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Behaviour. Causes of behaviour. Photoreceptors. Photoreceptors are cells that are sensitive to light.
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Photoreceptors • Photoreceptors are cells that are sensitive to light. • Animal photoreceptors sense light with a photopigment called rhodopsin. Molecules of rhodopsin change structure when light is absorbed and stimulate nerve endings, then return to their normal state. • Photoreceptor cells on their own only detect the intensity of light, but can provide an image when aggregated into an organ. • The greater number of photoreceptor cells, the greater resolution and detail, allowing more complex responses.
An ommatidium of an insect compound eye Each ommatidium ‘sees’ a point of light – having many of these in a compound eye allows an insect to perceive an image made of many dots of light of varying intensities.
Apical dominance • Auxin at the apical meristem (top of the plant) is produced in high concentrations, so the shoot is stimulated to grow. • The lateral buds remain dormant, as high concentrations inhibit their growth. • As auxin diffuses down the plant it becomes less concentrated, and is inactivated by enzymes and hormones in the lower parts of the plant. • Near the bottom of the plant, the concentration is low enough to stimulate the lateral buds to grow out sideways. • This causes the triangular shape of trees such as conifers. This process is called apical dominance.
Nastic responses • Nastic movements are non-directional responses to stimuli (e.g. temperature, humidity, light intensity). The movement can be due to changes in turgor or in growth. • Nastic movements differ from tropic movements in that the direction of tropic responses depends on the direction of the stimulus, whereas the direction of nastic movements is independent of the stimulus' position. • The rate or frequency of these responses increases as intensity of the stimulus increases. • Example: the opening and closing of flowers (photonastic response).
Examples… Thigmonasty in Mimosa • When the leaves of the Mimosa plant are touched they droop down and the leaflets fold up. • It happens in seconds, due to the loss or turgor pressure in special cells at the joints of the leaves and leaflets. • The cells pump out potassium ions, which causes water to be lost rapidly by osmosis. • The folding effect spreads from the touched leaf to neighbouring leaves. • The transmission involves an electrical impulse rather like in animal nerve cells, but may also involve a hormone. • It takes about 10 minutes to ‘reset’ the cells. Thigmonasty in the Venus fly trap (MB 19) Similar mechanism to shut its trap. Read the information on page 19, and discuss why the trap has a memory. Sleep movements by runner beans / opening and closing of flowers • Many legumes (runner beans) lower their leaves in the evening then raise them in the morning (called sleep movements). Mechanism similar to Mimosa. • Many flowers open their petals in the morning and close at night; or vice versa. Mechanism similar to Mimosa. Why do plants do this?
Watch it on Photonasty in action: Protective leaf movements of Oxalis acetosella Oxalis triangularis Photonasty Timelapse
Summary of Movement responses (MB 53)
Taxes (MB page 52) A taxis (pl. taxes) is a directional response of the WHOLE organism or cells (slater, sperm, algae) to a directional stimulus. Examples include: Phototaxis… Thermotaxis… Chemotaxis… Hydrotaxis… Geotaxis… Rheotaxis… Tropotaxis: Two or more receptors compare the stimulus simultaneously to determine the direction to move in. Examples: (Sharks lateral line system). Klinotaxis: A single receptor is used to calculate the direction of the stimulus (maggots larva, light) Examples:
Tropotaxes and Klinotaxes: an overview Tropotaxis:taking simultaneous samples from paired receptors. In positive tropotaxis, the animal orients the body axis so that the stimulus is received by both sense organs at equal strength, then moves forward. If the stimulus increases on one side, the animal turns toward this side, and so moves up a gradient. Tropotaxis is most common in chemical orientation. Klinotaxis: A single receptor is used to calculate the direction of the stimulus (maggot larvae only have one receptor for light and must keep turning its head from side to side to detect the intensity of light).
Tropotaxes and Klinotaxes: an overview Example: antenna-crossing experiments of Martin Martin chilled honey bees to keep them from stinging, then glued their right antennae facing to the left, and their left antenna facing right. The bees were first trained in a Y maze to follow an odor to a food source, then given the crossed-antenna treatment and presented with a choice between the odor previously associated with food and an unfamiliar control odor in the other arm of the Y. Control bees with unmanipulated antennae went correctly toward the conditioned odor, as did bees whose antennae were glued but in the normal position, as a control for the effect of gluing. Bees whose antennae were glued in the crossed position always chose the wrong arm of the maze, proving that they were performing tropotaxis by simultaneous sampling across both antennae. If they had been orienting by successive samples in klinotaxis, treating the input from both antennae as a single sample, they would have moved correctly despite the crossed antennae.
