environment where it is suitable for germination to occur in that particular seed. Quiescent seeds are ripe, and these seeds are already ripe; therefore, it is possible that they are quiescent because cool and winter conditions can be classified as harsh environmental conditions to tropical seeds. There will be a prevention of the series of complicated chemical and metabolic processes, due to the presence of abscisic acid as previously mentioned.

Germinated and Sprouted Seedlings

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Candidate number: 000763-014 CONCLUSION AND EVALUATION

In conclusion, my hypothesis was disproved completely as I have explained above in the analysis. This may be because the seeds have entered into a period of dormancy and became quiescent due to being subject to harsh environmental conditions, considering that they are tropical seeds. Complex chemical and metabolic processes have been inhibited just because the temperature has been changed drastically, which conveys how important temperature is as a factor of germination. In the process, the importance of water was also learned as a factor of germination, and how it starts off a series of complicated chemical processes in order for germination to occur. I would definitely say that there is more to learn and understand about the topic of germination because there are very few resources that guide you on the theory of germination and its processes. It would be nice to find a book, article or website that fully explains this interesting process. In future, I would love to learn more about germination theories if possible because I like gardening and flora in general. There are several ways in which I could improve my experiment. The main one is to find a way in which I can provide oxygen to the plants in cool and winter conditions while they are being stored in the refrigerator. This is one factor of germination, and it would be good to find out if the seeds could germinate in cool conditions at least if oxygen was being provided regularly along with water. Secondly, I think a few more trials would have given me a chance to have a solid analysis on the results that I procured. As always, the more trials there are, the better the average and there would be minimal uncertainties, as much as can be avoided, to give reliable results and lead to a good conclusion. It would be good to find an environment that is perfectly suitable for investigating normal germination conditions in order to lead to a more solidly-based analysis. A more solid analysis may mean more data and theory that can be extensively used to explain how the germination of tropical seeds is affected in cool and winter conditions. This investigation yielded numerical data but which can’t exactly be examined through graphs since Page | 17


calculations are not necessary; possibly in the next experiment, rate of germination can be investigated. Also, the room temperature was in a range, which made it a little difficult to pinpoint the exact germination temperature of a specific seed. I would need to conduct the experiment in a room where temperature is can be kept under constant control, which can improve the reliability of my data quite significantly. One factor that I could possibly make sure of is the health of the seeds. If the seeds aren’t healthy, the germination process would take longer than usual or not be in the right condition to ever germinate. Also, seed age can interfere with the germination process; garden plants usually have quite low shelf-lives (1-2 years). There was no way I could be sure of the freshness of the seeds since they were externally packed. Next time, it would be good if fresh seeds straight from the plants can be obtained.

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APPENDIX DATA COLLECTION Room temperature (26oC) Name of Plant

Estimated Germination Time (days)

Groundnut Marigold Tomato Field pea Dahlia Lilliput

10-15 5-7 10-15 5-7 5-7 5-7

Actual Germination Time (days) Trial 1 Trial 2 Seed Seed Seed Seed Seed Seed 1 2 3 1 2 3 15 15 15 14 14 14 7 6 7 6 7 6 12 12 11 10 11 11 3 3 4 4 3 3 5 7 7 5 5 6 7 5 5 6 7 5

Mean Germination Time (days)+ 1 day

Actual Germination Time (days) Trial 1 Trial 2 Seed Seed Seed Seed Seed Seed 1 2 3 1 2 3 -


Actual Germination Time (days) Trial 1 Trial 2 Seed Seed Seed Seed Seed Seed 1 2 3 1 2 3 -


15 7 11 3 6 6

Cool conditions (3oC) Name of Plant



10-15 10-14 10-15 5-7 5-7 5-7

-

Winter conditions (-12oC) Name of Plant



10-15 10-14 10-15 5-7 5-7 5-7

-

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Candidate number: 000763-014 Cool conditions (7oC) Name of Plant



10-15 10-14 10-15 5-7 5-7 5-7

Actual Germination Time (days) Trial 1 Trial 2 Seed Seed Seed Seed Seed Seed 1 2 3 1 2 3 14 14 14 14 14 14 7 7 7 7 7 7 -


14 7 -

And then to room temperature (26oC) Name of Plant



10-15 10-14 10-15 5-7 5-7 5-7

Actual Germination Time (days) Trial 1 Trial 2 Seed Seed Seed Seed Seed Seed 1 2 3 1 2 3 Already germinated at 7oC Already germinated at 7oC -


-

Dependent variable: Germination Time (days) Independent variable: Temperature Controlled variables: Exposure to light, Amount of water given to seeds

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WORKS CITED LIST AND BIBLIOGRAPHY Allott, Andrew. IB Study Guides Biology for the IB Diploma. Glasgow: Oxford University Press, 2007. Clegg, C.J. Biology for the IB Diploma. London: Hodder Education, 2007. Field pea. Purdue. 25 Oct 2011. Web. Gardening. Gardening. 15 Sep

2011. Web. Gardening. Plant care.
germination-process.aspx> 20 Sep 2011. Web. Germination. Wikipedia. 15 Jul 2011. Web. Germination. Cactus-Art.
book/Dictionary/Dictionary_G/dictionary_germination.htm> 15 Jul 2011. Web. Germination. Plant-Phys. 15 Jul 2011. Web. Germination. Buzzle. 15

Jul 2011. Web. Germination. Gardening central. 25

Sep 2011. Web. Germination. The Seed site. 25 Sep 2011. Web. Marigold. Plant biology. 25 Oct 2011. Web.

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IB Biology Extended Essay

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