ORIENTATION RESPONSES How organisms position themselves in relation to their surroundings

ORIENTATION RESPONSES

How organisms position themselves in relation to their surroundings

What are the abiotic stimuli?STIMULUS PREFIXLight Photo-Gravity Gravi- Temperature Thermo-Water (or Humidity) Hydro- (or Hygro-)Chemicals Chemo-Touch Thigmo-Current (in water) Rheo-

Simple Animal Orientation Responses

• Taxis• Kinesis

TAXIS (plural Taxes)

– Orientation and movement of whole animal towards or away from external stimulus that is coming from one side only

– Described as positive (toward) or negative (away from) a stimulus

– Moving toward light = positive photo–taxis

Examples of animal taxes

• Earthworms and slaters move away from sunlight back down into the soil = Negative phototaxis

• Snails move away when their feelers touch something ….

= Negative thigmotaxis• Flatworms and sharks move towards meat

= Positive chemotaxis

Mosquito moves toward warm skin

What’s the advantage?

• Puts the animal in a more favourable position• Avoids unfavourable conditions (hot, cold etc)• Increased survival and reproduction

How do animals determine the direction of the stimulus?

• Two sense organs: By comparing the input from receptors on each side of the animal at the same time

• Differences between sides show the direction of the stimulus (eg. Snail antennae)

• OR One sense organ: Compare the change from a single sensor over time, using its body orientation to determine stimulus direction

KINESIS (pl. kineses)= Non-directional response to a change in

stimulus intensity ….. It is not orientating– Animal may simply turn randomly or change its

rate of movement

– Slater moves more when it is hot= thermokinesis

More terms to know

Orthokinesis = the stimulus intensity determines the organism’s speed of movement

Klinokinesis = the stimulus intensity determines the organism’s rate of turning

Examples of Kineses

• Slaters move faster in bright light and slower in dim light = photo-orthokinesis

• Woodlice: move faster and turn more in high humidity vs. low humidity (hygro-)

= hygro-orthokinesis, hygro-klinokinesis• Human body lice turn more at 35°C than at

lower temps = thermo-klinokinesis

What’s the advantage?

• Puts the animal in a more favourable position• Eg. Slaters will end up in dark, damp places

which prevents dessication• Avoids unfavourable conditions (hot, cold etc)• Increased survival and reproduction

BIOZONE questions

• Taxes and Kineses• Do all the questions on page

NCEA 2006 question

• Much of animal behaviour is innate, or inborn. Such behaviour patterns may be quite simple, or are produced in response to simple stimuli. They include kineses and taxes.

• (a) Describe an example of kinesis in a named animal.

• (b) Explain why this behaviour would be an advantage to your named animal in its normal environment.

Plant Orientation ResponsesPlants are capable of a number of movements in

response to environmental stimuli.eg. Temperature, humidity, light, touch, chemicals

1. NASTIC RESPONSES: non-directional responses to stimuli

2. TROPISMS: Directional growth responses towards or away from a directional stimulus

Nastic Responses

• The rate or frequency of these responses increases as intensity of the stimulus increases.

• They are named with the suffix "-nasty" and have prefixes that depend on the stimuli

Eg. Photonasty, thigmonasty

Examples on you tube

• Mimosa pudica: the sensitive plant• Venus fly traps – jaws of death

Eg. Mimosa plant

• When the sensitive leaves are touched, they droop down and fold up rapidly

• Thigmonasty• Advantage: why?• Reduces the plant’sSurface area for grazingAnd abiotic stress.

Venus Fly Trap Plant

What happened?

What was the stimulus?

Advantages?

Other examples

• Opening/closing of tulip flowers due to changes in air temperature– Called?

• Opening of evening-primrose flowers at dusk

– Called?

PLANT TROPISMS

• Directional growth response that occurs in response to an external directional stimulus

• May be positive (towards stimulus) or negative (away from stimulus)

• Tropism comes from a Greek word ‘tropos’ meaning “to turn” or “to change”

Why?

