Section 6: Organisms respond to change in their enviroments Flashcards
(255 cards)
1
Q
What is homeostasis?
A
The process by which a living organism maintains a stable internal environment.
2
Q
True or False: Homeostasis only involves temperature regulation.
A
False
3
Q
What is primarily responsible for thermoregulation in humans?
A
The hypothalamus.
4
Q
Fill in the blank: The maintenance of blood glucose levels is an example of ________.
A
homeostasis.
5
Q
What is the role of negative feedback in homeostasis?
A
To counteract changes from a set point to maintain stability.
6
Q
Which hormone decreases blood glucose levels?
A
Insulin.
7
Q
What is the primary function of the kidneys in homeostasis?
A
To regulate water and electrolyte balance.
8
Q
True or False: Positive feedback mechanisms are commonly used in homeostasis.
A
False
9
Q
What is the role of the pancreas in homeostasis?
A
To regulate blood sugar levels by secreting insulin and glucagon.
10
Q
What is the term for the body’s ability to respond to changes in the internal environment?
A
Responsiveness.
11
Q
Multiple Choice: Which of the following is NOT a component of homeostasis? A) Sensor B) Control Center C) Effectors D) Stimulus
A
D) Stimulus
12
Q
What happens when body temperature rises above the normal range?
A
Sweating occurs to cool the body down.
13
Q
Fill in the blank: The ________ is responsible for thermoregulation in the human body.
A
hypothalamus.
14
Q
What is osmoregulation?
A
The regulation of water and solute concentrations in the body.
15
Q
True or False: The body can tolerate significant deviations from its set points.
A
False
16
Q
Which part of the brain regulates thirst?
A
The hypothalamus.
17
Q
What is the effect of glucagon on blood glucose levels?
A
It increases blood glucose levels.
18
Q
Multiple Choice: Which hormone is responsible for water reabsorption in the kidneys? A) Aldosterone B) Insulin C) Glucagon D) Testosterone
A
A) Aldosterone
19
Q
What is the function of baroreceptors?
A
To detect changes in blood pressure.
20
Q
Fill in the blank: The ________ feedback mechanism amplifies a response.
A
positive.
21
Q
True or False: Homeostasis is only important for survival in extreme environments.
A
False
22
Q
What is the primary role of the adrenal glands in homeostasis?
A
To respond to stress and regulate metabolism.
23
Q
Multiple Choice: Which of the following processes helps in thermoregulation? A) Evaporation B) Condensation C) Filtration D) Respiration
A
A) Evaporation
24
Q
What is the role of the liver in blood glucose homeostasis?
A
To store and release glucose as needed.
25
Fill in the blank: The ________ senses changes in temperature.
hypothalamus.
26
What is the main function of the integumentary system in homeostasis?
To protect the body and help regulate temperature.
27
True or False: All organisms maintain homeostasis in the same way.
False
28
What role do effectors play in homeostasis?
They carry out responses to restore balance.
29
What is the function of the thyroid gland in homeostasis?
To regulate metabolism and energy levels.
30
Multiple Choice: Which system is primarily involved in chemical signaling for homeostasis? A) Nervous B) Endocrine C) Muscular D) Skeletal
B) Endocrine
31
What is thermogenesis?
The process of heat production in organisms.
32
Fill in the blank: ________ is the process of maintaining a stable internal environment.
Homeostasis
33
True or False: Maintaining pH balance is a part of homeostasis.
True
34
What does the term 'set point' refer to in homeostasis?
The normal range or level for a physiological parameter.
35
What is the role of the hypothalamus in regulating body temperature?
It acts as the body's thermostat.
36
Multiple Choice: Which of the following is a method of heat loss? A) Conduction B) Convection C) Radiation D) All of the above
D) All of the above
37
What is the significance of homeostasis for organisms?
It allows them to function optimally despite external changes.
38
Fill in the blank: The ________ system plays a key role in controlling homeostasis.
nervous.
39
True or False: Homeostatic mechanisms can be overridden by conscious thought.
True
40
What is the primary purpose of feedback systems in homeostasis?
To maintain equilibrium in the body.
41
What is the role of sweat glands in homeostasis?
To cool the body through evaporation.
42
Multiple Choice: Which part of the nephron is primarily responsible for water reabsorption? A) Glomerulus B) Loop of Henle C) Collecting duct D) Proximal tubule
C) Collecting duct
43
What is the function of the respiratory system in homeostasis?
To regulate oxygen and carbon dioxide levels in the blood.
44
Fill in the blank: Homeostasis involves the regulation of ________ in the body.
internal conditions.
45
True or False: All homeostatic processes are automatic and do not require energy.
False
46
What is the function of the circulatory system in homeostasis?
To transport nutrients, gases, and wastes throughout the body.
47
Explain the importance of Homeostasis
Enzymes and other proteins are sensitive to temperature and ph changes this these factpros must be controlled
Changes in water potential of the blood and tissue fluids may cause cells to shrink and expand as a result of osmosis
Organisms with the ability to maintain a constant internal environment internal environment are more independent of changes in the external environment
48
Why is maintaining a constant temperature so important in mammals
Because enzymes function within a narrow range of temperatures
Fluctuations from optimum temperature means enzymes function less efficiently. If the variation is extreme the enzyme may be denatured and cease function all together
A constant temperature means that reactions occur at a predictable and constant rate
49
Suggest why maintaining a constant blood glucose might be important in mammals
Ensures constant water potential
Could cause cells to shrink or expand due to osmosis
In both situations cells cannot operate normally
50
Explain the advantage of having separate negative feedback mechanisms to control deviations away from normal
It gives a greater degree of homeostatic control
51
Explain why negative feedback is import at in maintaining a system at a set point
If the information is not fed back once an effector has corrected any deviation and returned the system to the set point, the receptor will continue to stimulate the effector and an over-correction will lead to a deviation in the opposite direction from the original one
52
What does the hormone Adrenaline do. in short
Break glycogen down to glucose
53
How does Adrenaline cause the conversion of glycogen to glucose
Adrenaline binds to receptor site in liver cell
The binding causes the protein to change shape which activates adenyl cyclase
The activated adenyl cyclase converts ATP to cyclic AMP
The cAMP acts as a second messenger that binds to kinase enzyme catalysing the conversion of glycogen to glucose
54
What does the active protien kinase enzyme catalyse
the conversion of glycogen to glucose
55
How is the enzyme kinase activated
When cAMP acts as a second messenger and binds to it changing its shape
56
When adrenaline binds to a protein what enzyme does it activate and what does that enzyme do
adenyl cyclase converts ATP to cyclic AMP
57
How does glucagon convert glycogen to glucose
Binds to receptor in cell surface membrane
Changes shape of protein
Enzyme adenyl cyclase activated
adenyl cyclase converts ATP to cAMP
cAMP activates protein kinase which catalyses conversion of glycogen to glucose
58
What is the 1st and 2nd messenger in the blood regulation second messenger system.
