Topic 9 Bio Flashcards
Homeostasis definition
Maintenance of a state of dynamic equilibrium despite changes in the external or internal environment
What do we need to regulate with homeostasis
pH
Core temperature
Body Fluids - Water
Two types of glands and difference
Endocrine gland secretes directly into bloodstream
Exocrine gland releases chemicals (enzymes) via a duct
What are hormones
Chemical signals. Either proteins/peptides or steroids
What are the neurosecretory cells
nerve cells in the hypothalamus that secrete the message from the hypothalamus to the pituitary gland
Type 1 (releasing factor/ inhibiting factor) - Produce substance that makes or stops hormone being released
Type 2 (hormone itself) - stored in pituitary gland until needed
Describe the structure of the pituitary gland
Posterior and anterior putuitary gland
What is a tropism
A directional response to specific environmental cues
What area of the plant are most sensitive to hormones
Reigon of cell division and elongation
Define homeostasis
The maintenance of a state of dynamic equilibrium through the responses of the body to external and internal stimuli
What is thigmotropism
Climbing plants have a sense of touch. They sense where the object and spiral around it
Define homeostasis
The maintenance of a state of dynamic equilibrium through the responses of the body to external and internal stimuli.
What type of effectors do hormones target?
Organs.
What type of effectors does the nervous system target?
Muscles and glands.
What is negative feedback?
A response to a change in the body that counteracts or opposes the initial change.
What is positive feedback?
Where effectors work to increase an effect that has triggered a response.
Provide an example of a positive feedback loop.
A woman going into labor.
As the baby’s head pushes against the cervix, receptors in the cervix send nerve impulses to the brain, specifically the pituitary gland that releases a hormone called oxytocin. This hormone acts on the effector (muscle in the uterus) to stimulate/enhance muscle contractions. The stronger the muscle contraction, the more the head of the fetus pushes on the cervix which stimulates the brain. This is a continuing loop until the fetus is delivered.
What’s the difference between exocrine and endocrine glands?
Endocrine glands produce hormones and release them directly into the bloodstream. Exocrine glands produce chemicals like enzymes which release them along small tubes or ducts.
Similarities of the hormonal and nervous system?
- Both systems help maintain homeostasis and coordinate body functions.
- Both use chemical messengers (the nervous system uses neurotransmitters, while the endocrine system uses hormones).
- Both involve target cells, which respond to specific signals via receptors.
Differences of the hormonal and nervous system?
- Nervous system provides fast, but short-lasting responses whereas hormonal system provides slow but long-lasting responses.
- Nervous system is highly specific whereas hormones lead to widespread effects.
- Hormones are transported in the blood whereas nervous impulses are carried on neurons.
What are the two types of hormones?
Peptide and Steroid.
How do hormones target specific organs?
The cells of the target organs have specific receptor molecules on the surface of their membranes that bind to hormone molecules.
What can stimulate the release of hormones?
Direct nerve impulse, or hormones.
Describe the structure of the pituitary gland.
Divided into posterior and anterior lobes.
Which hormones are released from the posterior lobe?
Oxytocin - Stimulates contraction in cells of the uterus and mammary tissue; ADH - Osmoregulation in kidneys.
Which hormones are released from the anterior lobe?
FLAT PG: TSH - Controls secretion of thyroxine (Metabolism); FSH - Stimulates oestrogen release in females and sperm production in males; LH - Stimulates ovulation and formation of corpus luteum in females and testosterone production in males; Prolactin - Production of milk in mammary tissue; GH - Stimulates growth of body cells; ACTH - Controls hormone release in adrenal glands.
How do peptide or non-lipid-soluble hormones trigger a response?
- Hormone (First messenger) binds to a receptor on the cell membrane.
- This triggers a series of membrane-bound reactions which results in the formation of a secondary messenger (most commonly cAMP (Cyclic AMP) which is formed from ATP by adenylyl cyclase).
- Secondary messengers can activate a number of different enzymes which control many different reactions (such as breakdown of glycogen into glucose). These enzymes include protein kinase or glucagon phosphorylase.
