Stimuli and Response Flashcards
1
Q
What is a taxis?
A
A simple response whose direction is determined by the direction of the stimulus, therefore the organism will either move towards a favourable stimulus or away from an unfavourable stimulus.
2
Q
What is a positive taxis?
A
An organism moving towards a favourable stimulus
3
Q
What is a negative taxis?
A
An organism moving away from an unfavourable stimulus.
4
Q
What is an example of positive phototaxis?
A
Plants moving towards the light.
5
Q
What is an example of negative phototaxis?
A
Earthworms moving away from the light
6
Q
What is an example of positive chemotaxis?
A
When some species of bacteria will move towards a region where glucose is more highly concentrated.
7
Q
What is kinesis?
A
When an organism responds to a specific stimulus by moving more or moving less but not in a specific direction (the movement is not towards or away from a specific stimulus).
8
Q
What is the point of kinesis?
A
The rapid movement usually occurs in order to move an organism into a more favourable or stable environment, so will happen after a dramatic change to the environment.
9
Q
What is one example of kinesis?
A
Woodlouse moving towards bodies of water in dry conditions. They move from a more damp area to a dry one, they will move more rapidly in every direction, as this increases their chance of moving into a damp area.
10
Q
What are the six different types of gene mutation?
A
Substitution of bases Deletion of bases Addition of bases Duplication of bases Inversion of bases Translocation of bases
11
Q
What is the definition of a stem cell?
A
A stem cell is a cell that is able to replicate itself while maintaining an undifferentiated state and is then able to differentiate into mature cell types.
12
Q
What are the two types of stem cells in humans?
A
Embryonic and adult
13
Q
What type of stem cells are embryonic stem cells?
A
Pluripotent stem cells
14
Q
What does pluripotent mean?
A
A pluripotent stem cell can differentiate into many (but not any) type of cell
15
Q
What type of stem cell are adult stem cells?
A
Multipotent stem cells
16
Q
What does multipotent mean?
A
Multipotent stem cells can differentiate into a limited amount of different types of mature cells (usually just those within the tissue or organ in which they were found)
17
Q
where are embryonic stem cells found?
give two examples
A
embryonic stem cells can be taken from spare embryos that are created during IVF.
They can also be taken from the cell removed from an embryo for preimplantation genetic diagnosis at the 8 cell stage of embryo development.
18
Q
Where are adult stems found? Is this difficult?
A
They are found in many adult organs (i.e. the brain, the skin etc.), but they are very difficult to harvest.
19
Q
describe the process of Therapeutic Cloning
A
- The nucleus of an ovum cell is removed and replaced with a nucleus from the cell of a patient
- The cell is then given a small electric shock to cause it to start dividing
- Once the blastocyst stage, the stem cells can be removed and are cultured to produce genetically identical tissues for the patient.
20
Q
what is the government’s perspective of therapeutic cloning?
A
Therapeutic cloning has been allowed by the government, but all embryos must be destroyed after 90 days, to avoid human cloning.
21
Q
What does totipotent mean?
A
A totipotent stem cell is capable of giving rise to any cell type.
22
Q
Name four conditions/situations that stem cell research could aid
A
- People with parkinson’s disease by replacing faulty brain cells
- People with diabetes by replacing insulin producing tissue in the pancreas
- People with damaged nerves by replacing spinal nerves to allow limbs to work again
- People who need organ transplants
23
Q
What are the 6 different types of gene mutation?
A
Substitution of bases Deletion of bases Addition of bases Duplication of bases Inversion of bases Translocation of bases
24
Q
What happens in substitution of bases mutation?
A
A nucleotide is replaced by another of a different base.
25
What are the three situations that can occur due to a substitution of bases mutation?
- the new bases creates a stop codon, causing the polypeptide to be released, meaning that the polypeptide is significantly different and possibly non-functional.
- The new base forms a codon for a different amino acid causing the shape and function of the protein to differ (it could be non-functional)
- A different codon is formed, but it codes for the same amino acid, so has no effect on the polypeptide chain or protein
26
What is deletion of bases mutation?
What is the effect of deletion of bases mutation?
When a base is deleted, this causes a frame shift as each of the bases have been shifted to the left.
Most triplets will therefore be different and will code for different amino acids, which may result in the production of a non-functional protein.
27
What is addition of bases mutation?
An extra base is inserted into the sequence, causing the frame to shift to the right.
28
What are the possible effects of an addition of bases mutation?
If three bases are inserted, creating a new codon, this would not have as much effect on the final polypeptide, but would still result in a different polypeptide (as would be the case if just 1 or 2 new bases were added).