1st messenger is glucagon or adrenaline
2nd messenger is cAMP
59
What is the advantage of using a 2nd messenger in the control of blood glucose
1. Signal amplification allows a small amount of hormone to produce a large response.
2. Enables a faster response as the second messenger rapidly diffuses through the cell to trigger a response.
3. More than one hormone can activate it
60
What is glycogenesis
Conversion of glucose into glycogen
insulin
61
What does insulin activate
Glycogenesis - conversion of glucose to glycogen in liver and muscles
increases permeability of muscle cell membranes so they can absorb more glucose
increases rate of repiration in muscle cells
increases fat synthesis
62
If the blood glucose concentration is too high what happens
B cells in the islet of langerhans detect change
Hormone insulin secreted
which activates - glycogenesis, inc rate of respiration, inc fat synthesis, inc permeability of muscle membrane so they absorb more glucose
63
What is the break down on glycogen to glucose called and what triggers it
glycogenolysis
glucagon or adrenaline
64
What happens when blood glucose levels are low
A-cells in islets of langerhans detect change
release hormone glucagon
glucagon binds to receptor activates adenyl cyclase which converts ATP to cAMP which activates glycogenolysis that converts glycogen to glucose
also acticvates enzymes involved in formation of glucose from non-carbs - glyconeogenesis
decreases rate of respiration of glucose in cells
65
What is gluconeogenesis and what hormone activates it
production of glucose from sources other than carbohydrates
glucagon
66
What cells produce glucagon and insulin and where are they
Islets of langerhans in the pancreas
a cells produce glucagon
b cells produce insulin
67
what three factors influence blood glucose concentration
diet
hydrolysis in the small intestine of glycogen = glycogenolysis
gluconeogenesis = production of glucose from sources other carbohydrates
68
______ lowers the blood glucose concentration
Insulin
69
______ increases glucose concentration
glucagon
70
What are 2 symptoms of diabetes
tiredness
increased thirst and hunger
71
State one difference between the causes of type 1 and type 2 diabetes
Type 1 is caused by an inability to produce insulin
Type 2 is caused by receptors on body cells losing their responsiveness to insulin
72
Describe how both type 1 and 2 diabetes are controlled
Type 1 is controlled by the injection of insulin
Type 2 is controlled by regulating carbohydrate intake in the diet and matching this to the amount of exercise taken
73
Suggest why tiredness is a symptom of diabetes
Diabetes is a condition where insulin is not produced by the pancreas, leading to fluctuations in blood glucose levels. Id the level is below normal there may be insufficient glucose for eh release of energy by cells during respiration
Muscle and brain cells in particular may therefore be less active, leading to tiredness
74
Suggest lifestyle changes to reduce you risk of developing type 2 diabetes
Match your carbohydrates intake to the amount of exercise that you take. Avoid becoming overweight by not consuming excessive quantities of carbohydrate and by taking regular exercise
75
List the structure of the nephron in order the blood is filtered
afferent arteriole
Renal (bowman’s) capsule - cells called podocytes
Glomerulus
efferent arteriole
Proximal convoluted tube
Loop of Henle
distal convoluted tube
Collecting duct
76
Describe the process of ultrafiltration in the kidney. (3 marks)
1. High hydrostatic pressure in the glomerulus forces small molecules out of the blood.
2. Molecules pass through the capillary endothelium, basement membrane, and podocytes.
3. Large molecules like proteins and blood cells are too big to pass through.
77
How is the proximal convoluted tubule adapted for reabsorption? (3 marks)
1. Microvilli increase surface area for absorption.
2. Many mitochondria provide energy for active transport.
3. Carrier proteins for facilitated diffusion and active transport.
78
Explain the role of the loop of Henle in producing concentrated urine. (4 marks)
• Sodium ions are actively transported out of the ascending. limb.
• This creates a water potential gradient in the medulla.
• Water leaves the descending limb by osmosis.
• Filtrate becomes more concentrated as it moves down.
79
What is the role of ADH in osmoregulation? (4 marks
• ADH binds to receptors in the collecting duct walls.
• Aquaporins are inserted into the membrane.
• This increases water reabsorption by osmosis.
• Urine becomes more concentrated.
80
How does a longer loop of Henle benefit desert animals? (2 marks)
• Creates a steeper water potential gradient in the medulla.
• Allows more water reabsorption, producing very concentrated urine.
81
Describe the differences in composition between blood plasma, glomerular filtrate, and urine. (3 marks)
• Blood plasma: Contains proteins and cells (not filtered).
• Glomerular filtrate: Similar to plasma but lacks large proteins and cells.
• Urine: High in urea and salts, low in glucose and amino acids (reabsorbed).
82
State where the cells which monitor the water potential of the blood are located
hypothalamus
83
What is a taxis?
