Abiotic factors – Notes

1. Light (photo-): the intensity, colour, direction or duration2. Gravity (geo-): organisms need to know ‘up’ and ‘down’, orientation3. Temperature (thermo-): the average and the range4. Water (hydro-): the humidity, soil moisture, speed of current, salinity, turbidity (cloudiness), depth, average rainfall6. Chemicals (chemo-): inorganic nutrients, carbon dioxide, oxygen, salitness, pH, poisons, pheromones7. Touch (thigmo-): a response to a solid object

Biotic Factors

• These include the relationships between members of the same species (intraspecfic) and with members of other species (interspecfic).

Intraspecific Relations

• Competition; food, resources, space, light, water and mates.

• Aggressive interactions; territories, hierarchies.

• Co-operative interactions; group formation for defense, and to help survival

Interspecific Relationships

Organism

• Stimulus- a change in the environment (external or internal) that causes a response in an organism.

• Receptor- any cell or group of cells that can detect this change.

• Effector; a cell or group of cells that respond.

Response of organisms to the environment

• The response of organisms to signals from the environment is called behaviour.

• If the behaviour is genetic, we say the behaviour is innate.

• If the behaviour is not genetic is is considered to be learned

Nature versus Nurture:Revisiting an Old Debate

NatureBehaviors are: • Innate • Hard-wired • Instinctual • Genetically

determined

Nurture

Behaviors are: • Learned • Flexible • Not genetically

determined

Behavior results from both genes and environmental factors

Introduction

This topic is divided into three main headings:

1. Orientation responses to abiotic environment

2. Timing responses to abiotic environment and

3. Responses to biotic environment –relationships between organisms

1. Orientation Responses

These will include:• Tropisms • Nastic responses• Taxes• Kineses• Homing• Migration

When studying these responses you

must look at the adaptive advantages that the population gains from them.

You must also link the responses to the genetic make-up of the population and its possible evolution.

Loggerhead and leatherback hatchlings are known to orient to the Earth's magnetic field: for these tests, each hatchling was placed into a nylon-Lycra harness.

PLANTS

ANIMALS

Response What it means Which Organism

Tropisms Growth towards or away from a stimulus coming from one direction.

Plants Only

Taxes Movement of the whole organism towards or away from a stimulus coming from one direction.

Mainly animals plus a few mobile plants.

Kinesis A non-directional response to a stimulus or a change in activity rate, in response to a change in the intensity of the stimulus

Animals only

Nastic Movements

A response to a stimulus that is independent of the direction of the stimulus.

Plants only

Homing The ability to find and return to the home site. Animals only

Migration Annual mass movement of animals, from breeding areas to other non-breeding areas and then returning.

Animals Only

PLANT MOVEMENTS

• Plants are “rooted” to the spot • Time lapse photography : plants are capable of

movements in response to environmental cues• Two main types of plant movements:

– Tropisms– Nastic movements (Turgor)

These are involuntary!! Plants don’t think! It’s just a response.

TROPISMS• A tropism is a directional growth response to an

external stimulus and it may be positive (towards the stimulus) or negative (away from the stimulus)

• Often caused by hormones• Types of Tropism

– Phototropism– Geotropism (Gravitropism)– Thigmotropism– Hydrotropism– Chemotropism The Thale Cress is

regulated by blue to UV light

Phototropism• Directional growth response of a plant organ to a

light stimulus

This shoot is positively phototrophic

• Phototropism results from faster cell growth on the shaded side of the shoot than on the illuminated side

Shadedside ofshoot

Light

Illuminatedside ofshoot

• Darwin’s experiments showed that coleoptiles only bend toward light when their tips are exposed.

• Therefore – tip must contain photoreceptor

• Bending takes place below the tip so message must travel from sensor area (tip) and elongating cells lower down(effector).

PHOTOTROPISM & AUXINS

PHOTOTROPISM & AUXINS

Boysen –Jensen confirmed that the light-activated substance in the tip was mobile

Gelatin – permeable

Mica – non-permeable

Chemical Messengers: Hormones• Hormone:

–Chemical secreted in one part of a plant/animal and transported to target sites where it affects growth or activity

Shoot tip placed on agar block.Chemical (later called auxin)diffuses from shoot tip into agar.

Agar

Control

NO LIGHT

Block withchemicalstimulatesgrowth.

Offset blocks withchemical stimulatecurved growth.