What are examples of peptide hormones?
Insulin, Adrenaline, Glucagon.
How do steroid or lipid-soluble hormones trigger a response?
- Pass through the membrane and act as the internal messenger.
- Binds to a receptor molecule to form a hormone-receptor complex.
- This complex can act directly as a transcriptional factor regulating gene expression.
What are examples of steroid hormones?
Oestrogen, Testosterone.
What are tropisms?
Directional growth responses to specific environmental stimuli.
What is an example of an auxin?
Indoleacetic acid (IAA).
How do auxins cause cell elongation?
- Auxins bind to receptor sites on the cell membrane (Tropisms).
- This leads to activation of H+ pumps which actively pump H+ ions into the cell wall spaces.
- This lowers the pH, ~5, an optimum for a specific enzyme.
- This enzyme breaks the bonds between adjacent cellulose microfibrils allowing them to slide over each other enabling them to stretch.
- The cell absorbs water through osmosis which causes cells to expand and elongate as a result of turgor pressure.
- As cells mature, IAA is destroyed by enzymes and pH rises causing reformation of bonds between cellulose microfibrils.
What is apical dominance?
Suppression of growth of lateral buds caused by hormones produced by the apical bud.
How does apical dominance work?
- Auxins are synthesized in the meristem of cells in the apical/terminal bud.
- Auxins diffuse away from the tip.
- Where concentration of auxins is high, auxins work as the agonist suppressing lateral growth caused by cytokinins (Antagonist).
- As concentration falls, cytokinins promote lateral growth as they become dominant.
- Cytokinins are produced in the base of the shoot.
Why are negative feedback loops more common than positive feedback loops?
Negative feedback prevents a change maintaining dynamic equilibrium whereas positive feedback amplifies change and makes conditions unstable.
How do hormones have a specific effect despite being present in all tissues?
Only cells with the receptors for hormones will have an effect. Peptide hormones will only cause change to a cell which has the specific receptor on its cell membrane. Steroid hormones will only have an effect if the receptor found in the cytoplasm can bind with the hormone. Cells without receptors are unaffected.
Role of gibberellins
- Stimulate seed germination.
- Stem elongation in synergy with auxins.
- Stimulate fruit development.
Role of cytokinins
- Promote lateral bud growth.
- Promote cell division in meristems.
- Antagonistic with auxins in apical dominance.
- Work in synergy with ethene in leaf abscission.
How do gibberellins promote seed germination?
- Seed absorbs water activating the embryo. 2. The embryo secretes gibberellin. 3. Gibberellin diffuses into the aleurone layer. 4. The aleurone layer produces amylase. 5. Amylase diffuses into the endosperm layer. 6. Amylase then breaks down starch into maltose.
What is abscission?
Leaf loss.
How do growth regulators work?
Synergistically - Complementing each other and giving a greater response.
Antagonistically - Substances with opposing effects.
CPAC 14: Effect of gibberellins on amylase production
- Dilute the stock gibberellin solution to several set concentrations.
- Cut the seeds in half (one half should contain the embryo and the other half should contain the endosperm). Discard the half containing the embryo.
- Sterilize the half containing the endosperm by placing it in the sodium hypochlorite solution.
- Wash the seeds through distilled water 5 times until there is no smell of bleach.
- Place the seed halves in the gibberellin concentrations and leave for 12-48 hours. Leave lids of sample bottles loose to prevent conditions becoming anoxic.
- Use sterile forceps to move seed halves onto a sterile petri dish with starch agar. Partially tape the lids (to prevent conditions becoming anoxic). Leave for 12-48 hours.
- Pour potassium iodide onto the plates and measure the zone of inhibition/’clear zone’ around the seed half.
Why would you need to sterilize and incubate the seeds in CPAC 14?
Sterilizing is necessary to avoid contamination with bacteria which could also produce amylase. Seeds must be incubated to allow for synthesis of proteins for diffusion and digestion to occur.
