Unit 6 Survival, Response, Receptors and Heart rate control

Question 1

Why do organisms need to respond to stimuli

Answer 1

• Organisms increase their chance of survival by respnding to stimuli via different response mechanisms

Question 2

Outline a response to stimuli in plants

Answer 2

• Tropisms can be positive or negative, Plants respond to light and gravity
• Controlled by a Plant Growth Factor = Indoleacetic Acid (IAA) - auxin

Question 3

Explain Gravitropism in plants

Answer 3

ROOTS - positivive gravitropism
- In roots high conc of IAA inhibits cell elongation
- Gravity causes IAA to accumulate on lower side of root
- Root cells elongate faster on upper side so root bends downards

Question 4

Explain Phototropism in plants

Answer 4

SHOOT - positive phototropism
- Shoot tip produces IAA, stimulating cell elongation
- If light is present on one side, the IAA diffuses to the opposite side (shaded side)
- So high conc of IAA so cells on shaded elongate more and shoot bends towards the light

Question 5

Outline the role of a simple reflex

Answer 5

• A reflec is a rapid, automatic repsonse to protect you from danger
  3 neurons: sensory, relay, motor

Question 6

Outline Taxes and Kinesis

Answer 6

Taxes
- Dircetional response to stimuli where organisms moves its body towards favourable stimulus or away from unfavourable stimulus
- e. g helps avoid predator
Kinesis
- Non-directional movement from an unfavourable area to a favourable area
- Organism will increase the rate it changes direction in unfavourable area until they reach favourable area where moves slowly

Question 7

Outline the role of a receptor

Answer 7

• Receptors only respond to a specific stimuli and stimulation leads to establishment of a generator potential which can cause a response
• 2 examples include Pacinian corpuscle and retina of eye

Question 8

Outline role & structure of Pacinian corpuscle

Answer 8

• Found deep in skin, mainly in fingers and feet
• When pressure applied, deforms neurone in plasma membrane and, stretches Na+ channel so Na+ diffuses in which leads to establishment of generator potential

Question 9

Outlline the 1 part of the human retina

Answer 9

• The human retina contains 2 types of photoreceptors, rods and cones
  RODS
• Rods process images in black and white and detect low light intensity as many rod cells connect to 1 bipolar neurone(retinal convergence) then SN
• Made of rhodopsin broken down by light energy in low light intensity
• stimuli will be merged together = low visual acuity
  ROD CELLS FURTHER AWAY

Question 10

Outlline the 2nd part of the human retina

Answer 10

CONES
- Cones proccess images in colour and detect high light intensity as one cone cell connects to 1 bipolar neurone then SN
- Made of iodopsin(Red, green, blue) broken down by light energy at high light intensity
- Each stimuli can be distinguished = high visual acuity so cones send sperate set of impulses to the brain
FOUND IN FOVEA which receieves highest intentisity of light

Question 11

Outline how the heart is controlled and role of 2 nodes

Answer 11

• Myogenic stmiulation = Contract on its own accord, rate of contraction controlled by wave of electrical activity
• Sinoatrial node located in the right atrium and known as pacemaker
• Atrioventricular node loacted near border of right and left ventricle wihtin atria
• Bundle of his runs through septum
• Purkinje fibres in walls of ventricles

Question 12

Describe the processes in the control of the heart rate

Answer 12

• Cradiac muscle is myogenic
• SAN sends wave of electrical activity across atria causing atrial contraction
• Non-conductive tissue prevents immediate contraction of ventricles
• AVN delays impulse whilst blood leaves atria and ventricles fill
• AVN sends wave of electrical activity which spreads across both ventricles and impulses down Bundle of His/Purkinje fibres
• Causing ventricles to contract from base up after full

Question 13

Outline the main parts controlling heart rate

Answer 13

Medulla Oblongata in the brain controls the heart rate, via autonomic nervous system
INCREASE HR through sympathetic nervous system (sinoatrial node)
DECREASE HR through parasympathetic nervous system

Question 14

Outline the changes of heart in response to pH

Answer 14

pH = detected by chemoreceptors
- During exercise more CO2 or lactic is released into blood which lower pH of blood (acidic)
- Excess acid removed to prevent enzymes denaturing
- Detected by chemoreceptors causing heart rate to increase as electrical impulses sent to the medulla oblongata so more impulses to SAN via the sympathetic nervous system
- (to increase frequence of electrical impulses)
- Increase blood flow to lungs to remove CO 2 more rapidly through alveoli and take in O 2

Question 15

Outline the changes of heart in response to blood pressurepressure

Answer 15

Blood pressure = pressure receptors
- High blood pressure can cause damage to to walls of arteries detected by pressure receptors
- Detected by pressure receptors causing heart rate to decease as impulses sent to the medulla oblongata so more impulses sent to SAN via the parasympathetic nervous system
(to decrease frequence of electrical impulses)
- Low Blood pressure can cause insufficent supply of oxygenated blood to respiring cells and removal
- Detected by pressure receptors causing heart rate to increase as impulses sent to the medulla oblongata so more impulses to SAN via the sympathetic nervous system

Question 16

probability explain

Answer 16

• If a p-value reported is less than 0.05, then that result is said to be statistically significant. & reject null hypothesis
  less than 0.05 probability of being due to chance
• If a p-value is greater than 0.05, then the result is insignificant & accept null hypothesis
  more than 0.05 probability of being due to chance