Other controls:Blocks with nochemical haveno effect.

HAND-OUT

• Went concluded that a coleoptile curved toward light because its dark side had a higher concentration of the growth-promoting chemical, which he named auxin.

HOW DOES AUXIN WORK?• Stimulates cell elongation

GEOTROPISM (GRAVITROPISM)

• Geotropism is the directional growth response of a plant organ to the stimulus of gravity

• Roots – positively gravitropic• Shoot – negatively gravitropic • Even when the seed is planted underground in

the dark

• Gravitropism is a response to gravity

It may be caused by the settling of special organelles on the low sides of shoots and roots

This may trigger a change in the distribution of hormones

Figure 33.9A

INVESTIGATING GRAVITROPISM

Gravitropism / GeotropismThe experiment below shows the effect of gravity on the growth of a seedling. After germinating, the young seedling (top) is turned on its side. Several days later (bottom), its roots have turned downwards and its shoot upwards in response to gravity.

• Gravitropism is an important adaptation

GRAVITROPISM & AUXINS• The plant probably

detects the direction of Earth’s gravitational pull through the sinking of starch granules

• This somehow causes auxin to move to the bottom side of the growing tip

GRAVITROPISM & AUXINS• Auxin concentration may determine the

direction of growth• Low concentrations of auxin stimulate root tip

growth downward but inhibit shoot tip growth upwards

• And vice versa It ensures that the shoot will grow upward toward

light and the roots will grow down into the soil, no matter how the seed lands in the soil

THIGMOTROPISM• Thigmotropism is the directional growth of plants in

response to rubbing / touch on one side of a stem or tendril

• Occurs in vines and other climbing plants

Touched cells produce auxin & transport it to untouched cells. These will then elongate faster so growth bends around the object

• Thigmotropism is a response to touch

It is responsible for the coiling of tendrils and vines around objects

It enables plants to use other objects for support while growing toward sunlight

Figure 33.9B

HYDROTROPISM• Hydrotropism is a directional growth response in

which the direction is determined by the gradient in water concentration

• Difficult to observe for roots grown in soil”– Can’t observe without disturbing soil– Gravitropism is usually stronger than root

hydrotropism– Root hydrotropism has been studied in humid air

rather than soil– Roots cannot “sense” water & grow towards it!

CHEMOTROPISM• Directional growth in

response to certain chemicals.

• Eg. Pollen tube grows towards the ovary in the flower= chemotropism

NASTIC MOVEMENTS• The response of plant organs to diffuse stimuli

that do not come from any particular direction• So response is independent of stimulus

direction, unlike tropisms– Photonasty– thigmonasty– Thermonasty

Nastic Responses

Nastic movements are plant movements that occur in response to environmental stimuli but unlike tropic movements, the direction of the response is not dependent on the direction of the stimulus.

Nastic Responses and Turgor Pressure

• Turgor pressure is the force pushing against the cell wall due to the influx of water into the cell. It is the mechanism involved in turgor movements– Osmosis – movement of water from a high

concentration to a low concentration through a semi-permeable membrane

TURGOR MOVEMENTS• Nastic Turgor – rapid, reversible movements

resulting from turgor pressure changes within the cells– Not generally related to the direction of the

stimulus

RAPID LEAF MOVEMENTS

Mimosa plant: When the sensitive leaves are touched they droop down & leaflets fold up Very fast – takes about 1 secDue to loss of turgor pressure in specialized cells at joints of leaves & leaflets

Venus Fly Trap

The Venus fly trap uses a similar mechanism to the Mimosa to shut its trap when a fly touches the sensitive hairs on its leaf

PHOTONASTY

• A response to a change in light intensity

• Does not include growth

• Eg. Prayer Plant• Eg Evening Primrose

flowers at dusk • Low light intensity is the

stimulus

THERMONASTY

• A response to change in temperature

• Eg. Tulip

Discuss the response of Mimosa pudica to the sudden shock stimulus, and compare it to the plant’s growth response under a constant directional light source.In your answer:• identify and describe both the rapid leaf response and the slower growth response• explain how both the rapid leaf response and the slower growth response happen• compare and contrast both responses in terms of their significance to the plant’s survival.