What is photomorphogenesis?
Pattern of plant growth and development determined by light intensity and type.
What is phytochrome?
A plant pigment e.g inactive Pr and active Pfr.
What are the color conversions of Pr and Pfr?
- Pr turns instantly to Pfr in red light.
- Pfr turns instantly to Pr in far-red light.
- Or.. Pfr turns slowly to Pr in the dark.
When and why do SDPs and LDPs flower?
SDPs tend to flower in spring and autumn where days aren’t longer than 12 hours, enough critical length of darkness so that the concentration of Pfr falls below a threshold, stimulating flowering, germination, etc. LDPs tend to flower in the summer, when days are longest, because there is sufficient conversion of Pr to Pfr above a certain level of threshold which stimulates flowering, germination, etc.
What is photoperiodism?
A developmental response to relative lengths of light and dark periods.
What is the evidence for plant hormone florigen?
- If the whole plant was kept in the dark but 1 leaf, flowering occurs as normal.
- If the same leaf was now covered up after the stimulus, flowering does not occur.
- If two or more plants grafted together, where only 1 was exposed to good light patterns, all the plants would flower.
What is florigen actually?
FTmRNA. A mRNA linked with the FT gene (Flowering locus T), which can move cell to cell through plasmodesmata.
What is etiolation?
The rapid upward growth of a plant grown in the dark, using up food reserves in an attempt to reach light; No chlorophyll is formed so pale yellow leaves.
How does Pfr act as a transcription factor?
- Pr is converted into Pfr.
- Pfr moves into the nucleus through nuclear pores.
- A nuclear protein called PIF3 binds only to Pfr form.
- Complex activates gene transcription and formation of mRNA.
How is the nervous system broken down?
Nervous system:
- Central nervous system:
- Brain
- Spinal cord
- Peripheral nervous system:
- Voluntary system
- Autonomic system:
- Sympathetic nervous system
- Parasympathetic nervous system.
Label a neurone.
- Cell body + Nucleus
- Dendron (Dendrites to cell body)
- Axon (Cell body to axon terminal)
- Dendrites
- Myelin sheath (Schwann cell)
- Node of Ranvier
- Axon terminal.
How is the myelin sheath formed?
Schwann cells wrap themselves around the axon repeatedly to form many layers of Schwann cell membranes, with the cytoplasm and nucleus squeezed to the outside.
What two ways increase the speed of nerve impulses?
- Thicker the fibre, the faster the impulses.
- Myelin sheath.
Explain how resting potential is achieved.
- Sodium/Potassium pump creates concentration gradient across membrane by increasing K+ conc. inside the cell and increasing Na+ conc. outside the cell.
- Membrane is relatively impermeable to Na+ but allows for passive diffusion of K+ ions out of the cell.
- This makes the inside of the cell more negative and outside more positive.
- Build up of negative charge inside the cell creates an electrical gradient which pulls K+ back into the axon.
- The two gradients acting on K+ oppose forces and reach equilibrium at a potential difference of -70mv.
Explain how an action potential is achieved.
- Neurone is stimulated.
- Voltage-gated Na+ channels open to cause influx of Na+ and positive charge into the axon (Depolarisation) ~+40mv.
- Voltage-gated Na+ channels close, and voltage-gated K+ channels open which cause the outflux of K+ and positive charge out of the axon (Repolarisation).
- Membrane becomes hyperpolarised as too much K+ leaves the cell, causing voltage-gated K+ channels to close, and K+ diffuses back into the axon to recreate resting potential.
What is the threshold potential?
The critical level to which a membrane potential must be depolarized to initiate an action potential. Weak stimulus causes only some Na+ gates to open, but very strong stimulus above threshold doesn’t result in greater action potential.
What is the refractory period?
A period immediately following action potential in which a nerve is unresponsive to further stimulation.
Made up of the:
- Absolute refractory period which happens in the first ms when it is impossible to restimulate a potential.
- Relative refractory period after the absolute refractory period where a neurone can be restimulated, but only by a much stronger stimulus than before.
