3.3 Biology (Plants and Animals)

innate behaviour

A behaviour that is instinctive from birth and does not need to be learned

learned behaviour

behaviour of an individual organism that is acquired by experience and not present in all members of its species

photo~

light

geo/gravi~

gravity

thermo~

temperature

hydro~

water

chemo~

chemical

thigmo~

touch

tropism

A growth response of a plant toward or away from a directional stimulus

nastic response (turgor response)

fast and temporary movement of a plant that occurs independent of the direction of the stimulus

positive tropism

growth of a plant toward a stimulus

negative tropism

growth of a plant away from a stimulus

Auxin

a plant hormone that promotes or inhibits cell elongation

How does auxin work in shoots?

In the shaded side of a plan, Auxin relaxes the cell membrane, allowing water to enter and make the cells turgid. This elongates these cells, causing the shoot to bend towards the light. (Cells on light side have auxin but it is denatured by the UV light, thus these cells don't elongate)

Where is auxin produced in plants?

tips of the shoots and roots

How does auxin work in roots?

Statocytes produce statoliths which sink to the bottom side of the root due to gravity. The auxin uses this signal to travel to the lower side of the root and inhibit elongation in these cells, causing the root to bend down.

Statocytes

Cells in the middle of the root tip that produce statoliths

statoliths

starch granules that move freely due to gravity and therefore sink to the bottom of the root.

How does a nastic response occur?

1. Pulvini cells pump K+ ions out of the cytoplasm which also causes water to leave the cell via osmosis.
2. This causes a sudden drop in turgor, causing the leaf to drop.
3. After the disturbance is removed. turgor is restored and the leaf restores to normal.

Turgor

water

Differences between tropism and nastic response:

Tropism is slow, directional, permanent, and caused by cell elongation and turgor pressure.
Nastic responses are fast, non-directional, temporary, and caused by turgor pressure only.

Benefits of tropisms

In shoots: More sunlight/other resources thus more photosynthesis can be done. Therefore, they have more energy for growth and reproduction.

In roots: More nutrients/water/etc. thus more photosynthesis can be done. Therefore, they have more energy for growth and reproduction.

taxes

Movements of an animal towards or away from a stimulus.

positive taxes

Movement of an animal towards stimuli

negative taxes

Movement of an animal away from stimuli

kinesis

random movement of an animal in response to a non-directional stimulus.

orthokinesis

Orientation response in animals in which the strength of the stimulus determines the speed of movement (more intense = faster movement)

Klinokinesis

Orientation response in animals in which the strength of the stimulus determines the rate of turning (more intense = more turning)

Differences between taxes and kineses:

Taxes save energy, are directional, and create more intra-specific competition.
Kineses use energy, are non-directional, cause less competition, and help the animal avoid predation.

Homing

The ability of an individual to return to its home site over unfamiliar territory

Migration

An active, regularly repeated movement in a particular direction by a population of animals

What triggers migration?

photoperiod, temperature, food availability, desire to reproduce, internal circadian rhythm

How do animals navigate?

Using: magnetic navigation, visual cues, celestial navigation (sun and other stars), olfactory cues.

visual cue navigation:

moving from one familiar landmark to another, more effective over shorter distances.

magnetic field navigation:

Sensing Earth's magnetic field and using field lines as a compass.

Solar navigation:

using the sun as a compass, must have an accurate sense of time passing to use this.

stellar navigation

using stars to navigate, only works on clear nights.

olfactory/chemical navigation

using unique chemical signatures (odours) to locate destination.

sonar navigation

using sound waves to navigate as they bounce off objects in their path.

Ambient pressure navigation

Using atmospheric pressure changes to navigate.

advantages of migration

remain in favourable conditions (eg. summer), breeding sites and mate availability, better food supply, greater genetic mixing, only alleles of successful individuals are passed on.

Risks of migration

High energy expenditure, starvation, exhaustion, exposure to new predators, being caught/lost in storms.

are there greater advantages or risks of migration, and why?

advantages of migration outweigh the risks otherwise they wouldn't migrate.

endogenous rhythm

Rhythms controlled by an internal biological clock that continue without external cues.

exogenous rhythm

A rhythm that continues only when external cues are present.

circadian rhythm

≈24 hours

Circatidal rhythm

≈12.4 hours

Circa-semilunar rhythm

≈14.7 days

Circa-lunar rhythm

≈29 days

circaannual rhythm

≈365 days

diurnal rhythm

active during the day, inactive at night

nocturnal rhythm

active at night, inactive during the day

crepuscular rhythm

active at dawn and dusk, inactive at other times

suprachiasmatic nucleus (SCN) definition and function:

The 'central clock' of the brain.
It takes information on light (day length) from the retina and secretes certain amounts of melatonin to the pineal gland to regulate the circadian rhythm.

Actogram

Graph that plots activity of an individual over time

Zeitgeber

Environmental stimulus that entrains biological rhythms (time giver)

Free running period

The period of a biological rhythm (time it takes to repeat) in the absence of environmental time cues.