Kinesis (pl. Kineses): pp. 52-53 A kineses is a non-directional response of the individual to the intensity of a stimulus. The rate of turning or speed of the organism relates to the intensity of the stimulus., As the response is non- directional, we do not mention positive or negative when describing the response of the organism. Examples: …
Types of kineses • Orthokinesis: • Klinokinesis:
Environmental Stimuli Behaviour Response Type Advantage to organism Plant Responses Usually part movement Animal Responses Usually whole org. movement Stimulus Taxes Tropisms Nastic Responses Kinesis Protection from Predator/ desiccation Non-directional Directional
Homing and Migration HOMING: (MB page 53) The return to a home base after a journey usually daily in search of food or mates. MIGRATION: (MB pages 53 – 54) The regular, repeated mass movement of animals usually annually or once in a lifetime for breeding or avoidance of climatic extremes.
Migration: Triggers (MB page 55) • Maturation • Environmental clues • Innate Genetic drive • Endogenous circadian rhythm
Questions Plant responses: Pathfinder, end of Unit 7 (page 26) Animal orientation responses: Pathfinder, end of Unit 2 (page 8)
Methods of homing and migration (MB page 55 – 59) • Methods used to find home are often the same methods that animals use to migrate long distances. • Survival of an animal may depend on the accuracy of its navigation. • Navigation can be complex – not fully understood in some cases. Homing Pigeons can use more than one sense (e.g. if they were blind-folded). • A certain amount of learning involved (e.g. experienced birds navigate better than young).
Methods Mix-UpFind the method term, definition and example for each of the three methods in the table below. Find the meaning of the terms listed in bold.
Methods Mix-UpFind the method term, definition and example for each of the three homing and migration methods in the table below.
Watch it on ‘Supernatural’ powers of ocean animals
Methods used by animals to navigate (MB 56-59) Visual clues Solar navigation Magnetic fields Star (stellar) navigation Chemical navigation Sound used as sonar
SELF CHECK! Questions in MB page 61
Requirement for timing(MB page 62) Biological clock This is an internal timing system which continues without external time cues, and controls the timing of activities of plants and animals. Examples: • Circadian • Circatidal • Circasemilunar • Circalunar • Circannual
Definitions that you need to know: Period of the rhythm Phase shift Free running period when the biological clock is running without any clues from the environment Entrainment (resetting) This is the resetting of the biological clock on a regular basis. This forces the biological clock to take up the period of the environment, and is done by a zeitgeber Zeitgeber (‘time giver’) This is the environmental agent that resets the biological clock. This could be light, temperature, tides, etc. Circa this means ‘about’. Photoperiod the response of plants and animals to the lengths of day and night are called photoperiodic responses
Advantages of having a biological clock • Organisms need a method of sleeping and waking in constant conditions • Prediction of events like migration and hibernation in response to approaching environmental extremes (winter, drought) • Physiological readiness and synchronicity for mating
Biological clocks are used for five things… What are they? (MB page 62)
BIOZONE EXERCISES: BIORHYTHMS (page 188-189)
Human rhythms (MB page 65-) • Sleep • Temperature changes • Heart rate rhythms • Pain rhythms • Alcohol metabolism rhythms • Efficiency curve for learning • Renal rhythms • Birth and death • Endocrine system rhythms Disturbing the sleep rhythms: Jet lag and Shift work
Actograms Actogram — a type of graph or chart commonly used in circadian research to plot activity (present or absent) against time .
Day - neutral plants Let’s do it… Biozone: Plant rhythms Photoperiodism in plants
The phytochrome system Phytochrome is a photoreceptor, a pigment that plants use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night (photoperiodism) and to set circadian rhythms. It also regulates other responses including the germination of seeds, elongation of seedlings, the size, shape and number of leaves, the synthesis of chlorophyll, and the straightening of the epicotyls or hypocotyls hook of divot seedlings. It is found in the leaves of most plants.
Who? What? Wow!Other plant hormones Giberellins Cytokinins Abscisic Acid (ABA) Ethelene gas Florigen
