As well as responding to biotic (living) and

abiotic (non-living) factors, plants need to

respond to external stimuli. This is to...

Avoid abiotic stress

Avoid being eaten

Maximise photosynthesis

Cope with changing conditions

Survive long enough to reproduce

Tropism is a directional growth response in which the direction

of the response is determined by the direction of the external

stimulus...

Phototropism shoots grow towards the light to

photosynthesise

Geotropism roots grow towards the pull of gravity

Chemotropism attracted to chemicals (e.g. Pollen tubes

grow down the style to the ovary for fertilisation)

Thigmotropism shoots of climbing plants wind around

other plants or solid structures to gain support

Responding towards a stimulus is known as positive tropism

and vice versa.

Abscisic Acid:

Stimulates stomata closure under water stress

Inhibits shoot growth

Induces seeds to synthesise storage proteins

Induces gene transcription

Auxins (IAA)

Stimulate cell division and cell elongation

Stimulate differentiation of xylem and phloem

Delays leaf senescence and fruit ripening

Increases stretchiness of cell wall

Inhibit or promote leaf and fruit abscission

Stimulates growth of flower parts

Stimulates ethylene production at high concentrations

Cytokinin

Stimulates cell division

Stimulates morphogenesis in tissue culture

Stimulates growth of lateral buds – release of apical

dominance

Stimulates leaf expansion resulting from cell enlargement

Ethylene

Stimulates release of dormancy

Stimulates shoot and root growth and differentiation

Stimulate leaf and fruit abscission

Stimulate flower and leaf senescence

Stimulates flower opening/fruit ripening

Gibberellins

Stimulates cell division and elongation

which leads to cell elongation

Stimulates enzyme production

Can delay leaf and citrus fruit senescence

The hormones are actually referred to as plant growth

regulators by scientists. The presence of auxin promotes

the active transport of hydrogen ions through the ATPase

enzyme into the cell wall. The resulting low pH allows

optimum conditions for the wall-loosening enzymes to

work. These enzymes break bonds within the cellulose

so the walls become less rigid and can expand as the

cells take in water.

A shoot bends towards a light source because auxin is

transported to the tip of the shoot to the cells in the

shade so the cells take up more water and elongate. As

the cells elongate more on the shaded side, the shoot

bends towards the light source

Cytokinins stop the leaves of a deciduous tree senescing

by making sure the leaves act as a sink for phloem

transport. The leaf is therefore guaranteed a good supply

of nutrients. If cytokinin production drops, the supply

dwindles and senescence begins and is usually followed

by abscission. Also, the auxin production drops so

ethene production increases and cells in the abscission

zone are more sensitive to ethene. This increases

cellulase production which digests the walls of the cells in

the abscission zone, eventually separating the petiole

from the stem.

The growing apical bud at the tip of the shoot inhibits growth of lateral buds further down the shoot.

Auxins are produced in the tip of the main shoot and inhibit the growth of side shoots. When the tip of the main shoot is removed, or an auxin transport inhibitor is applied below the apex of the main shoot, the side shoots grow. This shows that auxin is produced in the apex of the main shoot and transported to lateral buds to inhibit their growth. In low concentrations of auxin, side shoot growth isn’t inhibited. This is also shown where, as the plant grows taller, the lateral buds at the bottom of the plant start to grow larger – they are further away from the main shoot (there is a lower concentration of auxin so their growth is less inhibited). Cells of genetically dwarf plants grow considerably when treated with Gibberellic acid.

Growing cuttings

Producing fruit without seeds

Ripening fruit

Increasing the size of fruit

Controlling weeds (selective weed killers)

Animals need to respond to the environment

to stay alive. This is done using nerves and

hormones to control responses ranging

from muscle actions to running away from

a predator to fine control of balance,

posture and temperature regulation.

Central Nervous System, CNS (brain and spinal cord)

Peripheral Nervous System, PNS (neurones carry impulses

in/out of CNS)

PNS:

Sensory Neurones (impulses from receptor to CNS)

Motor Neurones (from CNS to effector)

Motor Neurones:

Somatic Motor Neurones (CNS skeletal)

Autonomic Motor Neurones (CNS cardiac muscle

smooth muscle in gut glands)

How does it differ?

