Biology A level Flashcards
What is energy needed for in living organisms?
-anabolic reactions in synthesizing complex substances from its monomers
- Active transport of substances
- Maintaining body temperature
- Bioluminescence and nerve impulse transmission
- DNA replication
What is Adenosine triphosphate?
- Adenosine triphosphate is a nucleotide derivative and consists of ribose, adenine and three phosphate groups.
- Energy is released when ATP is hydrolysed to form ADP and a phosphate molecule. This process is catalysed by ATP hydrolase.
- The inorganic phosphate can be used to phosphorylate other compounds, as a result making them more reactive.
- Condensation of ADP and inorganic phosphate catalysed by ATP synthase produces ATP during photosynthesis and respiration.
What is ATP stand for?
Adenosine triphosphate
Why is the energy released from hydrolysis of ATP?
- ATP is readily hydrolysed to release energy
- Immediate source of energy
- Small and water soluble, easily transported around cell
- Pi is a good leaving group, as ATP synthase can efficiently reattach the Pi to ADP to form ATP (reversible)
- Has a high turnover
- Links anabolic (energy requiring ) and catabolic (energy yielding) reactions
- ATP is produced from a variety of reactions
How is ATP synthesised by substrate link route?
- When ATP is made from ADP and a phosphate group which is transferred from a highly reactive intermediate
- An example would be during glycolysis - ADP joins with the inorganic phosphates transferred from triose bisphosphate molecules forming 4 ATP
(per glucose molecules). - This also happens in the Krebs cycle
- Only oxidative phosphorylation requires oxygen as the it is needed to combine with electron/proton in the final acceptor. No ETC would mean no proton gradient produced therefore Chemiosmosis (synthesis of ATP) does not occur.
How is ATP synthesised by chemiosmosis route?
- The movement of protons across a membrane which synthesises ATP
- Protons diffuse down a concentration gradient through a partially permeable membrane
- As protons flow down energy is released
- The energy is used in the attachment of ADP to an inorganic phosphate
- Only oxidative phosphorylation requires oxygen as the it is needed to combine with electron/proton in the final acceptor. ETC would mean a proton gradient is produced
What is respiration?
- Respiration is the breakdown of a respiratory substrate such as glucose to produce energy in the form of ATP. There are two types of respiration Aerobic and Anaerobic
- Some organisms and tissues are able to respire in both aerobic and anaerobic conditions.
- When yeast and plants respire under anaerobic conditions, they produce ethanol and carbon dioxide as end-products; mammalian muscle tissue produces lactate when oxygen is in low supply, which causes fatigue.
- Respiration is a multi-step process with each step catalysed by a specific intracellular enzyme.
What is aerobic respiration?
Aerobic respiration occurs in the presence of oxygen. Produces large amounts of ATP.
What anaerobic respiraton?
Anaerobic respiration occurs in the absence of oxygen. Produces less ATP and is less efficient.
What is the process in which organic molecules act as a fuel in respiration?
- Glycolysis
- Link reaction (oxygen present)
- Kerbs cycle (oxygen present)
- Oxidative phosphorylation (oxygen present)
What is a glycolysis reaction?
- Is the lysis of glucose to form 2 molecules of pyruvate (3C) which occurs in the cytoplasm of the cell
- Glycolysis is the first process of both aerobic and anaerobic respiration.
- In aerobic respiration which occurs in cytoplasm of cells.
- In this process glucose is phosphorylated to produce 1,6 bisphosphate (6C). This then breaks
into 2 triose phosphate (3C) molecules. - Each triose phosphate is then further oxidised into pyruvate producing 2 ATP molecules and 1
reduced NAD per triose phosphate molecule. - Overall 1 glucose molecule produces; two pyruvate molecules, 2 ATP and 2 NADH through
glycolysis. - If there is sufficient oxygen then pyruvate will enter the mitochondrial matrix for the link
reaction. - In anaerobic respiration the pyruvate is further converted into lactate with the help of NADH. Lactate is then converted back to pyruvate in the liver.
What is the link
reaction?
- The next step of aerobic reaction is the link
reaction. - Pyruvate enters the mitochondrial matrix
via active transport - First pyruvate undergoes oxidative
decarboxylation which forms an acetyl
group (2C) and NADH - Coenzyme A becomes bound to the acetyl
group forming Acetyl coenzyme A (CoA) - This helps deliver the acetyl group to the next stage of respiration
- Each glucose molecule produces 2 pyruvates hence the link reaction produces a total of 2
carbon dioxide, 2 NADH and 2 acetyl coenzyme A’s
What is the Kerbs cycle?
- Acetyl coenzyme A delivers the acetyl group to the Krebs cycle is a closed pathway and happens in the mitochondrial matrix
- The 2C acetyl group is accepted by the 4C oxaloacetate forming 6C citrate
- 6C citrate undergoes decarboxylation (removal of carbon dioxide) and dehydrogenation (removal of hydrogen) forming a 5C compound, carbon dioxide and reduced NAD
- The compound then undergoes further decarboxylation and dehydrogenation
(around 4 times) until eventually 4C oxaloacetate is reformed. - During this carbon dioxide, ATP, reduced NAD and reduced FAD are produced.
- The krebs cycle must take 2 turns per glucose molecule.
What is Oxidative phosphorylation steps?
- This stage involves chemiosmosis which takes place in the inner mitochondrial membrane (cristae)
- Reduced NAD and FAD are passed to the electron transport chain
- Reduced NADs and FADs release hydrogen atoms which then split up into H= and one electron
- Electrons move down the energy gradient across electron transport chain to release energy
- This energy is utilised to pump H+ ions from he matrix to the intermembrane space producing a proton gradient
- H+ then move down the concentration gradient through ATP synthase back into the matrix via facilitated diffusion
- ADP +Pi ATP, also occurs while the protons pass through ATP synthase. This happens by utilising the protons electrical potential energy for chemiosmosis
- oxygen acts as the final electron acceptor to form water. 1/2O2 + 2H+ + 2 e- + H2O
What will theoretically and realistically be reduced and gained from oxidative phosphorylation?
