Topic 6- responses to change in the environment

Question 1

What is a Kinesis response?

Answer 1

A nervous response in which organisms speed of movement and how often they turn increases in response to a stimulus

Question 2

What is a taxes response?

Answer 2

A nervous response in which an organisms full body will move toward or away from a stimulus. Certain bacteria display chemotaxis in which they move toward a chemical.

Question 3

Explain how the atrioventricular valve maintains a unidirectional flow of blood.
(2 Marks)

Answer 3

1. Pressure in left atrium is higher than in ventricle.
   OR when pressure above valve is higher than below valve it opens.
2. Pressure in left ventricle is higher than in atrium causing valve to close.
   OR when pressure in below valve is higher than above valve it closes.

Question 4

Exercise causes an increase in heart rate.
Describe the role of receptors and of the nervous system in the process.
(4 Marks)

Answer 4

1. Chemoreceptors detects rise in CO2.
   OR baroreceptors detect rise in blood pressure.
2. Send impulses to cardiac centre/ medulla.
3. More impulses to SAN.
4. By sympathetic nervous system for chemoreceptors.

Question 5

When the heart beats, both ventricular contract at the same time. Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN.
(2 Marks)

Answer 5

1. Slower/ fewer impulses along sympathetic/ parasympathetic pathway/ neurones.
2. Impulses from cardiac centre.
   OR impulses from medulla.
3. To SAN.

Question 6

The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey onto the fovea.
Explain how the fovea enables an eagle to see its prey in detail.
Do not refer to colour vision in your answer.
(3 Marks)

Answer 6

1. High visual acuity.
2. Each cone is connected to a single neurone.
3. Cone send separate sets of impulses to brain.

Question 7

The retina of an owl has a high density of rod cells. Explain how this enables an owl to hunt its prey at night.
Do not refer to rhodopsin in your answer.
(3 Marks)

Answer 7

1. High visual sensitivity.
2. Several rods connected a single neurone.
3. Enough neurotransmitter to reach/ overcome the threshold.

Question 8

Explain how applying pressure to the Pacinian corpuscle produces changes in membrane potential.
(3 Marks)

Answer 8

1. Pressure causes membrane to become deformed/ stretched.
2. Sodium ion channels in membrane open and sodium ions move in.
3. Greater pressure 9opens more channels/ more sodium ions move in.

Question 9

Multiple sclerosis is a disease in which multiple parts of the myelin sheaths surrounding neurons are destroyed. Explain how this results in slower responses to stimuli.
(2 Marks)

Answer 9

1. Less/ no statutory conduction/ actin potential unable to ‘jump’ from node to node.
2. More depolarisation over length/ area of membranes.

Question 10

Give an example of positive phototropism.

Answer 10

Plants grow and bend towards the light as they need the light for the LDR of photosynthesis, this is controlled by IAA.
Shoot tips produce IAA and it will diffuse to the most shaded part of the plant, elongating the plant.

Question 11

Give an example of negative phototropism.

Answer 11

Roots do not require light as their job is to anchor the plant into the ground, high levels of IAA in plant roots inhibits elongation. This causes the root to elongate more on the lighter side and therefore bend away from the light.

Question 12

What is the nephron made up of?

Answer 12

The Bowmans capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting ducts.

Question 13

Where is the glomerular filtrate created?

Answer 13

The renal (Bowmans) capsule

Question 14

What is the role of the proximal convoluted tubule?

Answer 14

Glucose and water are reabsorbed into the blood.

Question 15

What is the role of the loop of Henle?

Answer 15

To maintain a sodium ion gradient in the medulla, to enable the reabsorption of water.

Question 16

What is the role of the distal convoluted tubule and collecting ducts?

Answer 16

Reabsorption of water into the blood.

Question 17

Give an example of positive gravitropism.

Answer 17

IAA will diffuse from the upper side to the lower side of the shoot causing the shoot to bend and elongate upwards.

Question 18

Give an example of positive gravitropism.

Answer 18

IAA moves to the lower side of the roots so that the upper side elongates and roots bend downwards too anchor the plant.

Question 19

How are changes in blood glucose levels detected?

