Candidate number: 000763-014 Page | 1 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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Candidate number: 000763-014
Page | 1
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
Candidate number: 000763-014
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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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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.
Example structure of a seed (Allott 85)
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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
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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
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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