Thoretically
- Reduced NAD produces 3 molecules of ATP
- Reduced FAD produces 2 molecules of ATP
However, some energy is used to transport ADP into the mitochondrion and ATP into the cytoplasm therefore realistically
- Reduced NAD produces 2.5 molecules of ATP
- Reduced FAD produces 1.5 molecules of ATP
- Most ATP produced is 28 molecule
What is the balance sheet of respiration?
ATP used ATP made Net ATP NAD reduced
Glycolysis -2 4 +2 2
Link reaction 0 0 0 2
Krebs Cycle 0 2 +2 6
Oxidative 0 28 +28 0
phosphorylation
Total -2 34 +32 10
- 2 FAD is reduced only in the Krebs cycle
- Reduced FAD and NAD are oxidised in oxidative phosphorylation.
What happens in oxidative phosphorylation without oxygen?
- In the absence of oxygen, the final e- is not accepted and hydrogen can’t be disposed of in the ETC. Thus, reduced NAD is not oxidised and the chain stops.
This produces a small yield of ATP as only glycolysis occurs
What is alcohol fermentation in anaerobic respiration?
- Glycolysis takes place normally
- Ethanal is reduced to ethanol by accepting hydrogen from reduced NAD, with the help of enzyme alcohol dehydrogenase (this enzyme helps with removal of H from NADH)
- Reaction cannot be reversed, and remaining chemical potential energy in ethanol is wasted.
- Happens in yeast
- Irreversible
- Pyruvate undergoes decarboxylation forming ethanal
- The ethanal then acts as a hydrogen acceptor from NADH
- Produces ethanol which is a toxic to yeast cells and NAD is regenerated
What is oxygen debt and what is it needed for
Oxygen debt the post exercise uptake of extra oxygen to pay off oxygen deficiency which is needed for:
- Conversion of lactate to glycogen in the liver
- Oxidation of lactate to Co2 and H20
- Reoxygenation of haemoglobin in the blood
- A high metabolic rate, as many organs are operating above resting level.
What are the adaptations of rice for wet fields?
- Can respond to flooding by growing taller, ensuring top part of leaves and flower are held above water, allowing oxygen and carbon dioxide to be exchanged via stomata
- Contains loosely packed aerenchyma cells in the cortex of stems allowing oxygen to diffuse into deprived areas
- Air is trapped in between ridges of underwater leaves that have hydrophobic corrugated surfaces to keep air within the leaves’ contact
- Can tolerate high levels of ethanol (toxic) by the production of alcohol dehydrogenase which breaks it down
- Ethanol stimulates gibberellin, which in turn stimulates cell division, hence increasing internodal length
What is a raspatory substrate?
- The more hydrogens per molecule a substance has, the more energy value per unit mass, thus greater energy density
- This is because most of the energy liberated in respiration comes from oxidation of hydrogen to water
- To calculate the energy value of a substance, burn a known mass with oxygen in a calorimeter
- The energy is determined by the rise in temp of the water
What is the respritory quotient?
- Respiratory quotient (RQ) is the ratio of oxygen taken in to carbon dioxide given out.
- It is used to show what substrate is being used in respiration, and whether or not anaerobic respiration is occurring.
- RQ= volume of CO2 given our per unit time/
volume of O2 taken in per unit time - Respiratory substrate Respiratory quotient(RQ)
Carbohydrate 1.0
Lipid 0.7
Protein 0.9 - When values are closer to infinity or higher than 1.0, anaerobic respiration is occurring, values below 1 shows aerobic respiration
- No RQ value for muscle cells in anaerobic respiration as only lactate is produced with no CO2 being produced
What is a respirometer and how is it used?
- Measures oxygen uptake in a sealed container for respiring organisms eg germinating seeds or invertebrate organism
- CO2 produced is absorbed by soda lime/concentrated KOH or NaOH.
- The decrease in the volume of air results from their oxygen consumption and rises the anmometer fluid in the tube.
- Oxygen consumption per unit time can be measured by reading the level of the manometer fluid against a scale.
- Temperature must be kept constant via thermostatically controlled water bath.
- A control tube helps maintain pressure – it contains equal volume of inert material as the volume used in the experimental tube so that any changes in atmospheric pressure can be compensated for
- Finally, a graph of oxygen consumption against temperature can be plotted.
- this apparatus can also be used to measure RQ
- Manometer fluid stays constant when O2 consumption and CO2 production are equal (RQ=1)
What is photosynthesis?
Photosynthesis is a reaction in which light energy is converted to chemical energy in the form of glucose. Oxygen is a waste product of this reaction and is released into the atmosphere.
How is chloroplast adapted for photosynthesis?
- They contain stacks of thylakoid membranes called grana which contain the photosynthetic pigments such as chlorophyll. These are arranged as photosystems.
- They contain stroma which is the fluid surrounding the grana, stroma contains all the enzymes required for the light independent stage of photosynthesis
- Chloroplast appear as biconvex discs about 3-10 µm
What is a thylakoid membrane and how is it adapted for photosynthesis?
Thylakoid membrane: where light-dependent reactions occur
- Its membrane contains photosystems, inside which chlorophyll molecules are located.
- It also has accessory pigments, ETC and ATP synthase
What is grana and how is it adapted to undergo photsynthesis?
Grana: stacks of thylakoid membranes, increasing surface area for light dependent reactions. Its membrane:
- Holds ATP synthase for chemiosmosis
- Allows pigments to be arranged in light harvesting clusters (in funnel like structures) for efficient light absorption.
What is Stroma?
Stroma: contains enzymes for Calvin cycle (light independent reactions), 70S ribosomes, circular DNA, lipid droplets, starch grains
What are the adaptions of palisade tissue?