29
What is duplication of bases mutation?
When one or more bases are repeated. This produces a frame shift to the right.
30
What is inversion of bases mutation?
When a group of bases becomes separated and then rejoins in the same position in inverse order, which affects the amino acid that is produced.
31
What occurs in translocation of bases mutation?
A group of bases becomes separated from the DNA sequence on one chromosome and becomes inserted into the DNA of another chromosome.
32
What is the effect of translocation of bases mutation on the polypeptide chain produced?
As there is such a significant effect on the gene expression, so leads to abnormal polypeptides produced in the phenotype.
33
What health issues can translocation of bases mutation lead to?
Development of certain cancers and reduced fertility.
34
What are three causes of mutations?
- they can arise randomly/spontaneously during DNA replication
- Exposure to a high energy ionising radiation such as alpha/beta particles as well as short wave radiation such as X rays and UV rays
- exposure to chemicals such as nitrogen dioxide (caused by burning of fossil fuels) and benzopyrene (from tobacco smoke)
35
What is one possible positive outcome of mutations?
They can help produce genetic diversity, which is necessary for natural selection and speciation.
36
What are three negative outcomes from mutations?
- They can be harmful
- They can produce organisms that are less well suited to their environment
- If in body cells, mutation can lead to disruption of normal cellular activities, such as cell division, so can then lead to cancer.
37
What is leaching?
The process by which nutrients are removed from the soil (often by rainwater)
38
What happens in Leaching?
Rainwater will dissolve any soluble nutrients, such as nitrate ions and carry them deep into the soil, out of the reach of plants. These leached nitrate ions will then make their way into streams, rivers and freshwater lakes.
39
How can leaching affect humans?
If the river or lake that the dissolved ions end up in is a body of drinking water, these can prevent efficient oxygen transport in babies and has been related to stomach cancer
40
How can leaching affect the environment?
It can lead to eutrophication
41
What are the two types of receptors we need to know about in A level bio?
Pressure receptors in the skin and photosensitive receptors in the eyes
42
What are pacinian corpuscles?
receptors in the skin related to detecting pressure
43
How do pacinian corpuscles act as transducers?
It converts mechanical energy to electrical energy using chemical compounds
44
How do pacinian corpuscles work?
The pacinian corpuscle is made up of a lot of capsules surrounding a single nerve cell. Outside this nerve cell is a large amount of positively charged sodium ions (at resting potential). Normally, the sodium channels in the cell membrane are too narrow to allow sodium ions to pass through them. When pressure is applied, the pacinian corpuscle changes shape and allows these positively charged sodium ions to enter the cell. This influx of sodium ions changes the charge of the cell, causing it to depolarized and therefore produce an electrical current.
45
What is depolarisation?
In a cell or a membrane, the changing of electrical charge.
46
What are the two types of receptor cells in the eye called?
Rods and Cones
47
What are rods intended for?
For seeing in the dark.
48
What are cones intended for?
For seeing in colour
49
Why are both rod and cone cells transducers?
As they convert light energy to electrical energy via chemical energy.
50
Why can rod cells still function despite them receiving so little light in the dark?
Because many rod cells share a single sensory neuron. Therefore, the small amount of light energy from each of the different rod cells is combined to create an impulse along the neuron. Therefore the threshold value is more easily exceeded with multiple rod cells than if there was one rod cell.
51
How do rod cells convert light energy to electrical impulse?
All rod cells contain a pigment called rhodopsin. This is broken down by light into opsins which then create an electrical impulse.
52
What is saltatory conduction?
When the nerve impulse jumps between the nodes of ranvier instead of running through the whole axon.
53
How does the myelin sheath relate to the speed of an impulse through an axon?
Myelinated axons carry electrical energy quicker as the action potential jumps from one node of ranvier to the other, over the myelin sheath.
54
How fast does an impulse travel through a myelinated axon?
90m/s
55
How fast does an impulse travel through an unmyelinated axon?
30m/s
56
What are two factors that affect the speed of action potential?
Diameter of the axon and temperature
57
How does the diameter of the axon effect the speed of the nerve impulse?
The greater the diameter of the axon the faster the impulse, as there is more mass to carry the impulse at one time.
58
How does the temperature of a neuron affect the speed of the neuron?
At a higher temperature, there is a faster rate of diffusion of sodium ions into the axon, which therefore increases the speed of the impulse. The temperature also increases, which would increase the productivity of enzymes related to making ATP, so the rate of active transport of ions in and out of the axon would be faster, so the nerve impulse would be faster.
59
What is the refractory period?
A period of time after the axon has been depolarised where the channel proteins reclose, so no new action potential can be created.
