6- Survival and response, RP10, Receptors, Control of heart rate

What is a stimulus?

a change in an organism’s internal or external environment

Why is it important that organisms can respond to stimuli?

organisms increase their chance of survival by responding to stimuli

What is a tropism?

• growth of a plant in response to a directional stimulus

> positive tropism= towards a stimulus

> negative tropism= away from stimulus

Summarise the role of growth factors in flowering plants

• specific growth factors (hormone-like growth substances) e.g. auxin (such as IAA) move (via phloem or diffusion) from growing regions e.g. shoot/ root tips where they’re produced

• to other tissues where they regulate growth in response to directional stimuli(tropisms)

Describe how indoleacetic acid (IAA) affects cells in roots and shoots

• In shoots, high concentrations of IAA stimulates cell elongation

• In roots, high concentrations of IAA inhibits cell elongation

Explain gravitropism in flowering plants

1. Cells in tip of shoot/ root produce IAA

2. IAA diffuses down shoot/ root (evenly initially)

3. IAA moves to lower side of shoot/ root (so concentration increases)

4. In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation

5. so shoots bend away from gravity whereas root bend towards gravity

Explain phototropism in flowering plants

1. Cells in tip of shoot/ root produce IAA

2. IAA diffuses down shoot/ root (evenly initially)

3. IAA moves to shaded side of shoot/ root (so conc increases)

4. In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation

5. so shoots bend towards light whereas roots bend away from light

Describe the simple responses that can maintain a mobile organism in a favourable environment

1. Taxes (tactic response)

   • directional movement

   • movement towards or away from a direction stimulus

2. Kinesis (kinetic response)

   • non-direction response

   • speed of movement or rate of direction change changes in response to a non-directional stimulus

   • depending on intensity of stimulus

Examples:

> taxis= woodlice moving away from light to avoid predators

> kinesis= woodlice moving faster in drier environments to increase their chance of moving to an area with higher humidity to prevent drying out

Explain the protective effect of a simple (e.g. 3 neurone) reflex

• Rapid as only 3 neurones and few synapses (synaptic transmission is slow)

• Autonomic (doesn’t involve conscious regions of brain) so doesn’t have to be learnt

• Protects from harmful stimuli e.g. escape predators/ prevents damage to body tissues

What is RP10?

Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze

RP10- Describe how the effect of an environmental variable on the movement of an animal (e.g. woodlice) can be investigated using a choice chamber

1. Set up choice chamber (different compartments) to create different environmental conditions

   • e.g. humidity= add a drying agent to 1 side and damp filter paper to other

   • e.g. light= shine a light but cover one half with black card

2. Control other environmental conditions

   • e.g. if investigating humidity control light intensity with a dim even light above

3. Use a teaspoon to place a set number of animals e.g. 12 woodlice on centre of mesh platform and cover with lid

4. After a set amount of time e.g. 10 mins record the number of animals in each section

5. Repeat after gently moving woodlice back to centre

RP10- The woodlice were left for 15 mins before their movement was recorded when investigating the effect of humidity. Explain why (2 marks)

• time to establish humidity/ for substance to absorb water/ water from paper to evaporate

• woodlice no longer affected by handling

• so that behaviour is typical of that humidity

RP10- Explain how you would ensure the safe and ethical handling of animals (2 marks)

• safely- cover open wounds/ wash hands with soap after

  • to minimise risk of infection

• ethical- handle carefully/ return to habitat ASAP

RP10- Explain why a mesh platform is used when investigating the effect of humidity (1 mark)

to keep woodlice a safe distance from drying agent

RP10- Describe how the effect of an environmental variable on the movement of an animal (e.g. maggots) can be investigated using a maze

Mazes are used to investigate turning behaviour in response to different environmental conditions:

1. Change environment at one end of T shape e.g. add food source

2. Place animal e.g. maggot in stem of T

3. Record whether animal turns towards or away from food source

4. Repeat with a large number of maggots

   • wipe/ clean maze between trials

   • Repeat with food on other size of T

RP10- Explain why the same organism is not used more than once (2 marks)

