Untitled Deck Flashcards
(278 cards)
1
Q
ATP
A
adenosine triphosphate
2
Q
ATPase
A
Breaks down ATP into ADP and a phosphate ion
3
Q
How is ATP formed?
A
By adding a phosphate group to ADP
4
Q
Chemiosmosis
A
the flow of protons down an electrochemical gradient through atp synthetase coupled with the synthesis of atp from adp and a phosphate ion
5
Q
The Electron Transport Chain
A
high energy electrons pass from electron carrier to electron carrier which provides energy for the proton pumps to pump protons from the intermembrane space into the matrix which generates an electrochemical gradient, providing the energy for the protons to flow down an electrochemical gradient through ATP synthetase, synthesising ATP from ADP and a phosphate ion
6
Q
The names of the photosynthetic pigments
A
chlorophyll a, chlorophyll b, carotenoids, xanthophylls
7
Q
Where in the leaf is chlorophyll found?
A
palisade mesophyll
8
Q
How do you calculate an Rf value?
A
divide the distance the pigment has travelled by the distance the solvent has travelled
9
Q
absorption spectrum
A
how much light is absorbed at different wavelengths of light
10
Q
action spectrum
A
rate of photosynthesis at different wavelengths of light
11
Q
What did Engelmann do in his experiment?
A
He placed spirogyra in a suspension of motile aerobic bacteria and used a prism to refract the white light. The aerobic bacteria migrated towards the regions that had the highest oxygen concentrations, which corresponded the regions of red and blue light, so he concluded that the red and blue wavelengths were responsible for photosynthesis
12
Q
Where are the antenna complexes found?
A
in the plane of the thylakoid membrane
13
Q
Which pigment is found in the reaction centre of the antenna complex?
A
chlorophyll a
14
Q
What is light harvesting?
A
the absorption of light by the photosynthetic pigments
15
Q
What are the 2 photosystems?
A
photosystem I and photosystem II
16
Q
What happens in the light dependent stage of photosynthesis?
A
photons of light are passed to chlorophyll a and the electrons are raised to a higher energy level and passed to electron acceptors and used to synthesise ATP by phosphorylation or they are used to reduce NADP.
17
Q
What happens in cyclic phosphorylation?
A
high energy electrons pass from PSI to an electron acceptor. The electron is donated to the electron transport chain, which generates a proton gradient for chemiosmosis and then the electron is passed back to PSI.
18
Q
What happens in non-cyclic phosphorylation?
A
high energy electrons are passed to NADP and reduce it. PSI is an electron short, so PSII passes a high energy electron to the electron transport chain, generating a proton gradient which drives chemiosmosis and the electron is passed to PSI.
19
Q
What is the photolysis of water?
A
The splitting of water by light producing protons, electrons and oxygen. The electrons replace those lost from PSII, the protons reduce NADP and oxygen diffuses out of the chloroplast as a waste product.
20
Q
What happens in the Calvin Cycle?
A
Carbon Dioxide is taken up by 5C ribulose bisphosphate, forming an unstable 6C compound and then 2 molecule of glycerate 3 phosphate which is catalysed by rubisco. ATP and reduced NADP reduce G3P to triose phosphate, which is converted into glucose and then into starch. Most of the TP is converted into ribulose bisphosphate, which allows the calvin cycle to continue
21
Q
How can triglycerides be generated from the calvin cycle?
A
Acetyl CoA can be synthesised from glycerate-3-phosphate and converted into fatty acids. Triose phosphate can be converted into glycerol and reactions between them form triglycerides.
22
Q
How do limiting factors affect the rate of photosynthesis?
A
If they become too low, the rate of photosynthesis will decrease. If they increase, the rate of photosynthesis will also increase but beyond the saturation point it will level off.
23
Q
What are the limiting factors of photosynthesis?
A
light intensity, carbon dioxide concentration and temperature
24
Q
Macronutrients are
A
needed in substantial amounts
25
Micronutrients are
needed in tiny amounts
26
What is the symptom of nitrogen deficiency?
stunted growth
27
what is the symptom of magnesium deficiency?
chlorosis of the leaves
28
What happens in aerobic respiration?
the complete breakdown of glucose, releasing energy and ATP
29
What happens in anaerobic respiration?
The incomplete breakdown of glucose, releasing little energy and few ATP molecules
30
Where does glycolysis take place?
in the cytoplasm
31
What happens in glycolysis?
2ATP are broken down into 2ADP and glucose becomes 6C glucose diphosphate which is broken down into 2 3C Triose phosphate molecules. NADox loses 2H and is reduced. 2 molecules of ATP are synthesised from 2ADP + Pi and Pyruvate is formed.
