Plant and animal reponses

Meristems

the region of plant growth. Primary growth occurs at the opical meristems at the tips of roots and shoots.

Primary Growth

growth of the tips of roots and shoots is divided into three zones: zone of cell division, zone of elongation, zone of differentiation

Zone of cell division

this contains the meristematic cells. These cells undergo rapid mitosis to produce new cells

Zone of elongation

the new cells no longer divide; instead they begin to expand and elongate.

Zone of differentiation

once at full size, the new cells start to specialise into specific tissues such as xylem, phloem and root hair cells

Important Photohormones

Auxins, cytokinins, ethylene, abscisic acid, gibberellins

Auxins (IAA)

produced in the shoot and root tips. Promoted elongation in the shoots but inhibits elongation in the roots. Promoted apical dominance (growth of main shoot/root).

Cytokinins

Produced in the roots. Inhibits apical dominance by promoting lateral budding.

Ethylene

Ripens fruit and promotes abscission (detachment of fruit and leaves).

Gibberellins

Breaks seed dominancy and promotes germination

Tropic responses

Produced in the roots. Inhibits apical dominance by promoting lateral budding.

Ethylene; Ripens fruit and promotes abscission (detachment of fruit and leaves).

Gibberellins; Breaks seed dominancy and promotes germination

Tropic responses

tropic responses; plant growth response that occurs directional to the stimuli. Can be positive or negative

Light

Photo

Water

Hydro

Gravity

Geo

Chemical

Chemo

Touch

Thigmo

Sun

Helio

Electricity

Electro

Tide

Rheo

Food

Tropo

Temperature

Thermo

Response Mechanism (tropic)

Tropic responses are due to uneven distribution of Auxins that cause uneven elongation of cells in areas of primary growth

Effect of gravity (Tropism)

Causes it to accumulate in the lower sides of the stem and toots resulting in geotropism

effect of light

causes auxins to breakdown and accumulate in shady sides of shoots resulting in phototropism

Effect of water

Auxins are water soluble and accumulation root cells with a high water concentration resulting in hydrotropism

Transport of auxins

passively through the phloem of actively from cell to cell. Active transport allows for chemotropic and thigmotropic responses

Nastic response

nondirectional turgor movement in plants. turgor pressure is the pressure of the contents of the cell pressing against the cell wall and is regulated by the moving water into/out of the cell/vacuole. They are proportion to the stimuli

Most common nastic response

Most common nastic response; the opening and closing of stomata due to nastic movement of guard cells

Time frame (tropic vs Nastic)

nastic responses are immediate where as tropic responses occur over a long period of time

Reversibility (tropic Vs nastic)

Nastic responses are reversible, tropic responses are permanent

Response mechanism (nastic)

often rely on specialized joint-like thickening of the base of a leaf called a pulvinus

Pulvinus joint

consists of a vascular core (xylem and phloem) surrounded by a spongy flexible thin walled cell (two types, extensors and flexors)

Extensor vs flexor cells

extensors increase their turgor pressure during leaf ‘opening’ and decrease during ‘closing’. flexor cells do the opposite

How the response is affected (nastic)

response is affected due to active transport of sucrose and ions such as potassium and chloride. As these solutes are moved between extensors and flexors, water flows due to osmosis.

Photoperiodism

To ensure the best chance of survival and reproduction, plants need to be in sync with seasonal rhythms in temperature, precipitation, pollinator activity and sunlight

Stimuli of photoperiodism

Many stimuli could be used to detect the season, however, none are as reliable as the relative length of day and night (the photoperiodism)

Critical period

The critical duration of day/night required to stimulate or inhibit flowering

Long day plants

only flower is the day length exceeds their critical day length. This is generally around 14-16 hours. Long day plants generally flower in late spring and summer.

Short day plants

Only flower if the day length is less than their critical day length. generally, 8 - 10 hours. Theses plants generally flower in winter and autumn

Day neutral plants

photoperiod has no effect on day neutral plants. They instead generally inhibit flowering after reaching an age/development stage and /or in response to environmental cues such as a perios of sustained temperature.

taxes and kinesis

are simple innate movement in reponse to stimuli. This allows organisms to move to a favourable environment, giving them a survival advantage

taxes

directional movements, can be positive or negative

kinesis

non-directional to stimuli. instead the rate of movement changes in relation to the comfort zone of the organism. kineses are very common in single-celled organisms

Types of kinesis

orthokinesis and klinokinesis

Orthokinesis

changes the speed of movement proportional to the stimuli

Klinokinesis

Changes the rate of turning proportional to the level of stimuli

innate behaviour

those that occur instinctively due to genetics

learned behaviour

is developed overtime by modification of behaviour due to previous experience

Homing

an animals instinctive ability to navigate through unfamiliar territory and return to an original location using navigational cues.

