Organisms respond to changes in their internal and external environment Flashcards
Describe phototropism in plants
- Cells in the tip of the shoot/root produce IAA
- IAA diffuses down the shoot/root
- IAA moves to shaded side of the shoot/root
- In shoots, this stimulates cell elongation, whereas in roots, it inhibits cell elongation
- So shoots bend towards light whereas roots bend away from light
Describe how heart rate is controlled
- Baroreceptors detect a [fall / rise] in blood pressure and/or chemoreceptors detect a [rise / fall] in blood CO2 concentration or [fall / rise] in blood pH
- This sends impulses to the medulla / cardiac control centre which send more frequent impulses to SAN along the [sympathetic (increases heart rate) / parasympathetic (decreases)] neurones
- So [more / less] frequent impulses are sent from the SAN to / from the AVN so the cardiac muscle contracts [more / less] frequently
- So heart rate [increases / decreases]
Describe the locations of chemoreceptors and pressure receptors
Chemoreceptors and pressure receptors are located in the aorta and carotid arteries
Describe the Myogenic stimulation of the heart
- Sinoatrial node (SAN) acts as pacemaker - sends regular waves of electrical activity across the atria causing it to contract simultaneously
- Non-conducting tissue between atria/ventricles prevents impulse passing directly to the ventricles preventing immediate contraction of ventricles
- Waves of electrical activity reach the atrioventricular node (AVN) which delays the impulse, allowing the atria to fully contract and empty before ventricles contract
- AVN sends a wave of electrical activity down the bundle of His which branches into Purkyne tissue and causes the ventricles to contract simultaneously from the base up
Describe the differences in colour vision for rods and cones
- Rods only allow monochromatic vision (black and white)
There is only one type of rod that only contains one pigment - Cones allow colour vision
3 types of cones; red, blue and green
With different optical pigments → absorb different wavelengths
Stimulation of different combinations/proportions of cones gives a range of colour perception
Describe the differences in visual acuity for rods and cones
- Rods give lower visual acuity
Several rods are connected to a single neurone
Several rods send a single set of impulses to the brain (therefore, it cannot distinguish between separate sources of light)
Cones give higher visual acuity
Each cone is connected to a single neurone - Cones send separate (sets of) impulses to the brain (so can distinguish between 2 separate sources of light)
Describe the differences in sensitivity to light for rods and cones
- Rods are more sensitive to light
Several rods are connected to a single neurone Spatial summation is required to reach/overcome threshold to generate an action impulse - Cones are less sensitive to light
Each cone connected to a single neurone
No spatial summation
Describe how a generator potential is established in a pacinian corpuscle
- Mechanical stimulus (eg. pressure) deforms the lamellae and stretch-mediated sodium (Na+) channels
Na+ channels in membrane open and Na+ diffuse into the sensory neurone - Greater pressure causes more Na+ channels to open and more Na+ to enter
- This causes depolarisation, leading to a generator potential - If generator potential reaches threshold it triggers an action potential (see section 6.2)
Describe the importance of the protective effect
Rapid - only 3 neurones and a few synapses involved
Automatic - so it doesn’t have to be learnt
Protects from you from harmful stimuli
Describe Kineses (kinetic responses)
- Non-directional response
- Speed of movement or rate of direction changes in response to a non-directional stimulus (a stimulus that doesn’t relate to the direction an insect is in e.g. conditions of environment)
- Eg. woodlice move faster when in drier environment to increase chances of moving to an environment with higher humidity to prevent drying out
Describe Taxes (tactic responses)
- Directional response (response by movement in a direction)
- Movement towards (positive taxis) or away from (negative taxis) a stimulus
- Eg. woodlice move away from light to avoid predators
Describe gravitropism in plants
Cells in the tip of the shoot/root produce IAA
IAA diffuses down the shoot/root
IAA moves to lower side of shoot/root
In shoots, this stimulates cell elongation, whereas in roots, it inhibits cell elongation
So shoots bend away from gravity and roots bend towards gravity
Describe the role of growth factors in flowering plants
Specific growth factors (hormone-like growth substances) eg. Auxins (such as IAA) move from growing regions eg. shoot / root tips (where produced) to other tissues where they regulate growth in response to directional stimuli
Describe the inhibition by inhibitory neurotransmitters feature of synapses
- Inhibitory neurotransmitters hyperpolarise the postsynaptic membrane so chloride channels will open and chloride ions will diffuse in, potassium channels will also open so potassium ions will diffuse out
- Therefore, more sodium ions are needed for depolarisation
So reduces chance of threshold being met and action potential formation at post-synaptic membranes