32
How much ATP is produced in glycolysis?
2 directly, 6 indirectly . Total = 8
33
What happens in the link reaction?
Pyruvate is dehydrogenated which reduces NADox. It is also decarboxylated so loses a CO2 and becomes 2C Acetate, which combines with coenzyme A forming Acetyl Coenzyme A.
34
Where does the link reaction take place?
mitochondrial matrix
35
How much ATP is produced from the link reaction?
0 directly, 6 indirectly. Total = 6
36
What happens in the Krebs Cycle?
The 6C compound is dehydrogenated, reducing NAD. The decarboxylation reactions releases CO2 and forms a 5C Compound, which is dehydrogenated and decarboxylated, forming a 4C Compound. ATP is produced by substrate level phosphorylation and 2 further dehydrogenation reactions (FAD and NAD) take place, regenerating the the 4C Compound at the beginning of the cycle so it can continue.
37
Where does the krebs cycle take place?
mitochondrial matrix
38
How much ATP is produced in the Krebs cycle?
2 directly, 22 indirectly (6 NAD x 3 & 3 FAD x 2). Total = 24
39
Overall, how much ATP is produced in aerobic respiration?
38 molecules of ATP
40
Where is the ETC in aerobic respiration found?
On the cristae of the inner mitochondrial membranes
41
How many proton pumps is NAD associated with and how many molecules of ATP can it generate?
3
42
How many proton pumps is FAD associated with and how many molecules of ATP can it generate?
2
43
Which reaction takes place in anaerobic respiration?
Glycolysis
44
How much ATP is produced in anaerobic respiration?
2 molecules of ATP
45
What happens in anaerobic respiration in mammals?
Pyruvate gains 2H from NADred and becomes lactate/lactic acid
46
What happens in anerobic respiration in yeast?
Pyruvate is decarboxylated, forming ethanal and releasing CO2. Ethanal gains 2H from NADred and forms ethanol.
47
How are lipids used as an alternative respiratory substrate?
They are hydrolysed into fatty acids and glycerol by lipase. Glycerol is converted into triose phosphate and enters via glycolysis. Fatty acids are split into 2 acetate molecules and enter the krebs cycle as Acetyl CoA.
48
How are proteins used as an alternative respiratory substrate?
They are hydrolysed into amino acids and deaminated forming a-keto and ammonia. Some keto acids are fed into glycolysis via pyruvate and some are fed into the krebs cycle via acetyl CoA.
49
How can bacteria be classified?
Coccus, spirillum and bacillus
50
What happens in the gram stain test?
The bacteria is stained with crystal violet and then the stain is fixed using lugol's iodine. The bacteria are decolourised using acetone and then a counter stain is applied using safranin.
51
How do gram positive bacteria stain and why?
Gram positive bacteria stain purple and remain purple after decolourisation and the counter stain because they have a thick peptidogylcan cell wall and they do not have an outer lipopolysaccharide layer so the mordant and the stain is retained within the cell.
52
How do gram negative bacteria stain and why?
Initially gram negative bacteria stain purple but this is lost after the acetone is applied because they have an outer lipopolysaccharide layer which is dissolved by the alcohol, so the stain is washed away, so they appear red after the counterstain with safranin.
53
Why are Gram-negative bacteria resistant to penicillin?
because the peptioglycan is protected by the outer lipopolysaccharide layer
54
What do bacteria need in order to be cultured?
nutrients, growth factors, a suitable temperature and a suitable pH
55
Obligate Aerobes
Only grow and metabolise in the presence of oxygen
56
Obligate Anaerobes
Only grow and metabolise in the absence of oxygen
57
Facultative anaerobes
grow and metabolise best in the presence of oxygen but can survive without
58
Why is Aseptic technique used?
to prevent contamination of the environment by the microorganisms and to prevent contamination of the cultures by the environment
59
examples of aseptic technique
Pass metal tools through a flame until they glow red
60
Autoclave glass equipment, heating at 121'C, under pressure for 15 minutes
61
Open the culture bottle using little finger and do not place the lid on the work surface
62
Sterilise the inoculating loop in the bunsen flame
63
Flame the neck of the bottle in the bunsen flame
64
Work close to the flame, which provides an updraft
65
Close the lid of the petri dish immediately and seal with tape, but do not seal completely, as that would bring about anaerobic conditions which would encourage pathogenic growth
66
How can bacteria be counted?
It can either be counted directly by counting each cell or it can be counted indirectly by measuring turbidity
67
What is a total count?
