Survival and response

Question 1

• What is a stimulus?

Answer 1

A detectable change in the internal or external environment that leads to a response in the organism

Question 2

• What is the sequence of events that lead to a response ?

Answer 2

stimulus - receptor - sensory neurone - relay CNS - motor neurone

Question 3

• What is a taxis?

Answer 3

simple response where an organism will move its entire body towards a favourable stimulus or away from an unfavourable stimulus

Question 4

• What is Kinesis?

Answer 4

organisms change the speed of movement and the rate it changes direction (direction of movement is random)

Question 5

• How will small organisms react in an unfavourable environment?

Answer 5

rate of turning slowly decreases so that it moves in a straight line increasing chance of it finding a new location with favourable conditions

Question 6

• How will small organisms react when they move from a beneficial area to an area with harmful stimuli?

Answer 6

its kinesis response will be to increase the rate it changes direction to return to favourable conditions

Question 7

• What is a tropism?

Answer 7

growth part of a plant (by cell elongation and cell division) in response to a directional stimulus

Question 8

• How does IAA affect roots and shoots differently?

Answer 8

→control cell elongation in shoots and inhibit cell growth in roots

Question 9

• How do shoots produce positive phototropism?

Answer 9

• Tip is sensitive to light
• shoot tip cells produced IAA which cause cell elongation
• IAA will diffuse towards the shaded side of the shoot = higher conc there
• That causes shaded side to elongate - causing plant to bend towards light source

Question 10

• How do roots produce negative phototropism?

Answer 10

• Tip is sensitive to light
• produce IAA moves from light side to dark side
• IAA inhibits growth is dark side
• causing roots to bend away from light

Question 11

• How do shoots produce negative gravitropism?

Answer 11

• IAA will diffuse from the upper side to the lower side of a shoot
• the cells will elongate and the plant grows upwards

Question 12

• How do shoots produce negative gravitropism?

Answer 12

• IAA diffuse to lower side of roots
• so upper side elongates and roots bends towards gravity

Question 13

• Why do roots response to small concentrations of IAA?

Answer 13

• roots response to lower concentrations because they are more sensitive
• roots are inhibited at lower concentration than shoots

Question 14

• What are the two major division of the nervous system?

Answer 14

• Peripheral nervous system
• Central nervous system

Question 15

• What is a reflex arc?

Answer 15

→ a rapid automatic involuntary response to a stimuli. A particular stimulus leads to the same response

Question 16

• A reflex usually contains what 3 neurones ?

Answer 16

• sensory
• motor
• relay

Question 17

• What is the motor neurone system made out?

Answer 17

• the voluntary neurone system - carries nervous impulses to body muscles and is under voluntary control
• automatic neurone system - which carries nervous impulses to glands, smooth muscle and cardiac muscle and is involuntary

Question 18

• Why do not all reflex actions go to the brain?

Answer 18

• • the shorter pathway to the CNS
• fewer synapses are crossed the faster the reaction time

Question 19

How do Pacinian corpuscles respond?

Answer 19

• pressure causes compression of corpuscle, deforms neurone plasma membrane as Pressure is transferred through the gel to the receptor
• stretch mediated sodium channels within the membrane respond to the pressure by opening to sodium ions channels
• Sodium channels are stretched when the membrane changes with applied pressure sodium ions enter by diffusion changing the charge inside the neurone (depolarisation), creating a generator potential
• the greater the pressure the more sodium channels open and a larger generator potential - if this reaches the threshold an action potential is generated down the sensory neeurone to the brain
• If pressure continues, the gel repositions itself and the stretch proteins channels close. The impulse stops (adaptation). It responds to a change in pressure not constant pressire

Question 20

What are stretch-mediated sodium channels?

Answer 20

Sodium channels that open when the and allow Na+ to enter the sensory neurone only when stretched and deformed

Question 21

• What some characteristics of rod cells?

Answer 21

• detect black and white only
  
  • more rodes than cones
  • respond to low light intensities

Question 22

• What are some characterisitics of cones?

Answer 22

• 3 different types of Iodopsin
  
  • Higher light intensities
  • Iodopsin resynthesised quicker than rhodopsin
  • have one single bipolar neurone ( so more sensory info going to brain - more detail)

Question 23

• What is the process for contraction in heart?

Answer 23

• SAN releases a wave of depolarisation across the atria, causing it to contract
  
  • A layer or not conductive tissue prevents waves crossing ventricles: This allows enough time for atria to pump all the blood into the ventricles
  • The wave of depolarisation enters AVN, after a short delay, AVN passes impulse between ventricles, along a series of purkyne tissues
  • Bundle of his conducts one wave through the A-V septum to base of the ventricles, where the bundle branches into smaller fibres of purkyne tissue
  • The wave of depolarisation released from purkyne tissue, causing ventricles to contract quickly

Question 24

• How do chemoreceptors work?

Answer 24

• chemoreceptors measure PH which is altered by changes in the C02 levels in the blood - found in the carotid artery and aorta
  
  • When c02 levels increase, chemoreceptors send an increased frequency of impulses to the cardiovascular centre in medulla oblongata
  • more impulses sent to SAN via parasympathetic nervous system causing the release of acetylcholine which means rate of electrical impulses initiated by SAN increases
  • Rate of heart contractions increase, blood flow increases, more CO2 removed

Question 25

- How do baroreceptors respond to high blood pressure?

Answer 25

- Baroreceptors measure the increased blood pressure - (found in carotoid artery and aorta) this increases the frequency of impulses to the part of the medulla oblongata which decreases heart rate (cardioinhibitory centre) - More impulses sent to SAN via parasympathetic nervous system cause the release of acetylecholine which causes SAN to reduce the heart rate and inhibits transmission of impulse from AVN - Rate of electrical impulses initiated by SAN decreases, Rate of heart contractions decreases

Question 26

Give one similarity and one difference between taxis and a tropism ?

Answer 26

Taxis and tropism are directional movements towards/away from stimulus in taxis whole organism moves whereas tropism is a growth response

Question 27

When testing for the effect of temperature on the movement of worms suggest reasons why it is important to ensure the light is dim and even.

Answer 27

worms may move towards/away from bright light dim ensures heat from light not a variable

Question 28

the pea seedlings were kept in the dark when doing an investigation surrounding the pea roots' response to gravity?

Answer 28

respond to light