Responses of Plants & Animals to Their External Environments

Question 1

What is meant by an ‘Adaptive Advantage’?

Answer 1

Any trait/characteristic that results in an organism having an increased chance of survival in its environment, and thus greater opportunity to reproduce successfully

Question 2

What is a ‘Biological Clock’?

Answer 2

Any innate/internal/endogenous mechanism that enables an organism to keep track of time.
These can be altered or entrained by various environmental cues though, known as zeitgebers in order to keep the internal biological rhythm synchronised to external rhythms

Question 3

Briefly describe a Biological Clock

Answer 3

Any innate and internal/endogenous (originating within) mechanism that enables an organism to keep track of time. These are genetically determined and may be altered/entrained via various environmental cues known as zeitgebers.

Under natural conditions, the internal clock must be continuously entrained by outside stimuli/zeitgebers, as it may become unsynchronised with changes in day-length depending on seasons etc.

Question 4

What is an Effector?

Answer 4

A (biological) component that produces a response/action after receiving a signal/stimulus (from a receptor)

Question 5

What is an Endogenous Rhythm, and how does it differ from an Exogenous Rhythm?

Answer 5

(‘Endo’ - ‘internal’ / ‘Exo’ - ‘external’)

A biological/internal rhythm that continues even in the absence of external cues.
Whereas, an exogenous rhythm is a biological pattern that occurs ONLY in response to external cues (and thus ‘disappears’ when these/zeitgebers are removed).

Question 6

What is meant by ‘Entrainment’?

Answer 6

The synchronisation of an organism’s biological clock and thus rhythms to the rhythms/patterns of its external environment (via external cues/zeitgebers).

Question 7

What is an ‘Environmental Cue’ or ‘Stimulus’?

List the Main 8 Stimuli as well as their Prefixes:

Answer 7

A signal/trigger from the environment that can entrain an endogenous rhythm/regulates and leads to an exogenous rhythm.

Examples:

• Light (photo)
• Temperature (thermo)
• Gravity (gravi or geo)
• Chemicals (chemo)
• Touch (thigmo)
• Water (hydro)
• Current (rheo)
• Food (tropho)

Question 8

What are ‘Choice Chambers’?

Answer 8

Devices that offer small invertebrates/organisms two or more contrasting environments
(eg. differing in humidity, temperature, illumination, pH, etc.)
and allows them to move freely to whichever one they ‘prefer’.

They have the purpose of providing a way to observe orientation responses in the organism to certain stimuli.

Question 9

What is meant by an ‘Innate Behaviour’, and what are the four main characteristics of one?

Answer 9

These are genetically programmed/determined behaviours (ie those inherited from the organism’s parents and thus determined by its genes/DNA).

They are:
1) HERITABLE: encoded in the DNA and passed from one generation to the next

2) INTRINSIC: present in animals raised in isolation from others
3) STEREOTYPIC: performed in the same way each time and by each individual
4) INFLEXIBLE: not modified by development or experience

Question 10

What is meant by a ‘Learned Behaviour’ and what are its four main characteristics?

Answer 10

These are behaviours that occur as a result of an organism’s experience or through the observation and imitation of other individuals (and is the antithesis of ‘innate behaviors’).

They are:
1) NON-INHERITABLE: acquired only through observation and/or experience

2) EXTRINSIC: absent in individuals raised in isolation from others (exhibiting the same behavior)
3) ADAPTABLE: capable of modification to suit changing conditions
4) PROGRESSIVE: subject to improvement/refinement through practice and time

Question 11

What is a ‘Free-Running Period’ and what general trends does it show/how is it calculated?

Answer 11

This is the period of a bio-rhythm under constant environmental conditions (ie when all external cues/zeitgebers are removed).

If this period does not exactly match the length of period for the rhythm of the organism’s environment (eg it is slightly longer/shorter than 24 hrs for a circadian-based behaviour), then the onset/start of the activity will drift out of synchrony with the external environment and thus begin later/earlier depending on whether it is longer or shorter respectively.

