AP Bio- Regulation 7: Responses

Responses

Cellular: Change in Gene Expression, metabolism, transport, etc.

Phototropism:

Growth in response to a light source.

Mediated by the hormone auxin in plants.

Effects

• controls cell division & differentiation
• phototropism

-growth towards light

• asymmetrical distribution of auxin
• cells on darker side elongate faster than cells on brighter side (due to auxin accumulation in darker side cells)
• apical dominance

Positive or Negative Feedback?

Feedback At Work:

Example 1:

Photo Reponses In Plants

Example 5:

Signaling in Animal Populations

Environment

Can be from:

Abiotic Source

Biotic Source

Other cells

Tends to involve:

Organism:

1. Reception

2. Integration

3. Effecting of Response

(Use of sensory organs)

(Use of nervous/endocrine system)

Stimulus

Response

Photoperiodism:

Changes in organism behavior due to the length of day or night.

(Use of muscles, glands)

Why feed instead of eat?

Big Questions:

seed germination in response to light

How do feedback loops help organisms respond to the environment?

How are behavioral feedback loops coordinated among multiple mechanisms in an organism?

Organism

Visual Displays:

Reproductive responses are triggered by a variety of physiological and environmental cues.

These responses usually involve visually ostentatious displays (“mating behaviors”)

Pheromones are chemical signals that transmit information between organisms.

Widely used in many lineages of animals.

Pheromone-controlled behavior can get wildly complex:

Visual Displays in a Human Sub-population

Make Sure You Can:

flowering responses in "short day" and "long day" plants

Complexity Will Emerge!

Auxin

Explain how organisms can incorporate signals from the environment into physiological feedback loops.

Explain how behavioral feedback loops are coordinated among multiple physiological systems.

Any Questions?

A Flowering Hormone?

Not all wavelengths of light are created equal in plant responses

How can this be explained?

How Auxin Works:

• Activates proton pumps, which pump H+ into the cell wall.
• This activates expansins, which elongate the cell wall.

Phytochromes!

Example 4:

Quorum Sensing in Prokaryotes

Example 3:

Taxis & Kinesis

Example 2:

Circadian & Seasonal Responses in Animals

Taxis & Kinesis are controlled by negative feedback loops in response to environmental stimuli.

Biofilms are aggregate mats of bacteria held together by secreted polymers.

Your mouth is full of biofilms:

Quorum sensing is a mode of group response that relies upon determined actions once certain thresholds are reached.

Bacterial colonies can change their behavior once certain population densities occur.

The trigger for these responses is the presence of signaling molecules in threshold concentrations in the environment.

These molecules serve as operon regulators

Circadian Rhythms:

24-hour behavioral cycles are mediated by environmental cues acting on physiology (e.g. melatonin levels)

Even absent environmental cues, hibernation occurs in many animals (“obligitative hibernation").

Data from squirrels kept in constant lighting in a lab for two years:

Hibernation/Migration

Both Hibernation and Migration are triggered & regulated by changes in physiology & day length.

Why are these responses necessary?

Cellular Level:

The changes in motility of cells in response to chemical signals.

Yellow = Actual Rate

Orange = Theoretical (nonhibernatory) rate

Metabolic

Rate

Body Temperature & Metabolism

in Belding's Ground Squirrels

100

kcal/day

0

kcal/day

35 C

25 C

15 C

Temp.

5 C

Fruiting bodies (spore producing structures) are only created in response to environmental signals (food availability) and signals from other cells.

-5 C

Black = Body Temp.

Green = Burrow Temp.

Blue = Outside Temp

-15 C

Sep.

June

Dec.

Mar

The role of the Superchiasmatic Nucleus (SCN) in controlling CR in mammals

Jet lag ("desynchronosis") seems to result from confusion between environmental signals (sunrise and sunset) and internal hormonal cues.

Normal melatonin cycle in humans: