1. Environmental factors
and
TROPISM

2. A period of inactivity in a mature seed before it begins to grow
Dormancy
A period of inactivity in a mature seed before it begins to grow
It’s like the seed is in a “sleep-state”
Remains dormant until conditions are right for growth and development of the new plant.

3. Changes in the Environment
can affect the survival of individual organisms and entire species
Some changes happen outside the organism and are called external stimuli
Examples are light intensity, day length, gravity, and temperature.
Some changes happen inside the organism and are called internal stimuli
Examples are germs, dehydration, lack of energy etc.

4. Plant growth or turning in response to an environmental stimulus
TROPISM
Plant growth or turning in response to an environmental stimulus
(“tropo” – ”turn”) .
There are many types of tropisms :
Phototropism
Geotropism
Thigmotropism
Hydrotropism
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5. POSITIVE NEGATIVE Tropism can be…
If the plant moves TOWARD the stimulus
If the plant moves AWAY from the stimulus

6. PHOTOTROPISM Movement of plants toward light POSITIVE Phototropism
(“Photo” – light)
Movement of plants toward light
POSITIVE Phototropism
Stem tip growing TOWARD the light
NEGATIVE Phototropism
Root tip growing AWAY from the light

8. IMPORTANCE OF PHOTOTROPISM
Helps leaves be in the best position possible to receive enough light for photosynthesis

9. EXAMPLES OF PHOTOTROPISM
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10. Auxins Auxins are one of the hormones used by plants for growth.
It is made at the tips of stems and roots
In the shoots any concentration promotes growth.
At the root, high concentration inhibits (slows down) growth, small concentration promotes growth.

11. How Auxins Work with Phototropism
Sunlight breaks down auxins, so shoot tip in direct sunlight has lowest auxin concentration
shaded area has highest auxin concentration
so more growth occurs in shaded part of shoot
this leads to lop sided growth so plant bends towards the light

12. Auxin Experiment
A - when the tips are removed, no auxin is made so the stems do not grow B – when the tips are covered, auxin moves to all parts of the stem causing all parts to grow C - when the tips are lit from one side only auxin accumulates on the shaded side causing it to grow more than the illuminated side

13. growth of a plant in response to gravity.
Geotropism
(“Geo” – Earth)
growth of a plant in response to gravity.
Negative Geotropism
Positive Geotropism
It is the growth of a plant toward the center of the earth-down with gravity
Ex. roots growing down
Negative Geotropism
It is the growth of a plant away from the center of the earth-opposite from the pull of gravity
Ex. stems grow up
Positive Geotropism
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14. IMPORTANCE OF GEOTROPISM
Pulls roots down to anchor a plant
Roots can get needed water and minerals

15. EXAMPLES OF GEOTROPISM
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16. growth of a plant in response to touch/contact
THIGMOTROPISM
(“Thigmo” – “touch”)
growth of a plant in response to touch/contact
Positive Thigmotropism
toward touch
Photo by Christopher Meloche
Negative Thigmotropism
away from touch
(some plants close up when touched)

17. IMPORTANCE OF THIGMOTROPISM
to support leaves as they grow higher to reach the sun to make more food (photosynthesis).

18. EXAMPLES OF THIGMOTROPISM
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19. Hydrotropism Movement by plants toward water Positive Hydrotropism
(“hydro” – “water”)
Movement by plants toward water
Positive Hydrotropism
toward water
Negative Hydrotropism
Away from water

20. Importance of Hydrotropism
Roots search for and grow toward water, because it is needed for photosynthesis and to support cell structure