- Contain large numbers of chloroplasts
- Large vacuole helps in pushing chloroplast to edge of cell for max light absorption and short diffusion pathway
- Chloroplasts can move towards light and away from intense light to avoid damage
- Elongated & arranged to intercept maximum light
- Closely packed to absorb maximum light
- Large surface area for diffusion of gases
- Moist cell surfaces for diffusion of gases
- Thin cell walls for maximum light penetration and diffusion of gases
How are enzymes in photosynthesis equipped for there job?
The enzymes involved in photosynthesis have a higher optimum temperature, so are not damaged by the high temperatures.
Where does the light dependant stage take place?
Takes place in the thylakoid membranes
What are photosystems?
- Photosystems are required to trap wavelengths of light (photons) to energize the electron found in the primary pigment (chlorophyll α)
- Photosystem I absorbs wavelengths of 700nm
- Photosystem II absorbs wavelengths of 680nm
What is photoactivation?
Photoactivation is the excitation of an e- to a higher energy level, causing it to escape a chlorophyll molecule
What are accessory pigments?
Accessory pigments are arranged in light harvesting clusters that pass on absorbed energy to the primary pigment at reaction centre
What is involved in the light dependent stage of photosynthesis?
- thylakoid membranes
- Photosystems
- Photoactivation
- Accessory pigments
What is the stages of the light-dependent reaction of photosynthesis?
- Light energy excites electrons at the reaction centres of the photosystems (in the chlorophyll molecule in the thylakoid membrane), causing them to pass to an electron acceptor at the start of the electron transport chain. This is called photoionisation.
- Electrons are released from photosystem II (PSII) and they pass down the chain from one electron carrier to the next in a series of redox reactions. ATP
is produced via chemiosmosis. The electrons then leave PSII and enter photosystem I. Again they go down the electron transport chain and ATP is
produced again. This process again generates ATP from ADP and inorganic phosphate. - Light splits water into protons (H+ ions), electrons and oxygen (waste). The electrons are used to replace the electrons that leave photosystem II. This process is called photolysis of water. The protons are pumped across the membrane using the ATP created in step 2 in a process called chemiosmosis. This creates a chemical potential gradient.
- Reduced NADP is generated as the electrons in the electron transport chain are transferred to NADP along with a proton.
- Protons return to the stroma through ATP synthase via facilitated diffusion which produces ATP. Approximately 4 protons make one ATP molecule. Both ATP and reduced NADP are used in the light-independent stage of photosynthesis.
What is cyclic photophosphorylation?
- Only involves Photosystem I
- E- is photoactivated and is accepted by e- acceptor rather than falling back into the photosystem and giving out thermal energy
- It is then passed on via a chain of electron carriers, during which, enough energy is released to synthesize ATP by chemiosmosis
- ATP is then passed on to light independent reactions
- Electron then returns to Photosystem I
What are the stages of non-cyclic photophosphorylation?
- Accessory pigments in PSII absorb photons of light. The energy is passed onto primary pigment, exciting primary pigments e- to a higher energy level and causing them to escape the photosystem.
- Photolysis: photosystem II contains a water splitting enzyme that catalyses the lysis of water in the presence of light:
- Oxygen diffuses out of the chloroplast and into the air
- The protons build up in the thylakoid lumen causing a gradient to be formed
- The electrons in water replace the electrons that have left the primary pigment - The energized electrons are taken up by electron acceptors, and are passed down the ETC, which generates energy to pump protons from stroma to lumen. e- then travel to PS I, where more light is absorbed by the chlorophyll molecules and the e- are reenergised. H+NADP→NADPH
- The combination of the water splitting and the proton pumping caused protons to build up inside the thylakoid lumen, generating a proton gradient across the thylakoid membrane. ATP is therefore photophosphorylated using the ATP synthase enzyme in exactly the same way as respiration.
What is the difference between cyclic and non-cyclic photophosphorylation?
Cyclic
- Only photosystem I involved
- e- emitted returns to same photosystem
Non-cyclic
- Both photosystems involved
- e- emitted from PSII is absorbed by PSI
- Reduced NADP produced
- Photolysis of H2O, O2 by product
What is the light independent stage?
Light-independent reaction, also known as the Calvin cycle, is the final stage of photosynthesis which uses ATP and reduced NADP from the light dependent stage to produce glucose. These set of reactions take place in the stroma.
How dose the light independent reaction occur?
1) RuBP is combined with carbon dioxide in a reaction called carbon fixation, catalysed by the enzyme RUBISCO.
2) RuBP is converted into two glycerate 3-phosphate (GP) molecules
3) Reduced NADP and ATP are used to reduce each GP molecule to triose phosphate. In this process, the reduced NADP becomes oxidised.
4) Some of triose phosphate molecules are used to make glucose (every 6 cycles) which is then converted to essential organic compounds such as polysaccharides, lipids, amino acids and nucleic acids.
5) Remaining triose phosphate molecules are used to regenerate RuBP with the help of ATP
What is the Calvin cycle?
- 6C→2 X G3P (3C)
- G3P is reduced and activated to form triose phosphate (TP or PGA). The ATP and NADPH from the light-dependent reactions is used in this step. The ADP and NADP return to the thylakoid membrane for recycling
- Most of the triose phosphate regenerates the RuBP using ATP
- Some of the triose phosphate molecules condense to hexose phosphates, to in turn form glucose, cellulose, sucrose and starch.
- Others converted to amino acids, lipids, or acetyl coenzyme A (CoA)
What is a limiting factor?
if a process is affected by more than one factor, the rate will be limited by the factor which is nearest its lowest value
What is the limiting factors of photosynthesis?
- Light intensity
- As light intensity increases, ATP and reduced NADP are produced at a higher rate
- Carbon dioxide concentration
- As concentration increases, more carbon fixation takes place and an increased rate of TP production in the Calvin cycle
- Temperature
- The rate of enzyme-controlled reactions will also increase however when temperature goes above optimum the enzymes will denature, thus the rate is
slowed
- The rate of enzyme-controlled reactions will also increase however when temperature goes above optimum the enzymes will denature, thus the rate is
What is a glasshouse?