OTHER RESPONSES TO LIGHT

• Etiolation:– If a plant has reduced light or is grown in the dark it

becomes etiolated– Leaves grow small & yellow & there are long

internodes– Yellow colour comes from pigment

protochlorophyll, which needs light to turn it into green chlorophyll

ETIOLATION

• These are morphological adaptations for growing in darkness– Collectively referred to as

etiolation

Etiolation of a Potato

After a week’s exposure tonatural daylight. The potatoplant begins to resemble a typical plant with broad greenleaves, short sturdy stems, and long roots.

This transformationbegins with the reception oflight by a specific pigment,phytochrome.

Animal Orientation ResponsesFall into 4 categories :

1. Taxes; a directional response towards or away from the directional stimulus

2. Kineses; a non-directional response in which the rate of turning or movement is related to the intensity of the stimulus

3. Migrations-Seasonally repeated mass movements of a species from a breeding area to a feeding area (and usually back again unless animal only lives to breed once)

4. Homings; A journey from a foraging area back to a home base (over some familiar territory )

TAXIS

• Plural = taxes• Movement of the whole organisms towards

or away from a directional stimulus• Occur in animals, algae or bacteria

KINESIS

• The change in rate of movement of the whole organism in response to the change in intensity of a non-directional stimulus

• Are NOT said to be positive/negative as the stimulus is not directional– Orthokinesis: The speed of the movement is

related to the intensity of the stimulation– Klinokinesis: The amount of random turning is

related to the intensity of the stimulation

MIGRATION

• The annual mass movement of organisms from an area where they breed to an area where they do not breed

• Usually involves the return journey• Occur in animals only

MIGRATION

• True migration – “round trip” – the return to the original breeding site from the over-wintering site completes the journey

• Triggers to migration:– Drop in temperature– Days becoming shorter– Genetic drive that is innate (inbuilt)

Why Migrate???ADVANTAGES DISADVANTAGES

Animals remain in a favourable temperature so they are more likely to

survive as less energy is required to keep them warm

Animals may get caught in a storm & die or get blown off

course (get lost)

They have a constant food supply Could get eaten by a predator en-route

Better breeding conditions & therefore more offspring are

likely to survive

It is a huge investment of energy – some may not make the whole

journey

Can lead to a reduction in parasitism, predation, spread of

disease

They may starve en-route

Genetic mixing

METHODS used for Homing & Migration

1. Visual Cues2. Magnetism3. Sun Compass4. Star Compass5. Chemical Navigation6. Sound (as sonar)

Figure 37.11A

FEEDINGGROUNDS

Siberia

Arctic Ocean

Alaska

NORTHAMERICA

PacificOcean

AtlanticOcean

Migrating gray whales use coastal landmarks to stay on course

Baja CaliforniaBREEDING GROUNDS

1. VISUAL CUES & Migration

2. Magnetism

• Loggerhead and leatherback hatchlings are known to orient to the Earth's magnetic field: for these tests, each hatchling was placed into a nylon-Lycra harness.

Many animals are sensitive to magnetism and these organisms can follow the earths magnetic field lines ie. they have a magnetic

compass.If a magnet is placed on the head of an animal that relies on its

magnetic compass to navigate (eg. Homing pigeons) the birds will fly off course

Star trails over Maunga Kea mountain in Hawaii show how animals could use movement of stars across the sky to orient themselves in a certain direction

4. STAR COMPASS

Warblers use star compass to

navigate – if night is overcast birds

get lost

5. Chemical Navigation & Migration: Salmon

• Salmon are marine fish as adults• Migrate up rivers to spawn• Return to SAME unique stream as the one in which

they hatched as fry• Identify it by unique chemical “signature” (odour)

5. Chemical Navigation & Homing: Fire Ants

• Fire ants leave a trail of drops of volatile chemicals for other ants to follow

• One trail lasts only 80 seconds but is added to by each successive forager

• Ensures that trail doesn’t last long after the food source has been depleted

• In the experiment, Tinbergen placed a circle of pinecones around a nest opening

1

Nest

• After the female flew away, Tinbergen moved the pinecones a few feet to one side of the nest opening– When the female wasp returned, she flew to the

middle of the circle of pinecones rather than to the actual nest opening

Nest

2

No Nest

• Tinbergen next arranged the pinecones in a triangle around the nest and made a circle of small stones off to one side of the nest opening

– This time the wasp flew to the stones

Nest

3

No Nest

• The wasp cued in on the arrangement of the landmarks rather than the landmarks themselves

• This experiment demonstrated that the wasp did use landmarks and that she could learn new ones to keep track of her nest

• Natural selection preserves behaviors that enhance fitness.