Counting living and dead cells
68
What is a viable count?
only counting living cells
69
What happens if the dilution is too great?
there will be too few colonies on the plate for the count to be statistically sound
70
What happens if the dilution is insufficient?
The colonies merge which leads to an underestimate in numbers
71
1 in 10 dilution
1 in 10, 10 in 100, 1 in 1000, 1 in 10,000, 1 in 100,000
72
83 colonies in 1cm3 of a 10-3 dilution
83 x 103 = 83,000 in 1 cm3 of original sample
73
1 in 100 dilution
1 in 100, 1 in 10,000, 1 in 100,000
74
55 colonies in 1cm3 of a 10-2 dilution
55 x 102 = 5500 in 1cm3 of original sample
75
What is another method of measuring growth directly?
using a haemocytometer
76
How can growth be measured indirectly?
Using a colorimeter
77
What affects the size of a population?
Birth rate, death rate, immigration, emigration
78
How do fugitive species control their numbers?
They reproduce rapidly and they rapidly invade new environments
79
How do equilibrium species control their numbers?
through competition in a stable environment
80
What are the phases of the one step growth curve?
lag, log, stationary, death
81
What does the lag phase represent?
The time taken for the individuals in the environment to reach sexual maturity, find a mate and gestate their young
82
What happens in the log (exponential) phase?
The population increases logarithmically
83
What happens in the stationary phase?
The population has reached its carrying capacity and the birth rate is equal to the death rate
84
What does the death phase represent?
the population has decreased to such an extent that the death rate is greater than the birth rate
85
What are biotic factors?
Competiton, new diseases, parasitism, increase in predator numbers
86
What are abiotic factors?
temperature, light intensity, water availability
87
What is a population crash?
a sudden, dramatic decrease in population number that occurs when the population greatly exceeds its carrying capacity
88
Population growth =
(births + immigration) - (deaths + emigration)
89
Why do predator prey interactions cause both populations to oscillate?
due to negative feedback mechanisms
90
The rate of growth in the log phase =
(number of bacteria at day 9 - number of bacteria at day 4) divided by (9-4)
91
density dependent factors
competition, predation, parasitism, disease
92
What do density-dependent factors do?
their effect increases as the population increases. They determine the carrying capacity and weaken individuals.
93
Density independent factors
earthquake, tsunami, volcanic eruptions, extreme weather, wildfires
94
How can abundance be measured?
Capture-mark-recapture, kick sampling, random sampling, systematic sampling
95
What is an ecosystem?
a characteristic community of interdependent species and their habitat, which is comprised of abiotic and biotic factors and is dynamic so changes over time
96
What do producers do?
They are autotrophic and absorb light energy, converting simple inorganic compounds into more complex organic compounds
97
What do consumers do?
they are heterotrophic and they ingest or absorb organic carbon from other organisms
98
What do herbivores do?
they feed on organic matter produced by producers
99
What do carnivores do?
they feed on other animals at lower trophic levels
100
What do detritivores do?
they feed on dead organic matter
101
What do decomposers do?
they break down organic compounds into simple inorganic compounds which can be absorbed by plant roots
102
Why is not all of the energy that reaches producers absorbed?
light is reflected from the wrong leaf surface, wrong wavelengths of light cannot be absorbed by the pigments and light passes through the leaf but does not hit the photosynthetic pigments
103
Why is the length of food chains limited?
because there would be insufficient energy to support more trophic levels
104
photsynthetic efficiency =
the quantity of light energy incorporated into biomass divided by the quantity of light energy hitting the leaf multiplied by 100
105
Gross Primary Productivity (GPP)
the rate of production of chemical energy in biological molecules by photosynthesis per unit area and time (kJm-2y-1)
106
Net Primary Productivity (NPP)
the energy in the biomass of the plant which could pass to the primary consumers at trophic level 2 during feeding (kJm-2y-1)
107
GPP =
solar energy hitting the leaf - energy not used
108
NPP =
GPP - respiration
109
Secondary productivity
the rate at which heterotrophs accumulate energy in the form of new cells and tissues
110
Why do herbivores have a lower secondary productivity than carnivores?
because the protein-rich diet of carnivores is more readily and efficiently digested and less energy is lost as waste
111
The efficiency of energy transfer =
energy incorporated into biomass after transfer divided by energy available before transfer multiplied by 100
112
Why don't pyramids of number provide meaningful information?
because they do not take the size of the organism into account and they are often inverted and difficult to draw to scale, and they provide no information about the energy at each trophic level
113
Why are pyramids of biomass inaccurate?
because not all biomass is available to the next trophic level and they may be inverted
114
Why are pyramids of energy useful?