60
How/in what way does the impulse travel along the neuron?
In one way, from the cell body along the axon to the terminals.
61
What is the "all or nothing" theory of neural impulses?
Action potential only occurs if a stimulus reaches a threshold value. If this threshold is not reached, there will be no action potential. Therefore, the axon either completely fires (all) or doesn't at all (nothing) depending on whether the threshold is met.
62
How can we detect the size of a stimulus using a neuron?
By the magnitude/number of impulses. A larger stimulus will reach the threshold more times/will create a larger potential so either larger or multiple impulses are generated.
63
what sort of ion channels are in the presynaptic neuron?
Calcium channel ions
64
What happens when an action potential reaches the presynaptic cell?
Calcium ion channels open, which allows an influx of calcium ions. These in turn break down the vesicles containing the neurotransmitters, which allows them to be released when the meet the membrane of the presynaptic cell.
65
What happens when an excitatory neurotransmitter reaches the postsynaptic cell?
Sodium channels open. This leads to the postsynaptic cell becoming depolarised and creating a potential.
66
What two organelles does the presynaptic cell contain??
Mitochondria and Smooth endoplasmic reticulum
67
How are the two organelles used in the presynaptic cell?
After neurotransmitters are broken down, ATP from the mitochondria is used to recombine the parts to reform the neurotransmitter. The neurotransmitter is made in the smooth endoplasmic reticulum.
68
What does unidirectionality mean?
It refers to how synapses can only travel in one direction- from the presynaptic to the postsynaptic cell.
69
What does summation mean?
Low frequency action potentials often produce insufficient amounts of neurotransmitters to trigger a new action potential. They can be added up together, in summation, to reach the threshold.
70
What is spatial summation?
When a number of different neurons together release enough neurotransmitter to exceed the threshold value to create a potential.
71
What is temporal summation?
When the same neuron repeatedly receives neurotransmitters and is depolarised, therefore reaching the threshold through repetition
72
What are histones?
They are basic proteins that associate with DNA in the nucleus and help condense it into chromatin. DNA coils around histones.
73
What are transcription factors?
Where do they occur?
They are molecules that help RNA polymerase bind to the template DNA strand. Each transpositional factor will bind to a specific sequence on the DNA and stimulate transcription.
Only in Eukaryotic cells.
74
What hormone can act as an activator of transcription factors?
Oestrogen
75
How does oestrogen activate transcription factors?
Oestrogen will bind to a transcription factor in the cytoplasm. This binding causes the transcription factor to change shape. The transcriptor then enters the nucleus through a nucleic pore. The transcription factor then binds to the DNA at a specific point due to its new shape.
76
How does coiling of the histones relate to transcription?
When DNA is loosely coiled around the histone the DNA is more accessible to transcription factors. When DNA is tightly coiled/packed, it is inaccessible to to transcription factors and therefore can't be transcribed.
77
What happens in the acetylation of histones and how does this affect transcription?
An acetyl group is added to the histone. This lessens the attraction of the DNA to the histone. This makes the DNA less tightly wrapped around the histone so is therefore more accessible to transcription factors, so the gene is expressed.
78
What occurs in deacetylation/ decreased acetylation?
The addition of an acetyl group causes the histone to be more attracted to the phosphate group in the DNA, causing the DNA to more tightly coil/close around the gene, causing it to not be expressed.
79
What occurs in methylation?
A methyl group is added to a cytosine base and therefore inhibits transcription.
80
What are the two ways methylation affect transcription?
1- By attracting proteins that induce deacetylation of the DNA strand, causing the DNA to be more tightly wrapped around the histone, so the DNA is not transcribed.
2- It prevents the binding of transcriptional factors, which prevents transcription.
81
What is Heterochromatin?
A tightly packed, dense form of chromatin which deeply winds in DNA.
82
What is Euchromatin?
A lightly packed form of chromatin that has loosely coiled DNA.
83
What is small interfering RNA?
A type of RNA that destroys mRNA before translation so therefore protein synthesis can not occur.
84
What is the process by which siRNA inhibits gene expression?
An enzyme cuts double stranded RNA into small sections called siRNA. One of the two siRNA strands combines with an enzyme which then go to the mRNA strand and binds to complementary bases. The enzyme then cuts the mRNA into small sections. This means the mRNA can not be translated and the genes can not be expressed.
85
What are muscle fibres made up of?
Myofibrils
86
What are myofibrils made up of?
Small units called sarcomeres.
87
What are sarcomeres made up of?
two proteins- actin and myosin
88
What are the differences between the I band and the A band?