- A better understanding of the environmental factors on rate of photosynthesis allows us to manage the growth of plants in protected fields increasing yield of crop.
- Sensors monitor light intensity, humidity and concentration of CO2 and control optimum conditions
- Plants are grown hydroponically- in nutrient soil solution where its contents vary depending on the plants stage of growth
- Pests and fungal diseases are fewer, further improving yield
What are the adaptations of C4 plant?
- Higher optimum temperature than C3 plants (45 oC)
- Mesophyll cells tightly packed so not allowing O2 to reach bundle sheath cells
- Avoids photorespiration
- Dimorphic nature of chloroplasts
How dose the Calvin cycle occur in C4 plants?
- In C4 plants the Calvin cycle occurs in the bundle sheath
- Carbon dioxide is absorbed by mesophyll cells that contain the enzyme PEP carboxylase which catalyses the combination of CO2 with PEP (3C)
- Oxaloacetate (4C) is formed and is converted into malate (4C)
- It is then passed onto the bundle sheath cells and CO2 is removed forming pyruvate (3C)
- The CO2 continues normally like in the Calvin cycle
What are C3 plants?
C3 plants forms a 3C molecule after splitting the 6C compound during the light independent stage of photosynthesis
What are examples of C4 plants?
C4 plants such as maize, sorghum and other tropical grasses
What is photorespiration?
Photorespiration is the reaction when RuBP combines with oxygen instead of CO2 so Calvin cycle cannot occur.
This usually happens in high temperatures (as stomata close to prevent water loss, causing O2 build up) and high light intensity.
How do you separate photosynthetic pigments?
- This can be done by extracting the pigments from a leaf and then carrying out chromatography.
How do calculate Rf value?
Rf value = distance moved by solute / distance moved by solvent
What are photosynthetic pigments involved in?
Photosynthetic pigments are involved in absorbing light required for photosynthesis and subsequently convert it to chemical energy. The colour of pigments is determined by the light they reflect.
What is absorption spectrum?
Absorption spectrum: is a graph that shows the absorbance at different wavelengths of light
- A low absorption means that those wavelengths are not absorbed, but instead are reflected or transmitted therefore plants seem to be green as it is absorbed least
- Carotenoids mainly absorb in the blue-violet region.
What is an action spectrum?
Action spectrum: graph shows the rate of photosynthesis at different wavelengths of light
- Lowest absorbance corresponds to lowest rate of photosynthesis as slower light dependent reactions.
- Note that rate is higher at lower wavelengths, this is not only due to greater absorption but also as lower wavelengths contains more energy
How do carry out chromatography?
- Grind leaf using a mortar and pestle with solvent such as propanone
- Leaf extract contains mixture of pigments
- Allow the sample to evaporate to concentrate the pigment
- Draw a pencil line and place extract on it using a capillary tube
- Place paper vertically in jar of different solvent
- Solvent rises up paper with each pigment traveling at different speeds hence pigments separated
- Distance moved by each pigment is unique
- Repeat with a different solvent, placing the chromatogram 90° to the original alignment
What are two groups of pigments?
- Chlorophylls (Primary Pigments)
- Carotenoids (Accessory Pigments)
Define homeostasis
Homeostasis is maintaining a relatively constant environment for the cells within the body, despite changes in external environment
What is homeostasis controlled by?
Controlled by the composition of blood, and hence the tissue fluid
What is homeostasis?
Homeostasis serves to ensure that a constant internal environment consisting of factors
such as temperature, water potential, pH and blood glucose level is maintained, despite
changes in the external environment of the organism.
How does the features of tissue fluid influence cell activity?
- Temperature - low temp, slow metabolic reactions. High temp however denatures enzymes and proteins
- Water potential - low water potential causes water to enter a cell and burst. High water potential causes water to leave and cell to shrink.
- Water potential is the ability of water to move freely so if it is high water will leave not enter.
- Concentration of glucose if too low, no energy for cell to respire, if too high would affect osmotic balance and disturb cells
What are the two systems homeostasis uses?
This is done through two coordination systems:
- Nervous system, electrical impulse along neurons
- Endocrine system, in the form of chemical messengers (Hormones) that travel in the blood
Define stimuli
A stimuli is a change in physiological factors, such as temperature, pH of blood, water potential etc
What are the stages involved in homeostasis control?
- Involves receptor that detects stimuli
- Receptor sends information to the central control in the brain or the spinal cord
- The input is processed and instructions are sent to the effector
- Effectors such as muscles and glands cause the factor to return to its ideal value or set point
What is negative feedback in homeostasis?
- Negative feedback keeps factors within narrow limits, making it close to set point as possible
- When a factor is increased, an effector is stimulated that makes the factor decrease, and vice versa
What is positive feedback in homeostasis?
- Is not used in keeping conditions constant as it increases effect when stimulus is increased
-This is useful in other areas such as transmission of nerve impulses where the factor must be increased
What is deamination?
- Deamination is the removal of an amino group (NH2) from a molecule. This is done in the liver when there is an excess of protein, rather than wasting a useful energy source.
- The –NH2 and a hydrogen atom are removed leaving behind a keto acid
What is the functions of the liver?
The liver is responsible for the breakdown of excess of amino acids coming from the digestion of protein.
Why must excess amino acid be excreted?
The reason why the excess amino acids need to be excreted is because nitrogenous substances are damaging to the body therefore if they are not used up, they must be excreted.
How urea formed?
- Since ammonia is very soluble and highly toxic compound it is converted immediately to urea
2NH3 + CO2 CO(NH2)2+ H2O - Urea is the main nitrogenous excretory product, however we also produce creatinine and uric acid
- Creatine is made in the liver from amino acids that is used as an energy store in muscles
- Uric acid is made from the breakdown of purines
What are the function of the kidney?