A taxis is a simple response whose direction is determined by the direction of the stimulus
taxes are classified according to whether the movement is towards the stimulus (positive taxis) or away from the stimulus (negative taxis) and also by the nature of the stimulus
84
Name the type of response of a species of bacteria moving away from the waste products they produce.
Negative chemotaxis - wastes are often removed from an organism because they are harmful. moving away prevents the waster harming the organism and thus increases its chance of survival.
85
Name the type of response of sperm cells of a moss plant being attracted to a chemical produced by the female reproductive organ of another moss plant.
Positive chemotaxis - increases the chances of sperm cells fertilising the egg cell which helps produce more moss plants. Cross-fertilisation increases genetic variability, making species better able to adapt to future environmental changes
86
Name the type of response of a young stem of seedling growing away from gravity
Negative gravotropism - takes the seedlings above the ground and into the light, where they can photosynthesise. more photosynthesis means more carbohydrate san so a better chance of survival
87
What is a tropism?
The growth of part of a plant in response to directional stimulus
88
What is indoleacetic acid (IAA)?
A plant growth factor which belongs to group of auxins
89
Describe how the shoots of flowering plants grow towards light. (positive phototropism)
Cells in the tip of the shoot produce IAA, which is then transported down the shoot
IAA is initially transported evenly through all regions as it begins to move down the shoot
Light causes the movement of IAA from the light side to the shaded side of the shoot
A greater concentration of IAA builds up on the shaded side of the shoot than on the light side
As IAA causes elongation of shoot cells, the cells on the shaded side elongate more causing it to bend to this light
90
Describe how gravitropism works in flowering plants
Cells in the tip of the root produce IAA when is then transported along the root
Gravity influences the movement of IAA from the upper side to the lower side of the root
A greater concentration of IAA builds up on the lower side of the root than on the upper side
As IAA inhibits elongation of root cells and there is a greater concentration of IAA on the lower side, the cells on this side elongate less that those on the upper side causing it to bend downwards
91
Contrast how IAA works in the roots and the shoots of flowering plants.
I AA increases cell elongation in the shoots however inhibits cell elongation in the roots
92
Suggest two advantages to a plant of having roots that respond to gravity by growing in the direction of its force
Response ensures that roots grow down into the soil, anchoring the plant firmly and bringing them closer to water (needed for photosynthesis)
93
What are the importances of having a reflex arc?
They are involuntary and therefore do not require decision making by the brain
They protect the body from harm
They are fast
94
The nervous system has two major divisions:
Central nervous system (CNS) brain and spinal cord
Peripheral nervous system (PNS) receptors, sensory and motor neurones
95
What are the three receptors you must know?
Pacinian corpuscle
Rods
Cones
96
The stimulation of a receptor leads to the establishment of a…
generator potential which can cause a responses
97
What stimulus does the pacinian corpuscle respond to? where are they?
pressure
deep in the skin, mainly fingers and feet
98
Describe the resting state of the pacinian corpuscle.
Stretch-mediated sodium channels are too narrow for sodium to diffuse into the sensory neurone therefore resting potential is maintained
99
Describe what happens when a large amount of pressure is applied to skin.
Deforms the Pacinian corpuscle and the membrane around its neurone becomes stretched
This stretching widens the sodium channels in the membrane and sodium ions diffuse into the neurone
The influx of sodium ions changes the potential of the membrane ( ie it becomes depolarised ) thereby producing a generator potential
The generator potential in turn creates an action potential (nerve impulse) that passes along the neurone and then, via other neurone, to the central nervous system
100
Describe a resting neurone.
The membrane is polarised
The inside of the membrane is negative with respect to the outside (resting potential)
Higher concentration of sodium ions outside than inside
101
Describe the structure of a Pacinian corpuscle
In the center you have the end of a sensory neurone
This is surrounded by connective tissue layers
Between each layer of connective tissue there is a layer of gel
102
Describe the stretch-mediated sodium channel
A special type of sodium channel that changes its permeability to sodium when it changes shape / is stretched
103
Explain why brightly coloured objects often appear grey in dim light
Only rod cells are stimulated by low-intensity (dim) light. Rod cells cannot distinguish between different wavelengths / colours of light, therefore the object is perceived only in a mixture of black and white, i.e. grey.
104
Where are rods and cones found?
In the retina
105
Are there more rod cells or cone cells?
Rod cells
106
What are the two types of photoreceptors cells in the retina?
Rod cells and cone cells
107
What pigment is found in rod cells?
Rhodopsin, which is sensitive to low light intensities
108
What pigment is found in cone cells?
Iodopsin, which requires higher light intensity to break down
109
How many types of cone cells are there, and what do they detect?
Three types: each sensitive to red, green, or blue light wavelengths.
110
What type of vision do rod cells provide?
Monochromatic (black and white) vision in dim light.
111
What type of vision do cone cells provide?
Trichromatic (colour) vision in bright light
112
Where the rod cells predominantly located in the retina?
In the peripheral regions of the retina
113
Where are cone cells predominantly located in the retina?
Concentrated in the fovea, the central part of the retina
114
How do rod cells connect bipolar neurones?
Multiple rod cells synapse with single bipolar neuron, leading to spatial summation
115
How do cone cells connect bipolar neurones?
Each cone cell connects to its own bipolar neuron, allowing for high visual acuity
116
Why do rod cells have high sensitivity to light?
Due to spatial summation, the combined effect of multiple rod cells increases the likelihood of reaching the threshold to generate an action potential
117
Why do cone cells have low sensitivity to light?
Each cone cell operates independently, requiring higher light intensity to reach the threshold for an action potential
118
What is the visual acuity of rod cells?
Low visual acuity because rod cells share the same neural pathway.
119
What is the visual acuity of cone cells?
High visual acuity due to the one-to-one connection with bipolar neurones
120
In what lighting conditions are cone cells most effective?
Bright light conditions (photopic vision)
121
In what lighting conditions are rod cells most effective?
Dim light conditions (scotopic vision)
122
DO cone cells contribute to colour vision?
