Unit Si Flashcards
(111 cards)
1
Q
What is a stimulus?
A
A change in an organism’s internal or external environment.
2
Q
Why is it important that organisms can respond to stimuli?
A
Organisms increase their chance of survival by responding to stimuli.
3
Q
What is a tropism?
A
Growth of a plant in response to a directional stimulus.
4
Q
What is positive tropism?
A
Growth towards a stimulus.
5
Q
What is negative tropism?
A
Growth away from a stimulus.
6
Q
Summarise the role of growth factors in flowering plants.
A
- Specific growth factors (hormone-like growth substances) regulate growth
- Auxins (such as IAA) move from growing regions to other tissues in response to directional stimuli.
7
Q
How does indoleacetic acid (IAA) affect cells in roots and shoots?
A
- In shoots, high concentrations of IAA stimulates cell elongation
- In roots, high concentrations of IAA inhibits cell elongation.
8
Q
Explain gravitropism in flowering plants.
A
- IAA produced in shoot/root tip diffuses down
- IAA moves to lower side, increasing concentration
- In shoots, it stimulates cell elongation; in roots, it inhibits cell elongation.
9
Q
Explain phototropism in flowering plants.
A
- IAA produced in shoot/root tip diffuses down
- IAA moves to shaded side, increasing concentration
- In shoots, it stimulates cell elongation; in roots, it inhibits cell elongation.
10
Q
What are taxes in simple responses?
A
Directional responses, where organisms move towards or away from a directional stimulus.
11
Q
What are kinesis in simple responses?
A
Non-directional responses that involve changes in speed of movement or rate of direction change based on stimulus intensity.
12
Q
Explain the protective effect of a simple reflex.
A
- Rapid response due to few neurones and synapses
- Autonomic, not requiring conscious brain involvement
- Protects from harmful stimuli.
13
Q
Describe how the effect of an environmental variable on the movement of an animal can be investigated using a choice chamber.
A
- Set up choice chamber with different compartments
- Control other environmental conditions
- Record number of animals in each section after a set time.
14
Q
Explain the ethical handling of animals during investigations.
A
- Handle carefully and return to habitat ASAP
- Cover open wounds and wash hands to minimize infection risk.
15
Q
Describe how the effect of an environmental variable on the movement of an animal can be investigated using a maze.
A
- Change environment at one end of T-shape (e.g., add food)
- Place animal in stem of T
- Record turning behavior and repeat with multiple trials.
16
Q
What is the structure of a Pacinian corpuscle?
A
A sensory receptor that detects mechanical pressure.
17
Q
How is a generator potential established in a Pacinian corpuscle?
A
- Mechanical stimulus deforms lamellae
- Stretch-mediated sodium channels open, allowing Na+ to diffuse into sensory neurone.
- This causes depolarization and establishes a generator potential.
18
Q
What does the Pacinian corpuscle illustrate about receptors?
A
- Receptors respond only to specific stimuli
- Stimulation leads to establishment of a generator potential.
19
Q
What are the differences in sensitivity to light for rods and cones in the retina?
A
- Rods are more sensitive to light (multiple rods connect to one neurone)
- Cones are less sensitive (each cone connects to a single neurone).
20
Q
What are the differences in visual acuity for rods and cones in the retina?
A
- Rods give lower visual acuity (multiple rods send single impulse)
- Cones give higher visual acuity (each cone sends separate impulses).
21
Q
What are the differences in sensitivity to color for rods and cones in the retina?
A
- Rods allow monochromatic vision
- Cones allow color vision with three types (red, green, blue-sensitive).
22
Q
What does myogenic mean in relation to cardiac muscle?
A
It can contract and relax without receiving electrical impulses from nerves.
23
Q
What is the role of the sinoatrial node (SAN) in the heart?
A
Acts as the pacemaker, sending regular waves of electrical activity across the atria.
24
Q
Describe the myogenic stimulation of the heart.
A
- SAN sends waves of electrical activity to atria
- AVN delays impulse to allow atria to fully contract
- Impulse travels through Bundle of His and Purkyne tissue to ventricles.
25
Where are chemoreceptors and pressure receptors located?
In the aorta and carotid arteries.
26
What role do baroreceptors and chemoreceptors play in controlling heart rate?
* Baroreceptors detect changes in blood pressure
* Chemoreceptors detect changes in blood CO2 concentration or pH.
* They send impulses to the medulla to adjust heart rate.
27
What is resting potential in a neurone?
