Module 5 Flashcards
1
Q
The Need for Communication Systems
A
Keeping Cells Active • All organisms needs to maintain a limited set of conditions • Need to respond to changes in external and internal environments • This is because cellular activities rely on enzymes which require a specific set of conditions to work effectively • Organs need to coordinate their activity to maintain optimal internal conditions that support survival
2
Q
2 Cell Signalling
A
When cells communicate by signalling, one cell releases a chemical • This chemical is detected by another cell • The second cell then responds to this signal. can be neuronal or hormondal
3
Q
Neuronal System of cell signalling
A
• Network of neurons • Quick signals • Rapid responses
4
Q
Hormonal System of cell signalling
A
• Uses blood to transport signals • Endocrine organs secrete hormones directly into blood • Carried all over the body • Only recognized by specific target cells • Enables long-term responses to be coordinated • Specific target cells have receptors that have a shape that is complementary to the shape of the hormone
5
Q
Homeostasis
A
is the regulation of internal environments independently of external environments These include: • Temperature • Blood glucose concentration • Blood salt concentration • Water content • Blood pressure • Blood carbon dioxide partial pressure (blood pH)
6
Q
Negative Feedback
A
• Reversal of a change in the environment to return to the optimum position • Receptor detects the change • Communication systems inform the effectors • The effector reacts to reverse the change • Eg: maintaining blood pressure
7
Q
Positive Feedback
A
• Response causes change to increase • Destabilizes the system • Usually more harmful • Does not lead to homeostasis • Can be useful in certain situation • Eg: childbirth - uterine contractions • Pathway:
8
Q
○ A stimulus
A
is any change in the environment that causes a response
9
Q
○ A response
A
is a change in behavior or physiology as a result of a change in the environment
10
Q
External Environment
A
○ Environment may change slowly – E.g. — Global Warming ○ It may change quickly ○ The changes must be monitored and the organism must respond to them
11
Q
Internal Environments
A
Some cells are not exposed to the external environment, but are protected by epithelial tissues ○ As cells undergo metabolic reactions there is a change in the environment ○ Activities of the cells alter their own environments in this way
12
Q
Endotherms
A
• Can maintain body temperature within strict limits • Independent of external temperatures • Internal sources of heat used to maintain body temperatures • Can increase respiration rates to generate heat
13
Q
advantages of being an endotherm
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○ Constant body temperature regardless of external environment ○ Activity possible in cooler temperatures ○ Able to inhabit cooler parts of the world
14
Q
disadvantages of being an endotherm
A
• There are also disadvantages: ○ Significant part of energy intake used to maintain body temperature ○ Moor food required ○ Less energy from food can be used for growth
15
Q
Physiological adaptations of endotherms
A
: ○ Sweat glands in skin ○ Hairs on skin ○ Capillaries near skin surface
16
Q
endotherms in Hot environment
A
Sweat glands Secrete sweat - water has high specific heat capacity, therefore heat escapes body and converted into evaporation of sweat
Blood capillaries under surface of skinCapillaries dilate to increase surface area - heat from blood transferred out of the body and through the skin more efficiently
Erector muscles controlling hairs on skin
Relax so hair is flat against skin - air can freely circulate over the skin, cooling it down
17
Q
endotherms in Cold environment
A
Sweat glands Sweat glands inactive
Blood capillaries under surface of skinCapillaries close to reduce heat lost through the skin
Erector muscles controlling hairs on skin Contract so hair stands on end - this serves to trap air over the skin which acts as a layer of insulation
18
Q
Ectotherms
A
• Organism that relies on an external source of heat to regulate its body temperature
19
Q
ectotherm advantages:
A
○ Less food used in respiration ○ Less food required ○ Greater proportion of energy derived from food can be used for growth
20
Q
ectotherm disadvantages:
A
○ Less active in cooler temperatures ○ May not be capable of activity during cold winters
21
Q
Physiological adaptations of ectotherms
A
○ Do not use internal energy source to maintain body temperature ○ When they are active, increased respiration in muscles will generate some heat ○ Temperature regulation relies on increasing the exchange of heat with their environment – When cold, they will change behavior to increase absorption of heat fro its environment – When hot it will increase heat loss to the environment ○ Warm-up by lying on a hot surface
22
Q
Excretion =
A
the removal of metabolic waste products from the body
23
Q
Metabolic waste =
A
Unneeded byproducts produced as a result of normal metabolism. These need to be removed from the body as they can become toxic in large quantities.
24
Q
Carbon Dioxide as a metabolic waste compound
A
• Excess carbon dioxide is toxic • High levels of carbon dioxide have many effects: ○ Reduce the oxygen carrying capacity of the red blood cells ○ Combines with haemoglobin to form carbaminohaemaglobin, which has a lower affinity for oxygen ○ Dissolve the blood plasma, causing respiratory acidosis
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Nitrogenous Compounds as a metabolic waste compound
• The body is unable to store amino acids or proteins • However, it is wasteful to excrete amino acids • Instead, they are transported to the liver and deaminated • The removed amino groups initially forms the very toxic ammonia • This is then converted to the less toxic urea, which is transported to the kidneys for excretion • The remaining keto acid can be directly respired, or converted to a carbohydrate or fat for storage
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Oxygenated Blood in the liver
Oxygenated Blood ○ Travels from the aorta ○ Hepatic artery
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Deoxygenated Blood in the liver
Travels from the digestive system ○ Hepatic portal vein ○ Rich in products of digestion
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how blood exits the liver
blood exits via the hepatic vein
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• Sinusoids
Oxygenated and deoxygenated blood mix ○ Pass into special vessels called sinusoids ○ Join together to form the hepatic vein ○ Blood flowing along the sinusoids come into very close contact with the liver cells
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Liver Cells
• Called hepatocytes • Cuboidal shape • Microvilli • Many metabolic functions
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Kupffer Cells
Specialised macrophages • Move in sinusoids • Break down and recycle old red blood cells • Haemoglobin is broken down into bilirubin ○ This is the brown pigment in faeces
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Deamination
• Amino acids broken down into keto acids and ammonia • Ammonia is highly toxic
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Ornithine Cycle
• Ammonia must be converted into a less toxic form • Ammonia is combined with carbon dioxide to produce urea • Urea is less soluble and less toxic • Urea is filtered out of the blood in the kidneys and concentrated in the urine
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detoxification.