The I band is lighter as it only contains actin and contains the Z disk, while the A band contains both myosin and actin so is therefore darker in appearance, but does contain the H zone, which is lighter as it contains only myosin.
89
What occurs in contraction?
Myosin interacts with actin to create a cross bridge.
90
How does action potential travel from the postsynaptic cell to the sarcoplasmic reticulum?
Via T tubules
91
What occurs when action potential reaches the sarcoplasmic reticulum?
Calcium ion channels open and calcium diffuses into the sarcoplasm.
92
How do calcium ions interact with tropomyosin and how does this relate to myosin?
The calcium ions bind to tropomyosin. This causes the tropomyosin protein to move and unveil the myosin binding site. This allows for myosin to attach to the actin protein and form the myosin-actin crossbridge.
93
How does myosin cause actin to move?
Once attached to actin, the myosin protein heads change shape. This pulls the actin filaments along the crossbridge, which then triggers the release of a molecule of ADP.
94
How does ATP interact with myosin?
After myosin has changed shape and caused movement of actin, an ATP molecule is added to the myosin head, causing it to change shape and detach from the actin filament, therefore breaking down the crossbridge.
95
What role does ATPase play in contraction.
It breaks down ATP attached to the myosin head, causing the myosin heads to return to their original position before contraction. The myosin can now attach to another area further down the actin filament.
96
What is a benign cancer?
A type of cancer that is less harmful as it stays in one particular part of the body.
97
What is a malignant cancer?
A more dangerous cancer as it makes its way into the bloodstream and spreads around the rest of the body.
98
What are five features of a benign tumor?
- They have a normal-looking nucleus
- They have adhesion molecules that help them stick to tissues around them
- They are surrounded by a capsule of dense tissue
- They grow slowly
- The cells are differentiated
99
What are five features of a malignant tumor?
- They grow rapidly
- They have no adhesion molecules
- Their nuclei appear denser and darker
- It is not surrounded by a capsule, but instead has finger-like protrusions that grow into surrounding tissue
- They require radiotherapy and chemotherapy to be treated
100
What is cancer?
cancer is a type of disease that is caused by damage to the genes that regulate mitosis and the cell cycle. This leads to unrestricted cell growth that can cause a tumor.
101
What are two genes that can become mutated and create cancer?
Tumor Suppressor Genes and Oncogenes
102
What are oncogenes?
They are mutated versions of proto-oncogenes
103
What is the function of proto-oncogenes?
They stimulate a cell to divide when growth factors attach to a protein receptor on a cell surface membrane.
104
How can oncogenes cause cancer (2 ways)
They can become permanently switched on, resulting in excess cell division. They do this either by-
- causing the receptor proteins on cells to remain constantly switched on and not require growth factors
- cause excessive production of growth factors
105
What are tumor suppressor genes?
They are genes that make proteins that slow down cell division, repair mistakes in DNA and trigger Apoptosis
106
What is apoptosis?
Programmed cell death
107
How can tumor suppressor genes cause cancer?
If the TSGs are suppressed they can cause uncontrolled cell growth. This can occur due to hypermethylation of the gene. This will lead to tumor suppressors not being produced.
108
What is hyperglycemia?
When glucose levels in the blood are above normal
109
What is hypoglycemia?
When glucose levels in the blood are below normal
110
What is glycogenesis?
The creation of glycogen from glucose
111
What is glycogenolysis?
The breaking down of glycogen to produce glucose.
112
What is gluconeogenesis?
The making of new glucose from proteins and fats
113
What is adenylyl cyclase?
An enzyme involved in the secondary messenger model.
114
What happens in the first stage of the secondary messenger model?
Adrenaline binds to a protein receptor on the cell surface membrane of a liver cell. This causes the protein to change shape. This then leads to the activation of an enzyme called adenylyl cyclase. This enzymes converts ATP to AMP by releasing two phosphate groups.
115
What happens in the second stage of the secondary messenger model?
The AMP then binds to the enzyme protein kinase, which then catalyses glycogenolysis, therefore putting more glucose into the blood plasma and regulating blood glucose levels.
116
What two hormones does the pancreas produce?
Insulin and glucagon
117
What type of cells is the pancreas made up of?
alpha and beta cells
118
What hormones do beta and alpha cells produce?
Alpha cells produce glucagon and beta cells produce insulin.
119
Where do glycogenesis, glycogenolysis and gluconeogenesis all occur?
In the liver
120
What is one issue that arises with too much glucose in the blood?
It can reduce water potential and affect osmosis.
121
What is an issue that arises with too little glucose in the blood?
Brain cells do not get sufficient energy and will therefore die.
122
What condition do beta cells react to?