- Blood enters the kidney through the renal artery and subsequently passes through the capillaries in the cortex of the kidneys.
- Blood enters the glomerulus through the afferent arteriole and exits through the efferent arteriole. The efferent arteriole is narrower, thus a high pressure is created. This pushes smaller molecules (glucose, urea, water and sodium) into the
Bowman’s capsule from the blood. This process is known as ultrafiltration. - Selective reabsorption occurs in the proximal convoluted tubule. Here, useful substances such as amino acids, glucose, vitamins are reabsorbed back through the tubules in the medulla. Sodium ions and glucose are cotransported back into the
blood through a sodium-potassium pump. Water moves down a water potential gradient into the blood. - The substances to be excreted pass along the tubules and ureter and finally reach the bladder where they’re disposed of as urine.
- The filtered blood passes out of the kidneys through the renal vein.
What is the structure of the kidney in the cortex?
- Bowman’s capsule
- Proximal convoluted tubule
- Distal convoluted tubule
What is the structure of the kidney in the medulla?
- Collecting duct
- Loop of Henle
What is ultrafication?
Involves filtering small molecules out of the glomerulus and into the Bowman’s capsule due to hydrostatic pressure build up
How does ultrafunction happen?
- Hydrostatic pressure builds up in the glomerulus due to the wider afferent and narrower efferent arterioles
- This causes the hydrostatic blood pressure in the glomerulus to rise above that of the Bowman’s capsule.
- Water from blood therefore goes down its water potential gradient through the endothelium of the capillary walls, the basement membrane and podocytes, thus filtering substances.
What are features of a bowman’s capsule?
- Endothelium: one cell thick cell with many holes
- Basement Membrane: makes up inner lining of bowman’s capsule and acts as filter for large molecules eg large Mr proteins, WBC and RBC
-Podocytes: inner lining of bowman’s capsule with large holes
What are the adaptions of cuboidal epithelial cells in the Proximal Convoluted Tubule?
- Microvilli to increase surface area for many co-transporters for maximum reabsorption
- Tight junction between cells so that fluid can’t pass between them
- Many mitochondria to provide ATP for (Na+–K+) pump on basal membrane
- Folded basal membrane providing large surface area for (Na+–K+) pump
- Removal of Na+ from the cell: Na+–K+ pumps in the basal membrane use ATP pumping 3 Na+ out and 2K+ in, lowering its concentration inside the cell
- Passive movement of Na+/glucose/amino acid inside the cell
- Na+ goes down its concentration gradient via a cotransporter that brings along glucose/amino acids.
- This a secondary active transport as ATP was not used for pumping
- Na+ into the PCT cell but has occurred as a result of actively transporting Na+ out of the cell
- Glucose and amino acids diffuse down their gradient from cell into blood via transport proteins in the basal membrane - Reabsorption of water:
- Removal of ions from the tubule increases its water potential, and increases the solute potential of the cell
- Thus, water diffuses down its gradient into the cell, and is reabsorbed in the blood via osmosis - Reabsorption of urea: urea is a small molecule and passively gets reabsorbed
What are the steps of reabsorption in the loop of henle?
- Na+ & Cl- are actively transported out of higher end of ascending limb into the tissue fluid
- This increases concentration of ions in tissue fluid
- Water is therefore lost from the descending limb
- Loss of water concentrates Na+ and Cl− along the descending limb.
- This concentrates the fluid inside the loop, so ions passively move down their concentration gradient, into the tissue fluid
What is the distal convoluted tubule (DCT)?
- First part functions the same way as ascending limb
- Second part functions the same way as collecting duct
What happens in the reabsorption of water in DCT and Collecting duct?
- Fluid in ascending limb is dilute due to loss of ions and urea, concentrating tissue fluid in medulla
- When fluid enters collecting duct from DCT, it returns to the concentrated medulla region, thus water moves out by osmosis into the tissue fluid and is reabsorbed, concentrating urine
What is osmoregulation?
Involves the control of water potential in body fluid
What monitors water potential in the blood?
Osmoreceptors in the hypothalamus constantly monitor water potential in the blood
What happens when the water levels in the blood decreases?
- Osmoreceptors detect and send impulses to the posterior pituitary gland to secrete antidiuretic hormone (ADH)
- ADH in the blood binds to receptors on the cells of collecting duct, activating intracellular enzymes
- Vesicles that contain aquaporin in the cell are stimulated to fuse to membrane
- This causes duct to become permeable to water hence water moves out, down its concentration gradient
- Volume of urine decreases and becomes more concentration
What happens when the water levels in the blood increases?
- Osmoreceptors no longer stimulate ADH production, so aquaporins moved back into cytoplasm as vesicles, making cells impermeable to water again
- This process is very slow because ADH molecules take 15-20 mins to be broken down in the blood and another 15-20 mins for aquaporins to be removed from the membrane
What happens when the blood glucose concentration is too high?
- The rise in glucose concentration is detected by the beta cells in the pancreas
- Insulin, a hormone, is secreted by beta cells, inhibiting the action of alpha cells
- Insulin travels to target cells known as hepatocytes in the liver, fat and muscle cells
- Binding of insulin to the receptors on the plasma membrane of these cells causes adenyl cyclase to convert ATP into cyclic AMP (cAMP)
- cAMP acts as a secondary messenger and activates certain enzyme controlled reactions in the cells to stimulate the opening of glucose channels in the surface membrane, thus causing more glucose to enter the cell, which is then converted to glycogen or fats (stored in the muscle) and subsequently used for respiration
What happens when the blood glucose concentration is too high?