The process in which the liver metabolises toxic substances to render them harmless is called
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• Bowman’s Capsule
○ Ultrafiltration unit ○ Filters blood ○ Separates large particles from small particles
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• Proximal Convoluted Tubule (PCT)
○ Involved in selective reabsorption ○ Re-absorbs valuable substances, such as glucose ○ In the PCT fluid composition is altered by reabsorption of all sugars, most salts and water ○ 85% of water is reabsorbed here
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Loop of Henle
○ Creates low water potential in the medulla ○ Allows water to be reabsorbed
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Distal Convoluted Tubule (DCT)
○ Involved in osmoregulation ○ Varies the amount of water reabsorbed into the blood ○ In the descending limb the water potential is decreased – Salts added – Water removed
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• Glomerulus
○ Site of filtration ○ Tight, knot-like, high pressure capillary bed
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Afferent arteriole
○ Brings blood from the renal artery
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Efferent arteriole
○ Narrow vessel that restricts blood flow ○ Raises blood pressure
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Peri-tubular capillaries
○ Low pressure capillary bed ○ Runs around the convoluted tubules ○ Absorbs fluid from them
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Vasa Recta
○ Un-branched capillaries ○ Similar in shape to the Loop of Henle ○ Descending limb carries blood deep into the medulla ○ Ascending limb brings blood back to the cortex
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Venule
○ Carry blood to the renal vein ○ Blood carried to the heart
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• Ascending Limb
○ In the ascending limb water potential is increased ○ Salts are removed by active transport
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• Collecting Duct
In the collecting duct water potential is decreased again – Water is removed
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Ultrafiltration
is the process by which substances in the blood enter the Bowman’s capsule from the glomerulus:
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how does the structure of the afferent and efferent arterioles ensure blood remains under high pressure
Blood flows into glomerulus from the afferent arteriole • This is wider than the efferent arteriole • Difference in diameter ensures the blood remains under high pressure
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The barrier between the Bowman’s capsule and the capillary has three layers,,,,
○ Endothelium of capillary – Narrow gaps between cells – Blood plasma and dissolved substances can pass through ○ Basement membrane – Fine mesh of collagen fibres and glycoproteins – Acts as a filter to prevent the passage of molecules with a RMM of over 69,000 – Most proteins are held in the capillaries of the glomerulus ○ Epithelial cells of the Bowman’s capsule – Podocytes – Specialized shape Finger like projections called major processes Ensure gaps between cells Fluid from blood can pass into the lumen of the Bowman’s capsule • High pressure forces some water and solutes through the basement membrane and into the Bowman’s capsule • This liquid is now known as the ‘glomerular filtrate’
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What is left in the capillary? after ultrafiltration?
• Proteins • Blood cells • Molecules bigger than 69,000 RMM will remain in the blood
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Selective reabsorption
As fluid moves along the nephron, substances are removed • Sodium-Potassium pumps move sodium ions from the cells lining the PCT into the tissue fluid • This reduced the concentration of sodium ions in the cytoplasm
• Sodium ions are transported into the cell, along with glucose or amino acids, by facilitated diffusion • As the glucose and amino acid concentrations rise indies the cell, these substances diffuse out of the opposite side of the cell into the tissue fluid • Process may be enhanced by the active removal of glucose and amino acids • Tissue fluids substances diffuse into the blood and are carried away • Reabsorption of salts, glucose and amino acids reduced the water potential in cells and increases it in the tubule fluid • Water will enter cells • Larger proteins can be absorbed by endocytosis
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Adaptions of the PCT
• Microvilli increase surface area • Membrane contains co-transporter proteins that transport glucose and amino acids with sodium ions in facilitated diffusion • Many mitochondria
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Reabsorption of Water in The Loop of Henle
• Salts can be transferred from the descending limb to the ascending limb • Increases concentration of salts in the tubule fluid • Salts diffuse out into the surrounding medulla tissue • Medulla tissue has a very low water potential • Amount of water reabsorbed controls water potential of blood
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Process of water reabsorption
• As the fluid moves down, the water potential falls ○ Water is lost to surrounding tissue fluid ○ Sodium and chloride ions diffuse into the tubule • As the fluid moves up the ascending limb, the water potential rises ○ At the base, sodium and chloride ions diffuse out ○ Sodium and chloride ions are actively transported out ○ Wall of the ascending limb is impermeable to water ○ Fluid loses salt, but not water, when moving up the ascending limb
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Hairpin counter current multiplier
Close arrangement of the ascending and descending limb • Increases the efficiency of salt transfer from the ascending to descending limb • Salt concentrations build up in the surrounding tissue • Movement of salts into the medulla creates a low water potential • Removal of ions from the ascending limb means at the top, urine is dilute • Water is then reabsorbed, according to the needs of the body
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The Collecting Duct
Fluid flowing in contains lots of water • Carries fluid back down the collecting duct to the pelvis
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The Control of Blood’s Water Potential
| • Drop in Water in the Blood
Brain releases antidiuretic hormone (ADH) • ADH travels from the loop of Henle
22snaprevise.co.uk
• Cell have membrane bound receptors for ADH • ADH binds to receptors • Chain of enzyme controlled reactions occurs inside the cell • Aquaporins sent in vesicles to the cell surface membrane • Aquaporins inserted into cell surface membrane • Walls of collecting duct and DCT more permeable to water • More water moves into the medulla by osmosis • Water potential of the blood rises back to the set level • Brain stops releasing ADH
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Causes of kidney failure
• Diabetes mellitus • Heart disease • Hypertension • Infection
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Assessing kidney function/failure:
Estimate glomerular filtrate rate (GFR) • Achieved by measuring concentration of substances in urine • Presence of proteins indicates failure of the filtration of blood as they are normally too large to enter the Bowman’s capsule
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Treatment 1: Renal Transplants
• Old kidneys usually left in place • Donor can be live or deceased • Kidney surgically attached to blood supply and bladder • Patient must take immunosuppressant drugs to prevent rejection
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Treatment 2: Dialysis
• Waste removed from blood by passing it over a dialysis membrane • Partially permeable membrane allows the exchange of substances between blood and dialysis fluid • Any excess substances diffuse out of the blood and into the dialysis fluid
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Treatment 3: Haemodialysis
• Blood from an artery is passed into a machine and dialyzed • Heparin added to avoid clotting • Performed at a clinic • Three times a week
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Treatment 4: Peritoneal Dialysis
Uses filter in the abdominal membrane • Permanent tube implanted in the abdomen • Dialysis solution fills space between organs and membrane • Solution drained after several hours • Patient able to walk around • Can be carried out at home
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Gas Chromatography and Mass Spectrometry
Sample vaporized in the presence of a gaseous solvent • Passed down a long tube lined by an absorption agent • Each substance dissolved differently in the gas • Remains there for a unique and specific length of time • Eventually substance moves out of the gas and is absorbed into the lining • This is then analysed to create a chromatogram • Chromatograms of standard drugs and urine samples are taken, allowing unidentified substances to be easily identified
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Pregnancy test
• Once implanted, human embryos secrete a hormone called hCG • This is a small glycoprotein • Pregnancy tests contain monoclonal antibodies which bind to the hCG • Any hCG in the urine will attach to antibodies tagged with a blue bead • The hCG-antibody complex then moves up to the surface of the strip where it sticks to a band of immobilised antibodies • All the hCG bound antibodies are held in one place, forming a blue line • There is always a control blue line to use as a comparison • 2 blue lines indicate pregnancy
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Testing for anabolic steroids
• Anabolic steroids increase protein synthesis • Results in build-up of cell tissue • Can give an advantage in sports, but have dangerous side effects • Anabolic steroids have a half-life of 16 hours • Remain in the blood for many days • Small molecules • Can enter the nephron easily
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Sensory receptors
are specialised tissues in the body that detect changes in the environment. They work by converting energy — acting as transducers — from one form into electrical energy, which relays a signal to another part of the body.