Inside of axon has a negative charge relative to outside.
28
Explain how a resting potential is established across the axon membrane.
* Na+/K+ pump actively transports 3 Na+ out and 2 K+ into axon
* Creating an electrochemical gradient with higher K+ inside and higher Na+ outside.
29
Describe the process leading to depolarization and action potential generation.
* Stimulus opens Na+ channels, Na+ diffuses in
* If threshold is reached, action potential is generated
* Voltage-gated Na+ channels open, causing rapid influx of Na+.
30
What is the all-or-nothing principle?
For an action potential to be produced, depolarization must exceed threshold; all action potentials are the same size.
31
How does an action potential pass along non-myelinated and myelinated axons?
Non-myelinated axons propagate action potentials continuously; myelinated axons use saltatory conduction to jump between nodes of Ranvier.
32
What is the all-or-nothing principle in action potentials?
For an action potential to be produced, depolarisation must exceed threshold potential. Action potentials produced are always the same magnitude/size/peak at the same potential.
## Footnote
Bigger stimuli increase the frequency of action potentials.
33
How does an action potential pass along non-myelinated axons?
Action potential passes as a wave of depolarisation. Influx of Na+ in one region increases permeability of adjoining region to Na+, causing voltage-gated Na+ channels to open, leading to depolarisation along the whole length of the axon.
34
How does an action potential pass along myelinated axons?
Depolarisation occurs only at the nodes of Ranvier, resulting in saltatory conduction where local currents cause depolarisation, eliminating the need for depolarisation along the entire axon.
35
What effect does damage to the myelin sheath have on nerve impulses?
It leads to less or no saltatory conduction, causing depolarisation along the whole length of the axon, resulting in delayed muscle contraction.
36
What is the refractory period?
Time taken to restore the axon to resting potential when no further action potential can be generated due to closed/inactive Na+ channels.
37
Why is the refractory period important?
It ensures discrete impulses are produced, limits frequency of impulse transmission at a certain intensity, and ensures action potentials travel in one direction.
## Footnote
In the second half of the refractory period, an action potential can be produced but requires greater stimulation to reach threshold.
38
What factors affect the speed of conductance in neurons?
Factors include:
* Myelination
* Axon diameter
* Temperature
39
What is the function of cholinergic synapses?
Synapses that use the neurotransmitter acetylcholine (ACh).
40
Describe the process of transmission across a cholinergic synapse.
1. Depolarisation of pre-synaptic membrane opens voltage-gated Ca2+ channels.
2. Ca2+ diffuses into pre-synaptic neurone, causing vesicles with ACh to fuse with the membrane and release ACh into the synaptic cleft.
3. ACh diffuses across to bind to receptors on post-synaptic membrane, opening Na+ channels and causing depolarisation.
41
What happens to acetylcholine after synaptic transmission?
It is hydrolysed by acetylcholinesterase, and the products are reabsorbed by the presynaptic neurone to prevent overstimulation.
42
How do synapses result in unidirectional nerve impulses?
Neurotransmitter is only made in/released from the pre-synaptic neurone, and receptors are only located on the post-synaptic membrane.
43
What is summation by synapses?
Addition of a number of impulses converging on a single post-synaptic neurone, causing a rapid buildup of neurotransmitter to reach threshold and generate an action potential.
44
Describe spatial summation.
Many pre-synaptic neurones share one synaptic cleft/post-synaptic neurone, collectively releasing sufficient neurotransmitter to trigger an action potential.
45
Describe temporal summation.
One pre-synaptic neurone releases neurotransmitter many times over a short time, providing sufficient neurotransmitter to trigger an action potential.
46
What is the role of inhibitory neurotransmitters at inhibitory synapses?
They hyperpolarise the postsynaptic membrane, making it less likely to reach threshold. This is achieved by opening Cl- channels (Cl- diffuses in) and K+ channels (K+ diffuses out).
47
What is the structure of a neuromuscular junction?
Similar to a synapse, but receptors are on muscle fibres and there are more of them. Muscle fibres have clefts to store enzymes like acetylcholinesterase.
48
Compare transmission across cholinergic synapses and neuromuscular junctions.
Cholinergic synapse: neurone to neurone; neurotransmitters can be excitatory or inhibitory. Neuromuscular junction: motor neurone to muscle; always excitatory.
49
How do drugs affect synaptic transmission?
Some drugs stimulate the nervous system (e.g., by mimicking neurotransmitters), while others inhibit it (e.g., by blocking neurotransmitter release or receptor binding).