Hyperglycemia
123
What condition do alpha cells react to?
Hypoglycemia
124
What is one way (relating to protein channels) that insulin lowers glucose levels in the blood?
It opens glucose transport carrier proteins in cells, which the allows for more glucose to diffuse into the cell, out of the blood plasma.
125
What is one way (relating to respiration) that lowers glucose levels in the blood?
It can increase the rate of respiration in cells, so they therefore use up more glucose, so take more glucose from the blood.
126
How do alpha cells react to hypoglycemia and what processes does this activate?
they release glucagon into the blood plasma, which then triggers glycogenolysis and gluconeogenesis.
127
What area controls heart rate?
the medulla oblongata
128
What is the first node involved in impulse traveling to the heart?
The sinoatrial node
129
What do chemoreceptors recognise?
What is the response?
When an increase of CO2 in the blood cause it to become more acidic (pH is lowered).
A message is sent to the medulla oblongata to increase the heart rate, which leads to CO2 being removed from the blood and normal blood pH being reinstated
130
What do pressure receptors recognise (in relation to heart rate)?
What is the response?
They recognise when blood pressure is higher than normal and therefore send impulses to the medulla oblongata which (via the parasympathetic nervous sympathetic and sinoatrial node) decreases the heart rate. The opposite happens for low blood pressure.
131
What is the Hardy-Weinberg principle?
P squared + 2pq + q squared = 1
Dominant homozygous frequency + heterozygous frequency + recessive homozygous frequency
or
p + q = 1
132
What are the two parts of the pituitary gland?
The anterior pituitary and the posterior pituitary gland
133
What role does the pituitary gland have in osmoregulation?
It releases and produces ADH when cells in the hypothalamus shrink.
134
What is osmoregulation?
The control of water and salt levels in the body
135
What is Bowman's Capsule?
It is a capsule in the nephron where the pathway of water/urine starts. It is where the blood leaves its waste products, which is then swept away by water
136
What is osmoregulation?
The control of water and salt levels in the body
137
What is Bowman's Capsule?
It is a capsule in the nephron where the pathway of water/urine starts. It is where the blood leaves its waste products, which is then swept away by water
138
What is the pigment found in cone cells?
Iodopsin
139
What is the pathway of an impulse from the retina?
First the light strikes the rod and cone cells, then this creates acetylcholine which then creates a charge/generator potential in the bipolar neurons and an action potential is then created, which then travels through the ganglion cells to the optic nerve.
140
What is rhodopsin broken down into?
Retinal and opsin.
141
What are the three types of coloured lights that cone cells detect?
Red, green and blue
142
What happens when cells receive too much light?
The rhodopsin is broken down too quickly and is therefore broken down faster than it can be reformed.
143
What are three features of Rod cells?
Low visual acuity,
sensitive to low light intensities
black and white vision
144
What are three features of Cone cells?
High visual acuity
High light intensity
can see in colour
145
how come rod cells have poor visual acuity?
As the brain can not tell which cell is struck by light, so it can't tell which cell to focus on.
146
What is the resting potential of neurons?
-65mv
147
What ions diffuse in and out of the neuron?
Na+ out, K+ in
148
How are leakage channel proteins important?
They are closed at resting potential to prevent sodium ions from diffusing back into the cell and the channel proteins that are specific to potassium are open, allowing them to diffuse out of the cell.
149
How many Na+ ions are transported out of the cell for every 2 K+ ions?
3 Na+ for every 2 K+ ions
150
What type of molecules can't pass through the phospholipid bilayer?
Charged molecules
151
What happens in depolarization (flow chart)
Stimulus detected ------ voltage gated Na+ ion channels open -------- cell is less negative ---- depolarisation -----After the threshold reached, more Na+ ion channels open---- cell reaches +40mv, action potential reached
152
What happens in repolarization?
Na+ ion channels close, K+ ion channels open, K+ ions leave the cell making the cell more negative.
153
What happens in hyperpolerisation?
Potassium ion channels close slowly, Potassium ions continue to leave the axon, the potential difference across the membrane becomes more negative than the resting potential and the sodium/potassium pump works to restore resting potential.
154
What happens in the refractory period?
This is a period of time after an action potential when it is impossible or another action potential to occur. the Na+ ion channels are closed. This ensure that the action potential only travels in one direction. This also produces discrete impulses, meaning we can distinguish between 2 different action potentials. It also limits the number of action potentials that can be fired.
155
How is resting potential maintained?