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Pacinian corpuscles
• Pressure sensor in skin • Consists of concentric rings surrounding a nerve ending • Pressure causes the rings to apply pressure on the sensory nerve fibre • Nerve fibre detects change in pressure - not constantly applied pressure
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Stimulus Sensory receptor Energy change Ultimate response
| Stimulus Sensory receptor Energy change Ultimate response
Change in light intensity
Rods and cones in retina of eye
Light to electrical Increased light intensity = iris constriction
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Stimulus Sensory receptor Energy change Ultimate response
| Change in temperature
Change in temperature Heat receptors in skin and hypothalamus
Thermal to electrical Capillaries change diameter, erector muscles contract/relax, etc
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Stimulus Sensory receptor Energy change Ultimate response
| Chemicals in food
Chemicals in food Chemical receptors on tongue
| Chemical to electrical Pleasure centres in brain activated
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Stimulus Sensory receptor Energy change Ultimate response
| Change in sound
Change in sound Vibration receptors in ear cochlea
Kinetic (sound wave) to electrical
Sound heard
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Sensory neurons
• Carry AP from sensory receptor to CNS • Long dendron • Short axon
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Relay neurons
• Connect sensory and motor neurons • Many short dendrites • Short axon
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Motor neurons
* Carry AP from CNS to effectors (muscles, glands)
| * Cell body is within CNS • Long axon
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Myelinated and non-myelinated neurones
• 1/3 of neurons are myelinated • Schwann cells create the myelin sheath ○ Several layers of membrane ○ Thin cytoplasm • Gaps in the sheath are called the nodes of Ranvier • Peripheral neurons in the CNS are non-myelinated ○ Still associated with Schwann cells ○ Several neurons wrapped in one loose Schwann cell ○ Action potential moves along in a wave
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Advantages of Myelination
• Myelinated neurons can transmit action potential more quickly than non-myelinated neurons ○ 100-120 m/s • Non-myelinated neurons tend to be slower ○ 2-20 m/s • Myelinated neurons carry signals from sensory receptors, to the CNS and from CNS to effectors • Carry signals over long distances • Enables rapid response to a stimulus by saltatory conduction
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Generation of nerve impulses
• At rest neurones have higher concentration of sodium outside the cell ○ Steep concentration gradient across cell membrane ○ Cell charge is -60mV compared to extracellular environment • Sodium can move into the cell by gated channels ○ Causing cell to depolarise — become electrically charged • Gated channels stimulated to open by action of synapse • A few channels open — a few sodium ions move into the cell • The membrane depolarises ○ Becomes less negatively charged compared to the extracellular environment • If the threshold potential is reached (enough sodium ions enter the cell to surpass threshold), this initiates a positive feedback loop ○ Threshold is -50mV • More sodium channels open • Cell becomes more depolarised• Action potential has been established ○ Charge is now +40mV
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Transmission of nerve impulses along a neuron
• Once the electrical impulse has been established, a local current exists in the cytoplasm of the neuron • This local depolarisation triggers neighbouring voltage-gated channels to open • Action potential travels in one direction along the cell
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Refractory period
• Almost immediately after the cell becomes depolarised, it begins to repolarise • When sodium channels open, potassium ion channels open as well • Potassium diffuses down the concentration gradient out of the cell • This outflux of positively charged ions makes the cell’s charge become more negative • Eventually the potential difference (difference in charge across the cell membrane) overshoots ○ This is called hyperpolarisation • The original, resting potential (-60mV) is restored • Regions of the neuron that are in the refractory period cannot become re-charged • This ensures the action potential moves in a single direction
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synapse
A synapse is a junction between two neurons. The space between the neurons is called the synaptic cleft and is about 20nm wide. An action potential travels from one neuron to the next via the synapse via substances called neurotransmitters such as acetylcholine (ACh).
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Cholinergic Synapse
• Presynaptic action potential causes release of a transmitter substance ○ Presynaptic = the first neuron with the action potential ○ Postsynaptic = the neuron receiving the action potential ○ Diffuses across the gap ○ Generates a new action potential in postsynaptic neuron • Synapses that use acetylcholine as the neurotransmitter are called cholinergic substances
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Synaptic Knob •
Region at the end of the axon which is slightly bulged and stores neurotransmitter • Contains many mitochondria ○ Active process ○ Lots of ATP required • Large amount of SER • Vesicles of acetylcholine ○ Transmitter substance ○ Chemical ○ Diffuses across the synaptic cleft • Voltage gated calcium ion channels in the membrane
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Postsynaptic Membrane
Contains specialized sodium channels that can respond to the transmitter substance ○ 5 polypeptide molecules ○ 2 have a receptor that is specific to acetylcholine • When acetylcholine binds, the sodium channels will open
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Transmission Across the Synapse
• Action potential arrives at synaptic knob • Voltage-gated ion channels open • Calcium ions diffuse into the synaptic knob • Calcium ions cause the synaptic vesicles to move to and fuse with the presynaptic membrane • Acetylcholine released by exocytosis • Acetylcholine diffuses across cleft • Acetylcholine binds to the receptor sites on the sodium ion channels in the postsynaptic membrane • Sodium channels open • Sodium ions diffuse across post synaptic membrane into postsynaptic neurone • Excitatory postsynaptic potential (EPSP) is created • EPSPs can combine, reaching the threshold potential • New action potential created in the postsynaptic neurone
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Acetylcholine esterase
• Enzyme in the synaptic cleft • Hydrolyses acetylcholine to ethanoic acid and choline • Stops transmission of signals • Ethanoic acid and choline are recycled • Re-enter synaptic knob by diffusion • Recombined to acetylcholine using ATP from respiration in the mitochondria • Stored in synaptic vessels for future use
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Action Potentials and Cell Signalling
• All or nothing response • Does not vary in size or intensity • Process are the same in all neurons and cholinergic synapses
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Role of Synapses
• Several presynaptic neurons converge to one postsynaptic neuron ○ Allows signals from different part of nervous system to create the same response ○ Useful when different stimuli are warning us of danger
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One presynaptic nerve may diverge to many postsynaptic neurons
Allow one signal to travel to several parts of the nervous system • Useful in the reflex arcEnsure signals are transmitted in the right direction • Only presynaptic knob contains vesicles of acetylcholine
Filter out low-level signals • Low-level stimuli may create action potentials • These are unlikely to pass across a synapse to the next neuron • Vesicles of acetylcholine will not be released
Summation • Low-level signals may be amplified • Persistent stimulus may cause several action potentials • May cause generator potentials to join together to produce an action potential
Acclimatisation • Synapses may run out of transmitter substance and become fatigued • No longer respond to stimulus • Helps to avoid over stimulation The creation of specific pathways within the nervous system is the basis of conscious thought and memory.
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Hormones =
molecules produced and secreted by endocrine glands directly into the blood. They act as messengers and transport signals from one gland to a specific target tissue or organ to produce a desired effect.
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Endocrine glands
• Release molecules directly into the blood • No duct involved
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Exocrine glands
• Secrete molecules into a duct • Molecules are then carried to where they are needed
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Target Cells •
Cells receiving the hormone must have a complementary receptor • Hormone binds to this receptor • Hormones bind to target cells • These cells are usually grouped together to form target tissues
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Nature of Hormones
• There are 2 types: ○ Steroid hormones ○ Protein and peptide hormones (Derived from amino acids) • Proteins are not soluble in the membrane • Steroid hormones can pass through and have a direct effect on DNA in the nucleus
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difference between first messengers and second messengers
First messengers are hormones that do not enter target cells. This includes all non-steroid hormones. They exert their action by binding to signalling proteins on the cell surface membrane, which triggers a change inside the cell, usually carried out by a second messenger. cAMP is an exemplary second messenger. First messengers often trigger the action of a second messenger via a G protein, which is a protein that spans the cell surface membrane and enables communication between molecules outside the cell and molecules inside the cell.
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adrenal glands
e endocrine glands that are located just above the kidneys. They are present on either side of the body.