Biological Timing

• The environment displays regular cycles based on the movement of the earth and moon– The earth rotates on its axis every 24 hours causing day

and night.– The tilted earth orbits the sun every 365.25 days,

causing seasonal changes in day length and temperature.

– The gravitational pull of the moon causes tides on earth.– The moon orbits the earth every 27.3 days, causing

visible phases of the moon.

Animals vs Plants

Animal

• Biological clocks are generally endogenous and can be re-set by external stimuli.

Plants

• Plant biological clocks are generally exogenous and depend on external stimuli in the environment.

Rhythms Geophysical cycle Length of cycle Biological rhythm Known zeitgebers

Solar year 365.25 days Cirannual Photoperiod

Lunar month 29.5 days Circamonthly Light of the full moon

Solar day 24 hours Circadian Light, temperature, humidity

Tidal 12.4 hours Ciratidal Tidal activity

Biological Clocks

• The existence of circadian and circannual rhythms means that animals must have a way of keeping track of time

• They have an internal clock which lets them predict and prepare for changes to come

• The biological clock in animals is found in the hypothalamus of the brain

• It is• Sensitive to environmental cues• Can be stopped and reset• Is very accurate• Is inherited

Biological Clocks Cont…

• Biological clocks are used for:• Control of the daily rhythms of the body• Reproduction timing• Preparing for migration by eating of plenty of food• Preparing for winter by storing of food, increasing

thickness of coat and hibernating• Navigating by the sun or stars

Definitions

• Biological clock is an internal timing system which continues without external time clues, and controls the time of activities of plants and animals

• Period of the rhythm the time it takes to complete one cycle of activity

• Phase shift when the onset of the period of the rhythm is changed either earlier or later. This occurs when you travel around the earth into different time zones. It can be artificially induced by controlling the light and dark periods

Definitions cont….

• Free running period this is the time when the clock is running without any clues from the environment, so it ‘runs free’

• Entrainment this is the resetting of the clock on a regular basis, forcing it to take up the period of the environment

• Zeitgeber – the environmental agent that resets the biological clock eg light or temp

Definitions cont….

• Circa – because each of the rhythms is not exactly the time length stated, eg daily is not 24 hours, their names start with circa (which means ‘about’)

• Photoperiod – the responses of plants and animals to the lengths of day and night

Biological Timing responses to the abiotic world

• All organisms respond to various cues• The responses can be:

• Annual cycles – yearly changes of the season• Daily – night and day• Lunar – monthly, often related to the moon• Tidal – related to the ebb and flow of the tides

• It is to an individual’s advantage to synchronise its activities to these rhythms

• There are three basic ways to do this

Synchronising to rhythms

• Exogenous - A rhythm that is control by the external, environmental stimulai detected by the organisms

• Endogenous – A rhythm that is controlled by an internal biological clock

• Combination – of both endogenous and exogenous

Endogenous

• Sometimes it is hard to tell if a rhythm is endogenous or exogenous. It is endogenous if it can be shown that one of the following criteria apply:

• The rhythm may have a frequency that is not exactly the same as the period of an external environmental factor, eg light, temperature etc

• The period of the endogenous rhythm usually deviates from the natural rhythm when studied under constant laboratory conditions

• The rhythm may persist when the organism is moved from one part of the world to another

Endogenous Rhythms• Circadian: a daily activity period, approx 24 hours• Circatidal: a tidal activity period, approx 12.4 hours• Circa-semilunar- a spring /neap tidal activity

period, approx 14.7 days• Circalunar – monthly activity period, approx 29

days• Circannual – yearly activity period, approx 360 days

(it is usually short of or exceeds 365).

Circadian Rhythms

• Animals are active at different times of the day• Diurnal – active during the day, inactive at night• Nocturnal – active at night, inactive during the day• Crepuscular – active at dawn and dusk• Arrhythmic – no regular pattern – tend to be found

were changes in the microclimate are negligible

Circamonthly Rhythms

• Some animals synchronise their behaviour with the phases of the moon

• Changes associated with tidal patterns are also considered circamonthly (lunar)

• The spawning behaviour of some marine worms is synchronised by the moon so that the egg and sperm are released at the same time

• Grunion fish also work on this method of spawning, using the tides

Circannual Rhythms cont….