When is homing need

when a species is displaced from their familiar territory during migration, mating or even simply during hunting or other regular activity

Navigational cues/methods

position of the sun, position of the star patterns (celestial navigation), orientation of Earth’s magnetic field, direction of ocean currents, scents and pheromones (olfaction) and sound

Navigating familiar terrain

many animals use this navigating, however, this is not considered a type fo homing as it only occurs in familiar territory

migration

The movement of animals from one region to another. True migration involves annual or season movements, or involves a major habitat change as a part of a species life

How is migration controlled

migration is genetically controled by initiated by the environment. For migration to occur the advantages must outweigh the disadvantages

complete migration

all members of the population will migrate

Partial migration

some members of the population will migrate

differential migration

all members of the population migrate but not necessarily all at the same time of travelling the same distance. The differences are often due to age or sex

irruptive migration

members of the population do not migrate at all some years and do migrate other years

advantages of migration

new/more resources, constant food supply, find mates, greater genetic mixing, better breeding conditions, reduces predation, disease and parasitism, remain in an favourable climes, lead to colonisation of new areas

limitation of migration

uses lots of energy, animals can run out of energy before reaching their destination and die, risk of getting lost or eaten on the way

migration stimuli

cues for migration involve complex interactions between internal and external stimuli

external stimuli (migration)

changes in weather, food and water supply and lenght of day

Internal stimuli (migration)

circannual rhythm (internal calendar), fat reserves, sex maturity

Rhythms

most environments on earth undergo predicatble fluctations due to the time of day, month (moon phase) and year. Animals have a survival adventage if they can predict, prepare and respond to these fluctuations

Keeping time

rhythms are maintained due to endogenous pacemakers (biological clocks) and exogenous zeitgebers (environmental cues)

Biological clocks

The bodies innate time keeping sytem. Occurs due to complex interaction of certain genes and proteins called a molecular clock. Pressent in almost all tissues in the body. The master clock is a group of 20,000 cells in the anterior hypothalamus called the SCN. This clock maintains circadian rhythm

entrainment

the process by which a biological clock is affected by environmental cues. Can occur at different levels of organisation from indivdual cells to whole organisms.

Jet lag

When the clock becomes out of sync with the environment you experience jet lag. Synchronization can only be restored with tim eand entrainment by zeitgebers. Humans have a natural biological clock that lasts 24hs and 11mins (± 16mins)

Suprachiasmatic nucleus (SCN)

the Suprachiasmatic Nucleus is located above the chiasma of your optic nerve adjacent to the pineal gland When light enters the eye, special photoreceptor cells in the retina detect blue light and send a nerve impulse to the SCN. This signal increases the production and accumulation of CLOCK and BMAL1 proteins

CLOCK and BMAL1

inhibit the secretion of melatonin by the pineal gland preventing sleepyness. They promote the transcription of period (PER) and cryptochrome (CRY) proteins which inhibits the secretion of melatonin and the transcription of PER and CRY protein leading to wakefulness.

Diurnal

Active during the day. This provides many advantages for animals that have poor visibility in low light (like humans)

Nocturnal

Active during the night. Advantageous for avoiding predators and competition. In some areas it can be an adventage to avoid the heat.

Crepuscular

Active during twilight (dusk and dawn) adventageous for avoiding the heat while utilising light for activities such as hunting.

Actograms

diagrams/graphs to show animal activity patterns over a period, demonstarting the circadian rhythm of animals.

Purpose fo actograms

Shows a period when zeitgeber is present and a period when it is removed, there is useful for determining the relative influence of endogenous (internal) and exogenous (external) factors.

phase shift

When no zietgebers are present, the organism is siad to be in a ‘free running’ period.If the activity pattern was entirely endogenous, it would remian relatively similar. However, in the absence of environmental cues the activity pattern is likely to drift. The amount of drift is the phase shift.

Levels of ecological organisation

1. organism, 2. population, 3. community, 4. ecosystem, 5. biome, 6. biosphere

population

all the same organisms

community

all the same species within an environment

ecosystem

all the biotic and abiotic factors within an environment

biome

a major biotic community characterised by dominant factors

Biosphere

the zone of all life on earth

interspecific relationships

the way different species within a community interact with each other eg, mutualistic, exploitative, commensalistic

mutualistic relationship

benefits both species

commensalistic relationship

benefits one species while not harming the other

exploitative

benefits one species while harming the other

competitive

harming both species

symbiosis

used to describe a close and long-term interaction between organisms of different species. Symbiotic relationships can be mutualistic commensalistic or parasitic