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• Adrenal Medulla
○ Centre of the gland ○ Manufacture and release adrenaline ○ Effects include: – Relaxation of smooth muscle in the bronchioles – Increase volume of heart – Increase heart rate – Vasoconstriction – Dilation of pupils – Stimulate conversion of glycogen to glucose – Increase mental awareness – Cause body hair to erect
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Adrenal Cortex
○ Uses cholesterol to produce steroid hormones ○ These have an important role in the body – Secretes mineralocorticoids which help to control the concentration of sodium and potassium in the blood – Secretes glucocorticoids which help to control the metabolism of carbohydrates and proteins in the liver
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Adrenaline
• Adrenaline is an amino acid derivative secreted by the adrenal glands • Cannot enter target cell • Binds to target cell • Target cells is associated with adenylyl cyclase • Adrenaline is the first messenger molecule • First binds to specific receptor on cell surface membrane • Binding activates adenyl cyclase • This enzyme converts ATP to cyclic AMP (cAMP) • cAMP is a secondary messenger molecule • Causes an effect inside the cell by activating enzyme action
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The pancreas
is an organ with both exocrine and endocrine functions. It is positioned just below the stomach.
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The pancreas Structure
• Lumpy appearance • Functional unit: islets of langerhans • Bile duct comes from liver and gall bladder • Exocrine enzymes are secreted into this duct • Endocrine hormones are secreted into surrounding blood vessels
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The pancreas Secretion of Enzymes
Manufactures digestive enzymes • This is the exocrine function • Secrete enzymes into the pancreatic duct • Duct contains: ○ Amylase ○ Trypsinogen ○ Lipase ○ Sodium hydrogen carbonate
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The pancreas Secretion of Hormones
Areas in the pancreas called the Islets of Langerhans contain 2 types of cells ○ Alpha cells ○ Beta cells • Alpha Cells ○ Secrete glucagon • Beta cells ○ Manufacture and secrete insulin
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Blood glucose is too high
• Detected by the beta cells • Target cells are hepatocytes • Respond by producing insulin • Insulin binds to adenylyl cyclase ○ Converts ATP to cyclic AMP (cAMP) • cAMP causes: ○ More glucose channels to open ○ Glucose to be converted to glycogen ○ Glucose converted to fats ○ More glucose used in respiration • Activates a series of enzyme controlled reactions • Reduces blood sugar
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Blood glucose is too low
• Detected by the alpha cells • Release glucagon • Target sites are hepatocytes • Glucagon causes: ○ Glycogen to be converted to glucose (glycogenolysis) ○ Fatty acids to be used in respiration ○ Production of glucose by conversion of amino acids and fats (glycogenesis) • Overall effect increases the blood glucose concentration
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Regulation of Insulin Secretion
• Cell membrane of beta cells contain Ca and K ion channels • K ion channels normally open • Ca ion channels normally closed • K ions diffuse out, making the inside more negative • When glucose concentrations outside are too high, glucose molecules diffuse into the cells • Glucose used in the metabolism to produce ATP • Extra ATP causes K ion channels to close • K can no longer diffuse out • This alters the potential difference across the membranes, making the inside less negative • Change in potential difference opens the Ca ion channels • Ca ions enter the cell • Cause insulin containing vesicles to move to the cell surface • Exocytosis occurs
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Type 1
• Insulin-dependent • Caused by auto-immune disease • Body attacks its own beta cells • Body no longer able to manufacture sufficient insulin • Cannot store excess glucose as glycogen
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Type 2
• Non-insulin dependent • Sufferers can still produce insulin • Constantly high insulin levels due to too much sugar intake • Target cells’ sensitivity to insulin declines • Beta cells may become ‘exhausted’ and die — thereby producing less insulin in the long term • Certain factors can increase the likelihood of diabetes: ○ Obesity ○ Diet high in sugars ○ Asian or Afro-Caribbean heritage ○ Family history
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Treatment • Type 1
Insulin injections ○ Blood glucose levels are monitored
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Treatment • Type 2
○ Diet controlled and monitored
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why plants need t respond
Plants need to respond to their external environment in order to avoid stress, avoid being eaten and ensure sufficiently long term survival
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Types of plant chemical defences
• Alkaloids ○ Make plants taste bitter to deter herbivores • Pheromones ○ Released from one plant and affect another • Tannins ○ Toxic to microorganisms/herbivores ○ Make the leaf taste unpleasant
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Types of plant responses:
• Tropism ○ Directional growth responses • Phototropism ○ Shoots grow towards light ○ Enables them to photosynthesise • Geotropism ○ Roots grow towards the pull of gravity ○ Anchors them in the soil ○ Helps them to take up water as a raw material • Chemotropism ○ Occurs on flowers ○ Pollen tubes grow down the style towards ovaries ○ They are attracted by chemicals • Thigmotropism ○ Shoots out of climbing plants wind around other plants ○ Gain support
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plant Response to the Environment
• Hormones co-ordinate plant response • Produced in a variety of cells ○ Not in endocrine glands ○ Often known as plant growth regulators • Hormones move around the plant ○ Diffusion ○ Active transport ○ Mass flow in phloem and xylem Nastic response = a non-directional response to stimuli, e.g. thigmonasty — Mimosa pudica plant responds to touch by folding its leaves.
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synergism and antaganism
synergic and amplify each other’s’ effects. Others are antagonistic and oppose each other’s’ effects
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Auxins
Cell elongation • Inhibit growth of side-shoots • Responsible for regulating plant growth • Inhibits the growth of side shoots • Inhibits leaf abscission • Action: ○ Causes cell elongation ○ Increases stretchiness of cell wall by increasing the AT of hydrogen ions ○ ATPase enzyme moves more ions through the plasma membrane, into the cell wall ○ Low pH allows wall loosening enzymes to work ○ These break bonds in the cellulose, allowing the cells to expand
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Cytokines
• Promote cell division
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Gibberellins
• Promotes seed germination • Promotes growth of stems
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Abscisic Acid
• Inhibits seed germination • Causes stromal closure when the plant is water stressed
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Ethene
• Promotes fruit ripening
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Plant Growth
• Growth occurs by 2 process in the meristem tissue ○ Cell elongation ○ Cell division • Apical Meristems are located behind shoots and are responsible for shoots getting longer • Lateral bud meristems are found in buds and give rise to shoots • Lateral meristems are found near the outside of shoots and root and make them wider • 2 cell walls are formed ○ Primary does not have uniformly arranged fibres ○ Secondary has uniformly arranged fibres
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Cause of Phototropism
• Shoot bends towards a light source • Shaded side elongates faster than the lit side • Light causes cells to actively unload IAA • Unloaded from cells in light, towards those in shade • Causes the shoot to bend
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Leaf Loss
Cytokinins stop the leaves of deciduous plants from senescing (turning brown and dying) ○ Makes sure the leaf acts as a sink from phloem transport ○ Guaranteed to have a good supply of nutrients • If cytokinin production drops, so will the supply of nutrient and senescence will begin • Process: ○ Leaf senescence causes auxin production at the top of the leaf to stop ○ Makes abscission zone more susceptible to ethene ○ Drop in auxin production causes an increase in ethane production ○ Increases production of the enzyme cellulose – Digests walls of cells in the abscission zone – Causes petiole to separate from stem
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Experimental Evidence for The Role of Auxins
Auxin paste applied to exposed tip • Buds did not grow
Auxin inhibitor applied below tip • Ensure it was auxin preventing the buds from growing • Lateral buds grew
Shoot tip cut off of kidney bean • Auxin concentration increased in lateral buds • Cytokinins can spread more evenly • Abscisic acid levels drop • Proved a causative effect
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The experimental evidence for the role of gibberellin
Gibberellin concentration in tall and dwarf pea plants compared • Higher in tall plants
Grafted a plant which has the enzyme, but no gibberellins onto a normal plant • Plant grows tall • Does not have its own gibberellins • Uses those from the normal plant and its own enzymes
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The Commercial use of Plant Hormones
| auxin
• Used as a rooting powder for cuttings • Can promote the growth of seedless fruit in unpollinated flowers • Artificial auxins can be used as herbicides • Promote and inhibit fruit drop