- The rise in glucose concentration is detected by the beta cells in the pancreas
- Insulin, a hormone, is secreted by beta cells, inhibiting the action of alpha cells
- Insulin travels to target cells known as hepatocytes in the liver, fat and muscle cells
- Binding of insulin to the receptors on the plasma membrane of these cells causes adenyl cyclase to convert ATP into cyclic AMP (cAMP)
- cAMP acts as a secondary messenger and activates certain enzyme controlled reactions in the cells to stimulate the opening of glucose channels in the surface membrane, thus causing more glucose to enter the cell, which is then converted to glycogen or fats (stored in the muscle) and subsequently used for respiration
What happens when blood glucose concentration is too low?
- Alpha cells detect change and secrete a hormone called glucagon
- Glucagon secretion inhibits beta cell action
- Glucagon binds to the receptors on the cell surface membrane which causes a conformational change
- This activates G-proteins which activates adenylyl cyclase enzymes
- cAMP (a secondary messenger) formation is initiated
- This activates protein kinases which then leads to initiation of a cascade of enzymes
- The final enzyme that is activated is
How is the homeostatic control of glucose carried out?
The homeostatic control is carried out in the pancreas by a tissue called the islets of Langerhans which consisting two types of cells:
- α cells which secrete glucagon
- β cells which secrete insulin
When blood glucose levels rise, what do α and β cells?
The α and β cells detect the change α responds by stopping secretion of glucagon β responds by secreting insulin into the blood
What happens when blood glucose concentration is low or high?
- When glucose is in low concentration our cells may not have enough glucose for respiration, hence might not be able to carry out its normal function
- On the contrary, high concentrations can effect normal behaviour of cells as they may lose water due to the concentration gradient built (cells become flaccid)
What is insulin?
Insulin is a signalling molecule that targets the liver and muscle cells and binds to a receptor
What does insulin do?
This stimulates the cells to increase rate of glucose absorption by making vesicles carrying glucose transporter proteins (GLUT) to bind onto cell membrane
What is glycogenesis?
Glycogenesis is the condensing of glucose molecules to glycogen which can later be converted to glucose in respiration.
What do α and β cells do when glucose levels fall or adrenaline levels rise?
- α responds by secreting glucagon into the blood
- β responds by stopping secretion of insulin
What is Gluconeogenesis?
Gluconeogenesis is a new glucose made from amino acid and lipid
What is the optimum blood glucose concentration?
It is important to keep the blood glucose concentration in the correct range of about 90mg per 100cm3.
What is Type 1 diabetes?
Its insulin dependent diabetes, where the pancreas is incapable of secreting enough insulin due to
Why does type 1 diabetes happen and what is the treatment?
- Lack of gene that codes for insulin
- Autoimmune disease
Treatment : insulin injections and mini pumps, controlled diet
What is type 2 diabetes?
Non-insulin dependent diabetes is when the pancreas secretes insulin but liver and muscle cells do not respond properly.
What is the consequence of type 2 diabetes?
- Hunger and thirst are a consequence as kidney cannot reabsorb glucose, which passes in urine along with extra water and salts
- Instead cells metabolise fats and proteins instead which leads to build up of keto acid which is toxic.
- Blood glucose levels may fall as there was no glycogen stored when glucose was in the blood.
What can urine tests give early indications of and how?
- Diabetes: presence of excessive glucose and ketones in urine, as blood glucose level rises above renal threshold and so not all reabsorbed
- High blood pressure/kidney infection: presence of proteins as they are too large to be filtered out
Why is urine analysis used?
- Much easier to collect than blood samples
- Urine tests can give early indications of health problems
What are dipsticks used for and what do they contain?
- Urine analysis to measure: pH, glucose, ketones and proteins
- Glucose dipsticks contain glucose oxidase and peroxidase
What is a positive dipstick tests?
Positive test: glucose oxidase oxidises glucose to form gluconolactone and hydrogen peroxide
- Peroxidase catalyses reaction of hydrogen peroxide and chromogen (colourless chemical) forming a brown compound
- The colour formed is compared to a chart, the more glucose present, the darker the colour (semi- quantitative)
What are biosensors used for?
Allow people with diabetes to monitor their blood glucose concentration much quicker than dipsticks
What are the features of biosensors?
- They also contain glucose oxidase which catalyses the same reaction
- However, a current is generated, detected and amplified which gives a reading within seconds (quantitative)
- The more the glucose present the greater the reading
When does stromata open?
- Increase in light intensity
- Low CO2 concentrations
When does stomata close?
- Darkness
- High CO2 concentrations
- Low humidity
- High temperature
- Water stress
What happens during the homeostasis of plants?
- Stomata has daily rhythms of opening and closing even if kept in constant light/dark
- Opening during day maintains inward diffusion of CO2 and outward diffusion of O2 and water vapour
- Closing during the night as it does not respire and conserves water
What is abscisic acid?
A stress hormone that causes the closure of stomata in difficult conditions
What are the stages abscisic acid goes through to close the stomata?
- ABA binds to receptors that inhibit proton pumps and stimulate movement of Ca2+ ions into the cell.
- Ca2+ acts as a second messenger, activating channel proteins to allow negatively charged ions to move out
- This causes potassium ions to move out and also closes K+ channels so that they can’t enter
- Water potential increases inside the cells, which diffuses down its water potential gradient by osmosis.
- The cell becomes flaccid and stomata closes
What causes the stomata to close?
Stomata closes when hydrogen ion pumps stop and potassium ions leave the guard cells. Water then leaves the cells, causing it to become flaccid and closing the stomata
What are the stages that causes the stomata to open?
- ATP proton pumps actively move H+ ions out of the guard cells
- This causes potassium channels to open & move into the cell due to the electrochemical gradient produced
- Electrochemical gradient is the combination of an electrical gradient caused by the release of H+ ions (making inside more negative) and a concentration gradient due to low levels of K+ inside
- Influx of K+ ions inside the cell increases the solute potential and reduces water potential, thus water enters by osmosis making cells turgid
- The stomata has uneven cell wall thickening; walls adjacent to pore is very thick, whereas the walls furthest from pore is thin
- When cells are turgid, the outer end cells lengthen, causing the guard cells open.
What does the endocrine and nervous system have in common?