For Circadian Patterns:
- If the activity gets later each day (free-running period > 24hrs) add the value of the ‘Phase-Shift’

• If the activity gets earlier each day (free-running period < 24hrs) subtract the value of the ‘Phase-Shift’

Question 12

Give a more specific definition of what is meant by ‘Zeitgeber’ (and how it differs slightly from the general term of ‘Environmental Cue’):

Answer 12

(‘Zeit’ - Time / ‘Geiber’ - ‘Giver’) (German)

The term given to the environmental cues that reset/entrain an organism’s biological clock.
Whereas ‘environmental cues’ are simply factors of the environment an organism may exhibit a response to.

Question 13

What is ‘Phase-Shift’ and how is it calculated?

Answer 13

The amount by which the onset of a rhythm’s/activity’s period shifts each day.

It is calculated from an Actogram by:

1) Selecting a complete actogram pattern (ie one that does not run off the page)
2) Drawing a vertical line from the beginning of the activity bar at which the zeitgeber(s) were removed (ie the phase shift start point). This line should cross through the time scale on horizontal axis)
3) Draw a second vertical line at a measurable/reasonable number of days after this so that a gradient may be derived
4) Draw a diagonal line connecting these two vertical lines that follows the general gradient of the Phase-Shift pattern
5) Count the number of days and hours between your two chosen points/vertical lines. Then, divide the number of hours by the number of days to give the Phase-Shift, and convert any decimal values into minutes by multiplying decimal portion by 60 sec, as answer must be rounded to hours and minutes

Question 14

What is the purpose of a ‘Biological Clock’?

Provide an example:

Answer 14

This endogenous mechanism allows organisms to anticipate environmental changes before they occur, and thus allows them to time the onset of their activities/rhythms according to the arrival of ‘optimal conditions’.

For example, a nocturnal animal may use an internal and innate biological clock to help time its return to its burrow before sunrise occurs

Question 15

Briefly explain ‘Biological Rhythms’:

Answer 15

These rhythms arrive due to the fact our environment undergoes predictable, cyclical fluctuations as a result of changes in seasons, tides, and the time of day.

(Therefore, being able to predict/anticipate/prepare for these rhythmic patterns from repeating events is a highly beneficial trait)

Question 16

Briefly summarise ‘Daily Rhythms’:

Answer 16

The Day-Night Cycle is caused by the rotation of the Earth on its axis, and ‘Daily Rhythms’ are classified as ‘Circadian’ (‘Circa’ - ‘about’ / ‘Diem’ - ‘day’)

Question 17

Briefly explain ‘Lunar Rhythms’:

Answer 17

The orbit of the Moon around the Earth and its gravitational pull on our oceans leads to observed tidal rhythms with an approximate period of 12.4 hours. Whilst the illumination of the Moon by the Sun causes the ‘phases of the Moon’.

‘Circalunar’ - approx period of 29.5 days
‘Circatidal’ - approx period 12.4 hours (therefore two high/low tides per day)

Question 18

What are ‘Phytohormones’?

Answer 18

(ie ‘Plant Hormones’)
These are chemical compounds produced in small concentrations that are utilised to regulate integral stages of plant life-cycles as they are transported around the plant in order to trigger/stimulate or switch-off various responses (caused by certain environmental cues).