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The Commercial use of Plant Hormonesgibberlines
• Fruit Production ○ Delays senescence ○ Make fruit last longer on shop shelves • Brewing ○ Barley seeds germinate, with amylase breaking down stored starch into maltose ○ Genes for amylase production are turned on by gibberellins ○ Adding gibberellins can speed the process ○ Malt is produced by drying and grinding the seeds • Sugar Production ○ Sugar canes sprayed with gibberellins ○ Stimulates growth between the nodes ○ Sugar is stored in these internode cells ○ Can increase sugar yield by up to 4.5 tonnes per hectare • Breeding ○ Gibberellins speed up process ○ Speed up seed production in young plants ○ Inhibiting gibberellins can also make flowers short and stocky
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The Commercial use of Plant Hormones cytokinns
• Delay leaf senescence • Prevent yellowing of lettuce leaves • Help mass produce plants ○ Promote bud and shoot growth ○ Produces short shoot with a lot of side branches
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The Commercial use of Plant Hormones ethenee
• Speeds up fruit ripening • Ethene can be inhibited to prevent fruit ripening
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CNS
• Made up of grey matter and white matter • Myelin makes the fibres appear white • Involves only the brain and spinal cord
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PNS
• Contains all the nerves that are not in CNS • This includes motor nerves which can be subdivided: ○ Somatic Motor Neurons – Carry impulses from CNS to skeletal muscles which are under conscious control – Voluntary - e.g. muscle locomotion – Most neurons are myelinated – Connections only ever consist of one neuron ○ Autonomic Motor Neurons – Carry impulses from the CNS to cardiac muscle, smooth muscle in the gut wall, blood vessels, glands and bladder – All of these are under unconscious control – Involuntary — e.g. intestinal smooth muscle contractions – Most neurons are non-myelinated – Connections can consist of more than one neuron Connect at a ganglion
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Autonomic Nervous System
• Involuntary part of the PNS • Can be further subdivided: ○ Sympathetic – Prepares us for vigorous activity – Fight or flight response Involves noradrenaline – Motor neurons are connected by ganglia Same signal can stimulate many motor neurons in different organs ○ Parasympathetic – Relaxing responses Involves acetylcholine – Maintains a suitable state for non-threatening conditions The sympathetic and parasympathetic nervous systems each have their own neurons. The two systems are antagonistic. • They have opposite effects on an unconscious process ○ Parasympathetic nerves increase blood flow to the gut wall ○ Sympathetic nerves decrease blood flow to the gut during vigorous exercise
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Effects on Heart para and sympa
Parasympathetic ○ Heart rate slowed ○ Less blood needed • Sympathetic ○ Heart rate increases ○ Much more blood and oxygen needed
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para and sympa Effects on Salivary Glands
• Parasympathetic ○ Saliva production stimulated ○ Food can be eaten in non-stressful situations • Sympathetic ○ Saliva production inhibited ○ Feeding not the main priority
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para and sympa Effects on Iris
v• Parasympathetic ○ Circular muscles contract ○ Pupil constricts the retina Sympathetic ○ Radial muscles contract ○ Pupil dilates ○ Better image
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Cerebrum
• Largest part • Involved in ‘higher’ brain activities • Divided into 2 hemispheres ○ Left side controls muscles on the right side of the body • Connected via corpus callosum • Outermost layer is highly folded ○ Consists of a thin layer of nerve cell bodies known as the cerebral cortex
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Cerebral Cortex
Subdivided ○ Sensory Areas – Receive impulses indirectly from receptors ○ Association Areas – Compare input with previous experiences to interpret and judge response ○ Motor Areas – Sends impulses to effectors
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Cerebellum
• Contains over half of all nerve cells • Inputs into the cerebral cortex ○ Fine tunes the effectors response • Tensioning of muscles in order to manipulate tools effectively • Input is unconscious ○ Muscle memory • Processes information from: ○ Balance organs of the inner ear ○ Retina ○ Joints ○ Muscle spindle fibres • Controls co-ordination of movement and posture
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Medulla Oblongata •
Controls: ○ Action of smooth muscle in the gut ○ Breathing movements ○ Heart rate
• Regulatory centre for vital processes found here: ○ Cardiac centre ○ Respiratory Centre
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Hypothalamus
• Controls the autonomic nervous system and endocrine glands • Controls most of the homeostatic mechanisms
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Pituitary Gland
Not part of the brain • Attached at the base • Endocrine gland • Secrete a variety of hormones
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Reflex actions
are responses to external stimuli that do not require conscious coordination. They are immediate responses and their rapidity is achieved by bypassing the brain between sensation and reaction. The brain is informed afterwards about the stimulus/reflex.
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Blinking reflex
• Passes through part of brain — is cranial reflex • Receptor and effector in same place ○ Therefore called a reflex arc • Stimuli: ○ Foreign body touching eye (corneal reflex) ○ Sudden increase in light intensity (optical reflex) ○ Sudden movements close to eye ○ Loud noise
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Knee jerk reflex
• Passes through spinal cord - is a spinal reflex • When tendons connecting quadriceps with patella are tapped, they stretch • When they stretch, they pull the quadriceps muscle • The quadriceps muscle senses risk of over-stretch ○ Detected by muscle spindles • Reflex is to contract the muscle immediately • Causing knee jerk reaction
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• Reflexes are key to survival
• Provide effective protection from dangerous positioning/posture or incoming threats • E.g. when you touch a hot object, you withdraw your hand — this is a reflex that prevents you from getting burnt
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fight or flight’
The term ‘fight or flight’ refers to a set of physiological changes which occur in the body when danger is detected, and we need to either run away or fight it. It is a function of the sympathetic nervous system and incorporates several hormones as well.
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Combined nervous and hormonal response
○ Pupils dilate, making retina more sensitive to e.g. motion ○ Heart rate and blood pressure increase – Equips muscles with optimal oxygen supply and waste removal ○ Arterioles to digestive system and skin constrict – Blood re-directed to muscles — prioritised organs during fight or flight ○ Arterioles to muscles and liver dilate ○ Blood glucose increases – Ready to deliver respiratory substrate to muscles ○ Metabolic rate increases ○ Erector pili muscles contract – Consequence of adrenaline — sign of aggression○ Ventilation rate and depth increases ○ Endorphins released by the brain – Higher pain threshold ○ Sweat production increases
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Co-ordination of Changes
• Perception of threat comes from visual or auditory stimuli • Signals sent to the brain by sensory receptors • Information enters the cerebral cortex and person is consciously aware of the threat • Cerebral cortex activates the hypothalamus, stimulating activity in the sympathetic nervous system • Nervous impulse sent through sympathetic nerve to the adrenal glands, near the kidneys • Triggers the release of adrenaline — main hormone involved in fight or flight ○ Medulla also secretes noradrenaline, which works with adrenaline • Hypothalamus also releases corticotropin releasing factor (CRF) into the pituitary gland ○ Stimulates the release of adrenocorticotropic hormone (ACTH) ○ Stimulates hormones which help the body to resist stressors ○ These are stimuli that can cause a stress response
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how does the Heart muscle responds to the presence of the hormone adrenaline
Beats faster • Beats stronger: myocytes contract with greater contractile force
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why is heart is Supplied with nerves from the medulla oblongata
• Found at the base of the brain • Region of the brain that co-ordinates the unconscious functions of the body • Nerves connect to the SAN • Nerves can affect the frequency of the contractions
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The heart has 2 main nodes that contain nerve cells
○ Sinoatrial node ○ Atrioventricular node
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Controlling Heart Beat
SAN sends an electrical impulse over the atrial walls • Causes atria to contract • Conducted to AVN, where the electrical wave of excitation is conducted down the Purkinje fibres • Causes the ventricles to contract • Layer of insulation exists between the atria and ventricles to prevent the first wave of impulse from the SAN from travelling all the way down • This layer causes a pause at the AVN
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vRate of Initiation
• Controlled by: ○ Nerves that run from the brain ○ Hormones in the blood – E.g. — Adrenaline
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nerves that control heart beat?