They show the quantity of energy transferred from one trophic level to the next. They are never inverted and they allow comparison of enery transfer between trophic levels in different communities
115
What is succession?
a sequence of changes in the composition of a community over time. It will eventually lead to a climax community, which has high biodiversity and is highly productive
116
What is each stage of succession called?
a sere
117
Primary succession
begins from bare rock, which is colonised by the pioneer species. These species change the surface of the rock by penetrating it and allowing humus to accumulate, allowing grasses and ferns to colonise the area. This further changes the rock surface and over many generations it allows more soil to accumulate and other higher plant species to invade. As the community of plants becomes more diverse, the diversity of animals also increases and eventually a climax community is established.
118
secondary succession
begins from bare soil, which has been exposed after wildfire. A climax community is achieved much faster because the soil is already present and may contain viable bulbs, seeds and spores. However, a climax community may be prevented due to grazing sheep, heather moorland management, farming of land and deforestation.
119
The carbon cycle
CO2 from the atmosphere is fixed into carbohydrate by the light independent stage of photosynthesis. Respiration releases CO2 into the atmosphere, as does the burning of fossil fuels. The microorganisms responsible for decay also respire and release CO2 into the atmosphere. Carbon that is fixed in organic molecules passes from trophic level to trophic level along food chain during feeding. Over millions of year, fossil fuels are formed from the remains of dead plants and animals and the carbon rich molecules become fossil fuels over time.
120
Why is the balance of the carbon cycle being disrupted?
because of deforestation and the burning of fossil fuels
121
How is increased CO2 in the atmosphere affecting the environment?
it has led to global warming, which drives climate change, causing the polar ice caps to melt and the sea levels to rise, there is increased frequency of extreme weathers, increased desertification and soil erosion and increased extinction rate.
122
What is a carbon footprint defined as?
the total amount of carbon dioxide produced directly due to the actions of an individual or service per year
123
Why does agriculture have a carbon footprint?
due to the production of farm tools, insecticides, fungicides and fertilisers, farm machinery that is powered by fossil fuels and transport of products
124
How the carbon footprint of agriculture be reduced?
by producing less meat, only growing meat for human consumption, reducing packaging and transport distances and finding alternatives for rice paddies
125
What is the nitrogen cycle?
The flow of inorganic and organic nitrogen within the abiotic and biotic elements of an ecosystem
126
What happens in nitrogen fixing?
atmospheric nitrogen is fixed into soluble inorganic compounds by azotobacter which is a free-living bacteria found in soil and fixes nitrogen gas into ammonium ions and rhizobium which is found in the root nodules of legumes and uses nitrogenase to fix nitrogen gas into soluble ammonium.
127
When and how does nitrification take place?
it takes place after an organism dies and bacteria and fungi release nitrogenous compounds during decomposition, the products of which are ammonium ions.
128
Nitrosomonas converts ammonium into nitrite and nitrobacter converts nitrite to nitrate, which is then absorbed into the plant root hair cells by active transport.
129
What is denitrification?
the loss of soluble nitrate compounds from the soil. In anaerobic conditions the nitrate can be converted back into the atmospheric nitrogen and lost from the soil. Ploughing fields means the soil mixes with the air so pseudomonas is inhibited and the growth of nitrosomonas, nitrobacter and azotobacter is encouraged.
130
Summary of the nitrogen cycle
Decomposers break down large organic molecules in the plants remains into inorganic ammonium, in a process called ammonification. Nitrosomonas converts ammonia into nitrite and the nitrobacter converts nitrite into nitrate in a process called nitrification. Pseudomonas converts inorganic nitrogen sources into nitrogen gas during denitrification. Azotobacter and rhizobium fix free nitrogen gas into ammonium and nitrates during nitrogen fixing.
131
How can human activities improve the availability of soluble nitrate?
by the addition of chemical fertilisers, manure and treated sewage to the soil, as well as planting legumes such as clover and ploughing or draining to improve the aeration of the soil.
132
How can nitrates decrease biodiversity?
Excess nitrates on grassland can lead to increased weed growth which reduces biodiversity. Draining wetlands destroys unique habitats and nitrate pollution in waterways causes eutrophication, which ultimately causes a decrease in dissolved oxygen and a decrease in biodiversity.
133
What is eutrophication?