• Hibernation - This is the way some animals survive over winter by slowing their metabolic rate

• Aestivation – this is a form of hibernation over summer when the weather gets too dry or temperature gets too hot

• Reproduction – the method by which most animals reproduce when conditions are most favourable, ie spring

Actograms

• An actogram is a graph that shows when an organism is active and inactive

• Note–LL = constant light–DD = constant darkness–LD = natural light cycles–LD 12:12 = 12hr light 12hr dark

Actogram Tricks

• Actograms can show 2 days on one line – double plotted actogram

• The period is measured from the beginning of activity to when the activity begins again

• Use a RULER to determine this for several days and work out the AVERAGE

• Use a ruler to CHECK how many mm represents 24hours and work out the PERIOD

Circadian vs. Daily Rhythm• Daily cycle = the length of a day• A circadian Rhythm = free-running

cycle of about a day. It has to be entrained with a zeitgeber each day to keep it in time with the daily cycle

Interpreting an Actogram

1. Determine whether there is one rhythm (circadian) or two rhythms (ciratidal) per 24hrs

2. Draw a line of “best-fit” to show the general direction of the activity pattern. The general shape of the pattern can beThe onset of the activity is DELAYED (phase

delay)Which means that the rhythm will be 24hrs (or 12hrs) PLUS some timeThe onset of the activity is ADVANCED(phase

advanced)Which means that the rhythm will be 24hrs (or 12hrs) MINUS some time

Interpreting an Actogram

3. Work out the phase shift for the activity pattern from the beginning of the line you have drawn to the end of the line.

4. Divide this number by the number of days – this will tell you how much the rhythm is shifting per cycle (period)

Things we all know about plants:• Spring – Flowering

– Change in growth pattern: leaves → buds– Flowering occurs later after embryonic flowers become

viable Autumn Leaves change colour and fall off the trees senescence & abscission

Winter – No new growth - dormancyTypes of flowering – annual, biennial or perennials

BIOLOGICAL CALENDAR?• Unreliable indicators of time of year

–Temperature –Moisture –Light levels

• Reliable: length of day/night –Varies with season–Varies with latitude

• Detected by phytochrome

PHOTOPERIODISM• The regulation of seasonal activity by day-length

or photoperiod– Short Day plants – Long Day plants– Day Neutral plants

= Long nights= Short nights

LONG DAY PLANTS= Short Night

• Flower when days lengthening– ie. Spring & early summer– Approx 14 hr day

• If transport to tropics – don’t flower– Critical Day Length not reached– Examples: Radish, lettuce

SHORT DAY PLANTS= Long Night

• Flower when days are shorter– Approx 10 hour day– Autumn eg Chrysanthemum– Early spring eg. strawberry

• Some overlap in critical day length ie. 11 hours

• But don’t flower at same time

PHYTOCHROMES & MEASURING TIME

DAY NEUTRAL PLANTS• Insensitive to photoperiod• Flower regardless of day length as longs as they

have enough light for normal growth– Eg. Most plants native to the tropics– Eg. Tomato, dandelion & garden pea

3 way classification system = oversimplified age of plant, temperature etc.

NIGHT LENGTH IS WHAT COUNTS

• If long night interrupted by few minutes of light – prevents short-day plants flowering & long-day plants are induced to flower

• How could you use this commercially?

SHORT DAY PLANT

Night Interruptions

Leaves detect the flowering Stimulus

• So, modify the experiment:• Different wavelengths of light used to interrupt

the night• Red was most effective

– Prevented flowering in SDP– Induced flowering in LDP

• Discovered that red (660nm) light effects are cancelled out by following with far-red light (725nm)

Phytochrome: Photosensitive Pigment

• Far-red reversibility of red light = characteristic of known pigment called phytochrome

• Two states– Pr – primarily absorbs red light (660nm)

– Pfr – absorbs far-red light (725nm)

– When Pr absorbs light it is converted to Pfr & vice versa

Phytochrome• Extracted & purified

– Blue protein present in plant cell membranes– Blue because reflects blue light– Absorbs red wavelengths

So how do plants use Phytochrome to measure photoperiod?

• Still contested• Best Guess = Pfr is the active form:

– In SDP Pfr inhibits flowering, so plants need long nights in order to flower (Pfr → Pr)

– In LDP Pfr induces flowering : short night so not all Pfr → Pr

– Evidence that this mechanism involves an internal clock also

LDP = SNP

• Needs short night• Needs Pfr still present at end of night• Pfr promotes flowering for LDPs