50
How do skeletal muscles work?
They work in antagonistic pairs, with one muscle (agonist) contracting to pull on bone while the other (antagonist) relaxes.
51
Describe the gross structure of skeletal muscle.
Made of bundles of muscle fibres attached to bones by tendons, containing sarcolemma, sarcoplasm, multiple nuclei, myofibrils, sarcoplasmic reticulum, and many mitochondria.
52
What is the ultrastructure of a myofibril?
Made of two types of long protein filaments, myosin (thick) and actin (thin), arranged in functional units called sarcomeres.
53
What do I-bands and A-bands represent in myofibrils?
I-bands are light bands with only thin actin filaments; A-bands are dark bands with thick myosin filaments and some actin.
54
What happens during muscle contraction at the sarcomere level?
Myosin heads slide actin along myosin, causing sarcomeres to contract; H zones and I bands get shorter, while the A band stays the same.
55
What roles do calcium ions, tropomyosin, and ATP play in myofibril contraction?
Calcium ions bind to tropomyosin, exposing binding sites on actin for myosin heads to attach. ATP provides the energy for myosin movement and detachment.
56
What is the role of phosphocreatine in muscle contraction?
It provides inorganic phosphate to rapidly regenerate ATP from ADP, supporting short bursts of vigorous exercise.
57
Compare slow twitch and fast twitch skeletal muscle fibres.
Slow twitch: specialised for slow, sustained contractions, high myoglobin, many mitochondria. Fast twitch: specialised for brief, intensive contractions, low myoglobin, high glycogen.
58
What is homeostasis in mammals?
Maintenance of a stable internal environment within restricted limits by physiological control systems, usually involving negative feedback.
59
Why is maintaining stable core temperature important?
High temperature denatures enzymes; low temperature reduces kinetic energy, both leading to fewer enzyme-substrate complexes.
60
What is the consequence of maintaining stable blood pH?
Above or below optimal pH breaks ionic/hydrogen bonds in enzymes, leading to denaturation.
61
What is core temperature?
The temperature of the body's internal environment.
62
What happens to enzymes if the core temperature is too high?
Hydrogen bonds in tertiary structure break, causing enzymes to denature.
63
What is the consequence of enzyme denaturation?
Active sites change shape, and substrates can’t bind, resulting in fewer enzyme-substrate complexes.
64
What occurs if the core temperature is too low?
Not enough kinetic energy leads to fewer enzyme-substrate complexes.
65
Why is stable blood pH important?
Optimal pH is crucial for maintaining ionic/hydrogen bonds in enzyme structures.
66
What happens to enzymes when blood pH is above or below optimal levels?
Enzymes denature, changing the shape of active sites and reducing enzyme-substrate complex formation.
67
What is the effect of low blood glucose concentration (hypoglycaemia)?
Not enough glucose for respiration, leading to less ATP produced.
68
What are the consequences of high blood glucose concentration (hyperglycaemia)?
Water potential of blood decreases, causing water loss from tissues via osmosis.
69
What is negative feedback in homeostasis?
A mechanism where receptors detect changes and effectors respond to counteract those changes.
70
List examples of factors controlled by negative feedback.
* Blood glucose concentration
* Blood pH
* Core temperature
* Blood water potential
71
What is positive feedback?
A mechanism that amplifies changes from normal, such as during childbirth or blood clotting.
72
What factors influence blood glucose concentration?
* Consumption of carbohydrates
* Rate of respiration of glucose
73
What is glycogenesis?
The conversion of glucose to glycogen.
74
What is glycogenolysis?
The conversion of glycogen to glucose.
75
What is gluconeogenesis?
The conversion of amino acids and/or glycerol to glucose.
76
How does insulin decrease blood glucose concentration?
Insulin increases glucose channel proteins in cell membranes, enhancing glucose uptake.
77
What is the role of glucagon in blood glucose regulation?
Glucagon increases blood glucose concentration by promoting glycogenolysis and gluconeogenesis.
78
How does adrenaline affect blood glucose concentration?
Adrenaline promotes glycogenolysis, increasing blood glucose concentration.
79
Describe the second messenger model of adrenaline and glucagon action.
Hormones activate adenylate cyclase, converting ATP to cAMP, which activates protein kinases.
80
What is an advantage of the second messenger model?
It amplifies the signal from the hormone, allowing rapid increases in glucose.
81
What distinguishes Type I diabetes from Type II diabetes?
