Plants and Animals

Environment and Responses

Abiotic factors include temperature, light intensity, humidity, wind speed, salinity, pH, water, oxygen, carbon dioxide and mineral levles, and substrate. Some abiotic factors only apply in certain environments.

Biotic factors are the influences and interactions with other living organisms, which include:

• competition (intraspecific and interspecific)

• exploitation (predation, herbivory and parasitism)

• mutualism

Photoreceptors are found in the retina in the eye

Chemoreceptors detect chemicals

Mechanoreceptors in the cochlea of the ear - detect sound wave vibrations in air or water.

Innate behaviour is not modified by experience and is thus inflexible and stereotyped; is genetically determined.

Learnt behaviour changes as a result of experience; is flexible and not rigid.

Animal responses are innate behaviour and learnt behaviour

Plant responses are growth and turgor responses

Growth responses are brought by slow permanent changes in cell size

Turgor responses are reversible and are brought by changes in the cell water content and in come cases occur in less than a second.

Plant responses DO NOT need specialised receptor and effector cells.

Adaptations

Structural adaptations are aspects of the structure of the body

Behavioural adaptations are aspects of the behaviour of the organism

Physiological adaptations are aspects of the chemical processes of the body.

Ecological Niche

The Fundamental niche for an organism is the niche that it would occupy if all the necessary environmental conditions were present. The limits to the fundamental niche are set by an organisms physiological tolerance to abiotic factors.

The Realised niche is the actual niche that an organism occupies. It is not as extensive as the fundamental niche, with the boundaries of a realised niche typically being set by biotic factors.

Gause’s Principle

This principle asserts that no two species can exploit the environment in exactly the same way and coexist – one of the species will be excluded.

Daily Rhythms

Daily Rhythms are linked to the day-night cycle.

Nocturnal animals are night-active

Diurnal animals are day-active

Crepuscular animals are active in the twilight of dawn and dusk.

Annual Rhythms

Annual Rhythms are those associated with the combined effects of the Earth orbiting the Sun.

Tidal Rhythms

Tidal Rhythms are caused by the gravitational pull of the moon. The Earth and Moon rotate around their common center of gravity.

Lunar Rhythms

Lunar Rhythms are linked to the rotation of the moon around the Earth, and are much less common than daily or tidal rhythms.

Semi-Lunar Rhythms

Semi-lunar rhythms are also associated with the rotation of the moon around the Earth.

Compound Rhythms

The environment changes in a more complex way on the shore than elsewhere, because the cycle of day and night occurs as well as the cycle of the tides. The tidal cycle has a slightly different period from that of the day-night cycle.

Internal and External Timing

Endogenous rhythms are internally driven. They involve an internal ‘clock’, independent of changes in the external environment.

Exogenous rhythms are externally driven. Regular rhythms that are driven solely by external events.

Entrainment

Free-running, endogenous rhythms do not usually exactly coincide with those of the environment, showing that under natural conditions the internal clock must be continually reset or entrained by the environment.

Entrainment is not just a compensation for inaccuracies of the internal clock. Even if circadian rhythms had a period of exactly 24 hours, entrainment would still be necessary for two reasons:

• It allows organisms to adjust to seasonal change in time of dawn and dusk.

• it allows migratory animals that make considerable east-west movements to continually update their clocks.

Entrainment involves a process called phase shifting, in which the time of the peaks of an endogenous rhythm are advanced or retarded.

Photoperiod Responses

Photoperiodism in Plants

Photoperiodism is the regulation of seasonal activity by daylength or photoperiod.

Long-day plants (LDPs) only flower when the photoperiod exceeds a certain value, known as critical day length.

Short-day plants (SDPs) only flower when the photoperiod is less than thee critical day length.

Day-neutral plants are insensitive to photoperiod.

A brief period of light during the night can reverse photoperiodic responses. The reversibility of the effects of red and far-red light is characteristic of processes involving a pigment called phytochrome. This pigments is already known to be involved in a number of growth processes such as germination of some seeds.

Bud dormancy is not a passive absence of growth - it is a state that is actively maintains by a growth inhibitor called abscisic acid (ABA).

Leaf fall (abscission) is another photoperiodic effect. Abscission is a complex process involving changes in a layer of cells at the base of the leaf called the abscission layer. After the breakdown of many leaf-cell constituents (such as protein and chlorophyll), and the export of amino acids and certain minerals (such as magnesium), the cells of the abscission layer break down, causing the leaf to fall off. A layer of cork which previously formed seals off what would otherwise be a wound. Although short days act as an external stimulus, the internal chemical signals are complex and involve an interaction of several factors.

Other environmental factors besides daylength can influence flowering. Many plants native to temperate climates will not flower until they have been subjected to a prolonged period of cold. Promotion of flowering by chilling is called vernalisation.

Some periods have both a vernalisation and a photoperiodic requirement for flowering.

Adaptive Advantages of Photoperiodism

• reaches sexual maturity to coincide with pollinators being most active and present in greatest numbers, to increase chances of cross-pollination, or to reproduce vegetatively (asexually) when environmental conditions are optimum for offspring development and growth.

• expend significant energy and resources producing leaves and photosynthetic pigments when daylength and light intensities are at their maximum for maximum photosynthesis for growth and production of seeds.

• drop leaves to reduce transpiration when soil water may be frozen, and develop hardy buds that resist damage by frost or snow.

Photoperiodism in Animals

Diapause is a period of arrested development, common in insects and other arthropods native to climates with a cold season. Only after a period of exposure to cold conditions will the development resume.

