1. Plants keep track of the hours and the seasons!
Concept 22.3

2. Objectives
• Define circadian rhythm
• Explain how day length may affect plant
flowering.

5. Long-Day Plants
~ Jacob Miller
Long - Day is the name given to
plants that bloom when the
longer days come in the
summer. They bloom to receive
the critical amount it needs to
grow during its cycles.
Some examples are…
• Lettuce
• Spinach
• Tomatoes
• Black-eyed susans

6. Photoperiodism
• Photoperiodism is how the plant reacts to
change of light or length of day or night.
Christian Whited

7. Phytochromes
• *Phytochromes : (or pigmented
proteins)is how the plant
monitor the time of day.
• *Sunrise: the plant absorbs the
red light from the sun and this
triggers the plant. It also changes
the shape of the plant to active.
• *Sunset : all of that was said in
sunrise is reversed.
• By Teresa Mittermeier

8. Day Length and Seasons
- Day-Neutral Plants
- Plants that flower when they reach a particular stage of maturity.
- These will flower during any day length.
- Dandelions, tomatoes, and rice are common examples.
Madison Wiscott

9. ~Kelly Ugrin~

10. 1. Give an example of a circadian rhythm in a
plant or animal.
2. Describe the difference between a short- and
a long- day plant and give an example of each.
3. Explain how phytochromes are activated.
Jenna Voigt

11. 1. When a plant’s functions change throughout a 24 hour period. An organism’s
“biological clock” is set by daily signals from the environment, especially
sunlight.
2. Certain plants, such as chrysanthemums and poinsettias, flower in fall or
winter when the dark period exceeds a certain length called critical night
length. Which is also the same thing as short-day plants. Long-day plants, such
as spinach, lettuce, and irises, usually flower in late spring or early summer
when dark periods shorten.
3. When phytochromes absorb the red light that is abundant at sunrise, they
change shape to an active form that triggers a variety of plant responses. After
sunset, the phytochromes gradually change back to their inactive form.
Jenna Voigt

12. Short-Day plants when plants flower in fall or
winter when it stays dark out for a certain amount
of time.
Specific plants that bloom during this time are
 Chrysanthemums
 Poinsettias
They flower during fall and winter. Another name
for Short-Day plants would also be called critical
night length.
Jenna Voigt