Most neurones are non-myelinated

Conntection to effector consists of at least

2 neurones which connect at a ganglion

(somatic consists of 1 neurone)

Sympathetic Parasympathetic

Most active in times of stress Most active in sleep and relaxation

Neurones are linked at a ganglion just

outside the spinal cord – so pre-

ganglion neurones are very short

Neurones are linked at a ganglion

within target tissues, so pre-ganglion

neurones vary in length

Post-ganglion neurones secrete

noradrenaline

Post-ganglion neurones secrete

acetylcholine

Increases heart rate and ventilation

rate, dilates pupils

Decreases heart rate and ventilation

rate, constricts pupils

Cerebellum control of all higher order processes (e.g.

Memory, language, emotions, thinking)

Cerebral Cortex outermost layer, folded to give large

surface area

Cerebellum control and coordination of movement and

posture

Medulla Oblongata control heart rate, breathing rate and

smooth muscle of gut

Hypothalamus control of autonomic nervous system and

some endocrine glands

The conscious decision to move voluntarily

is initiated in the cerebellum. Neurones

from the cerebellum carry impulses to the

motor areas so the motor output to the

effectors can be adjusted appropriately.

Ligaments hold

the bones

together and

prevent

dislocation.

The synovial

membrane

produces synovial

fluid.

The synovial fluid lubricates joints and provides food and oxygen to the cartilage

The cartilage allows easy movement, absorbs shock and distributes load

Impulses at the NMJ cause vesicles to fuse with the pre-

synaptic membrane and release acetylcholine (ACh) into the

gap. ACh binds to receptors on the sacrolemma causing

depolarisation – the depolarisation wave travels down

tubules (T system). T system depolarisation leads to the

release of calcium ions from stores in the sarcoplasmic

reticulum. Calcium ions bind to protein in the muscle, causing

contraction. Acetylcholinesterase in the gap rapidly breaks

down ACh so contraction only occurs when impulses arrive

continuously.

The Brain controls the strength of contraction as

many motor neurones stimulate a single muscle.

Each one branches to the NMJ causing the

contraction of a motor unit. The more motor units

stimulated, the greater the force of contraction.

This is known as gradation of response.

Synapse Neuromuscular Junction

Post-synaptic membrane is the cell

surface membrane of a neurone

Post-synaptic membrane is the cell

surface membrane of a neurone

Neurotransmitter may be ACh or

noradrenaline

Neurotransmitter is ACh

Depolarisation of post-synaptic

membrane may be stimulatory or

inhibitory

Depolarisation of post-synaptic

membrane is stimulatory

In both, the neurotransmitter is secreted, diffuses across the

cleft, binds to receptors in the postsynaptic membrane and is

finally broken down

Support

Protection

Movement

Produce blood cells

Stores minerals

During

contraction,

the H band

shortens

and the A

band

doesn’t

change

Voluntary Muscle Involuntary Muscle Cardiac Muscle

Striated Unstriated Semi-striated

Contracts and fatigues

quickly

Contracts and fatigues

slowly

Contracts

spontaneously, doesn’t

fatigue

Cylindrical cells are

multinucleate

Short, spindle-shaped

cells with a single

nucleus

Cylindrical cells form

branched fibres with

intercalated discs joined

at ends

Involved in movements

of bones of skeleton

about the joints

Involved in movements

of materials along

internal tubes (e.g.

Peristalsis)

Involved in pumping

blood around the body

Controlled by somatic

nervous system

Controlled by autonomic

nervous system

Myogenic. Controlled by

autonomic nervous

system

An action potential arrives at the NMJ causing depolarisation

and the release of calcium ions from the sarcoplasmic

reticulum. Calcium ions diffuse through the sarcoplasm and

binds to troponin, which is covering the myosin binding site.

This removes troponin, thereby exposing the site. The

myosin head then binds to actin, forming a cross bridge. The

head group then bends causing thin filaments to slide past

thick filaments and overlap it more. This is the power stroke.

Also, ADP and Pi are released. ATP then binds to myosin,

breaking the cross bridge and causing the release of actin.

ATP is then hydrolysed and the myosin head resets back to

the resting position. It can now attach to the next binding site

along the actin filament.

The role of ATP is required to break the cross bridge connection

and re-set the myosin head forwards.

Maintenance

Anaerobic Respiration in Sarcoplasm production of lactic

acid which increases blood supply to the muscles

Aerobic Respiration in Mitochondria oxygen and a

respiratory substrate is needed to regenerate ATP

The transfer of a phosphate group from Creatine Phosphate

to ADP and Sarcoplasm

This is the full range of coordinated responses of animals to

situations of perceived danger. The combined nervous and

hormonal response makes the organism ready for actions that lead

to confrontation of the danger or escape from it. the cerebral

understanding of a threat activates the hypothalamus, stimulating

activity in the sympathetic nervous system. This triggers the

release of adrenaline from the adrenal medulla into the blood. The

hypothalamus also releases corticotropin releasing factor (CRF)

into the pituitary gland, stimulating the release of adreno-

corticotropic hormone (ACTH) from the anterior pituitary gland.