Calculating free running period

1. (time (m) the wake-up time has shifted) / (days it has shifted over) to find change per day.
2. If shifting right (sleeping in), add this time to 24h
If shifting left (waking earlier), subtract this time from 24h.

Advantages of internal body clock

- Not reliant on external cues (less energy sensing these)
- Awake at different times to predators
- Can predict a change in environment and respond accordingly
- Can sync rhythm with other members of the species (for mating, etc.)

Why is the time of flowering important?

- Plants of the same species all flower at the same time for cross-pollination (genetic variation)
- Plants are active at the same time as their pollinators
- Delicate flowering structures are not damaged by harsh environment (eg. not flowering in winter)
- Reduces competition with other plants

Flowering

The process of plants changing physiologically to produce flowers in response to the length of the night.

short day plants

plants that flower when days are short and nights are longer than the critical night length

long day plants

plants that flower when days are long and nights are shorter than the critical night length

Critical night length

The number of hours of darkness that determines whether or not a plant will flower

phytochrome

plant pigment that exists in two forms in leaves and controls photoperiodism.

phytochrome red (Pr)

Absorbs red light and is quickly converted to Pfr during the day.

phytochrome far red (Pfr)

Absorbs far red light and is slowly converted to Pr during the night.

how does phytochrome affect short day plants?

In short day plants, Pfr inhibits flowering.

When the nights are short, only some Pfr is converted to Pr. The remaining Pfr inhibits flowering.

When the nights are long, Pfr is completely converted back to Pr. This means the plants can flower.

how does phytochrome affect long day plants?

In long day plants, Pfr induces flowering.

When the nights are long, Pfr is completely converted to Pr. Therefore the plants can't flower.

When the nights are short, only some Pfr is converted to Pr. The remaining Pfr induces flowering.

Day neutral plants

A plant in which flower formation is not controlled by photoperiod and instead by other cues like temperature, moisture, or availability of nutrients.

What does far red light do to Pfr?

Quickly converts it to Pr

Interspecific (symbiotic) relationships

interactions between organisms of different species

mutualism

Relationship in which both organisms benefit (+/+)

commensalism

relationship in which one organism benefits and the other is not helped or harmed (unaffected) (+/0)

Amensalism

relationship in which one organism is harmed and the other is not helped or harmed (unaffected) (-/0)

Exploitation

relationship in which one organism benefits and the other is harmed (+/-)

interspecific competition

competition between members of different species, both are harmed (-/-)

predation

An interaction in which one organism kills another for food (+/-)

herbivory

interaction in which one animal (the herbivore) feeds on producers (such as plants) (+/-)

parasitism

A relationship in which one organism benefits by living in or on a host and the host is harmed (+/-)

What do species compete for?

Food, water, shelter, breeding sites, etc.

Gause's principle

Competitive exclusion: two or more resource-limited species cannot occupy the same biological niche.
(i.e coexist in a stable environment with identical patterns of resource use)

How do two species survive according to Gause's principle?

By occupying slightly different biological niches (eg. stratification in forests, zonation on rocky shores)

How do animals avoid predation?

Travel in groups
Camouflage
Have different endogenous rhythms to predators
Have warning colours
Structural defenses (shells, spikes, teeth, etc.)
Run/fly away
Monocular vision (eyes on side of head)

Allelopathy

A plant's production of a chemicals that inhibits growth of a competing species of plant.

Antibiosis

A fungus' production of a chemical that inhibits growth of bacteria.

Intraspecific relationships

Relationships between members of the same species

4 types of intraspecific relationships (4 F's)

Fighting (competition - aggressive)
Friends (community)
Family (parents, children)
F*cking (mating)

advantages of group formation:

Mutual defense from predators
Greater food aquiration
Easier access to mates
More adults to rear young
Reduction in heat loss
Hydrodynamic and aerodynamic effects
Sharing information
Grooming

(Defense, food, mates, heat, information)

Disadvantages of group formation:

More intraspecific competition
Only alpha individuals may be able to breed
More visible to predators
Increase in rate of disease spreading

Altruism

Behaviour that benefits another animal at a cost to the animal performing it.

Kin selection

The evolutionary strategy that favours the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction.

Benefits of synchronised breeding:

Lose fewer eggs to predators (all protected together)
Young born together can help each other
All young will reach breeding age at a similar time

agonistic behaviour

Aggressive behaviour towards another member of the same species involving threats and submission

Hierarchies

Group relationship of ranked order according to dominance and submissiveness of group members.

Benefits of a hierarchy for the group as a whole:

Reduces intraspecific competition (aggression), thus more energy can be spent on food collection, reproduction, etc.

Benefits of a hierarchy for the alpha(s):

Greater access to best food, mates, and territories, more likely to survive and reproduce.

Disadvantages of a hierarchy for the alpha(s):

Use more energy fighting, may get more injured defending their group and their position.

Benefits of a hierarchy for the omega(s):

Protection by the alphas, cooperation for food.

Disadvantages of a hierarchy for the omega(s):

Less access to good food, mates, and territories, therefore less likely to survive and to reproduce.