Unit 6 - organisms response to environment

Question 1

Give the importances of a reflex arc

Answer 1

-rapid
-protect against damage to body tissues
-don’t have to be learnt
-help escape from predators
-enable homeostatic control

Question 2

Define stimulus

Answer 2

a change in the external or internal environment

Question 3

Define receptors

Answer 3

specialised cells or proteins in cell membranes which detect stimuli - they are specific to one type of stimulus

Question 4

Define effectors

Answer 4

cells which bring about a response to a stimulus

Question 5

Explain the role of a sensory neurone

Answer 5

transmits impulses from receptors to the CNS or relay neurone

Question 6

Explain the role of a motor neurone

Answer 6

transmits impulses from CNS/relay to the effector

Question 7

when the heart beats, both ventricles contract at the same time. Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN

Answer 7

-impulses only through the bundle of His
-impulses passes through both ventricles at the same time

Question 8

explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon

Answer 8

-myelination provides electrical insulation
-in myelinated axons depolarisation occurs at nodes of Ranvier
- in non-myelinated axons depolarisation occurs along the whole length of the axon

Question 9

Describe how the heartbeat is initiated and coordinated

Answer 9

-SAN sends a wave of electrical activity across the atria, causing atrial contraction
-non-conducting tissue prevents immediate contraction of the ventricles
-AVN delays impulse while blood leaves the atria and fill the ventricles
-AVN sends wav of electrical activity dow the bundle of His
-the bundle branches into the purkyne tissues carrying the impulse upwards through the ventricle muscle from the base
-causing ventricles to contract from the base upwards

Question 10

Give one advantage of taxis to organisms

Answer 10

-to avoid competition
-to find a mate
-increase dispersal
-to avoid predators

Question 11

Use your knowledge of IAA to explain the curved growth of a shoot

Answer 11

-tip produces IAA
-IAA diffuse into the shoot
-more elongation of cells on one side than the other

Question 12

Describe the role of receptors and of the nervous system in the increasing of the heart rate

Answer 12

-chemoreceptors detect rise in CO2
-sends impulses to cardiac centre
-more impulses to SAN, by sympathetic or parasympathetic

Question 13

explain how a resting potential is maintained across the axon membrane in a neurone

Answer 13

-higher concentration of potassium ions inside, potassium ions diffuse out
-membrane less permeable to sodium ions as the sodium ion channels are closed
-3 sodium ions actively transported out and 2 potassium ions in

Question 14

Suggest and explain how the interaction between the circular and radial muscles can cause the pupil to constrict (narrow)

Answer 14

-circular muscle contracts
-radial muscle relaxes

Question 15

Explain how a high density of rod cells allows an organism to have good night vision

Answer 15

-high visual sensitivity
-several rods connected to a single neurone
-enough neurotransmitter to overcome threshold

Question 16

Describe how stimulation of a pancinian corpuscle produces a generator potential

Answer 16

-there are stretch mediated sodium ion channels in the membrane
-increased pressure deforms lamella, opening the sodium ion channels
-sodium ions diffuse in
-causing depolarisation

Question 17

Explain how inhibiting adenylate cyclise lowers blood glucose

Answer 17

-Less ATP is converted to cAMP
-Less kinase is activated
-Less glycogenolysis

Question 18

Explain how glucagon raises blood glucose concentration

Answer 18

-Secreted by alpha cells in the islets of langerhans in the pancreas
-binds to receptors on the cell surf ac e membrane of liver cells
-this activates enzymes in the liver that break down glycogen to glucose
-also activates enzymes that are involved in the formation of glucose from glycerol and amino acids
-glucagon also decreases the rate of respiration in cells

Question 19

Explain how insulin lowers blood glucose levels

Answer 19

• Secreted by bet a cells in the islets langerhans in the pancreas.
  -binds to receptors on the cell surface membrane of the liver cells
  -vesicles storing GLUT4 channel proteins move to the cell membrane fusing with it
  -this increases the number of channel proteins in the membrane - increasing the permeability for glucose
  -cells take up more glucose by facilitated diffusion
  -insulin also increases the rate of respiration in cells ‘

Question 20

What is a pacinian corpuscle

Answer 20

a receptor in the skin which responds to changes in pressure

Question 21

what is a photo receptor

Answer 21

receptors in the eyes which responds to changes in light

Question 22

what is glycogenesis

Answer 22

the formation of glycogen from glucose

Question 23

what is glycogenolysis

Answer 23

the breakdown of glycogen to glucose

Question 24

what is gluconeogenesis

Answer 24

the formation of new glucose molecules from non-carbohydrates

Question 25

Explain why a pancreas transplant would not be a suitable treatment for type II diabetes

Answer 25

-those with type II produce insulin -receptors are less sensitive to insulin -it is treated through exercise and diet

Question 26

Describe the roles of ATP in muscle contraction

Answer 26

-to break actinmyosin cross bridges -to bend the myosin head so action filaments are moved -for active transport of Ca2+ into the sarcoplasmic reticulum

Question 27

Define a reflex

Answer 27

a rapid automatic response which doesn’t have to be learnt

Question 28

What is taxis

Answer 28

a directional movement response where an animal moves towards or away from a stimulus