Nerves • Vagus Nerve ○ Sends signals to decrease heart rate • Acceleratory Nerve ○ Sends signals to increase heart rate • Both nerves connect to the medulla oblongata in the brain
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Medulla Oblongata
• Involved in many unconscious functions of the brain including breathing and heart rate • Specific regions of the medulla oblongata sense factors that require a change in heart rate • Cardiovascular centre can sense things like changes in carbon dioxide levels
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Interaction between control mechanisms
• Resting conditions ○ Heart rate controlled by SAN ○ Set frequency ○ Typically 60-80 beats per minute ○ Frequency of excitation waves can be controlled by the cardiovascular centre in the medulla oblongata
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Factors affecting heart rate
movement exercise adrenaline bloo pressure artificatal pacemakers
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affecting heart rate Movement
○ Limb movement is detected by stretch receptors in muscles ○ Impulses sent to the cardiovascular centre ○ Informs that oxygen is needed ○ Increases heart rate
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Exercise fecting heart rate
○ Muscles produce more carbon dioxide ○ Carbon dioxide reacts with water in blood plasma, lowering the pH ○ Drop in pH detected by chemoreceptors ○ Chemoreceptors send impulses to the cardiovascular centre ○ APs fired from chemoreceptors are passed to cardiovascular centre of the medulla oblongata ○ Signals sent down the accelerator nerve to increase heart rate ○ Heart rate increases ○ When we stop exercising concentration of carbon dioxide falls ○ Reduces activity of the accelerator pathway ○ Heart rate declines
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affecting heart rate Adrenaline
○ Secreted in response to stress, shock or excitement ○ Presence increases heart rate ○ Adrenaline binds to specific receptors on the membranes of cells in the SAN ○ Helps to prepare body for activity
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affecting heart rate • Blood Pressure
○ Monitored by stretch receptors in the walls of the carotid sinus ○ If blood pressure rises too high, signals are sent to the cardiovascular centre ○ Signals sent through the vagus nerve to decrease the heart rate ○ Heart rate is reduced
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affecting heart rate artificial Pacemakers ○
If the mechanism controlling heart rate fails, an artificial pacemaker can be fitted ○ 1928 – Needle electrode that is inserted into the heart wall – Not portable
53snaprevise.co.uk
○ Device further developed ○ Modern pacemakers are only 4cm long ○ They are implanted underneath the skin and at of the chest ○ Deliver pulses to the ventricle walls ○ Deals with conditions where the AVN is not functioning but the SAN may be
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neural Synapse
Neurone to neurone • Post synaptic stimulation leads to AP in postsynaptic membrane • Synaptic knob is smooth and rounded
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Neuromuscular Junction
• Neurone to sarcomere • Postsynaptic stimulation leads to depolarisation f sarcolemma and muscle contraction • End plate has a brush border
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simalaries between neural synapse and neuromuscular junction
Vesicles located in presynaptic cytoplasm • Vesicles release neurotransmitter into cleft on stimulation • Neurotransmitter diffuses across the gap and binds to postsynaptic membrane • Binding of the neurotransmitter results in depolarisation • Enzymes are present to degrade the neurotransmitter
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Muscle • Can be
involuntary… ○ Smooth muscle ○ Cardiac muscle ○ Controlled by autonomic nervous system • Or voluntary.. ○ Skeletal muscle
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Smooth Muscle
Innervated by neurons of the ANS • Involuntary contraction • Does not have a striped appearance • Spindle shape cells contain bundles of actin, myosin and a single nucleus • Contracts and fatigues slowly • Involved in the movement of materials along a tube
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Cardiac Muscle
There are 3 types: ○ Atrial muscle ○ Ventricular muscle ○ Specialised excitatory and conductive fibres • Contract in similar way to skeletal muscle, but with longer duration of contraction • Some muscle fibres are myogenic ○ Stimulate contraction without a nervous impulse • Innervated by the ANS • Sympathetic stimulation increases rate, parasympathetic decreases rate • Made of individual cells connected in rows • Dark areas are intercalated discs ○ Cell membranes that fuses to form gap junctions ○ Ions, and so Aps, are able to diffuse easily through this network of interconnections • Striated muscle
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Skeletal Muscles
• Voluntary muscles • Action of these muscles leads to the movement of the skeleton • Ligaments connect bone to bone • Tendons connect muscle to bone • Form fibres with many nuclei • Cell surface membrane is the sarcolemma • Cell cytoplasm is the sarcoplasm • Sarcoplasm contains: ○ Many mitochondria ○ Extensive sarcoplasmic reticulum ○ Myofibrils – Contractile elements – Contain smaller units called sarcomeres – Actin and myosin filaments • Called ‘striated muscle’ because of its striped appearance
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The Sarcomere
• Span from one Z-line to the next • Z-lines closer together during contraction • I-band and H-band are reduced • A-band does not change in length
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• I Band
○ Thin actin filaments
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• Z line
○ Region where actin myofilaments are anchored
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A band
○ Region containing the whole length of the myosin microfilament
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M band
○ Region where sarcomere connects to the skeleton
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H band
○ Thick myosin filaments only
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Thin Actin
○ 2 strands of actin coiled around each other ○ Composed of G actin subunits ○ Tropomyosin molecules form around the actin, reinforcing it ○ Troponin complex is attached to each tropomyosin molecule – Consists of 3 polypeptides – 1 binds to actin – 1 binds to tropomyosin – 1 binds to calcium ions
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Thick Myosin
○ Consists of myosin ○ Shaped like a golf club, with 2 heads ○ Heads stick out to form the cross bridge ○ Many of these myosin molecules stick together to form a thick filament
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Process of contraction
When a muscle is at rest, Ca concentration surrounding the fibrils is very low • Under these conditions, tropomyosin sits in the myosin binding sites and the contractile mechanism is ‘off’ • When the muscle is stimulated, a wave of depolarisation passes in through the T system • When the impulse reaches the SR it causes the release of Ca ions • Ca concentration increases • Ca ions bind to troponin causing it to change shape • Tropomyosin moves out of the myosin binding site on the actin filaments • Actin is now ‘on’ • ATP binds to the myosin and is hydrolysed to ADP and Pi, both of which remain bound to the myosin head • Pi is released, changing the shape of the myosin head and allowing it to form cross-bridges • ADP is released causing the myosin head to tilt and pull the actin filament over the myosin filament. This is the power stroke. • At the end of the power stroke, the ATP binds to the myosin head and the cross bridges are broken • If Ca concentration remains high, the cycle will be repeated
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End of Nervous Stimulation & muscle relaxation
ATP pump actively pumps Ca ions from the sarcoplasm to the cisternae of the SER • Ca ion concentration falls below the threshold level • Troponin is released and is bound back to Ca • This causes the tropomyosin to go back to the myosin binding sites • The muscle is now relaxes
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ATP in Muscular Contraction
• ATP provides the energy that allows binding, tilting and releasing on the myosin heads • It is the force that causes muscular contraction
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Maintaining ATP Supply
• Rate at which ATP is regenerate during respiration is dependent on oxygen • Aerobic respiration leads to increased levels of lactic acid in the blood, stimulating increased blood flow to the muscles • Muscles contain small reserves of ATP • ATP can be formed from creatine phosphate ○ Creatine phosphate can lose a phosphate group, donating it to ADP to form ATP • Glycogen is stored in the muscles, but when it has been used, the liver’s glycogen stores can be respired
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Motor Unit
• Some movements require a stronger contraction than others • Brain controls the strength of contractions • Many neurons can stimulate a single muscle • Each one branches to a neuromuscular junction, causing the contraction of a cluster of muscle cells — the motor unit • The more motor units stimulated the greater the force of contraction
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Photosynthesis
is the process by which plants and some other organisms convert light energy into chemical energy.