Yes, they are responsible for detecting different colours based on wavelength
123
What happens to rhodopsin when exposed to light?
it breaks down (bleaches), leading to the generation of a nerve impulse
124
Why is the fovea associated with sharp vision?
Because it contains a high density of cone cells, each connected to a single bipolar neuron, allowing for detailed vision
125
What is bipolar convergence in the retina?
Its when multiple rod cells connect to a single bipolar neuron
126
What effect does bipolar convergence have on sensitivity?
Increases sensitivity in low light because signals from several rod cells combine (summation) to reach threshold and trigger an action potential
127
Do cone cells show bipolar convergence?
No. Each cone cell connects to its own bipolar neurone
128
How does bipolar convergence affect visual acuity?
Rod cells have low visual acuity due to convergence; cone cells have high acuity because there’s no convergence
129
What is a bipolar neurone?
A bipolar neurone is a type of nerve cell that connects photoreceptor cells (rod or cone cells) to a sensory neurone (which leads to the optic nerve)
130
Where are bipolar neurones found in the eye?
In the retina, between the photoreceptors and sensory neurones.
131
What is the function fo a bipolar neurone?
To transmit electrical a impulses from rod or cone cells to the sensory neurone
132
What is summation?
Summation is the combining of several small nerve impulses to reach the threshold needed to trigger an action potential
133
Where does summation occur in the retina?
In rod cells, where multiple cells connect to one bipolar neurone.
134
Why is summation important in rod cells?
it allows detection of very low light levels by combining weak signals to reach threshold.
135
What is the purpose of the sympathetic nervous system?
helps us cope in stressful situations by heightening our awareness and preparing us for activity (flight or fight response)
136
What is the purpose of the parasympathetic nervous system?
inhibits effectors and slows down any activity - conserving energy adn replenishing the body’s reserves
137
What does the sympathetic nervous system trigger the heart rate to do?
Increase
138
What does the parasympathetic nervous system trigger the heart rate to do?
Decrease
139
What does it mean that the heart is myogenic?
It can initiate its own contractions without external nervous stimulation
140
What is the role of the sinoatrial node (SAN)?
Acts as the heart’s pacemaker by initiating electrical impulses causing atrial contraction
141
What is the function of the artrioventricular node (AVN)?
Receives impulses from the SAN, introduces a delay, and transmits them to the ventricles via bundle of His
142
What is the bundle of His and Purkyne tissue?
Specialised fibres that conduct impulses from the AVN to the ventricles, causing them to contract
143
What is the autonomic nervous system (ANS)?
A part of the nervous system that controls involuntary actions, including heart rate
144
What is the role of the medulla oblong at a in heart rate control?
It processes information from receptors and sends signals via the ANS to adjust heart rate
145
What are chemoreceptors and their function in heart rate regulation?
Receptors that detect changes in blood ph due to CO2 levels, influencing heart rate accordingly
146
What are baroreceptors and their role in heart rate control?
Receptors that detect changes in blood pressure, promoting adjustments in heart rate
147
How does the body respond to low blood pressure?
baroreceptors detect the drop, medulla increases sympathetic activity, increasing heart rate
148
how does the body respond to high blood pressure?
Baroreceptors detect the rise, medulla increases parasympathetic activity, decreasing heart rate
149
What is the neurotransmitter used by the sympathetic nervous system to increase heart rate?
Noradrenaline
150
What is the neurotransmitter used by the parasympathetic nervous system to decrease heart rate?
Acetylcholine
151
Explain how the autonomic nervous systemtem controls heart rate in response to changes in blood pressure (6marks)
• Baroreceptors in the aorta and carotid arteries detect changes in blood pressure.
• If blood pressure rises, baroreceptors increase the frequency of nerve impulses to the medulla oblongata.
• The medulla increases parasympathetic output and decreases sympathetic output.
• Parasympathetic nerves release acetylcholine, which acts on the sinoatrial node (SAN).
• This decreases the rate of SAN firing, leading to a slower heart rate.
• Conversely, if blood pressure falls, the medulla increases sympathetic output, releasing noradrenaline to increase heart rate.
152
Describe how the heart rate increases during exercise?
• During exercise, increased muscle activity raises CO₂ levels in the blood.
• Chemoreceptors in the aorta and carotid arteries detect the rise in CO₂.
• They send impulses to the medulla oblongata, which increases sympathetic nervous activity.
• Sympathetic nerves release noradrenaline at the SAN, increasing the heart rate.
153
Explain how the hears electrical activity is coordinated to ensure efficient pumping. 5 marks
• The SAN initiates an electrical impulse causing atrial contraction.
• A non-conductive layer prevents immediate transmission to the ventricles.
• The impulse reaches the AVN, introducing a delay to allow atria to empty.
• The impulse then travels via the bundle of His and Purkyne fibers to the ventricles.
• This causes ventricles to contract from the base upwards, efficiently pumping blood.
154
What is the role of chemoreceptors in regulating heart rate? 3marks
• Chemoreceptors detect changes in blood CO₂ levels.
• An increase in CO₂ lowers blood pH, which is detected by chemoreceptors.
• They send signals to the medulla, which increases sympathetic activity to raise heart rate, enhancing CO₂ removal.
155
Describe how the nervous system controls hear rate during rest and activity. 6marks
• At rest, parasympathetic nerves release acetylcholine at the SAN, reducing heart rate.
• During activity, increased CO₂ is detected by chemoreceptors.
• They send impulses to the medulla, which increases sympathetic output.
• Sympathetic nerves release noradrenaline at the SAN, increasing heart rate.
• This ensures adequate oxygen delivery and CO₂ removal during activity.
• Once activity ceases, CO₂ levels drop, and parasympathetic activity resumes to lower heart rate. D
156
Suppose the parasympathetic nerve connections from the medulla oblong at a to the sinoatrial node were cut. Suggest what might happen if a person’s blood pressure increases above normal.