Question 19

Briefly describe ‘Abscisic Acid’ (ABA):

Answer 19

ABA promotes ‘seed dormancy’;

• It accumulates within seeds during fruit germination, thus preventing premature seed germination within the fruit.
• ABA also inhibits germination during times/periods such as winter when environmental conditions are unfavourable (ie very low temperatures, low water availability etc)
• (Previously it was thought ABA played a role in ‘abscission’, however recent evidence suggests it is instead caused by auxins and ethylenes)

Question 20

Briefly describe ‘Giberellin’ (GA):

Answer 20

GAs ‘break dormancy’ and ‘initiate germination’;

• Absorption of water by seed causes GA production
• GA’s presence initiates the breakdown of energy-rich reserves of starch found within seed, thus providing embryo with energy required for germination
• Also cause stem and leaf elongation, which often results in ‘Bolting’ (when plants prematurely produce a flowering stem before the crop is harvested)

Question 21

State the suffix used for ‘Nastic Responses’:

And list the main Nastic Responses

Answer 21

‘~nasty’

• Nyctinasty (movement at night/in the dark)
• Photonasty (response to light)
• Thermonasty (response to temperature)
• Hydronasty (response to water)
• Thigmonasty (response to touch)
• Chemonasty (response to chemicals)

Question 22

Outline Four Key Differences between ‘Nastic’ and ‘Tropic’ Responses:

Answer 22

1)
Nastic Response: RAPID/REVERSIBLE
Tropic Response: SLOW/IRREVERSIBLE (usually involving elongation of cells)

2)
Nastic Response: Non-directional
Tropic Response: Directional

3)
Nastic Response: Rate of response is always PROPORTIONAL to INTENSITY of STIMULUS
Tropic Response: Rate is not determined by this

4)
Nastic Response: Tend to be in relation to changes in CELL TURGOR PRESSURE
Tropic Response: Tend to entail growth/elongation of cells

Question 23

Define ‘Photoperiod’:

Answer 23

The relative lengths of light and dark periods (day/night) over the course of 24 hours.

Question 24

List the three main ‘External Migration Cues’:

Answer 24

1) PHOTOPERIOD: longer days in summer/shorter days in winter cue some animals to migrate;
- Less sunlight results in lower rates of photosynthesis, thus less food/productivity, as well as lower temperatures

2) SHIFTING SEASONS: causes temperature and levels of precipitation change;
- Results in distinct wet and dry seasons

3) FOOD AND/OR WATER AVAILABILITY: lack of food/water due to extremes in temperature, lack of precipitation, or population pressure in area reaching its carrying capacity

Question 25

List the three main ‘Internal Migration Cues’:

Answer 25

1) CIRCADIAN RHYTHMS: ‘internal calendar’ in animal’s nervous system can assist them to know when to migrate;
- Some species have innate sense of when to migrate even without exposure to external stimuli

2) FAT RESERVES: low fat reserves may cue some species to move in search of food;
- In other species migration only occurs after fat reserves have built up

3) SEXUAL MATURITY: when animal reaches sexual maturity, hormones may trigger innate desire to migrate to breeding grounds

Question 26

Define an ‘Autotroph’:

Answer 26

An organism (typically plants) that is capable of producing its own food resources, (usually via photosynthesis).

Question 27

Define ‘Photosynthesis’ and give its chemical equation:

Answer 27

Process by which photoautotrophs (plants and bacteria) produce carbohydrates/glucose via capturing light energy from the sun through carbon-fixing (using carbon dioxide and water from the surroundings).

6CO2 + 6H2O → C6H12O6 + 6O2

Question 28

What is a ‘Phytohormone’?

Answer 28

These are chemical compounds/plant hormones produced in small concentrations, utilised to regulate integral stages of plant life-cycles through their transportation around the plant to trigger or switch off various responses.

Question 29

Define a ‘Biorhythm’:

Answer 29

A regular cycle of events in an organism controlled endogenously (although also typically modified in response to environmental cues).

Question 30

Where is the Biological Clock of humans located?

Answer 30

In the SCN (suprachiasmatic nuclei), in our Hypothalamus (part of the brain connected to eyes - sensing light/dark), and Pineal Gland (secretes melatonin - a sleep hormone).

Question 31

What are the Four Main Functions/Advantages of Biological Clocks?