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Respiration
is a process that is carried out by all living organisms. It involves the oxidation of glucose to produce carbon dioxide and water, as well as the ‘release’ of energy — often in the form of generating ATP from ADP and Pi.
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interrelationship between photosynthesis and respiration
The interrelationship between photosynthesis and respiration is highlighted in the fact that the products of one are the raw materials of the other. The overall effect of the two reactions in sync is the ability of life to convert sunlight into thermal/kinetic energy essential for life.
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Compensation point
Compensation point is the term used to refer the state in which a plant is when the rate of photosynthesis and the rate of respiration are equal. In other words, there is no net change in carbohydrate content because it is being generated at the same rate that it is being consumed.
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Chloroplasts
• Surrounded by an envelope • Outer membrane is permeable to small ions • Inner membrane is less permeable ○ Folded into lamellae ○ One granum consists of several stacked thylakoids ○ Between grana is the intergranal lamellae • The stroma is the fluid filled matrix, which contains the necessary enzyme to carry out the light dependent reactions
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Chloroplast Adaptations
• Many grana provide a large surface area for photosynthetic pigments • Photosynthetic pigments are arranged into photosystems • Proteins embedded in grana to hold the photosystems in place
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Photosynthetic Pigments
• A molecule that can absorb one or more specific wavelengths of light and reflect other wavelengths • Each pigment can absorb on wavelength • A wide variety of these maximizes energy absorption • These are arranged in photosystems
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Primary Pigments
These are found at the centre of the PS • They can absorb energy from the sun or from accessory pigments ○ E.g. Chlorophyll A (680,700,450)
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Accessory Pigments
These are found at the edge of the PS • Absorb light from the sun and pass this onto the primary pigments ○ E.g. Carotenoids, Chlorophyll B (500,640)
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Chlorophyll
• Head and a tail group • Head contain Mg atom
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• Photophosphorylation
○ When a photon hits a chlorophyll molecule, the energy is transferred to 2 electrons exciting them ○ Electrons captured by electron carriers and passed along a series of electron carriers ○ Energy is used to pump protons across the thylakoid membranes ○ Proton gradient is formed and protons flow down the concentration gradients through ATP channels ○ This is chemiosmosis ○ This produces a force which joins ADP and Pi to form ATP – ATP is used in the light independent stage of the reaction – The making of ATP using light energy is called photophosphorylation
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Cyclic Photophosphorylation
○ Only uses PS1 ○ Electrons pass to an electron acceptor, then return to the chlorophyll molecule from which they were lost ○ No photolysis of water ○ No generation of reduced NADP ○ Small amounts of ATP made ○ This may be used in the light independent reaction to actively transport potassium into the cell, lowering the water potential and causing ions to flow in by diffusion ○ This causes the guard cells to swell and the stomata to open
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• Non-cyclic Photophosphorylation
○ Involves both PS1 and PS2 ○ Light strikes PS2, exciting a pair of electrons ○ Electrons leave the chlorophyll molecule from the primary pigment reaction centre ○ Electrons pass along the chain of electron carriers○ Energy is released, which is used to synthesize ATP ○ Light strikes tPS1, causing the release of 2 electrons ○ Electrons from oxidized PS2 replace those lost from PS1 ○ Electrons from photolysed water replace those lost from PS2 ○ Protons fro photolysed water take part in chemiosmosis, to make ATP ○ They are captured in NADP in the stoma and used in the light-independent stage
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vNon light dependent stage
○ This takes place in the stroma ○ It is called the Calvin Cycle ○ Although light is not used, the products of the light-dependent stage are used, so the light independent stage will soon cease if light supply ceases
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he Calvin Cycle
○ Carbon dioxide from the air diffuses into the leaf ○ Diffuses through air spaces and reaches the spongy palisade layer ○ Diffuses through the cellulose cell walls and into the chloroplast envelope ○ In the stroma, carbon dioxide combines with the 5C ribulose bisphosphate ○ Reaction is catalysed by the rubisco enzyme ○ Two 3C compounds, called glycerate phosphate (GP) are produced – Some GP is used to make amino acids and fatty acids ○ GP is reduced and photophosphorylated to another 3C compound, triose phosphate (TP) ○ ATP and reduced NADP are used in this reaction ○ 5/6 TPs are recycled to ribulose bisphosphate – Pairs of TP combine to form hexose sugars
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In Cyclic phosphorylation: • Conversion of Energy
In Cyclic phosphorylation: – Light energy absorbed by PS1 – Energy excites electrons, raising their energy level – This causes electrons to be transferred to carriers – As electrons drop down energy levels, they release energy – Energy is used to pump H+ ions through ATP synthase from thylakoid space to the stroma – This is the process of chemiosmosis – In this process, ATP is produced – This process is used to make glucose
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Conversion of Energy○ In non-cyclic phosphorylation:
– Light energy causes hydrolysis of water – This is photolysis 2 electrons are produced, which pass into the PS2 – They are excited and transferred to the electron carriers – As they pass along the carriers, they release energy, – This is used to pump H+ ions into the stroma at the same time
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Role of Water in the Light Dependent Stage
• Photosystem 2 contain an enzyme that can split water into protons, electrons and oxygen • This is photolysis • Some of the oxygen is used in aerobic respiration • Water is a source of hydrogen ions, which are used in chemiosmosis • Protons are accepted by a coenzyme NADP, which is reduced to reduced NADP and used in the light independent stage
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Role of Carbon Dioxide in Light Independent Stag
• Carbon dioxide is the source of carbon and oxygen for the production of all large organic molecules • These molecules are used as energy stores for all life forms
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Factors Affecting the Rate of Photosynthesis
Light Intensity
CO2 concentration
Tempoerature
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how Light Intensity Affecting the Rate of Photosynthesis
If light intensity was dramatically reduced: ○ Levels of ATP and NADP would fall, as the light dependent reaction cannot occur ○ Conversion of GP to TP requires ATP and reduced NADP, so this process will slow down ○ As ATP is used to convert TP to ribulose bisphosphate, levels of this will also fall ○ Reduction in ribulose bisphosphate means less carbon dioxide can react ○ Eventually the whole cycle stops
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how Affecting c02 the Rate of Photosynthesis
If carbon dioxide concentration was dramatically increased: ○ More carbon dioxide fixation allows for more GP, TP and ribulose bisphosphate to be created ○ Stomata will be open more, causing an increased loss of water and wilting ○ Stress response will close the stomata ○ This will reduced carbon dioxide supply ○ Photosynthesis rate will slow
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how Affecting temperature the Rate of Photosynthesis
If temperature were raised: ○ Below 25 degrees activity in light dependent stages is minimally affected ○ Activity of molecules in the Calvin cycle are dramatically affected as they gain more kinetic energy ○ Higher temperatures will increase transpiration and cause the plant to wilt ○ Stress reaction will cause the stomata to close, reducing carbon dioxide availability ○ High temperatures may denature rubisco ○ At higher temperatures, rubisco is more likely to bind to oxygen than carbon dioxide ○ Photosynthesis rate will start to decrease
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The Need for Cellular Respiration
Respiration uses energy to make ATP. In living organisms, energy is the ability to do work. It is needed to drive metabolic reactions: • Anabolic reactions (building large molecules) • Catabolic (breaking down molecules) • Active transport • Secretion • Endocytosis • Replication of DNA • Movement of organelles and of cells themselves • Activation of chemicals
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Role of ATP:
• Phosphorylated nucleotide • High — energy intermediate compound • Created after glucose is broken down • Stores energy, which can be released quickly and in small amounts • Called the ‘universal energy currency’
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The Mitochondrion
The mitochondrion has also been called the ‘powerhouse of the cell’ because it is the main site of respiration in the cell. Structure • Inner membrane is folded into cristae, giving a large surface area • Matrix is enclosed by the membranes ○ Link reaction and Krebs cycle occur here Shape • 2-5 micrometers long • Densely packed cristae • Moved within the cell by microtubules
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Glycolysis
Glycolysis is the precursor to respiration and it takes place in the cytoplasm of the cell, not the mitochondrion.