Blood pressure remains high because the parasympathetic system is unable to transmit nerve impulses to the SA node, which decreases heart rate and so lowers blood pressure
157
The concentration of fluid in this tubule remains constant. Explain why.
Water is reabsorbed also
158
Explain the shape of the curve in the loop of Henle on a graph.
159
Explain the
160
Describe homeostasis
Homeostasis is the maintenance of a constant internal envioroment in organisms
161
Explain why mantaining a constant temperature is important in mammals
Mantaining a constant temperature is important because enzymes function within a narrow range of temperatures, fluctuations from the optimum temperature mean enzymes function less efficiently. If the variation is extreme, the enzyme may be denatures and cease to function altogether. A constant temperature means that reactions occur at a predictable and constant rate.
162
Explain the advantage of having separate negative feedback mechanisms to control deviations away from normal.
It gives a greater degree of homeostatic control
163
What three main hormones regulate blood glucose levels?
Insulin, glucagon and Adrenaline
164
Almost all bodies have glycoproteins receptors on their cell-surface membranes that bind specifically with insulin molecules. When it combines with receptors insulin brings about:
1. change in the teritary structure of the glucose transport carrier proteins, causing them to change shape and open, allowing more glucose into the cells by facilitated diffusion
2. increase in the number of carrier proteins responsible for glucose transport in the cell-surface membrane
3. activation on the enzymes that convert glucose to glycogen and fat
165
Glucagons actions include:
1. attaching specific protein receptors on their cell-surface membranes of liver cells
2. activating enzymes that convert glycogen to glucose (=glycogenolysis)
3. activating enzymes involved in the conversion of amino acids and glycerol into glucose (=gluconeogenesis)
166
Adrenaline raises the blood glucose concentration by:
1. attaching to protein receptors on their cell-surface membranes that bind of target cells
2. activating enzymes that causes the breakdown of glycogen to glucose in the liver
167
Differentiate the two forms of diabetes.
Type 1 (insulin dependant) is due to the body being unable to produce insulin. normally begins in childhood.
Type 2 (insulin independent) is normally due to glycoproteins receptors on body cells being lost or losing their responsiveness to insulin.
168
Differentiate how both types of diabetes are treated.
Type 1 - regular injections of insulin
Type 2 - regulating intake of carbohydrate into the diet and exercise
169
What is the role if the afferent arteriole and where is it located?
A tiny vessel that ultimately arises from the renal artery and supplies the nephron with blood. The afferent arteriole enters the renal capsule of the nephron where it forms the glomerulus
170
What is the role and location of the efferent arteriole?
A tiny vessel that leaves the renal capsule. it has a smaller diameter than the afferent arteriole and so causes an increase in blood pressure within the glomerulus. The efferent arteriole carries blood away from the renal capsule and later branches to from the blood capillaries.
171
Name the structure in the nephron where the majority of water is reabsorbed
Proximal convoluted tubule
172
Describe how the proximal convoluted tubule is adapted to its function
Micro villi to provide a large surface area to reabsorb substances from the filtrate; unfolding at their bases to give a large surface area to transfer reabsorbed substances into blood capillaries; a high density of mitochondria to provide ATP for the active transport
173
What restricts the movement of filtrate out of the glomerulus?
Capillary endothelial cells
Connective tissue and endothelial cells of the blood capillaries (basement membrane)
Podocytes
Epithelial cells of the renal capsule
The hydrostatic pressure of the fluid in the renal capsule space
The low water potential of the blood in the glomerulus
174
What does urine contain?
Water
Dissolved salts
urea
other small substances e.g hormones and excess vitamins
175
What things does urine not contain in a healthy person and why?
Proteins and blood cells - proteins are too large to be filtered out of the blood
Glucose - all glucose is absorbed at the selective reabsorption stage in the PCT
176
How does blood enter the many smaller capillaries which make up the glomerulus?
Through the afferent arteriole
177
The large proteins and blood cells that remain in the capillary’s of the glomerulus, where do they go?
This blood leaves via the efferent arteriole and
178
Where does selective reabsorption take place?
Proximal convoluted tubule
179
Describe selective reabsorption/ how all the glucose is reabsorbed.
1. Sodium ions are actively transported out of the cells lining in the PCT into blood capillaries which take them away. The sodium ion concentration of these cells is therefore lowered.
2. Sodium ions now diffuse down a concentration gradient from the lumen of the PCT into the epithelial lining but only through special carrier proteins by facillitated diffusion.
3. These carrier proteins are of specific types, each of which carries another molecule along with the sodium ions. This is known as co-transport
4. The molecules that have been co-transported into the cell then diffuse into the blood. This is how all the glucose is reabsorbed
always put reabsorbed in kidney not absorbed
180
Contrast the ascending limb and descending limb structure.
The descending limb, which is narrow, with thin walls that are highly permeable to water
The ascending limb, which is wider, with thick walls that are impermeable to water
181
What happens in the Distal convoluted tubule and collecting duct?
Due to all the sodium ions being actively transported out of the Loop of Henle, when the filtrate reaches the DCT it is very dilute
the filtrate moves into the DCT and collecting duct, this section of the medula is very concentrated.
Therefore, even more water diffuses out of the DCT and the collecting duct
What remains is transported to form urine
182
Describe the movement of ions in the loop of henle
Mitochondria int he walls of the cells provide energy to actively transported out sodium ions out of the ascending limb of the loop of Henle
The accumulation of sodium ions in outside of the nephron in the medulla lowers the water potential
Therefore water diffuses out by osmosis into the interstitial space and then the blood capillaries (water is reabsorbed into the blood
At the base of the ascending limb some sodium ions are transported out by diffusion, as there is now a very dilute solution due to all the water that has not moved out.
183
Suggest how the length of the loop of henle will differ for a desert animal compared to a human. Explain why?
Desert animals will have a longer loop of Henle. Therefore, more sodium ions that are actively transported out, and an even more negative water potential is created, resulting in more water being reabsorbed into the blood.