Describe the summation feature of synpases
- Addition of a number of impulses converging on a single post-synaptic neurone
- Causing rapid buildup of neurotransmitter
- So threshold more likely to be reached to generate an action potential
Describe the unidirectionality of synapses
- Neurotransmitter only made in/released from the pre-synaptic neurone
- Receptors only present on the post-synaptic membrane
Describe the factors that affect speed of conductance
- Myelination
- Depolarisation at Nodes of Ranvier only - this is called saltatory conduction
Impulse doesn’t travel / depolarise the whole length of the axon
Axon diameter - a larger diameter means less resistance to the flow of ions in cytoplasm - Temperature
Increases the rate of diffusion of ions as there is more kinetic energy - However, proteins/enzymes could denature at certain temperatures
Describe the nature and importance of the refractory period
Nature: Refractory period is the time needed to restore the axon to the resting potential when no further action potential can be generated because Na+ channels are closed / inactive / will not open
Importance:
Ensures discrete impulses are produced (action potentials don’t overlap)
Limits frequency of impulse transmission at a certain intensity (prevents over reaction to a stimulus)
Ensures action potentials travel in one direction
Describe the all-or-nothing principle
For an action potential to be produced, depolarisation must exceed the threshold potential
Action potentials produced are always the same magnitude / size / peak at the same potential
Describe the generation of action potential
Stimulus: Na+ channels open and membrane permeability to Na+ increases, which causes Na+ to diffuse into the axon down an electrochemical gradient (causing depolarisation)
Depolarisation: If threshold potential is reached, an action potential is generated - this is because more voltage-gated Na+ channels open and therefore, more Na+ diffuses in rapidly
Repolarisation: voltage-gated Na+ channels close and voltage-gated K+ channels open causing K+ diffuse out of axon
Hyperpolarisation - K+ channels are slow to close so there’s a slight overshoot as too many K+ diffuse out
Resting potential is then restored by the Na+ / K+ pump
Describe the establishment of resting potential
Na+ / K+ pump actively transports 3 Na+ out of the axon and 2K+ into the axon
This creates an electrochemical gradient as there is a higher concentration of K+ inside the axon and a higher concentration of Na+ outside the axon
This creates differential membrane permeability as the axon is more permeable to K+, which moves out by facilitated diffusion and becomes less permeable to Na+ due to the closed channels
Describe the role of phosphocreatine in muscle contraction
Releases high-energy phosphates
To recycle ATP (as reformation of ATP requires phosphate molecules)
Describe the role of calcium ions and tropomyosin in the cycle of actinomyosin bridge formation
Before contraction, they cover the myosin binding sites on actin molecules, preventing myosin heads from binding
Calcium ions cause tropomyosin proteins to change position on actin filaments
Describe the role of ATP in myofibril contraction
Binds to myosin heads and is hydrolysed
Releases energy for the myosin head bending
Provides energy to detach myosin head and reattach further along
Also provides energy for calcium ions to be actively transported back into the sarcoplasmic reticulum
Describe the role of the calcium ions in myofibril contraction
- Released from the sarcoplasmic reticulum
- Binds to a protein attached to tropomyosin on the actin filament which causes the protein to change shape
- Moves position of tropomyosin on actin which exposes myosin binding site so muscle contraction can occur
- Activates the enzyme ATP hydrolase
Describe the role of the myosin in myofibril contraction
- Myosin are thick filaments with moveable heads
- Myosin heads attach to binding sites on actin
- This enables formation of actinomyosin cross bridges
- Myosin heads move, pulling actin along
- Detaches from binding site and moves to original position
Describe the role of the actin in myofibril contraction
- Actins are thin filaments (proteins) involved in myofibril contraction
- They provide myosin binding sites for myosin heads to bind
- Which enables formation of actinomyosin cross bridges
Describe the role of the actin in myofibril contraction
- Actins are thin filaments (proteins) involved in myofibril contraction
- They provide myosin binding sites for myosin heads to bind
- Which enables formation of actinomyosin cross bridges
Describe how our body responses to increase / decrease in water potential
- Osmoreceptors detect increase / decrease in water potential so the hypothalamus produces less / more ADH
- Posterior pituitary gland secretes less / more ADH into blood
- ADH attaches to receptors on collecting duct and increases / decreases permeability of cells to water (aquaporins join cell surface membrane) so more water reabsorbed from DCT / collecting duct by osmosis
- Urine = Larger volume, less concentrated / smaller volume, more concentrated
Describe what is meant by osmoregulation
Control of water potential of the blood (by negative feedback)