This then stimulated a number of hormones from the adrenal

cortex which can help the body resist stressors. On perception of

threat, there is a period of heightened awareness where an animal

assesses (an autonomic response)

Pupils dilate, so more light enters with more detailed visual information

Heart rate and blood pressure increases, increasing the flow of blood

directed to muscles in case of explosive and sustained action

Blood glucose levels increase, which supplies respiratory substrate to the

muscles to regenerate ATP

Metabolic rate increases to mobilise nutrients

Arterioles to the digestive system and skin constrict; those to the liver and

muscle dilate

Increased sweat production increases metabolism so more heat is

generated to be removed

Endorphins released act as ‘natural painkillers’

Ventilation rate and depth increase so there is an increased removal of

carbon dioxide and supply of oxygen for heightened activity

Erector pili muscles in the skin contract so hairs stand up. this helps an

animal look bigger

Doesn’t need to be learned

Immediate survival value for a young, inexperienced

animal in a dangerous situation

Appropriate for invertebrates with a short life span

who don’t have time to learn

Requires few neurones

Likely to be appropriate for the animal’s habitat as

the alleles controlling it will have been subject to

natural selection

Innate Learned

Genetically determined Determined by relationship between

genetic make-up of the individual and

environmental influences

Rigid, inflexible, stereotypical in all

members of a species

Altered by experience so there is a

variety within a species

Unintelligent Forms basis of all intelligent and

intellectual activity

Escape Reflexes a particular stimulus brings about an

automatic response to avoid predators (e.g. Earthworms

withdraw underground in response to vibrations)

Taxes a directional movement in response to an external

stimulus (e.g. Woodlice move away from light to be less

visible to predators; negative phototaxis)

Kineses a movement in response to an external stimulus.

The rate of movement is related to the intensity but not the

direction of a stimulus (e.g. Woodlice in dry/bright conditions,

they will move around rapiddly and randomly until they are

more suitably placed)

The Waggle Dance worker honey bees perform this dance to

communicate the direction and distance of a food source to

others

Animal responses that change or adapt with

experience. It is adapted to respond to

changing circumstances of environments.

Habituation animals learn to ignore certain stimuli because

repeated exposure results in neither reward nor punishment.

This avoids wasting energy in making escape responses to

non-harmful stimuli

Imprinting young animals associate with another (usually a

parent). It only occurs during the sensitive (receptive) period

which helps learn skills from parents. After, they will only

follow and learn from objects that look like the first objects

Latent (exploratory) animals will explore new surroundings

and learn information that is not of immediate value but it will

be at some point in the future

Classical Conditioning a form of adaptive learning in which

the innate response is modified. The animal learns to

respond to a stimulus that is different from the usual stimulus

Operant Conditioning a form of adaptive learning in which

an animal learns to carry out a particular action in order to

receive a reward or avoid an unpleasant experience

Insight the ability to think and reason in order to solve

problems or deal with situations in ways that don’t resemble

simple, fixed, reflex responses or the need for repeated trial

and error

There is hierarchy within gorilla troops. There is usually a silverback (dominant male) which protects numerous females and mates with them to produce offspring. Male offspring eventually leave the group once they have reached a mature age to avoid conflict with the silverback and inbreeding which could lead to genetic defects. This is known as social organisation.

Communication systems also exist within troops, such as grunts to signal danger or issue threats and facial expressions for recognition. Grooming reinforces relationships.

Greater ability to detect and deter predators is achieved

by groups of individuals working together

Knowledge and protection of food is shared with the

group

Their brain is large which slows maturity. The security of

a group enhances survival and learning of immature

young

Females give birth to one (or few) infant(s) at a time, so

maternal care and group protection enhances survival

The young learn through observation and play with other

members

There are a range of dopamine receptors in the brain.

Depending on how effective the receptors are, there will be

different levels of dopamine in the brain. The different levels

are linked to a range of conditions (e.g. Schizophrenia, ADHD

and Parkinsons). The DRD4 receptor is one of the most

variable receptors. By studying the levels of dopamine in the

brain and the genotype of the individual, the alleles which

may influence different conditions can be investigated and

different drugs for the conditions can be developed.