184
Why must the water potential of the blood be controlled closely?
If the water potential becomes to low, water will move out the cells via osmosis
If the water potential becomes to high, water will move into cells via osmosis
Either of these situations could be very harmful
185
Where is ADH synthesised and stored?
Synthesised in the hypothalamus
Stored in the posterior pituitary gland
186
Describe how the body releases ADH when a person becomes dehydrated
Water potential of the blood decreases due to lack of water
Thus water leaves osmoreceptor cells via osmosis
osmoreceptor cells shrink
posterior pituitary gland releases ADH into bloodstream
187
Describe the action of ADH
ADH molecules attach to the cell surface receptors of the collecting duct
This triggers an enzyme called andenylate cyclase to produce the molecule cyclic AMP (second messenger)
cAMP triggers the vesicles to move to and fuse with the cell-surface membrane
the aqua porin molecules insert into the cell-surface membrane
Now a large number of water molecules move through the aqua porins into the cell by osmosis
ADH also increases the permeability of the collecting duct to urea, which therefore passes out, further lowering the water potential of the fluid around the duct
188
What does adrenaline trigger…
Glycogenolysis
the hydrolysis of glycogen to glucose
189
How many sodium and potassium ions does the sodium potassium pump move at once?
3 Na and 2 K
190
Describe how the movement of ions establishes the resting potential in an axon.
Active transport of sodium ions out of the axon by sodium-potassium pumps is faster than active transport of potassium ions into the axon.
Potassium ions diffuse out of the axon but few, if any, sodium ions diffuse into the axon because the sodium ‘gates’ are closed.
Overall, there are more positive ions outside that’s inside and therefore the outside is positive relative to the inside.
191
Neurones are adapted to carry electrochemical charges called…
impulses / action potentials
192
Each neurone comprises a cell body that contains a … and large amounts of …, which is used int he production of proteins and neurotransmitters
Nucleus
rough endoplasmic recticulum
193
What is the purpose of Schwann cells
surround the axon, protecting it and providing electrical insulation. They also carry out phagocytosis (the removal of cell debris) and play a part in nerve regeneration. Shawna cels wrap themselves around the axon many times, so that layers of their membranes build up around it.
194
What is the myelin sheath?
Made up of the membranes of the Schwann cells
These membranes are rich in a lipid known as myelin
forms covering to the axon
195
List three ways in which a response to a hormone differs form a response to a nerve impulse
Hormone response is slow, widespread and long-lasting
Nervous response is rapid, localised and short-lived
196
What is the resting potential value?
minus 70 mV
197
Describe the start of depolarisation in the axon
Stimulus / change in enviroment
causes voltage gated sodium chanel’s to open ~ sodium ions diffuse into the axon
Potassium chanel’s (permanently open) diffuse out of the axon
If about the threshold -55mV then more chanels open
sharp increase in voltage / depolarisation
198
Why can voltage not get any higher than the action potential?
voltage gated sodium chanel’s close when 40mV reached in the axon If about
199
Describe repolarisation
Potassium ion chanels opened ( x2 amount of potassium ions diffusing out of the axon ) becomes more negative as there are more positive ions on the outside of the axon
Hyperpolarisation / refractory period / overshoot
200
What is the role of the myelin sheath in an axon?
It acts as an electrical insulator, preventing depolarisation in the covered regions and enabling saltatory conduction.
201
What is saltatory conduction?
It is the jumping of the action potential from one node of Ranvier to the next, speeding up transmission.
202
Why does saltatory conduction occur in myelinated axons?
Because depolarisation only occurs at the nodes of Ranvier, where sodium channels are concentrated.
203
How does myelination affect the speed of nerve impulse transmission?
It increases the speed significantly compared to non-myelinated axons.
204
What happens at the node of Ranvier during an action potential?
Sodium ions enter the axon, causing local depolarisation which triggers the next node.
205
Why does the action potential not travel backwards?
The previous region is in the refractory period, during which it cannot be depolarised again immediately.
206
Describe what happens to the size of an action potential as it moves along an axon.
It remains the same / does not change
207
List three factors that affect the speed at which an action potential travels
1. Myelin sheath
2. The diameter of the axon ~ the greater the diameter the faster the speed of conductance due to less leakage of ions from a large axon making it hard to maintain membrane potentials
3. Temperature ~ effects rate of diffusion
208
What three purposes foes the refractory period serve:
1. Ensures that action potentials are propagated in one direction only
2. It produces secrete inmpulses (ensures action potentiols are separated from one another)
3. Limits the number of action potentials
209
Why is it that the impulse in a synapse / neurotransmitter only travels in one direction
Vesicle only found in pre-synaptic neurone
Receptors only on post-synaptic neurone so can only bind there
210
Contrast and compare a neuromuscular junction and a cholingergic synapse
Both are unidirectional due to the neurotransmitter receptors only being on the post synaptic membrane
Neuromuscular junction is only excitatory while cholinergic could be excitatory or inhibitory
Neuromuscular junction connects motor neurone to muscles while synapse connect two neurone, which could be sensory, relay or motor
Neuromuscular junction is the end point for the action potential while synapse while trigger another one
Acetylcholine binds to receptors only being on muscle fibre membranes while in synapse acetylcholine binds to receptors on post-synaptic membrane of a neurone
211
Name two common neurotransmitters.
Acetylcholine and dopamine
212
Describe and explain the role of summation at synapses. (4 marks)
• Summation allows small amounts of neurotransmitter to combine to reach threshold.
• Spatial summation: multiple presynaptic neurones release neurotransmitter at the same time.
• Temporal summation: one neurone releases neurotransmitter repeatedly over short time.
• Both allow generation of an action potential when one alone wouldn’t be enough.
213
Describe how an action potential results in the release of a neurotransmitter and how the neurotransmitter causes an action potential in the postsynaptic neurone. (6 marks)
• Action potential arrives at presynaptic knob.