Why is the refractory period important?
- Ensures that an action potential/impulse propagates in one direction only;
This is because it becomes impossible to stimulate an action potential immediately after repolarisation, which means it can only continue travelling in one direction down the neurone.
In unmyelinated axons, how is an impulse propagated along the nerve?
At a point on the membrane, the influx of Na+ causes depolarisation of the membrane at this part of the axon. This causes a change in the potential difference in the parts of the membrane adjacent to it, causing the trigger of a second action potential. The second action potential can only travel in one direction because of parts of the membrane upstream on the axon still in the refractory period.
In myelinated axons, how is an impulse propagated along the nerve?
- Depolarisation can only occur at the nodes of Ranvier between Schwann cells.
- Action potentials are transmitted from one node to another in saltatory conduction causing the impulse to jump, resulting in a much faster conduction along the nerve fibre.
Explain how an impulse is transferred at the synapse.
- Arrival of impulse causes Ca2+ channels to open, which move Ca2+ across the pre-synaptic membrane and into the synaptic knob by diffusion.
- Ca2+ causes synaptic vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft.
- Neurotransmitters will bind to specific receptors on post-synaptic membrane:
- Some neurotransmitters will bind to receptors which cause depolarisation due to the influx of sodium ions (EPSP/ Excitatory post-synaptic potential).
- Some neurotransmitters will bind to receptors which cause hyperpolarisation due to influx of negative/Cl- ions (IPSP/ Inhibitory post-synaptic potential).
What are the two main neurotransmitters in the PNS, their general effects, and type of nerves?
- Acetylcholine (Parasympathetic, found in cholinergic nerves).
- Norepinephrine (Sympathetic, found in adrenergic nerves).
Which enzyme breaks down Acetylcholine in the synaptic cleft?
Acetylcholinesterase.
Acetylcholine -> Acetate + Choline.
How does nicotine work?
- Attaches to acetylcholine receptors.
- Mimics the actions of acetylcholine, causing depolarisation in postsynaptic neurone.
Nicotine increases heart rate and pressure, and triggers release of dopamine neurotransmitter.
How does lidocaine work?
It blocks voltage-gated sodium channels, preventing production of an action potential in sensory nerves. Prevents you from feeling pain because stimulus cannot reach CNS.
How does cobra venom work?
- Blocks acetylcholine receptors in the post synaptic membrane.
- Prevents the transmission of impulses/depolarisation across synapses and motor neurone junctions with muscles.
- Muscles cannot contract during inhalation, leading to paralysis.
What do rod cells detect?
Light intensity.
How does cobra venom work?
- Blocks acetylcholine receptors in the post synaptic membrane
- Prevents the transmission of impulses/depolarisation across synapses and motor neurone junctions with muscles
- Muscles cannot contract during inhalation, leading to paralysis.
What do cone cells detect?
Colour.
Where are rod cells found?
Periphery of the retina.
Where are cone cells found?
Fovea.
Where is the blind spot in our eye?
Optic nerve.
Explain the difference in sharpness between light intensity and color.
The lower acuity in rod cells is due to the number of cells connected to a bipolar neurone (3:1). The brain wouldn’t be able to tell which of the three rod cells had received light whereas 1 cone cell is directly attached to 1 bipolar neurone.
Explain the difference in acuity (sensitivity) between light intensity and color.
The pigment in cone cells, Iodospin, is less sensitive to light than the pigment in rod cells, rhodospin. The spatial summation of three rod cells to 1 bipolar neuron means the more likely the sum of their action potentials reaches threshold level in the bipolar neuron, so can detect weak stimulus.
What is rhodospin made up of?
Retinal (Derivative of Vitamin A, in Cis and Trans form) and Opsin (Lipoprotein).
Explain the rod cell response in light.
- Light turns cis-retinal into trans-retinal which cannot bind to opsin, leading to the breakdown of Rhodospin
- Opsin causes sodium channels in Rod cell to close
- Na+ continues to be pumped out of the cell
- Inside of the cell becomes negative as positive ions are pumped out, leading to hyperpolarisation.