• Plants can alter their growth so they can grow towards more favourable conditions

(eg. More light, more water etc)

• Must detect where the conditions are better then alter their growth to "move" in the appropriate direction

PHOTOTROPISM= the directional growth response of a plant in

response to a light stimulus. • Different parts of a plant exhibit different

reactions to light.

• Stems and shoots exhibit positive phototropism (grow toward light)

• Most roots exhibit negative phototropism (grow away from light)

GRAVITROPISM= the directional growth response of a plant in

response to gravity. • Roots exhibit positive gravitropism (towards)• Stems and leaves exhibit negative gravitropism.

THIGMOTROPISM

• Thigmotropism is the growth response of a plant to physical contact (touch).

• Plants that cling to physical structures such as sticks exhibit positive thigmotropism.

HYDROTROPISM

• Directional growth in response to presence of water in the soil

• Roots = positive hydrotropism

(grow toward water)Note: stronger than

gravitropism

CHEMOTROPISM

• Directional growth in response to a chemical stimulus

• eg. Roots can grow towards or away from chemicals in the soil (copper pipe)

• eg. Growth of pollen tube towards ovary in flowers (ovary releases chemicals)

THIGMOMORPHOGENESIS !!An alteration in growth patterns caused by touch (eg. wind, rain)

Type of tropism? Positive or negative? One Advantage?

1. Roots of a seedling grow down ……………………..2. Stem of vine winds around a branch………………..3. Leaves of pot plant turn toward window………..4. Roots of willow grow sideways toward water……5. Roots grow away from copper pipes in soil….6. Shoots of seedling grow upward in dark lab…7. Pollen tube in flower grows toward ovary…..8. Tree grows sideways on an exposed mountain…

Control of Plant Growth• Plant growth is controlled by HORMONES• These are chemicals produced in one part of

the plant and transported to where they produce a growth response.

Terminology…

Coleoptile (co – le – op – tile)

is the protective sheath covering the emerging shoot in plants such as oats and grasses.

Auxins

• A group of hormones that regulate plant growth

• Indole Acetic Acid, IAA (the first auxin isolated) • Causes cell elongation in

stems

Phototropism in Coleoptiles….• Tip of shoot detects light

stimulus, auxin is produced• Auxin causes cell elongation

in the stem

If light comes from an angle:• Auxin moves to shaded side

of stem, cells elongate• Shoot bends towards light

Auxin moves to shaded side and causes cell elongation - stem bends towards light source

• More auxin on the shaded side

• Cells elongate• Stem bends

toward light over time

TROPISMS….. You tube clip:

Plant Physiology: Phototropic Response http://www.youtube.com/watch?v=zctM_TWg5Ik

Experiments with Grass/Oat Coleoptiles

•

Gravitropism in roots

• In roots, perception of gravity appears to depend on the settling of specialised organelles called statoliths in root-cap cells.

• When the plant is turned, within minutes the statoliths sink toward the source of gravity, to the side that is down.

• Auxin builds up on the lower side of the root cap, causing cell elongation and downwards growth of the root

THIGMOTROPISM

• Growth is inhibited on the side of stem being touched

• Cells elongate on the non-touching side due to auxin

• Causes the stem to coil around the object being touched

Worksheet

• Have a go at all the questions

Terminology time!COLEOPTILE = the protective sheath covering tip of the first new shoot from a seedDarwin studied phototropism in canary grass and oat coleoptiles. The coleoptile is a

hollow sheath of tissue which surrounds the apical axis (stem) of these and other grasses. Darwin demonstrated that these coleoptiles are phototropic in that they bend toward a light source. When he covered the tips of the coleoptiles, they were not phototropic but when he covered the lower portions of the coleoptiles, they were phototropic. Darwin concluded from these and other experiments that (a) the tip of the coleoptile is the most photosensitive region; (b) the middle of the coleoptile is responsible for most of the bending; and (c) an influence which causes bending is transmitted from the top to the middle of the coleoptile.

Read more: Phototropism - History Of Phototropism Research - Coleoptile, Darwin, Coleoptiles, Plant, Agar, and Light http://science.jrank.org/pages/5197/Phototropism-History-phototropism-research.html#ixzz10OQbtO20