By the sodium-potassium pump and 2 leakage channels. The pump actively transports sodium ions out of the neuron and potassium ions into it (3 sodium ions per 2 potassium ions so the charge is maintained as negative). In order to prevent sodium ions diffusing back down the concentration gradient, the channel proteins specific to sodium ions are closed. Some of the potassium protein channels are closed however most are open to maintain the negative resting potential.
156
What happens in depolarisation?
reaches -55mv It causes voltage gated sodium ion channels to open ----- allows sodium ions to diffuse into the cell----- makes the inside less negative
157
What happens in repolarization?
Voltage gated Na+ channel closes, K+ channels open, allows K+ ions to diffuse out of the cell and cause the cell to become ore negative
158
What is a neuron like at resting potential?
the neuron is polarised, meaning that the inside is negative and the outside is positive, there are more positive ions outside the cell.
The voltage is -65mv
159
What are four features of slow twitch muscle fibres?
- They contract slowly
- They give less powerful contractions over a long period of time
- They are adapted for aerobic respiration
- They have a large store of myoglobin (which is similar to haemoglobin and releases oxygen when the PO2 is really low), a rich supply of blood muscles and mitochondria
160
What are four features of fast twitch muscle fibres?
- Contract more rapidly
- More powerful contractions but over a shorter period of time
- Adapted for anaerobic respiration
- It has thicker and more numerous myosin filaments, so contraction can occur more and quicker, high concentration of glycogen and phosphocreatine- which can rapidly regenerate ATP from ADP in anaerobic conditions by releasing a phosphate group.
161
What two sort of glands does the endocrine system consist of?
Endocrine and exocrine glands
162
What type of effect does the endocrine system have?
A slow, long-lasting and widespread response
163
What are six features of the endocrine system?
Pituitary gland, thyroid gland, adrenal gland, pancreas, ovaries/uterus, prostate/testes
164
What are the three ways hormones can affect target cells?
- They can affect the permeability of the cell membrane
- They can cause the release of a "second messenger" inside the cell
- They can diffuse into the cell and promote or inhibit transcription
165
What is blood glucose controlled by?
the pancreas
166
What subsection of the pancreas controls blood glucose?
islets of langerhans act as both receptors and endocrine cells
167
What are the two types of cell in the islets of langerhans?
Alpha cells- larger, detect low glucose concentration and secrete glucagon
Beta cells- smaller, detect high glucose concentration, and secrete insulin.
168
What should resting blood glucose concentration be?
5mmol/dm-3
169
What is negative feedback?
The change in conditions caused by a stimuli is reversed and returned back to its set point/optimum conditions
170
What is positive feedback?
The change detected is increased further away from the optimum conditions and does not lead to homeostasis.
171
What way do sodium ions naturally diffuse?
into the axon
172
What is osmoregulation?
it controls the water potential of body fluids by controlling the water potential of blood by controlling both the volume and concentration of urine produced.
173
What is excretion?
it removes the waste products from the blood
174
What is the interaction between the glomerulus and the bowman's capsule?
In the bowman's capsule, the content of the blood is passed from the glomerulus to the capsule
175
what happens in ultrafiltration?
blood is filtered at the glomerulus and passes into the renal capsule (only small products are filtered through). High pressure is created in the glomerulus and forces water and small molecules to be filtered out of the blood. High pressure is created as the diameter of the afferent arteriole is bigger than the diameter of the efferent arteriole.
176
What are the conditions like in the glomerulus?
- low solute potential
| - very high pressure and very high water potential
177
What are the conditions like in the renal capsule?
- High solute potential
- relatively high pressure potential
- high water potential
178
How does pressure affect ultrafiltration?
The high pressure in the glomerulus forces the water to move from the glomerulus to the renal capsule.
179
What is the pathway for filtration?
Glomerular capillary endothelium- filtrate travels through fenestrations/pores in this structure
Basement membranes- filters out the larger molecules, it is the hardest layer for the filtrate to get through
Podocytes- have filtration slits so the components of the blood can pass through
Plasma and red blood cells are too big to pass through these layers.
180
What do the separate structures do in selective reabsorption?
Proximal convoluted tube- 85% of filtrate is reabsorbed
Loop of Henle- allows water to be absorbed onto the blood from the collecting duct
Distal Convoluted tubule- Makes final adjustment and where toxic substances can be secreted into filtrate (out of the blood)
181
What happens when your blood glucose is too high?
-Beta cells detect high glucose concentration and secrete insulin into the bloodstream
-Insulin binds to receptors on the surface of muscles and liver cells
- ACtivates enzymes that convert glucose to glycogen in liver cells
-This insulin controls the uptake of glucose into cells (regulating activity in channel proteins on cell surface membranes)
Excess glucose may be converted to fat
182
What happens when our blood glucose is too low?