If nitrates are used excessively or carelessly chemical fertilisers, manure and slurry can be washed into waterways, which increases the soluble nitrate concentration of the water, increasing algal and plant growth, forming an algal bloom which covers the surface of the water and block light at lower depths, so plants die because photosynthesis cannot take place. These plants are decomposed by aerobic bacteria and the concentration of dissolved oxygen in the water drops, so other organisms die of suffocation. The water becomes anaerobic, which encourages denitrifying bacteria so the nitrate levels fall.
134
Extinction
the complete loss of a species caused by natural selection, non-contiguous populations, loss of habitat, overhunting by humans, competition and pollution
135
Conservation
the protection, preservation, management and restoration of natural habitats and their ecological communities
136
How can conservation be achieved?
Protecting habitats
137
International cooperation restricting trade
138
Germ / Sperm banks & seed banks
139
Rare breed societies
140
Species reintroduction
141
Ecotourism
142
Why is maintaining biodiversity important?
to protect potential sources of new crops for agriculture and new pharmaceuticals for medicine. It is also important due to ethics and the fact that each life and their genes are precious and unique
143
Why has intensive farming led to a decrease in biodiversity?
because it has led to an increase in chemicals fertilisers, pesticides and herbicides, which has resulted in a loss of hedgerows
144
Why do monocultures reduce biodiversity and soil fertility?
because they only provide one type of crop but increase the need for chemical fertilisers and pesticides because they plants grow closely together and they are susceptible to the same pests and diseases
145
What are the consequences of over grazing?
soil compaction, inhibition of nitrogen fixing and nitrifying bacteria, reduced air spaces and a loss of soil fertility
146
What methods is agriculture to reverse the decline in biodiveristy and soil fertility?
Organic farming, set aside schemes and legislation
147
What is deforestation and what are the consequences?
The complete loss of trees in a defined area. The consequences of deforestation include soil erosion, lowland flooding, desertification, habitat loss, decreased biodiversity and climate change.
148
What is the managed forestry doing to increase biodiversity?
They are doing sustainable replanting and regeneration, through coppicing, selective cutting and long rotation time.
149
What is coppicing?
Cutting tree trunks at their base, leaving a stool from which new shoots grow and can be harvested for different uses, providing a variety of habitats
150
How is overfishing affecting fish stocks?
It is depleting fish stocks to such an extent that populations may become too low to recover, impacting food chains and entire ecosystems
151
What are commercial fishing methods and how are they damaging?
drift netting and trawling, they catch target and non-target species and damage the ocean floor, decimating habitats
152
How is the fishing industry being regulated?
Regulating mesh size
153
Quotas and landing size regulations
154
Exclusion zones
155
Legislation limiting the size of fishing fleets
156
Using lines not nets
157
What is fish farming?
large scale, intensive farming where fish are bred and mature in enclosed ponds
158
What are the disadvantages of fish farming?
the rapid spread of disease and parasites, the bioaccumulation of pesticides, nitrogenous waste pollution, they may contain high levels of toxic chemicals and they are larger and will outcompete wild fish for resources if they escape.
159
Why are air quality, soil quality and water quality monitored?
In order to determine the quality of the environment and asses any decline over time
160
What is included in an environmental impact assessment?
a description of the site and proposed project, a description of abiotic and biotic factors, and mitigation, ways of limiting environmental damage and maintaining biodiversity.
161
What do the planetary boundaries define?
the safe operating space for humanity which is within the inner blue circle.
162
What does the outer red circle represent?
It represents the zone of uncertainty and beyond this the planetary boundary has been crossed, it is high risk and events are unpredictable
163
What are the different planetary boundaries?
The climate change
164
Biosphere integrity
165
The land use
166
The biogeochemical flows
167
The stratospheric ozone
168
The ocean acidification
169
The fresh water
170
The atmospheric aerosol
171
The introduction of novel entities (chemical pollution)
172
What is homeostasis?
The maintenance of a constant internal environment by negative feedback, preventing wild fluctuations beyond the optimal range, allowing cells and metabolism to function efficiently
173
What conditions are kept around a set point?
Core body temperature, pH, water potential
174
How does negative feedback operate?
It operates by the receptor detecting a deviation from the set point. The receptor then sends instructions to a co-ordinator which communicates with one or more effectors that make corrective responses. The factor returns to normal and the information is fed back to the effectors, which stop making the correction
175
What is excretion?
the removal of metabolic waste from the body
176
What is the kidney responsible for?
the excretion of nitrogenous metabolic waste and osmoregulation
177
What is urea?
excess amino acids that have been deaminated in the liver and converted into ammonia and then into urea, which is less toxic and removed by the kidneys
178
How does blood enter and leave the kidney?
blood enters via the renal artery and leaves via the renal vein
179
What are the parts of the kidney?
ureter, bladder, urethra, renal vein, renal artery, medulla, cortex, pelvis, ureter
180
What is the nephron?
it is the functional unit of the kidney
181
Which part of the kidney are the bowman's capsule and proximal convoluted tubule found?
the cortex
182
Where is the loop of henle found?
medulla
183
What are the parts of the nephron?