In vertebrates, the part of the brain that controls seasonal activity is the hypothalamus. Besides its nervous connections, the hypothalamus also exerts control over the pituitary gland.

Orientation Responses in Animals

Orientation responses in animals can be grouped according to the complexity of the response.

• Relatively simple responses occur to abiotic factors. The response is made to remove the animal from unfavourable conditions and into favourable conditions. Two kinds of responses exist - taxes and kinesis; both are innate.

• More complex responses may occur over a long distance to a predetermined location that is out of sensory contact. The response may also take place over a long time frame. Though external abiotic factors may play an important part in direction-finding homing and migration responses often arise from internal factors and are not in direct response to either favourable or unfavourable conditions. Both homing and migration are based upon innate responses.

Homing is the ability of an animal to return over unfamiliar territory to its ‘home’.

Methods of navigation:

• landmarks

• solar navigation (sun compass)

• stellar navigation (star patterns)

• Magnetic fields (magnetic compass)

• Chemical navigation (scent trails)

• Sound navigation (sonar)

Taxes

A taxis is a movement of an organism either towards or away from an external stimulus; the response is a directional response. Except for unicellular organisms, taxes are confined to animals. Tactic responses are named according to the kind of stimulus that causes the response, as well as the direction of the response. Positive if the movement is towards the stimulus, negative if the movement is away from the stimulus.

• Positive Phototaxis is the movement towards light

• negative Phototaxis is the movement away from light

• Positive chemotaxis is the movement towards a chemical

• Negative chemotaxis is the movement away from a chemical

• Positive gravitaxis is the movement towards gravity

• Negative gravitaxis is the movement away from gravity

• Positive thermotaxis is the movement towards heat

• Negative thermotaxis is the movement away from heat.

• Positive thigmotaxis is the movement towards physical contact

• Negative thigmotaxis is the movement away from physical contact

• Positive rheotaxis is the movement towards a current

• Negative rheotaxis is the movement away from a current.

Tropotaxis involves simultaneous comparisons between impulse frequently from receptors on the two sides of an animal

Klinotaxis whereas tropotaxis requires at least two distinct areas of receptors, klinotaxis need only one, the animal compares the strength of the stimulus over time rather an space.

Kineses

In a kinesis, the direction of movement is random, bearing no relation to the direction of the stimulus. Therefore, kineses are non-directional responses. The rate of the activity is determined by the intensity of the stimulus rather than direction.

Orthokinesis - a stimulus intensities that governs the speed of the movement - faster in unfavourable conditions and slower in favourable. Results in the organism more likely to find and remain in favourable conditions.

Thigmokinesis - shown by many animals living in crevices

Klinokinesis - a stimulus intensity that determines the rate of turning. Higher rate of turning occurs in unfavourable conditions, resulting in an organism being more likely to find or return to favourable conditions. Slower rate of turning in favourable conditions means organisms is more likely to remain in these conditions.

Orientation Responses in Plants

Tropisms

Tropisms are the growth responses by parts of a plant to abiotic factors.

Plants are autotrophs, making their food from photosynthesis in the chloroplasts of their cells.

• Positive phototropism is the growth of the stem of a plant towards light

• Negative phototropism is the growth of the stem of a plant away light

• Positive gravitropism is the growth of the young root from the germinating seed downwards

• Negative gravitropism is the growth of the young root from the germinating seed upwards

• Positive hydrotropism is the growth of roots towards a water source

• Negative hydrotropism is the growth of roots away a water source

• Positive chemotropism is the pollen landing on the female stigma forming a pollen tube which contains male gametes

• Positive thigmotropism is the growth of stem of climbing plants or their tendrils towards and around a host plant.

Auxims are produced in the tips of shoots and set,s, and migrate throughout the the plant promoting elongation and differentiation of cells.

Gibberellins are similar production sites and effects as auxins. Produced in tips of roots and shoots and promotes growth by rapid elongation of cells, especially those of the stem between the nodes.

Cytokinins are produced in the the tips of the roots and promote mitosis.

Abscisic Acid (ABA) promotes formation of abscission zone, the layer of cells where leaves and fruits fall from a tree.

Ethene produces and accumulates in aging fruit promoting their ripening.

Phototropism

Phototropism is the most studied of all tropisms.

The absorption of light by riboflavin causes auxin to be transported from the illuminated to the shaded side of the coleoptile and towards the base, where it brings about cell elongation.

Auxin makes a cell wall more stretchable making it easier for the osmotic uptake of water and thus the enlargement of the cell. Because the cell wall stretches more readily in the lengthwise directions, auxin causes plant cells to elongate.

Gravitropism

The plumule (first shoot) is strongly negatively gravitropic

The radicle (first root) is strongly positively gravitropic

Nastic Responses

Nastice responses are rapid, reversible movement responses by parts of a plant to changes in abiotic factors. A nastic response removes a plant or part of a plant from unfavourable environmental conditions, placing it in favourable environmental conditions.

Nastic responses are non-directional responses so they do not have a positive or negative aspect to the movement. They occur in changes to the intensity of the stimulus, typically the rate or frequency of the response increased as the intensity of the stimulus increases. The rapid response typically results from changes in osmotic potential in certain cells.

Nyctinasty refers to the closing of petals of the flowers of certain plants.

Thigmonasty is a response to touch

Thermonasty is when the flowers of some plants close in low temperatures

Chemonastic and gravinastic responses have also been identified.