- Hyperpolarisation stops the release of inhibitory neurotransmitters which allows Bipolar neurone to depolarise and send impulse to the CNS.
Explain the rod cell response in dark.
- Darkness turns trans-retinal back into cis-retinal which can bind to opsin, leading to the formation of Rhodospin
- Sodium channels in Rod cell to open
- Na+ continues to be pumped out of the cell
- Leakage of Na+ back into the cell causes slight depolarisation of around -40mv
- This causes Ca2+ ions channels to open which allows Ca2+ ions to move in and neurotransmitters to be secreted across synaptic cleft
- Inhibitory neurotransmitters, glutamate, inhibit depolarisation of bipolar neurone by causing influx of negative charge (Hyperpolarisation).
What is grey matter?
Relay neurons and cell bodies of motor neurons.
What is white matter?
Nerve fibres.
What are the regions of the brain and their functions?
Medulla oblongata - Controls breathing and heart rate
Cerebellum - Control balance and coordination of movement
Cerebrum - Initiates movement, learning, memory etc.
Hypothalamus - Temperature regulation and osmoregulation
Corpus callosum - Connect the left and right hemispheres for communication.
What is the structure of the spinal cord?
- Inside grey matter
- Outside white matter
- Dorsal root/Sensory neurone
- Ventral root/Motor neurone
- Relay neurone
- Dorsal root ganglion (All cell bodies of sensory neurones).
Why is the nervous system divided into parasympathetic and sympathetic systems?
Sympathetic systems have a rapid response during activity, or physical and psychological stress, whereas parasympathetic systems have a slow response which maintains normal function and restores calm after stressful situations. The interplay between the two systems allows for fine control and allowing the body to match its responses exactly to the demands placed upon it.
What is the cardiac control centre?
The medulla oblongata.
What are baroreceptors and where are they located?
Stretch sensitive (Pressure) receptors located in sinuses of carotid arteries (Neck) and located on the walls of the aorta.
What are chemoreceptors and where are they located?
H+ concentration sensitive receptors located on the walls of the aorta and the body of carotid arteries.
How does the liver form urea?
Deamination of excess amino acids:
Amino acid + Oxygen -> Keto acid + Ammonia.
Very toxic ammonia is then converted to less toxic Urea through the ORNITHINE cycle. Ornithine cycle is a series of reactions in which ammonia, carbon dioxide, and water react to form Urea.
What is the structure of the kidney?
- Renal Cortex (Outer layer)
- Medulla (Inner layer)
- Renal Pelvis (Urine collection chamber from collection ducts)
- Renal Artery
- Renal Vein
- Fibrous capsule
- Ureter.
What is the structure of the nephron?
- Afferent arteriole (Blood coming in)
- Efferent arteriole (Blood going out)
- Glomerulus
- Bowman’s capsule
- Proximal convoluted tubule
- Loop of Henle
- Vasa recta
- Distal convoluted tubule
- Collecting duct.
Explain ultrafiltration.
- High blood pressure develops in glomerulus since efferent arteriole is smaller in diameter than the afferent arteriole
- This pressure forces blood components out through the capillary wall, except blood cells and large plasma proteins
- Podocytes are some of the cells lining the Bowman’s capsule which ensure any cells, platelets, or large plasma proteins don’t leave the blood by forming a mesh structure around the blood vessels
- The isotonic filtrate includes glucose, urea and salts.
Explain what happens in the proximal convoluted tubule.
- Selective reabsorption
- The cells lining the tubule are covered with microvilli which increases surface area
- Glucose, amino acids, vitamins, some salt, some water, and most hormones are actively transported into intracellular spaces, which then diffuse back into the blood.
What happens in the distal convoluted tubule?
- Secretes waste chemicals such as creatinine into the filtrate
- Pumps ions to control blood pH
- Helps control blood volume.
What happens in the loop of Henle?
- Descending limb is permeable only to water and ascending limb is only permeable to ions.