Ascending limb of loop of henle, descending limb of loop of henle, glomerulus, bowman's capsule, proximal convoluted tubule, distal convoluted tubule, collecting duct
184
What is ultrafiltration?
It is filtration under high pressure which forces small molecules and ions into the tubule. Large molecules and blood cells cannot pass through into the filtrate because they are too large
185
How does blood enter and leave the glomerulus?
Blood enters via the afferent and leaves via the efferent arteriole
186
How is a high hydrostatic generated?
because the afferent is wider than the efferent
187
How is the blood entering the glomerulus separated from the bowman's space?
because of the endothelium, the basement membrane and the squamous epithelial cells
188
How is the endothelium adapated for ultrafiltration?
it is one cell thick and it has pores called fenestrae through which the solutes pass
189
Why is the basement membrane important?
because it is the selective molecular and only allows small molecules to pass through
190
What are the squamous epithelial cells known as and why are they important?
they are known as podocytes and they have extensions called pedicels which wrap around the capillary, bringing it closer to the basement membrane. There are gaps between the pedicels which are called filtration slits
191
Why do the small molecules pass through to the bowman's space?
because the high hydrostatic pressure forces small molecules through the fenestrae of the endothelium, through the basement membrane and through the filtration slits between the pedicels into the bowman's space
192
The filtration rate =
volume of filtrate produced per minute divided by the volume of blood entering the kidneys per minute x 100
193
Selective reabsorption
The process by which useful substances such as glucose, amino acids and salts are reabsorbed back into the blood plasma, by facilitated diffusion and active transport.
194
How is the PCT adapted for selective reabsorption?
The nephron is closely associated with the vasa recta, so the reabsorbed substances pass from the the PCT into the blood plasma which is contained within the vasa recta capillaries. The cells lining the PCT are highly specialised cuboidal epithelial cells, which have microvilli to increase the surface area for reabsorption. They have many mitochondria to provide ATP for active transport, there are tight junctions between cells, basal channels increase the surface area of the cell membranes and the cells are closing associated with the capillaries of the vasa recta.
195
How are salts reabsorbed?
mainly by active transport but some by facilitated diffusion
196
How are glucose and amino acids reabsorbed?
by cotransport with sodium ions
197
How is water reabosrbed?
by osmosis
198
How are urea and small proteins reabsorbed?
by facilitated diffusion
199
Why is some glucose not always reabsorbed?
because if the concentration of glucose is too high the intrinsic transport proteins may become limiting so glucose will remain in the filtrate and be passed out in the urine.
200
What happens to the filtrate when it leaves the PCT?
It enters the descending limb of the loop of henle, which is permeable to water, so water leaves the filtrate and enters the blood, by osmosis, down a water potential gradient and Na+ and Cl- ions diffcuse into the descending limb from the medulla.
201
Why does the medulla have a low water potential?
because it is maintained by the ascending limb of the loop of henle expelling Na+ and Cl- by facilitated diffusion and then active transport
202
What happens to the filtrate as it leaves the descending limb by osmosis?
It becomes more concentrated, reaching its maximum concentration at the apex of the loop
203
What happens to the ions in the ascending limb?
it is impermeable to water but permeable to Na+ and Cl- so they leave by facilitated diffusion initially, but as the concentration of solutes decreases, active transport takes over
204
Why is the loop of henle known as a counter current multiplier?
because the filtrate flows in opposite directions and the concentration of solutes in the filtrate increases towards the apex, so the longer the loop of henle, the higher the concentration of solutes at the apex
205
How are animals in dry environments adapted?
very long loop of henle
206
how are animals in aquatic environments adapted?
short loop of henle
207
Why is having a longer loop of henle beneficial to organisms in dry habitats?
because the longer the loop is, the more ions can be pumped into the medulla, which lowers the water potential of the medulla and allows more water to be reabsorbed into the bloodstream by osmosis
208
What is osmoregulation?
the control of body fluid water potential by negative feedback
209
How does osmoregulation work?