Question 29

What is kinesis

Answer 29

a response where the number of random turns or the speed of an organism is related to the intensity of the stimulus

Question 30

Exercise causes an increase in heart rate, describe the role of receptors and the nervous system in this process

Answer 30

-chemoreceptors detect a rise in CO2 -sends impulses to the cardiac centre -more impulses send to the SAN via the sympathetic nervous system

Question 31

Explain how the uneven distribution of IAA causes a root to bend

Answer 31

-there’s a high concentration of IAA at the bottom of the root so inhibits elongation of cells -there’s a low concentration of IAA at the top of the roots so elongation of cells occurs

Question 32

Describe the role of glucagon in gluconeogenesis

Answer 32

-attaches to receptors on target cells and activates enzymes -non carbohydrates like fatty acids are converted into glucose

Question 33

Adrenaline binds to receptors on liver cells, explain how this causes the blood glucose concentration to increase

Answer 33

-Adenylate cyclise activated so cAMP produced -activates enzymes in the cell so gluconeogenesis occurs

Question 34

Describe a baroreceptor

Answer 34

-pressure receptors in the aorta and carotid arteries that detect changes in the blood pressure

Question 35

Describe a chemoreceptor

Answer 35

-chemical receptors in the aorta, carotid arteries and medulla that detect changes in the blood’s ph, carbon dioxide and oxygen concentration

Question 36

Explain how a fovea allows an organism to see in detail

Answer 36

-high visual acuity -each cone is connected to a single neurone -cones send separate impulses to the brain

Question 37

Describe the sequence of events involved in transmission across a cholinergic synapse

Answer 37

-depolarisation of the presynaptic membrane -calcium ion channels open and calcium ions enter -calcium ions cause the synaptic vesicles to move to the presynaptic membrane and release the neurotransmitter -neurotransmitter diffuses across the synaptic cleft -it attaches to the receptors on the post synaptic membrane causing the sodium ion channels to open -sodium ions enter the postsynaptic neurone leading to depolarisation.

Question 38

Describe how the influx of negatively charged ions can inhibit the postsynaptic neurones

Answer 38

-the inside of the postsynaptic neurone becomes more negative -more sodium ions are required to reach the threshold -threshold for action potential not reached

Question 39

Explain how blocking the calcium ion channels at some synapses can reduce impulses at the post synaptic membrane

Answer 39

-Fewer calcium ions can enter the synaptic knob -fewer synaptic vesicles fuse with the presynaptic membrane and less neurotransmitter is released -less neurotransmitter diffuses across the synaptic cleft -less neurotransmitter attaches to the receptors on the postsynaptic membrane -fewer sodium ion channels open so fewer sodium ions enter the postsynaptic neurone so fewer impulses are sent to the brain

Question 40

Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of a muscle contraction

Answer 40

-less calcium ions bind to troponin so troponin doesn’t change shape and expose the myosin binding site on the actin -fewer actinmyosin cross bridges formed -myosin head doesn’t pull actin filament

Question 41

Describe the sliding filament theory

Answer 41

-the muscle’s cell surface membrane is depolarised, so the Ca2+ channels on the sarcoplasmic reticulum open -Ca2+ diffuse from the sarcoplasmic reticulum into the sarcoplasm then into the myofibril -Ca2+ bind to troponin causing it to change shape -this causes the tropomyosin to move, exposing the myosin binding site on the actin -myosin heads bind to the myosin binding site on the actin forming actin myosin cross bridges -Ca2+ activate ATP hydrolyse in the head - hydrolysing ATP not ADP and Pi -the energy released from the hydrolysis causes the myosin head to bend ulling the actin filament in a rowing action -ATP binds to the myosin head, breaking the actin myosin cross bridge o the head can bind to another binding site.

Question 42

Describe the process of ultrafiltration

Answer 42

high hydrostatic pressure -urea/small proteins pass out -through pores in the endothelium -and through the basement membrane

Question 43

Describe and explain how the cells in the proximal convoluted tubule are adapted to allow rapid re absorption of glucose into the blood

Answer 43

-many microvilli provide a large surface area -many channel/carrier proteins for facilitated diffusion -many carrier proteins for active transport -many mitochondria to produce lots of ATP -many ribosomes to produce carrier/channel proteins

Question 44

Describe the effect of ADH on the collecting ducts in kidneys

Answer 44

-stimulates addition of channel proteins (aquaporins) into the membrane -increases permeability to water -more water is reabsorbed by osmosis

Question 45

Explain now adrenaline and glucagon a second messenger?

Answer 45

• They bind to receptors on the cell surface membrane on liver cells • this activates the enzyme adenylate cycles to convert ATP to camp • camp activates the enzyme protein kinase A which activates a cascade of reactions to breakdown glycogen into glucose (glycogenolysis)

Question 46

explain how auxin causes the elongation of cells (6)

Answer 46

-auxin stimulate proton pumps in the cell membrane -protons are pumped into the cell wall and activate proteins called expansins -they break some of the hydrogen bonds between chains of cellulose -cell walls become loose and 'stretchy' -potassium channel are stimulated and k+ move into the cell, reducing the water potential of the cytoplasm -water moves in by osmosis, increasing the cell volume causing the cell to elongate