• Voltage-gated calcium ion channels open.
• Calcium ions enter the presynaptic neurone by facilitated diffusion.
• Vesicles containing neurotransmitter (e.g. acetylcholine) fuse with the presynaptic membrane.
• Neurotransmitter released into synaptic cleft via exocytosis.
• Neurotransmitter binds to complementary receptors on postsynaptic membrane.
• Sodium ion channels open; Na⁺ enters postsynaptic neurone.
• Postsynaptic membrane becomes depolarised if threshold is reached, leading to an action potential.
214
What is temporal summation?
When a single presynaptic neurone releases neurotransmitters repeatedly in a short period to reach threshold.
215
What is spatial summation?
When multiple presynaptic neurones release neurotransmitters at the same time to reach the threshold in the postsynaptic neurone.
216
How is the neurotransmitter removed from the synaptic cleft?
It is broken down by enzymes and reabsorbed into the presynaptic neurone or diffuses away.
For Acetylcholine the enzyme is acetylcholinesterase
217
State why its neccessary for acetylcholine to be hydrolysed by acetylcholinesterase
To recycle the choline and ethan oil acid; to prevent acetylcholine from continuously generating a new action potential in the postsynaptic neurone
218
How does the neurotransmitter affect the postsynaptic membrane?
It binds to receptors, causing sodium channels to open and Na⁺ to enter, leading to depolarisation.
219
What is the role of calcium ions in synaptic transmission?
when an action potential arrives they cause the voltage gated calcium ion chanels to open so calcium ions diffuse into the pre-synaptic cleft
They trigger vesicles to fuse with the presynaptic membrane and release neurotransmitter into the synaptic cleft
220
What happens when an action potential reaches the presynaptic knob?
It causes calcium ion channels to open; Ca²⁺ enters the presynaptic neurone.
221
How does the muscle work? (pairs)
Antagonistic pairs against an incompressible skeleton to create movement
222
Contrast myosin and actin
Myosin is thicker and consisted of long rod-shaped tails with bulbous heads that project to the side
Actin which is thinner and consisted of two strands twisted around one another
223
what is the H zone and I band comprised of
H zone is only myosin and is thicker
I band is only actin and thinner
224
What are the two different types of muscle fibres
Slow and fast twitch fibres
225
Describe how a skeletal muscle fibre is adapted for its function (3 marks)
1. Muscle fibres are long and cylindrical to allow contraction over distance
2. Multi nuclear, formed by fusion of embryonic cells - supports high protein synthesis
3. Contain many mitochondria for ATP production during contraction
4. Packed with myofibrils for efficient, powerful contraction.
226
Describe the structure of a myofibril ( 4marks )
- Composed of repeating units called sarcomeres
- Sarcomere runs from one Z-line to the next
- Contains actin (thin filament) and myosin (thick filament)
- A band = dark (myosin + overlapping actin); I-band = light (only actin); H zone is = only myosin
227
What is the role of the sarcoplasmic reticulum in muscle contraction? (2marks)
Stores and releases calcium ions
Calcium ions trigger muscle contraction by initiating the interaction between actin and myosin
228
What is the function of the Z-line, I-band, and A-band in a sarcomere? (3marks)
1. Z-line: defines the boundary of a sarcomere
2. I-band: contains only actin filaments; shortens during contraction
3. A-band: contains all of the myosin filaments; remains the same length during contraction
229
Describe how calcium ions and ATP are involved in muscle contraction. (6marks)
• Action potential arrives at neuromuscular junction; depolarises sarcolemma.
• Calcium ions released from sarcoplasmic reticulum.
• Calcium binds to troponin on actin, causing tropomyosin to move and expose binding sites.
• Myosin heads bind to actin, forming cross-bridges.
• ATP is hydrolysed to provide energy for the myosin head to perform a power stroke.
• New ATP binds to myosin, causing it to detach and reset for the next cycle.
230
Describe the changes that occur in a sarcomere during muscle contraction. (4 marks)
• Sarcomere shortens.
• I-band shortens.
• H-zone narrows or disappears.
• A-band remains the same length (myosin doesn’t shorten).
231
Explain the roles of actin, myosin, and ATP in muscle contraction. (5 marks)
• Actin contains binding sites for myosin heads.
• Myosin heads form cross-bridges with actin.
• Myosin head uses energy from ATP hydrolysis to perform power stroke.
• ATP causes detachment of myosin head from actin.
• ATP hydrolysis re-cocks the myosin head.
232
What causes muscle relaxation? (3 marks)
• Calcium ions are actively transported back into the sarcoplasmic reticulum.
• Tropomyosin blocks the actin binding sites again.
• No cross-bridges form between actin and myosin.
233
Describe how a nerve impulse leads to muscle contraction at the neuromuscular junction. (5 marks)
• Action potential arrives at presynaptic knob.
• Calcium ions enter; cause vesicles to release acetylcholine into cleft.
• Acetylcholine diffuses across and binds to receptors on sarcolemma.
• Sodium channels open; sarcolemma depolarises.
• Action potential travels into T-tubules and causes calcium release from sarcoplasmic reticulum.
234
Explain how actin and myosin interact during muscle contraction. (6 marks)
• Calcium ions bind to troponin; tropomyosin shifts to expose binding sites.
• Myosin head binds to actin, forming a cross-bridge.
• ADP + Pi on myosin head is released — causes power stroke.
• Myosin pulls actin filament, sarcomere shortens.
• New ATP binds to myosin, causing it to detach.
• ATP hydrolysed; energy used to reset myosin head.
235
Describe how ATP and phosphocreatine are used in muscle contraction. (5 marks)
• ATP needed to detach myosin and reset head.
• ATP made by aerobic respiration in mitochondria.
• During intense activity, ATP made by anaerobic glycolysis and phosphocreatine system.
• Phosphocreatine donates phosphate to ADP → ATP (rapidly regenerates ATP).