Osmoreceptors in the hypothalamus detect a decrease in blood plasma water potential. A signal is sent to the posterior lobe of the pituitary which is the co-ordinator and releases the hormone ADH into the bloodstream, which is carried to the kidney and binds to the receptor points on the walls of the collecting duct and distal convoluted tubule. Aquaporins are intrinsic protein channels which are added to the cell membranes and allow more water to be absorbed by osmosis, which increases the water potential of the blood back towards the set point. This information is fed back to the hypothalamus and less ADH (no ADH) is produced.
210
Antidiuretic hormone
increases the permeability of the collecting duct and distal convoluted tubule, allowing more water to be reabsorbed, so a small volume of concentrated urine will be produced.
211
How does ADH work?
ADH binds to ADH receptor proteins in the phospholipid bilayer of the cell membrane. Aquaporin vesicles fuse with the cell membrane increasing the permeability of the membrane to water, allowing more water to be reabsorbed.
212
When ADH is released from the receptors the cell membrane folds, forming aquaporin vesicles, reducing the number of aquaporins and reducing the permeability of the membrane.
213
How does ADH work in low water potential?
More ADH is released, so the walls of the DCT and collecting duct become more permeable and the concentration of urine increases, but the volume decreases and the water potential returns to normal
214
How does ADH work in high water potential?
less ADH is released, so the walls of the DCT and collecting duct become less permeable and the concentration of urine decreases, but the volume increases and the water potential returns to normal
215
How can kidney failure be treated?
medication, low protein diet, drugs to reduce blood pressure, dialysis, kidney transplant
216
How does dialysis work?
It removes waste products and excess salts from the blood (haemodialysis) which is taken from an artery in the arm and passed through the dialysis tubing, which is surrounded by dialysis fluid, that flows in the opposite direction to the blood and is continuously replaced to maintain the concentration gradient. Clean blood is returned to the patient through a vein.
217
How does kidney transplant work?
Donor kidneys can either come from a living or a dead person and they must have compatible tissue and blood groups with the recipient. Immunosuppressant drugs must be taken for the rest of the patient's life to reduce the risk of rejection.
218
How is nitrogenous waste excreted in fish?
It is excreted as ammonia into the surrounding water by diffusion
219
How is nitrogenous waste excreted in birds?
It is excreted as uric acid, which is non-toxic
220
How is nitrogenous waste excreted in mammals?
Urea is produced, which requires ATP
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What is a stimulus?
a detectable change in the internal or external environment of an organism
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What do receptor cells do?
They act as transducers and detect energy in one form and convert it into electrical energy
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How does the electrical energy travel?
It travels along neurones as a nerve impulse?
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What does the nerve impulse do?
It initiates a response in an effector, which is always a muscle or gland
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What is the central nervous system made up of?
the brain and spinal cord
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What does the central nervous system do?
It processes information provided by a stimulus and coordinates a response
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What is the peripheral nervous system made up of?
neurones
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What is the somatic nervous system made up of and what does it do?
it is made up of pairs of nerves, which branch from the brain and spinal cord. The neurones carry impulses from receptor cells to the CNS and then from there to the effectors.
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What does the autonomic nervous system do?
it provides unconscious control of the internal organs e.g. heartbeat and breathing
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What are neurones?
They are highly specialised cells that carry nerve impulses in one direction
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What does the sensory neurone do?
carries nerve impulses from the receptor cells in the sense organ to the CNS.
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where is the relay neurone found and what does it do?
it is found in the CNS and it connects the sensory and motor neurones
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What does the motor neurone do?
it transports the nerve impulse from the CNS to the effectors
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What is the role of the dendrite?
to carry the impulse towards the cell body
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what does the cell body contain?
the nucleus and clusters of ribosomes
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What does the axon do?
carries impulses away from the cell body
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What is the node of ranvier?
a region of the cell membrane which is exposed and can be depolarised to speed up nerve transmission
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What do Schwann cells produce?
the myelin sheath which is an electrical insulator
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Why is the grey matter grey?
because it contains the cell bodies and synapses
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Why is white matter white?
because it contains myelinated axons
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What does the dorsal root do and where is the cell body of the sensory neurone found?
It allows the sensory neurone to enter. The cell body is housed within the dorsal root ganglion.
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What does the ventral root do?
It allows the motor neurone to exit
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What are the properties of a reflex action?
fast, automatic, protective
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The reflex arc
Stimulus - Receptor - sensory neurone - relay neurone - motor neurone - effector - response
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Examples of reflex actions
removing hand from a hot object, blinking, contraction of the iris
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Nerve nets
found in invertebrates such as jellyfish and hydra. There is no recognisable CNS and there are fewer types of receptor cells, so they can only respond to a limited number of stimuli and the detection of the stimulus cannot be detected, however the more intense the stimulus is, more nerve cells are triggered which initiates a greater response.