Stage 1 — Phosphorylation • Occurs in cytoplasm • 2 ATP molecules are hydrolysed, releasing phosphate group • Glucose 6-phopshate changes to fructose 6-phosphate • These sugars are then activated, forming hexose 1,6-biphosphate
Stage 2 — Splitting of hexosebisphosphate • Hexosebisphosphate is split into 2 triose phosphates
Stage 3 — Oxidation of Triose Phosphate • 2 hydrogen atoms removed from each triose phosphate • NAD combines with hydrogen, becoming reduced • Dehydrogenase enzymes used
Stage 4 — Conversion to pyruvate • Triose phosphate converted to a molecule of pyruvate • 2 molecules of ADP are phosphorylated to 2 molecules of ATP Net Products • 2 x ATP • 2 x NADH • 2 x Pyruvate ○ 2 molecules produced per glucose molecule ○ These are actively transported into the mitochondrial matrix for the next stage of aerobic respiration ○ In absence of oxygen, it is changed into lactate or ethanol in cytoplasm
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The Link Reaction
The link reaction occurs in the matrix inside the mitochondrion, once pyruvate has been actively transported there following glycolysis. • Pyruvate contains a carboxyl group • This disassociates to COO- and H+ • Carboxyl group removed in decarboxylation • This also releases a molecule of CO2 • Intermediate is then oxidised • H atom transferred to coenzyme NAD, producing NADH • Acetyl CoA is the final product
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The Krebs Cycle
The Krebs cycle Occurs in the mitochondrial matrix. It is a series of enzyme-catalysed reactions that ultimately oxidise acetyl group of Acetyl CoA to 2 molecules of carbon dioxide. 1. Acetyl group and oxaloacetate join forming Citrate (6C) 2. Citrate is decarboxylated (carbon dioxide lost) and dehydrogenated (pair of hydrogen atoms lost) by NAD+ 3. 5C compound formed 4. Hydrogen pair accepted by NAD, reducing it 5. 5C compound is then decarboxylated and dehydrogenated, forming 4C compound and another molecule of reduced NAD 6. 4C changed to another 4C compound, with ADP being phosphorylated to ATP 7. FAD becomes reduced and removing another hydrogen pair 8. 3rd 4C compound is further dehydrogenated, regenerating oxaloacetate
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ETC in respiration
• Electron transport chain (ETC) ○ Electron carriers are embedded in mitochondrial membrane ○ Co-enzymes NAD and FAD are reoxidised when they donate H atoms to these carriers ○ H atoms split into protons and electrons ○ Electrons move down the chain ○ They are finally donated to oxygen, the final electron acceptor
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chemosmosis in respiration
• Chemiosmosis ○ As electrons flow, energy is released ○ This is used to pump protons into the matrix
○ This builds up a proton gradient (and electrochemical gradient) ○ Potential energy builds up in the intermembrane space ○ Hydrogen ions are only able to diffuse through ATP synthase ○ This drives the reaction of ADP and Pi, forming ATP
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oxidative phosphorylation in respiration
○ This builds up a proton gradient (and electrochemical gradient) ○ Potential energy builds up in the intermembrane space ○ Hydrogen ions are only able to diffuse through ATP synthase ○ This drives the reaction of ADP and Pi, forming ATP
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Anaerobic respiration
Anaerobic respiration is a type of respiration that takes place in the absence of oxygen. It produces a byproduct called lactic acid — which builds up in our muscles when we exercise for a long period of time, and makes them ache afterwards.
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Anaerobic respiration In Animals
• Without oxygen, Link Reaction, ETC and Krebs cycle stop • Glycolysis can still occur • NAD+ is recycled • H atoms need to be removed from NADH molecules • Pyruvate is used as an H acceptor • In muscle cells, pyruvate is converted to lactic acid on accepting the H atom • Lactic acid is taken to liver • It is re-converted to pyruvate • This enters the link reaction in liver cells, where it is aerobically respired
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Anaerobic respiration In Animals
• NAD+ must be recycled • Pyruvate undergoes decarboxylation and reduction to form ethanol • If ethanol concentration increase to over 12%, the cells will be killed • Ethanol dissolves cell membranes, causing them to burst ATP yield is much lower in anaerobic respiration because the majority of it is formed in the oxidative phosphorylation — which requires oxygen as the final electron acceptor.
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Respiratory substrate
= an organic substance that can be used for respiration. • Majority of ATP produced in oxidative phosphorylation • More protons allows for more ATP to be produced • If a substrate has more hydrogen atoms, more ATP can be made
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Carbohydrates
Glucose in main respiratory substrate • Brain and blood cells can only use glucose • Lowest mean energy value 15.8 kJ/g
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Proteins
• Excess amino acids may become deaminated • Rest of molecule is changed into glycogen • If an organism is starving, protein from muscle can be hydrolysed to amino acids • Some is converted to pyruvate and enters the Krebs cycle • Slightly higher energy yield than an equivalent mass of carbohydrates • Mean energy value 17.0 kJ/g
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Lipids
• Triglyceride hydrolysed to glycerol • Glycerol can be converted to glucose • Fatty acids can’t be converted into glucose • Fatty acids are long chain hydrocarbons • These can produce lots of ATP by chemiosmosis during oxidative phosphorylation • Each fatty acid must be combined with CoA, using energy • The acetyl groups enter the Krebs cycle • Lipids have the highest mean energy value 39.4 kJ/g
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The respiratory quotient
is an indication of how aerobic the respiration is that is taking place. The formula for RQ:RQ = CO2 produced ÷ O2 produced
A RQ value that is above 1 indicates that some aerobic respiration is taking place.
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Practical investigations into factors affecting the rate of respiration. A good way to measure the rate of respiration of an organism is by using a respirometer. how does it work
Respirometers work because of the basic principle of respiration, wherein the respiring organism uses up oxygen, and releases carbon dioxide. It follows that the rate of oxygen usage and the rate of carbon dioxide production are direct indicators of the rate of respiration.
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set for using a respirometer
1. Set up the apparatus as shown ○ Manometer contains liquid that moves as oxygen in tube A is used up 2. The germinating seeds release carbon dioxide 3. Carbon dioxide is absorbed by the sodium hydroxide ○ Therefore has no effect on volume of air inside tube A 4. Germinating seeds use up oxygen ○ This decreases volume of air in the tube ○ Liquid in manometer is drawn up towards tube A 5. Rate of movement of liquid in manometer indicator of rate of respiration 6. Can change environmental conditions such as temperature, light intensity to observe how these factors affect rate of respiration