Answer 31

• Prediction of Events (migration, hibernation, etc.) which require a large build-up of food reserves
• Synchronisation of Internal Physiological Processes (eg. sperm and egg production with favourable environmental conditions for mating/production of offspring)
• Synchronisation of Social Activities (eg. congregation for mass hibernation, flocking in the non-breeding season for safety in numbers, etc.)
• Enables Animals that Utilise Solar/Stellar Navigation (changing celestial bodies) during Homing/Migration to ‘Adjust’ their Compasses

Question 32

Define ‘Ecological Succession’:

Answer 32

This is the observed process of change in the species structure of an ecological community over time.

(With one of its main ‘drivers’ being competition)

Question 33

Give a general definition of ‘Competition’:

Answer 33

An interaction between organisms or species in which the fitness of one is lowered due to the presence of the other.

Question 34

Define ‘Zonation’:

Answer 34

This describes the natural layering of of ecosystems that occurs at distinct altitudes, due to varying environmental conditions.

(May also occur horizontally in the case of rocky shore communities etc.)

Question 35

Define ‘Stratification’:

Answer 35

This is the subdivision of an ecosystem into layers of vegetation based on the sizes and types of plants present.

Vertical stratification occurs due to competition for sunlight mostly, and the varying degrees of light exposure different strata receive.

(Typically includes a ‘Canopy’, ‘Sub-Canopy/Understory Layer’, ‘Shrub Layer’, and ‘Ground Layer’).

Question 36

Define ‘Exploitative Competition’:

Answer 36

When one species either reduces a resource or uses a resource more efficiently than another, therefore depleting its availability to other species.

(However occurs both intraspecifically and interspecifically)

Question 37

Define ‘Interference Competition’:

Answer 37

When two organisms or species physically interfere with one another by aggressively trying to exclude one another from particular habitats.

Question 38

List Three Key Effects of ‘Interspecific Competition’ on ‘Species Evolution’:

Answer 38

May Result in:
1) The exclusion of a species from a habitat

2) Niche Separation
3) Local Extinction

(All due to the notion of one species ‘outcompeting’ another)

Question 39

Briefly Define the ‘Competitive Exclusion Principle’ (i.e ‘Gause’s Principle’)”

Answer 39

This states that two species that use the same limiting resource whilst occupying the same niche (i.e. with significantly overlapping niches) cannot coexist indefinitely, and must diverge from one another in some way in order to do so.

(Usually results in one outcompeting the other).

Question 40

What is ‘Niche Differentiation’?

Answer 40

A process by which Natural Selection drives competing species into different patterns of resource use or different niches;

May involve:

• Spatial Displacement (using same resource by occupying diff. areas or habitats)
• Temporal Displacement (eliminating direct competition by utilising same resource at diff. times)
• Morphological Differentiation (evolving diff. morphologies to allow use of same resource in diff. ways)

Question 41

What are the Three Main Components comprising an organism’s ‘Ecological Niche’?

Answer 41

• HABITAT: (abiotic/biotic factors e.g where it lives, what it eats).
• ADAPTATIONS: (any structural, physiological or behavioural traits that enable it to survive in its habitat, e.g. active at night).
• ROLE: (how organism fits into a food web or interacts with other species, e.g producer, consumer).

Question 42

Define and Contrast ‘Fundamental Niche’ vs ‘Realised Niche’:

Answer 42

The fundamental niche of an organism describes the full range of environmental conditions and resources an organism can possibly occupy and use (primarily based on and limited by its physiology), especially when limiting factors are absent in its habitat.

The realised niche of an organism is the niche the organism actually occupies in an ecological community due to limiting factors such as competition, or lack of resources.

Question 43

In Behavioural Ecology, what is the Basic Definition of an ‘Adaptive Behaviour’?

Answer 43

A behaviour which contributes directly or indirectly to an individual’s survival or reproductive success and is thus subject to the forces of natural selection.

Question 44

Define a ‘Tropism’

Answer 44

A growth or turning movement in response to an environmental stimulus.