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They only have one type of neurone and they are shorter, and branch in all directions. Impulses travel slower and in all directions.
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How is resting potential achieved?
by the active transport of 3Na+ out and 2K+ in by the sodium-potassium pumps. The axon is highly permeable to K+ and they move out through channels by facilitated diffusion, which means that the outside of the membrane becomes more positive than the inside, so the membrane is polarised.
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What is the resting potential?
-70mV
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How is the action potential generated?
A stimulus opens the voltage gated sodium channels, which causes an influx of Na+, causing the axon to be depolarised. The Na+ ions flood into the axon, down their concentration gradient, and the potential difference across the membrane is +40mV and this is an action potential. This is called depolarisation and the voltage gated sodium channels close, opening the K+ channels so the K+ ions leave the axon, down their concentration
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What is the action potential?
+40mV
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How can the action potential be measured?
using a cathode ray oscilloscope
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What happens during the absolute refractory period?
No further action potentials can be propagated along the axon until polarisation has been restored. This is known as the absolute refractory period, and is caused by depolarisation and repolarisation, and now new action potential can be generated.
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Why is it known as the all or nothing law?
because If the intensity of a stimulus is below a certain threshold, no action potential will be generated. If the intensity is above the threshold, a full action potential will be generated and the nerve impulse will be propagated along the axon.
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How is the brain prevented from being overloaded by minor stimuli?
because increases in the intensity of the stimulus will not generate a larger action potential
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Why are the voltage gated sodium channels opened?
because the impulse is propagated once a stimulus generates a full action potential due to the juxtaposition of positive and negative charges of the polarised and depolarised regions of the axon cell membrane, which generates localised electrical currents
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What affects the speed of transmission and why?
temperature (increased kinetic energy), the diameter of the axon (greater the diameter, lower the resistance to the movement of ions) and myelination (electrically insulates the axon). The nodes of ranvier expose the cell membrane so the action potential jumps from node to node, speeding up the rate of transmission in saltatory transmission.
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What do synapses do?
they produce neurotransmitters and pass nerve impulses from neurone to neurone
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How does synaptic transmission work?
When an action potential reaches the presynaptic membrane Ca2+ channel opens, allowing the Ca2+ to enter the synaptic knob. Synaptic vesicles, which contain neurotransmitters fuse with the presynaptic membrane and release the neurotransmitter by exocytosis. The neurotransmitter diffuses across the synaptic cleft and binds to receptor proteins on the postsynaptic membrane, which opens Na+ channel allowing an influx of Na+ into the postsynaptic neurone, which if sufficient, generates an action potential.
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How is the neurotransmitter acetylcholine broken down so it does not remain in the synaptic cleft?
it is broken down by cholinesterase into choline and ethanoic acid, which diffuse into the synaptic knob and are regenerated into acetylcholine and repackaged into synaptic vesicles, which requires ATP hence why the synaptic knob has many mitochondria.
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Why can acetylcholine not be left in the synaptic cleft?
because it would constantly initiate new impulses
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What are the functions of the synapse?
being able to transmit information from neurone to neurone, to pass impulses in one direction, to act as junctions, to prevent over stimulation, and to filter out low level stimuli.
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How do drugs act on synaptic tranmission?
they either amplify or inhibit it
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How do amplifying drugs act on the pre-synaptic?
Accelerates the production of neurotransmitters in the synaptic knob.
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Opens calcium channels in the presynaptic membrane
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Accelerates the release of neurotransmitter from the synaptic knob by exocytosis
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Blocks the removal por recycling of neurotransmitter substance from the synaptic cleft back into the synaptic knob
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How do inhibiting drugs act on the pre-synaptic?
Inhibits the production of neurotransmitter in the synaptic knob
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Closes calcium channels in the presynaptic membrane
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Inhibits the release of the neurotransmitter from the synaptic knob by exocytosis
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How do amplifying drugs act on the post-synaptic?
Makes the postsynaptic receptors more sensitive to the neurotransmitter
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Opens the sodium channels on the postsynaptic membrane
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Inhibits the activity of cholinesterase in the synaptic cleft
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Mimics the neurotransmitter substance
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How do inhibitory drugs act on the post-synaptic?
Makes the postsynaptic receptors less sensitive to the neurotransmitter
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Closes the sodium channels on the postsynaptic membrane
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Increases the activity of cholinesterase in the synaptic cleft
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Mimics the neurotransmitter substance