• PCr system is anaerobic and supplies short bursts of energy.
236
Compare the properties and functions of slow and fast twitch muscle fibres. (6 marks)
Slow Twitch:
• Contract slowly, fatigue resistant.
• Adapted for endurance (e.g. marathon).
• High mitochondria, myoglobin, blood supply.
• Mainly aerobic respiration.
Fast Twitch:
• Contract quickly, fatigue rapidly.
• Adapted for power/speed (e.g. sprinting).
• Fewer mitochondria, low myoglobin.
• Anaerobic respiration, high glycogen, phosphocreatine store.
237
Why do fast twitch fibres have more phosphocreatine than slow twitch? (2 marks)
• Used for rapid regeneration of ATP.
• Supports high-intensity, short-duration activity without relying on oxygen.
238
What is the advantage of slow twitch fibres having many mitochondria? (2 marks)
• Increases ATP production through aerobic respiration.
• Provides energy for long-duration, low-intensity activity.
239
Explain how a decrease in the concentration of calcium ions within muscle tissues could clause a decrease in the force of muscle contraction. ( 3 marks )
1. (Less/No) tropomyosin moved from binding site
OR
Shape of tropomyosin not changed so binding site not
exposed/available;
Ignore troponin.
Reject active site only once.
2. (Fewer/No) actinomyosin bridges formed;
Accept actin and myosin do not bind.
Reject active site only once.
3. Myosin head does not move
OR
OR
Myosin does not pull actin (filaments)
(Less/No) ATP (hydrol)ase (activation
240
Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration. 2 marks
Because the process oxidises reduced NAD which allows glycolysis to continue
241
Suggest why a trained mammal could exercise for longer than an untrained mammal. 3 marks
1. (More aerobic respiration) produces more ATP;
2. Anaerobic respiration delayed;
3. Less or no lactate;
242
The acetylcholine triggers the sarcomere of the muscle fibre to depolarise. what does this trigger?
This depolarisation triggers calcium ions to be released from the sarcoplasmic reticulum (the increased concentration of calcium ions triggers the actin and myosin filaments to slide together)
243
What is the condition of the binding sites on an actin filament when the muscle is not contracting?
the actin-myosin binding sites are blocked by a threadlike protein called tropomyosin
244
Describe the sliding filament mechanism of muscle contraction.
Tropomyosin molecule blocking actin-myosin binding site
Calcium ions released from the sarcoplamic recticulum bind to tropomyosin
Tropomyosin changes shape and pulls away from binding site
Myosin head now attaches to the actin-myosin binding site creating a an actin-myosin cross-bridge
Head of myosin changes angle moving the actin filament along. ADP molecule is released
ATP molecule attaches to myosin head causing it to detach from actin filament
Hydrolysis of ATP to ADP by ATPase provides the energy for the myosin head to resume its normal position
245
Dead cells can no longer produce ATP. Soon after death, muscles contract, making the body stiff - a state known as rigor morris. Explain why rigor morris occurs after death
• ATP is needed to detach myosin heads from actin after the power stroke.
• After death, ATP production stops.
• Myosin heads remain attached to actin, forming permanent cross-bridges.
• This causes muscles to become stiff and fixed, leading to rigor mortis.
246
Trained sprinters have high levels of phosphocreatine in the muscles. Explain the advantage of this
• Phosphocreatine rapidly regenerates ATP by donating a phosphate to ADP.
• This allows ATP to be produced without oxygen (anaerobically).
• Reduces the need for anaerobic respiration via glycolysis, so less lactate is produced, delaying fatigue.
247
Explain how the shape of the myosin molecule is adapted to its role in muscle contraction
• Myosin has a globular head which binds to actin to form cross-bridges.
• The head also has a binding site for ATP, allowing it to hydrolyse ATP for energy.
• The shape of the myosin head changes during the power stroke, pulling actin filaments past myosin.
248
What chemical can regenerate ATP in the muscle
Phosphocreatine
donates a phosphate to ADP
249
During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction.
Suggest how.
1. Low pH changes shape of calcium ion receptors
Do not accept tropomyosin does not move
2. Fewer calcium ions bind to tropomyosin;
Accept troponin
3. Fewer tropomyosin molecules move away;
4. Fewer binding sites on actin revealed;
5. Fewer cross-bridges can form
OR
Fewer myosin heads can bind
Must include idea of fewer at least o
250
Describe the role of calcium ions and ATP in the contraction of a myofibril. 5 marks
1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
2. (Calcium ions) cause movement of tropomyosin (on actin);
3. (This movement causes) exposure of the binding sites on the
actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes myosin heads to
bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each myosin head
causes myosin heads to detach (from actin sites)
251
ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use.
1. Releases energy in small amounts
2. releases energy instantaneously
3. Phosphorylates other compounds, making them more reactive;
4. Can be rapidly re-synthesised;
5. Is not lost from / does not leave cell
252
What is the role of ATP in myofibril contraction? 2 marks
1. (Reaction with ATP) breaks/allows binding of myosin to actin/
actinomyosin bridge;
2. Provides energy to move myosin head;
253
When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob.
Describe how ( 3marks)
1. Nerve impulse/ depolarisation of the membrane causes calcium chanel’s to open
2. Calcium ions enter via facillitated diffusion
3. Cause vesicles to fuse with presynaptic membrane
254
Use your knowledge of how myosin and actin interact to suggest how the myosin molecule moves the mitochondrion towards the presynaptic membrane. ( 2 marks )
Don’t include calcium ions or tropomyosin in your answer
1. Myosin head attaches to actin and performs a power stroke
2. Pulls mitochondria along the actin filament
255
Suggest and explain one advantage of the movement of mitochondria towards the presynaptic membrane when nerve impulses arrive at the synapse. 2 marks
1. Mitochondria supply ATP
2. To move vesicle/ for active transport of ions/ for myosin to move past actin
OR
Re-synthesise neurotransmitter