Question 45

Compare the Effects of Auxin Concentration on both Plant ‘Roots’ and ‘Shoots’:

Answer 45

Higher Auxin concentration in Shoot Cells leads to an increase in rate of cell elongation.

Higher Auxin concentration in Root Cells inhibits the rate of cell elongation.

Question 46

List Three Examples of Processes Facilitated by Auxin:

Answer 46

• Promotes Cell Division
• Promotes Elongation and Differentiation of Cells
• Promotes Secondary Thickening of Stem/Root

Question 47

List the Four Main Plant Hormones other than Auxin:

Answer 47

• Gibberellins
• Cytokinins
• Abscisic Acid
• Ethylene

Question 48

What is the Function of Gibberellins according to EP?

Answer 48

They promote stem elongation as well as being involved in flowering and seed germination.

Question 49

How does EP describe Cytokinins and their Function?

Answer 49

Cytokinins are hormones which promote cell division.

They are produced in growing zones such as the meristems at the tips of shoots, and often work in combination with auxin during organ development in plant embryos.

Question 50

How does EP describe Abscisic Acid and its Function?

Answer 50

Abscisic acid is involved in opening and closing of the stomata on leaves.

It also promotes and maintains seed dormancy by inhibiting cell growth.

Question 51

How does EP describe Ethylene and its Function?

Answer 51

Ethylene is a plant hormone involved in the ripening of fruit and abscission (the shedding of various parts of a plant, including the dropping of a leaf, fruit, flower or seed).

Question 52

Which part of the plant senses high levels of water in the soil?

Answer 52

The root caps.

Question 53

What is the ‘Coleoptile’ and why is it important?

Answer 53

The tip of a plant shoot, which is essential in sensing light, thus leading to phototrophic responses.

Question 54

What are the more technical terms for ‘Roots’ and ‘Shoots’?

Answer 54

Radicles and Plumules.

Question 55

What is ‘Nyctinasty’ and what is an Example + its ‘Adaptive Advantage’?

Answer 55

Nyctinastic responses occur in plants in response to the onset of darkness.

Nocturnal leaf folding may help plants to conserve water by promoting dew formation. Folding of the leaves in the canopy causes the air and soil to cool faster, producing dew which falls to the ground at the base of the plant.

Question 56

Describe ‘Epinasty’:

Answer 56

Epinasty is the downward bending of leaves or other plant parts resulting from growth of the upper side. This movement is often seen in plants during the flooding of roots.

Cells in the top part of the leaf and leaf stem outgrow cells on the bottom causing the leaf to drop from a horizontal position to a vertical position.

Epinastic movement is caused by ethylene, which is released by leaves when the roots are flooded. This hormone works by promoting cell expansion on the upper side of leaves, resulting in downward leaf movement.

Question 57

Describe ‘Hyponasty:’

Answer 57

A hyponastic response is the upward bending of leaves or other plant parts resulting from growth of the lower side.

Ethylene is a key regulator of the hyponastic response. This hormone works by promoting cell expansion on the lower side of leaves, resulting in upward leaf movement.

Submerged plants often show the hyponastic response, where the upward bending of the leaves and the elongation of the petioles might help the plant to restore normal gas exchange with the atmosphere.

Question 58

Describe the ‘Epinastic Strategy’ and its purpose:

Answer 58

The epinastic strategy may be adopted during flooding because the downward directed leaves act as sails in the wind.

The wind action on the leaf acts as a water pump, helping to move water out of spaces surrounding the roots as quickly as possible, and allowing respiration to resume.

Question 59

What Term is used to Describe Navigation Utilising ‘Unique Chemical Signatures’ or ‘Smells’?

Answer 59

Olfactory Navigation or ‘Olfaction’.

Question 60

What is ‘True Navigation’?

Answer 60

The use of recognised landmarks or geographical ‘identifiers’ in familiar territory, such as roads, mountains, rivers and islands.
However, is limited to only ‘familiar locations’.