- Both involve cell signalling
- Both involve signal molecule binding to receptor
- Both involve chemicals
How is information transferred in the nervous system?
- Form of transmission - Electrical impulses
- Formed at - Sensory neurone generates impulse
- Travel in - Neurones
- Speed - Instantaneous
- Duration - Short-term
- effects - Localised
- receptor location - On cell surface membrane
- Energy - Large amount
How is information transferred in the Endocrine System?
Form of transmission - Chemical messengers (Hormones)
Formed at - Secretory gland
Travel in - Blood (endocrine)
Speed - Slow
Duration - Long lasting
effects - Widespread
receptor location On cell surface membrane Cell surface membrane OR within cell
Energy - Less required
How is information transferred in the Endocrine System?
Form of transmission - Chemical messengers (Hormones)
Formed at - Secretory gland
Travel in - Blood (endocrine)
Speed - Slow
Duration - Long lasting
effects - Widespread
receptor location - Cell surface membrane OR within cell
Energy - Less required
What are the different types of neurones?
There are three types of neurones, sensory, motor and relay with different functions which differ by the position of the cell body within the neurone.
What is a sensory neuron?
- Swelling of spinal cord containing cell body known as ganglion
- Sensory neurones transmit impulses from receptors to the central nervous system.
What is a relay neurone?
- Intermediate Neurone (Relay/Connector): transmit impulse from sensory to motor neurone
- Relay neurones are located within the central nervous system and transmit the electrical impulses from sensory neurones to motor neurones
- Found entirely in CNS
What is a motor neurone?
- Cell body lies within CNS and contains the nucleus
- Dark specks in cytoplasm are rough ER regions
- Motor neurones are involved in transmitting electrical signals from the central nervous system to muscles and glands in the body
What is the structure of neurones?
- The structure of neurones is similar, as they all have a cell body composed of the nucleus as well as organelles such as mitochondria within the cytoplasm.
- Apart from the essential components, they also contain extensions called dendrites involved in conducting impulses towards the cell body, as well as axons which conduct them in the opposite direction, that is away from the cell body
What is a reflex arc?
A reflex arc is the pathway along which impulses are transmitted from receptor to an effector without involving the ‘conscious’ regions of brain
How is reflux action carried out?
- Impulses travel from sensory to relay (not always) and finally to motor neurone
- The effector acts before the brain processes the impulse and produces any voluntary movement.
- Hence, this is a reflex reaction, which is fast, automatic and is useful in response to danger
What is myelin?
- Myelin is made when specialised cells called Schwann Cells which wrap themselves around the axon, enclosing it within many layers
- About a third of axons on motor and sensory neurons are surrounded by myelin sheaths
What are nodes of ranvier?
The uncovered regions between Schwann cells are called Nodes of Ranvier
How does myelination increase the speed of conduction
- Myelination stops depolarisation from occurring, greatly increasing the speed of conduction
- It also prevents the leakage of ions and increases insulation, increasing speed of conduction.
- Myelin also causes saltatory conduction which is when action potentials jump from one node to the next, which is about 50 times faster than unmyelinated axon
- Diameter also affects speed of transmission; with thinner axons, there is greater resistance, hence, transmission is slower
What enables the neurons to carry out action potentials?
The structure of neurones, that is the length of axons as well as the polarised nature of the neurone membrane in the resting state where the outside of the membrane is positively charged and the inside is negatively charged enables the neurones to carry electrical impulses called action potentials.
What are nerve impulses?
Nerve impulses are signals transmitted along the axon, consisting of waves of depolarisation, causing changes in the potential difference across the membrane (action potential)
How is resting potential achieved?
- Plasma membrane being impermeable to Na+ /K+
- Sodium-potassium pumps that actively pump 3 Na+ out and 2K+ in, increasing the concentration of K+ inside, and Na+ outside
- There are more K+ channels than there are Na+, therefore K+ diffuses down its concentration gradient (outside the cell) faster than Na+ diffuses in.
- Many large negatively charged molecules inside cell
What is resting axons electrical potential?
Resting axons have a slightly negative electrical potential inside, producing a potential difference of about -70mV inside compared to the outside
What is the action potential of nerve Impulses?
It is the change in potential difference across the membrane due to changes in permeability of the membrane to Na+/K+ ions
What leads to action potential in the transmission of Nerve Impulses?
- An initial stimulus causes the opening of some voltage-gated channels causing Na+ to rush in, down its electrochemical gradient
- This causes the potential difference across the membrane to become less negative and is called depolarisation.
What happens if the potential difference in the nerve impulses reaches -50mVV?
- If this potential difference reaches -50mVV, then many more channels open, causing inside to become +30mVV
- This wave of depolarisation is an example of positive feedback
What is the all or nothing law in nerve impulses
- For an action potential to be produced, the potential must be raised to a minimum threshold potential of -50mVV. If lower than this, an action potential will not be generated
- This is known as the all-or-nothing law as the neurones either transmit impulse or do not
What happens during the action potentials in nerve impulses after 1ms?
- After 1ms, all Na+ voltage-gated channels close & K+ gated channels open, causing K+ to diffuse out, thus repolarising the membrane.
- The sodium potassium pump continues pumping these ions and maintaining their concentration across the membrane, allowing more action potentials to occur.
- Local circuits are set up, where the permeability of the neighbouring region of the axon is increased
What are the consequences of axons refectory period?
- Action potentials do not merge and so are discrete
- There is a minimum time between action potentials occurring at one place on neurone
- Length of refractory period determines max frequency at which impulses are transmitted
- Hyper polarisation occurs when the cell potential becomes more negative than resting potential as there is an excess outflow of K+
What is a refactory period in axons?
Axons have a refractory period after the action potential, where it is unresponsive to new stimulations.
How do action potentials carry information?
- Action potentials do not change in size whether large or small stimulus & has constant peak value of +30mVV
- The brain receives action potential from specific position of neurones and interprets the nature of the stimulus eg position: retina, nature: light
How do you know the strength of a stimulus?