Type I has insufficient insulin production; Type II involves receptor insensitivity to insulin.
82
How can Type I diabetes be controlled?
* Insulin injections
* Monitoring blood glucose
* Controlling carbohydrate intake
83
Why can't insulin be taken orally?
Insulin is a protein that would be hydrolyzed by digestive enzymes.
84
How can Type II diabetes be managed?
* Increase insulin receptor sensitivity with drugs
* Reduce sugar and fat intake
* Exercise regularly
* Lose weight
85
What is the structure and function of a nephron?
Nephron is the basic unit of the kidney, involved in filtration and reabsorption.
86
What is the function of Bowman’s capsule in the nephron?
Formation of glomerular filtrate through ultrafiltration.
87
What occurs in the proximal convoluted tubule?
Reabsorption of water and glucose (selective reabsorption).
88
How is glomerular filtrate formed?
High hydrostatic pressure forces small substances through capillary pores.
89
What mechanism allows glucose reabsorption in the proximal convoluted tubule?
Co-transport with Na+ ions against its concentration gradient.
90
What role does the loop of Henle play in nephron function?
Maintains sodium ion gradients in the medulla for water reabsorption.
91
How does ADH affect water reabsorption in the kidneys?
Increases permeability of collecting ducts and distal convoluted tubules to water.
92
What is osmoregulation?
Control of blood water potential through negative feedback mechanisms.
93
Describe the role of the hypothalamus in osmoregulation.
Detects changes in blood water potential and regulates ADH production.
94
What is the function of antidiuretic hormone (ADH) in the kidneys?
Stimulates water reabsorption by increasing permeability of kidney tubules.
95
What is the process for creating a calibration curve for glucose concentration?
* Create a dilution series of glucose
* Heat with Benedict’s solution
* Measure absorbance
* Plot graph of absorbance vs. concentration
96
How can glucose concentration in an unknown urine sample be identified?
* Perform Benedict’s test
* Measure absorbance
* Compare with calibration curve
97
Why can high blood glucose concentration lead to glucose in urine?
Saturation of glucose transport proteins in the proximal convoluted tubule.
98
What is the role of aquaporins in the collecting duct?
They increase permeability of cells to water
## Footnote
Aquaporins are channel proteins that facilitate water reabsorption.
99
How does the body respond to a decrease in water potential of the blood?
By increasing water reabsorption from the collecting duct and DCT
## Footnote
This occurs through osmosis.
100
What happens to the volume and concentration of urine when water is reabsorbed?
Volume decreases and concentration increases
## Footnote
This is a result of increased water reabsorption.
101
What common mistake is made regarding blood pressure in the glomerulus?
Not clarifying that pressure is high, not just increasing
## Footnote
Precision in language is important for marks.
102
Name two small molecules that pass out of the glomerulus into the renal capsule.
Water, glucose, ions, urea
## Footnote
Listing at least two is necessary for marks.
103
What is incorrect about the statement that molecules cross the cells of the capillary endothelium?
Molecules move through gaps (pores) between cells, not across the cells themselves
## Footnote
Understanding the filtration process is crucial.
104
What is the function of the basement membrane in glomerular filtration?
It acts as the key filter for molecules entering the renal capsule
## Footnote
The basement membrane is critical in preventing large molecules from passing.
105
What do the abbreviations PCT and DCT stand for?
Proximal convoluted tubule and distal convoluted tubule
## Footnote
These terms must be spelled out at least once for clarity.
106
What misconception exists about the cells of the PCT regarding glucose absorption?
It is often stated that they have carrier/channel proteins, but the key idea is their abundance
## Footnote
The focus should be on the number of proteins present.
107
What happens to the filtrate in the loop of Henle?
It eventually forms urine after moving to the distal convoluted tubule and collecting duct
## Footnote
Understanding the pathway of filtrate is essential.
108
What is the role of the hypothalamus and posterior pituitary regarding ADH?
The hypothalamus produces ADH, and the posterior pituitary releases it into the blood
## Footnote
Both parts must be accurately described for full understanding.
109
Fill in the blank: Water reabsorption refers to the movement of water into the _______.
blood
## Footnote
This emphasizes the direction of water movement.
110
What is the correct term to use when discussing the effect of ADH on urine production?
Volume
## Footnote
The term 'amount' is not accepted in this context.
111
What is the mechanism by which water is reabsorbed?
Osmosis, from high to low water potential
## Footnote
Naming osmosis is typically required to gain marks.