Describe the reabsorption of water by distal convoluted tubule and collecting ducts
- Water moves out of the distal convoluted tubule and collecting duct by osmosis down a water potential gradient
- This is controlled by ADH which increases permeability
Describe the role of the loop of Henle in maintaining a gradient of sodium ions
In the ascending limb, sodium ions actively transported out (so filtrate concentration decreases) and water remains as ascending limb is impermeable to water, this increases concentration of sodium ions in medulla (surrounding tissue around the loop of henle), lowering water potential of the medulla)
In the descending limb, water moves out by osmosis then reabsorbed by capillaries (so filtrate concentration increases) so sodium ions can diffuse back in essentially recycling the sodium ions
Describe the reabsorption of water by proximal convoluted tubule
Glucose in capillaries lowers water potential
So water moves by osmosis down a water potential gradient
Describe the reabsorption of glucose by proximal convoluted tubule
- Sodium ions actively transported out of epithelial cells to capillary
- Moves by facilitated diffusion into epithelial cells down concentration gradient, bringing glucose against its concentration gradient
- Glucose moves into capillary by facilitated diffusion down its concentration gradient
Describe the formation of glomerular filtrate
- High hydrostatic pressure in glomerulus as the diameter of afferent arteriole (in) is wider than efferent arteriole (out)
- Small substances eg. water, glucose, ions, urea forced into glomerular filtrate and are filtered by Pores between capillary endothelial cells, capillary basement membrane and podocytes
- Large proteins / blood cells remain in blood
Describe the causes and treatment of type 2 diabetes
- Often occurs because cells have fewer insulin receptors or their receptors are faulty and can no longer respond to insulin
- A significant risk factor for type 2 diabetes is long term obesity
- Treatment: Controlling diet e.g. avoiding foods that cause a rapid surge in blood glucose and by regular exercise
Describe the causes and treatment of type 1 diabetes
- Occurs when the cells in the pancreas responsible for the production of insulin are destroyed by the immune system
- Usually due to genetics that increase the chances of development
- Treatment: insulin-dependent and must inject themselves daily with insulin
Describe the secondary messenger model of adrenaline and glucagon action
- Adrenaline / glucagon (‘first messenger’) attach to specific receptors on cell membrane
- This activates enzyme adenylate cyclase
- Which converts many ATP to many cyclic AMP (cAMP)
cAMP acts as the second messenger - activates protein kinase enzymes - Protein kinases activates enzymes to break down glycogen to glucose
Describe the action of adrenaline in increasing blood glucose concentration
- Attaches to specific receptors on cell surface membranes of target cells eg. liver
- Activates enzymes involved in glycogenolysis (hydrolysis of glycogen to glucose)
Describe the action of glucagon in increasing blood glucose concentration
- Attaches to specific receptors on cell surface membranes of target cells eg. liver
- Activates enzymes involved in glycogenolysis (hydrolysis of glycogen to glucose) and enzymes involved in gluconeogenesis (conversion of glycerol / amino acids to glucose)
Describe the action of insulin in decreasing blood glucose concentration
- Attaches to specific receptors on cell surface membranes of target cells eg. liver / muscles
- Causing more glucose channel proteins to join cell surface membrane which increases permeability to glucose and more glucose enters cell by facilitated diffusion
- Activating enzymes involved in conversion of glucose to glycogen (glycogenesis) so lowers glucose concentration in cells and glucose enters cells by facilitated diffusion down conc. gradient
Describe the role of the liver in glycogenesis, glycogenolysis and gluconeogenesis
- Glycogenesis - converts glucose to glycogen
- Glycogenolysis - converts glycogen to glucose
- Gluconeogenesis - converts amino acids and/or glycerol into glucose
Describe the factors that affect blood glucose concentration
Consumption of carbohydrates - glucose is absorbed
Rate of respiration of glucose - uses up glucose rapidly e.g. during exercise due to muscle contraction
Describe why it is important we maintain the water potential of blood within restricted limits
- So that excess water does not enter or leave body cells by osmosis
- Causing cells to burst or dehydrate and shrive
Describe why it is important we maintain a stable blood glucose concentration
- To provide sufficient substrate for respiration
- To release energy for metabolic processes in the body
Describe why it is important we maintain stable blood pH
- To provide an optimum pH for enzyme activity
- Extreme changes in pH from the optimum will cause enzyme denaturation
Describe what homeostasis involves
Involves physiological control systems that maintain the internal environment with restricted limits i.e. maintains a relatively constant internal environment
Define the parasympathetic nervous system
part of the autonomic nervous system that promotes “rest and digest” functions,
