4. really cool stuff plants do

Question 1

tropisms

Answer 1

When a plant grows towards or away from and external stimulus
* Usually involves bending or curving
* Positive – response towards something
* Negative – a response away from something

Question 2

phototropism

Answer 2

Growing towards light
* Cells on the shady side elongate
* Caused by auxins
Light drives auxin to the shady side

Question 3

gravitropism

Answer 3

Response to gravity
* Roots grow down and shoots
grow up, even if plant is on its
side

Question 4

Starch-Statolith Hypothesis

Answer 4

Amyloplasts (starch containing plastids) that sense gravity are called statoliths
* These occur in cells called statocytes
* In stems, these are in the starch sheath around the vascular tissues
* When a root is placed sideways, amyloplasts in statocytes slide downward so that
the root grows in that direction

Question 5

hydrotropism

Answer 5

Growth towards water
* Hard to study because gravitropism is so pronounced
* Used a pea plant mutant that did not respond to gravity

Question 6

thigmotropism

Answer 6

Growth in response to touch
* Plants will grow around rocks or wind around support structures
* Tendrils have memory of what supports them

Question 7

Circadian Rhythms

Answer 7

Regular happenings in a plants life that occur on a 24 hour cycle
* Flowers open in the morning
* Controlled by Circadian Clocks at the cellular level
* These have 3 parts:
* Oscillator – generate rhythmic behavior
* Input – what carries environmental information to the oscillator (like morning sun)
* Output – What regulates biochemical and physical processes

Question 8

Circadian Clocks – Environmentally
synchronized

Answer 8

The environment controls these – the light/dark cycle
* Adjusts seasonally
* Example: When insects are at a stage to pollinate flowers, flowers will open
based on the insects feeding behavior

Question 9

Adjustments to Circadian Rhythms

Answer 9

Entrainment – when daylength changes, a plant must adapt to the
changing amount of light
Gating – There are differences in how a plant responds based on strength of the stimuli

Question 10

Photoperiod

Answer 10

The effect of daylength on flowering
* A “biological response to a change in the proportions of light and dark on a 24
hour cycle”
* Because daylength changes with time of year, this allows plants to determine
what season it is and change behavior accordingly

Question 11

short day plants

Answer 11

Flower early spring or fall
* Must have a light period shorter than a critical length
* Example: Poinsettias

Question 12

long day plants

Answer 12

Flower in the summer
* Only if light period is longer than a critical length
* Examples: Spinach; lettuce; some potatoes

Question 13

day neutral plants

Answer 13

Flower no matter what daylength

Question 14

phytochrome

Answer 14

the primary photoreceptor
This is a pigment found in the cytoplasm of plants
* Occurs in very small amounts
* Detect using a spectrophotometer
* Absorbs red (660 nm) & far red (730nm) wavelengths of light
Phytochrome mediates photomorphogenesis

Question 15

floral stimulus

Answer 15

Leaves perceive daylength and then form a substance that moves to
the shoot and induces flowering
* This substance was called “florigen” - a small protein (FT)
* This is produced in the companion cells of minor vein phloem of leaves,
transferred to the sieve tubes and transported to the shoot apical meristem
* FT works with another protein (FD) and activates genes that are floral
promotors

Question 16

Vernalization

Answer 16

• When plants must be exposed to cold in order to flower
• This is common in winter annuals & biennials
• Also necessary for garlic – planted in the fall and grows and flowers in
  the Spring
• Usually these all require a certain long day photoperiod too

Question 17

Dormancy

Answer 17

A special condition when growth will not occur unless the plant is
exposed to certain conditions
* Seed dormancy can be broken in various ways:
* Stratification – when a moist seed is exposed to low temperatures for many
days
* Scarification – Breaking the seed coat either physically or chemically

Question 18

Seed banks

Answer 18

where seeds (which hold all the genetic characteristics
of plants) are held just in case

Question 19

seed banks

Answer 19

where seeds (which hold all the genetic characteristics
of plants) are held just in case

Question 20

Dormant Buds

Answer 20

Starts in mid-summer after forming
Acclimation – the process where a plant gets prepared to shut down
in the winter. This leads to cold-hardiness – the ability to survive in
less than ideal conditions

Question 21

nyctinastic (nastic) movement

Answer 21

When a plant moves in response to
a stimulus
* Example: When leaves are oriented
horizontally during the day and
vertically at night

Question 22

Thigmonastic movements

Answer 22

Nastic movements from mechanical stimulation
* Examples:
* Sensitive plant – Mimosa pudica
* Venus flytrap – leaves spring shut on insects

Question 23

Heliotropism

Answer 23

Solar tracking – when leaves and flowers move diurnally, orienting themselves to the sun
* Examples: Sunflower; cotton; soybean
* Not like phototropism since it is not a result of uneven growth, rather it is like a nastic movement