- The brain interprets this from the frequency of the action potential-stronger stimuli have larger frequency
- Also strong stimuli cause more neurones to be stimulated hence the number of neurones carrying action potential can tell us about the strength
What is a receptor?
A receptor cell responds to stimulus by converting energy from one form to electrical impulse, initiating an action potential (acts as a transducer)
Where are receptor cells found?
- Receptor cells are often found in sense organs and are specialised cells which detect specific type of stimulus
- Some receptors are the ends of sensory neurones, thus there is no synapse between the receptor cells and sensory neurones.
What is the role of synapses?
- Ensures one-way transmission as the receptors are only in post synaptic neurone and vesicles are only in presynaptic neurone
- Decreases the overload of information in the brain as impulses with low frequencies do not reach the brain
- Involved in memory and learning due to the formation of new synapses that links neurones involved
- Interconnection of nerve pathways: sensory and relay have many dendrite increasing surface area for many synapses. This connects neurones from different parts of the body and spreads information throughout.
What are the receptors on the tongue?
The tongue is covered in many papillae, each papilla has many taste buds over its surface and within each taste bud lies around 50-100 chemoreceptors that detect different chemicals, giving different sensations
What is the receptor potential of the tongue?
- Na+ ions diffuse through highly selective channels of microvilli and cause depolarisation of the membrane: receptor potential.
- If receptor potential is below the threshold, it causes a local depolarisation of the receptor cell and doesn’t stimulate the sensory neurone to send impulses.
What leads to action potential in the tongues?
- If sufficient stimulation is produced, voltage-gated Ca2+ channels open; Ca2+ then enters, causing exocytosis of neurotransmitter vesicles
- Neurotransmitters cause action potential in the sensory neurone and eventually reaches the cortex of the brain
What is a synaptic cleft?
Region where two synapses meet, there is a small gap called the synaptic cleft
What is a synapses?
Synapses are junctions between two neurones.
What are the steps of synapses that have acetylcholine (ACh)?
- Action potential stimulates the opening of voltage gated Ca2+ channels at the presynaptic knob, causing an influx of Ca2+ into the cytoplasm
- This causes exocytosis of ACh vesicles, which fuse with the pre synaptic membrane, then diffuse across the synaptic cleft
- ACh has a complementary shape to the chemically gated receptor protein on the post synaptic membrane, and binds to it
- This changes the shape of the protein and opens the channel for the entry of Na+
- Na+ depolarises that part of the membrane; if pd is above threshold, an action potential is generated
- Acetylcholinesterase recycles Ach by breaking it into acetate and choline, preventing the permanent depolarisation of the membrane.
- Choline returns to presynaptic neurone and combines with Acetyl coA to form Ach again.
Define tendons
Tendons – non-elastic tissue which connects muscles to bones
Define ligaments
Ligaments – elastic tissue that joins bones together and determines the amount of movement possible at a joint
Define joints
Joints – the area where two bones are attached for the purpose of permitting body parts to move, they’re made of fibrous connective tissue and cartilage
Define skeletal muscles
Skeletal muscles- muscles attached to bones, they are arranged in antagonistic pairs
What are antagonistic muscle pairs?
Antagonistic muscle pairs- pairs of muscles which pull in opposite directions – as one muscle contracts, the other relaxes. Flexors and extensors are an antagonistic muscle pair such as triceps and biceps. When the triceps relaxes, the biceps contracts to lift the arm
Define neuromuscular junction
Neuromuscular junction - the junction between a motor neurone and a skeletal muscle fibre
What are striated muscles?
- Striated muscle is multinucleate (syncytium) and consists of several tissues eg connective, nerve, striated muscle, blood.
- It is made up of bundles of muscle fibres/cells (fascicles)
- Each muscle fibre is made up of regular arrangement of myofibrils, which produce the striated appearance of muscle fibres
What are the steps of myofibrils contraction?
- An impulse arrives as a neuromuscular junction, Ca2+ is released from the sarcoplasmic reticulum.
- Ca2+ binds to troponin, causing a shape change. Consequently, the tropomyosin moves away from the actin, uncovering binding sites
- Myosin binds to the uncovered actin binding sites, forming an actomyosin cross bridge.
- ADP and inorganic phosphate ions are released, causing the power stroke
- After this, ATP binds, causing myosin to unbind from the actin
- ATP breaks town to ADP and inorganic phosphate to return the myosin to its original
position - Ca2+ ions are reabsorbed, troponin moves back to its original shape and tropomyosin re-covers the binding sites.
What is the structure of mucsle fibres?
- The sarcolemma (cell membrane) splits into many infoldings called T-tubules
- Sacroplasm (cytoplasm) contains many mitochondria that generate ATP for muscle contraction
- The sarcoplasmic reticulum (SR) (endoplasmic reticulum) have many protein pumps that transport Ca2+ into the cisternae of SR
Define actin
Actin: globular protein; two chains of actin overlap to make up thin filament
Define myosin
Myosin: fibrous protein with globular head that makes up thick filament
Define tropomyosin
Tropomyosin: fibrous protein twisted around actin chain
Define troponin
Troponin: protein that is attached to the actin chain at regular intervals
What is the Z line of Myofibrils?
Z line: where actin filaments are attached to
What is M line of Myofibrils?
M line: where myosin filaments are attached to
What is A band of Myofibrils?
A band: includes the darker parts in the centre where actin and myosin overlap
What is H band of Myofibrils?
H band: the grey area within the A band where only myosin is present
What is I band of Myofibrils?
I band: the white area next to the Z line where only actin is present
What is the components of Myofibrils?
- Myosin
- Actin
- Tropomyosin
- Troponin
- Z line
- M line
- A band
- H band
- I band
What myofibrils made of?
Myofibrils are made of contractile units called sacromeres (between two Z discs) which are made of thin and thick protein filaments