- Alpha cells detect low blood glucose and secrete glucagon into the bloodstream
- Glucagon binds to receptors of muscle cells
- This then triggers enzymes that trigger glycogenolysis and gluconeogenesis
183
What are two effects of adrenaline?
attachment to protein receptors on the cell-surface membranes of target cells
activation of enzymes that cause breakdown of glucagon to glucose in the liver
184
What is the first messenger in the second messenger model, what does it bind to? What is this bound to?
Adrenaline
Transmembrane protein
adenyl cyclase (inactive)
185
What happens when adrenaline binds to the transmembrane protein?
It creates a receptor complex and the adenyl cyclase is made active
186
What does active adenyl cyclase do?
It converts ATP to cyclic AMP.
187
What does cyclic AMP do?
It binds to inactive protein kinase and makes it active. This then catalyses glycogenolysis and gluconeogenesis, so more glucose is produced.
188
What does the liver do?
filters blood from the digestive tract, detoxifies and regulates blood glucose concentration by the use of hormones.
189
What is the main characteristic of diabetes?
You are unable to metabolise carbohydrates properly, especially glucose.
190
What are the main characteristics of type 1 diabetes
| idea, symptoms, cause
- Body is unable to produce insulin
- Usually begins in childhood and involves a rapid onset of symptoms
- symptoms include frequent urination, glucose in urine, genital itching, weight loss and tiredness
- Usually due to an autoimmune response- meaning the immune system attacks beta cells
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how do we control type 1 diabetes?
- Injection of insulin 2-4 times a day
- cannot be taken by mouth as it would be broken down in digestion
- Insulin dose must be matched to glucose intake, blood glucose concentration must be monitored by biosensors
- Cannot be cured, however recent trials transplanting insulin-producing cells have been promising
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What are the main characteristics of type 2 diabetes
| idea, symptoms, cause
Glycoprotein receptors are lost or lose responsiveness
Can also be due to an inadequate supply of insulin
usually develops in people over 40
Develops slowly with (the same as type 1) symptoms but less severe
people who are overweight are more likely to develop this
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How do we control type 2 diabetes?
Regulating intake of carbohydrates in the diet
Can use insulin injections or drugs that stimulate insulin production
It is curable
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What is one difference between blood and filtrate?
Blood has red blood cells and plasma proteins while filtrate doesn't
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How can lipids be aerobically respired?
They are hydrolysed into fatty acids and glycerol. The fatty acids enter the krebs cycles and the glycerol is converted to glycerate 3 phosphate which is then used in glycolysis.
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What molecules are reabsorbed in selective reabsorption?
water, ions ,glucose, amino acids, small proteins and urea
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How does urea travel in selective reabsorption?
Urea goes from the proximal convoluted tubule to the blood because of diffusion gradients, as this is passive and not really intended to go back into the blood. The other ions move into the proximal convoluted tubule cells via active transport.
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What are three adaptations the proximal convoluted tubule?
microvilli, infoldings and lots of mitochondria
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How are sodium ions and other molecules transported into the blood?
Sodium ions are actively transported from the PCT cells into the blood. the blood carries sodium ions away. This creates a concentration gradient into the PCT cells, so sodium ions diffuse (via facilitated diffusion) from the lumen of the PCT into the PCT cells. Another molecule is carried with the sodium ions in facilitated diffusion, such as glucose.
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What is the filtrate composition like after selective reabsorption?
- 65% of water and ions have been reabsorbed
- 100% of glucose and amino acids have been reabsorbed
- Urea is not selectively reabsorbed that some urea will be reabsorbed passively by diffusion due to the loss of water and because the concentration of urea will increase.
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What is the role of the loop of henle in selective reabsorption?
To make the medulla concentrated with ions, lowering psy and promoting water being reabsorbed into the collecting duct.
202
Which of the descending and the ascending limb of the loop of Henle are permeable to water?
descending limb is permeable
| ascending limb is impermeable
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What happens in the descending limb of the loop of henle?
Water leaves and goes into blood vessels, sodium ions enter and water potential is lowered.
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What happens in the ascending limb of the loop of henle?
Water doesn't move, sodium ions exit. This then causes water to be drawn into the collecting duct.
205
What is acetylcholine broken down into?
acetate and choline
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What does the descending loop of henle do to the filtrate?
It transports sodium ions into it and water out of it so that when the filtrate reaches the hairpin loop it is highly concentrated.
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Why is it important that the hairpin loop in the loop of henle is highly concentrated?
So it has a lot of sodium ions that can then be absorbed into the interstitial region
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What does the ascending loop of henle do to the filtrate?