• reduces stress on maggots

• prevents chance of learned behaviours

RP10- Explain why a clean petri dish/ maze is used each time (2 marks)

• animals may leave chemicals/ scents

• which influence behaviour of other animals

RP10- Explain which statistical test should be used to analyse results

• chi-squared

• as data are categorical and comparing frequencies

• to see if there is a significant difference between observed and expected frequencies

  • expected= equal numbers each side

Describe the basic structure of a Pacinian corpuscle

Describe how a generator potential is established in a Pacinian corpuscle

1. Mechanical stimulus e.g. pressure deforms lamellae and stretch- mediated sodium ion (Na+) channels

2. So Na+ channels in membrane open and Na+ diffuse into sensory neurone

   • greater pressure causes more Na+ channels to open and more Na+ to enter

3. This causes depolarisation, leading to a generator potential

   • if generator potential reaches threshold it triggers an action potential

Explain what the Pacinian corpuscle illustrates

• Receptors respond only to specific stimuli

  • Pacinian corpuscle only responds to mechanical pressure

• Stimulation of a receptor leads to the establishment of a generator potential

  • when threshold is reached, action potential sent (all-or-nothing principle)

Explain the differences in sensitivity to light for rods & cones in the retina

RODS are more sensitive to light:

• several rods connected to a single neurone

• spatial summation to reach/ overcome threshold (as enough neurotransmitter released) to generate an action potential

CONES are less sensitive to light:

• each cone connected to a single neurone

• no spatial summation

Explain the differences in visual acuity for rods & cones in the retina

RODS give lower visual acuity:

• several rods connected to a single neurone

• so several rods send a single set of impulses to brain (so can’t distinguish between separate source of light)

CONES give higher visual acuity:

• each cone connected to a single neurone

• cones send separate (sets of) impulses to brain (so can distinguish between 2 separate sources of light)

Explain the differences in sensitivity to colour for rods & cones in the retina

RODS allow monochromatic vision:

• 1 type of rod/ 1 pigment

CONES allow colour vision:

• 3 types of cones- red- green- and blue- sensitive

• with different optical pigments= absorb different wavelengths

• stimulating different combinations of cones gives range of colour perception

Cardiac muscle is myogenic. What does this mean?

it can contract and relax without receiving electrical impulses from nerves

Label the sinoatrial node (SAN), atrioventricular node (AVN), Bundle of His and Purkyne tissue on a diagram of the heart

Describe the myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity

1. Sinoatrial node (SAN) acts as pacemaker= releases regular waves of electrical activity across atria

   • causing atria to contract simultaneously

2. Non-conducting tissue between atria/ ventricles prevents impulse passing directly to ventricles

   • preventing immediate contraction of ventricles

3. Waves of electrical activity reach atrioventricular node (AVN) which delays impulse

   • allowing atria to fully contract and empty before ventricles contract

4. AVN sends wave of electrical activity down bundle of His, conducting wave between ventricles to apex where it branches into Purkyne tissue

   • casuing ventricles to contract simultaneously from the base up

Where are chemoreceptors and pressure receptors located?

chemoreceptors and pressure receptors are located in the aorta and carotid arteries

Describe the roles of chemoreceptors, pressure receptors, the autonomic nervous system and effectors in controlling heart rate

1. Baroreceptors detect (fall/ rise) in blood pressure and/ or chemoreceptors detect blood (rise/ fall) in blood CO2 conc or (fall/ rise) in blood pH

2. Send impulses to medulla/ cardiac control centre

3. Which send more frequent impulses to SAN along (sympathetic/ parasympathetic) neurones

4. So (more/less) frequent impulses sent from SAN and to/ from AVN

5. So cardiac muscle contracts (more/ less) frequently

6. So heart rate (increases/ decreases)

Pink= for a fall in blood pressure OR rise in blood CO2 conc/ fall in blood pH

Blue= for a rise in blood pressure OR fall in blood CO2 conc/ rise in blood pH