Answer 19

In the pancreas, it contains endocrine cells in the islets of Langerhans, which release insulin and glucagon t bring blood glucose levels back to normal.

Question 20

Explain the bodies reaction to danger in relation to blood glucose levels.

Answer 20

Adrenaline is released from the adrenal glands when your body anticipates danger and this results in more glucose being released from stores of glucagon in the liver.

Question 21

Describe how blood glucose levels are returned to normal levels when an increase in detected.

Answer 21

-An increase in blood glucose levels is detected by beta cells in the islets of Langerhans (pancreas).
-Beta cells release insulin
-Liver cells become more permeable to glucose and enzymes are activated to convert glucose to glycogen.
-Glucose is removed from blood and stored as glycogen in cells

Question 22

Describe how blood glucose levels are returned to normal levels when a decrease is detected.

Answer 22

-Blood glucose levels decrease is detected y alpha cells in islets of Langerhans (pancreas)
-Alpha cells release glucagon, adrenal glands release adrenaline.
-Second messenger model occurs to activate enzymes to hydrolyse glycogen
-Glycogen is hydrolysed to glucose and more glucose is released back into the blood.

Question 23

What is meant by glycogenesis?

Answer 23

The process of excess glucose being converted to glycogen when blood glucose is higher than normal.
Mainly in the liver.

Question 24

What is meant by glycogenolysis?

Answer 24

The hydolysis of glycogen back into glucose in the liver.

Question 25

What is meant by gluconeogenesis?

Answer 25

The process of creating new glucose form non-carbohydrate stores in the liver.

Question 26

How does insulin decrease blood glucose levels?

Answer 26

1) Attaching to receptors on surface of target cells, changing teritary structure of channel proteins so more glucose is absorbed by facilitated diffusion. 2) More protein channels are incorporated into cell membranes so more glucose is absorbed from blood into cells. 3) Activating enzymes involved in the conversion of glucose to glycogen, resulting in glycogenesis in the liver.

Question 27

How does glucagon increase blood glucose levels?

Answer 27

1) Attach to receptors on the surface of target cells (liver cells) 2) When glucagon binds it causes a protein to be activated into adenylate cyclase and to convert ATP into cAMP. cAMP activates protein kinase that can hydrolyse glycogen into glucose. 3) Activating enzymes involved in the conversion of glycerol and amino acids into glucose.

Question 28

Outline the role of neurotransmitters in a synapse. (4 marks)

Answer 28

1) stored in vesicles in presynaptic neurone 2) Fuses with membrane 3) Diffuses across synaptic cleft between 2 nerve cells. 4) Binds too receptors on postsynaptic membrane 5) Opens sodium ion channels

Question 29

Suggest why damaged nerve cells are not replaced by mitosis. (2 marks)

Answer 29

1) Nerve cells are highly specific 2) Unable to divide to make identical daughter cells.

Question 30

Suggest a use of stem cells in the treatment of type 1 diabetes. (2 marks)

Answer 30

1) Stem cells replace damages beta cells. 2) Patient is able to produce insulin

Question 31

Describe the structure of a motor neurone and explain how the structure enables the action potential to travel in one direction only. (6 marks)

Answer 31

structure 1) Cell body with a nucleus 2) Dendrites on cell body 3) Long axon 4) Axon terminal/ synapse 5) Myelin sheath/ Nodes of ranvier/ Schwann cells unidirectional 6) Neurotransmitters receptors on dendrites 7) Neurotransmitters in vesicles at axon terminal.

Question 32

Outline the roles of ATP and ADP in muscle contraction. (3 marks)

Answer 32

1) Release of ADP (from myosin head) causes myosin to bend/ power stroke. 2) Binding of ATP (to myosin head) causes myosin to detach from actin/ breaks cross bridge. 3) ATP converted to ADP on myosin head.

Question 33

Suggest the effect of low concentration of calcium ions on the strength of muscle contraction. Give reason for your answer. (2 marks)

Answer 33

1) Lower force/ strength of contraction. 2) Less tropomyosin/ troponin moved from myosin binding site.

Question 34

As humans age, there is a decrease in body protein. Give the same of one boy protein which would result in reduced muscle power. (1 mark)

Answer 34

Actin/ myosin/ tropomyosin