It has sodium ions actively transported out and the water stays in it as the membrane is impermeable to water.
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What does the high concentration of ions in the medulla mean?
It means that the water leaves the collecting duct via osmosis, so it can be reabsorbed, so less water is lost in the urine.
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What does the countercurrent multiplier refer to?
When the filtrate in the collecting duct with a low water potential meets interstitial fluid that has an even lower water potential. This ensures a water potential gradient exists for the entire length of the collecting duct so lots of water can be reabsorbed.
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How is the high pressure in the glomerulus maintained?
As the afferent arteriole has a larger lumen than the efferent arteriole and the capillaries in the glomerulus are tightly coiled, restricting blood flow.
212
How does the length of each of these subsections change in muscle contraction?
I band
A band
H band
I band decreases
H band decreases
A band remains the same
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What does antidiuretic hormone do?
It allows for more water to be reabsorbed in the distal convoluted tubule and the collecting duct, preventing water loss.
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where is ADH produced and where is it secreted?
It is produced in the hypothalamus and secreted from the posterior pituitary gland
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What happens when water potential of blood is low?
Osmoreceptors are triggered as cells in the hypothalamus shrink. This then sends an impulse to the posterior pituitary gland, causing a release of ADH, which then passes into the blood and travels to the kidneys.
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What are the mechanisms of ADH that occur when it meets the cells in the kidneys?
ADH binds to receptors on the cells of the distal convoluted tubule or the collecting duct. This causes an enzyme called phosphorylase to be activated. This causes vesicles to move and fuse with the cell surface membrane. These vesicles contain aquaporins which can then transport water across the membrane, therefore increasing permeability. Therefore, more water passes into the medulla fluid and then into the blood vessels by osmosis.
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How does ADH affect urea?
Some urea passes with the water into the medulla, which lowers the water potential, so ensures that a concentration is maintained into the medulla and blood vessels, allowing more water to diffuse.
218
How does low water potential in the blood affect thirst?
osmoreceptors also send impulses to the thirst centre of the brain to increase the intake of water.
219
What is IAA?
It is an auxin/growth factor that inhibits the growth of roots but promotes growth in shoots.
220
Where in the plant is IAA produced?
In the tip of the root/shoot
221
What are reflex actions and what features/things carries this out?
They are automatic, rapid responses that do not involve conscious areas of the brain. This consists of motor neurons, sensory neurons and relay neurons.
222
What is the pathway of the electrical impulse in the control of heart rate?
The impulse spreads from the sinoatrial node, causing the atria to contract. This then reaches a atrioventricular node. There is a slight delay as the impulse can not travel through the atrioventricular septum (it does not conduct). The signal is then sent down through the bundle of his to the purkyne fibres and is then released to the ventricles, causing them to contract.
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What is the medulla oblongata?
It is the region of the brain that controls changes to heart rate
224
What is the cardioacceleratory centre?
A centre that is responsible for increases of heart rate that is linked to the sinoatrial node by the sympathetic nervous system.
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What is the cardioinhibitory centre?
A centre that is responsible for decreasing heart rate, it is linked to the sinoatrial node by the parasympathetic nervous system.
226
What is the pathway that occurs when heart rate is changed when there is too much CO2 in the blood?
Increased rate of respiration results in an increase in CO2 production and more acidic blood---- this is detected by chemoreceptors in the carotid arteries-- this increases the frequency of impulses to the cardioacceleratory centre in the medulla oblongata--- increases impulse from the CAC to the sinoatrial node via the sympathetic nervous system--- the sinoatrial node increases heart rate, which increases the removal of CO2 and returns the blood pH to normal.
227
What is the pathway that occurs when heart rate is changed when there is too little CO2 in the blood?
Decreased rate of respiration results in a decrease in CO2 production and lower blood pH---- this is detected by chemoreceptors in the carotid arteries-- this increases the frequency of impulses to the cardioinhibitory centre in the medulla oblongata--- increases impulse from the CIC to the sinoatrial node via the parasympathetic nervous system--- the sinoatrial node decreases heart rate, which decreases the removal of CO2 and returns the blood pH to normal.
228
What is the equation relating cardiac output, heart rate and stroke volume?
Cardiac output = Heart rate x Stroke Volume
229
What is nitrogen fixation? How can it be carried out?
It is when nitrogen gas is converted into ammonium ions. It can occur naturally when lightning strikes and can be carried out by either mutualistic bacteria or free-living bacteria.
230
What is ammonification?
When saprobionts break down dead organisms and release ammonium ions
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What is nitrification?
Ammonium ions are turned into nitrite ions which are then converted into nitrates