1. Active transport of Na+ & Cl- out of ascending limb initially by diffusion as the filtrate is hypertonic, and then active transport.
2. Water potential in the medulla and vasa recta decreases as concentration of ions increases.
3. Water moves out of descending limb by osmosis due to concentration gradient.
4. Water potential of filtrate decreases going down descending limb; highest at top of ascending limb.
What is the vasa recta?
A series of blood vessels that run parallel to the loop of Henle but flows in the opposite direction. This creates a countercurrent mechanism that maintains the NaCl concentration gradient in the renal medulla.
Other than the vasa recta, where exists a countercurrent multiplier in a nephron?
- The loop of Henle
- Ascending and descending loops run parallel but in opposite directions which maintains a strong concentration gradient.
What are the adaptations of the kangaroo rats?
- Spend most of their time in burrows below the surface of the desert which is both cooler and more stable
- Get all their water from their food
- Long loops of Henle: This results in lower water potentials because the loop is a countercurrent multiplier. This produces very concentrated urine
- The tubules have more microvilli and more mitochondria for efficient reabsorption.
What is the mechanism of ADH?
Osmoreceptors in hypothalamus detect low water potential in the blood. Sends nerve to pituitary gland to release ADH. ADH increases the permeability of the distal tubule and collecting duct.
1. ADH binds to ADH receptor
2. ATP turns into cAMP by adenylyl cyclase
3. cAMP causes a series of reactions which cause vesicle to fuse with the cell membranes
4. Vesicles have aquaporins which increase water reabsorption.
What are endotherms?
Animals who maintain body temperature through metabolic heat.
What are ectotherms?
Organisms whose temperature depends on the external environment for their body temperature.
What are features of ectotherms?
- Warm up using external sources
- Body temperature that often fluctuates widely
- Low energy demand (Low basal metabolic rate (BMR))
- Limited range of environments
- Behavioural temperature control.
Fish, reptiles, amphibians, invertebrates.
What are features of endotherms?
- Body heat from metabolism
- Core-body temperatures held constant within a narrow range
- High energy demand (High BMR)
- Cope with extreme conditions
- Behavioural and physiological temperature control.
Birds and mammals.
What are the ways to reduce core body temperature?
- Vasodilation - arterioles near the surface of our skin dilate, allowing more blood to flow through them. This increases the amount of heat that can be lost from the surface of our skin through radiation.
- Sweating - sweat glands increase the secretion of sweat. When sweat evaporates from our skin’s surface, it takes heat energy with it which cools us down.
- Hairs lie flat - erector pili muscles underneath our skin relax, which causes the hair on our body to lie flat. This means that less air is trapped by the small hairs on our skin, making us feel cooler.
What are the ways to increase core body temperature?
- Vasoconstriction - arterioles near the surface of our skin constrict, so less blood is able to flow through them. This minimizes the amount of heat that can radiate from the surface of our skin.
- Reduced sweating - sweat glands reduce the secretion of sweat. Sweat normally cools us down by removing heat energy from our bodies when it evaporates, so the less sweat secreted, the less heat is lost.
- Hairs stand up - erector pili muscles underneath our skin contract, which causes the hair on our body to stand on end. The hair traps a layer of air which is a good insulator, preventing heat loss from our body.
- Shivering - muscles contract in spasms, increasing the amount of respiration inside the muscle. Heat is generated as a by-product of respiration (Chemical inefficiency).
- Hormones - the hormones adrenaline and thyroxine are released. These hormones increase the amount of respiration happening in our bodies, resulting in the generation of more heat.
What causes vasodilation and vasoconstriction?
Sphincter muscles control flow of blood into capillaries near the surface of the skin. When the sphincter muscles contract around the arterioles, the capillaries become narrower (vasoconstrict). Vice versa for vasodilation.
Where is body temperature controlled in the body?
Body temperature is controlled by the thermoregulatory centre in the hypothalamus of the brain. Detected by thermoreceptors, sending a response down the autonomic motor nerves.
