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Organisms respond to changes in their internal and external environments
Terms in this set (24)
A woman takes moderate exercise. Explain what caA woman takes moderate exercise.
2. carbon dioxide concentration increases / pH falls / H+ increases / acidity
3. chemoreceptors in aortic / carotid bodies / medulla (accept reference to
aorta / carotid arteries not sinus);
4. (impulses to) medulla / cardioaccelerator centre;
5. increased frequency of impulses (award only once);
6. along sympathetic pathway to sinoatrial node / SAN (not pacemaker);
The heart controls and coordinates the regular contraction of the atria and ventricles. Describe how (5)
1. SAN → AVN → bundle of His /Purkyne fibres;
2. Impulses / electrical activity (over atria);
3. Atria contract;
4. Non-conducting tissue (between atria and ventricles);
5. Delay (at AVN) ensures atria empty/ ventricles fill before ventricles contract;
6. Ventricles contract from apex upwards;
Explain how the resting potential of -70 mV is maintained in the sensory neurone when no pressure is applied.
1. Sodium ions actively transported / pumped out and potassium ions in.
2. Membrane more permeable to potassium ions and less permeable to sodium ions;
The membrane potential at Q (sensory neurone) was the same whether medium or heavy pressure was applied to the finger tip. Explain why.
1. Threshold has been reached
2. (Threshold or above) causes maximal response / all or nothing principle.
Multiple sclerosis is a disease in which parts of the myelin sheaths surrounding neurones are destroyed. Explain how this results in slower responses to stimuli.
1. Less saltatory conduction/ impulse unable to jump from node to node
2. More depolarisation over length / area of membranes.
Cannabinoids include substances found in cannabis that can enter brain tissue. Scientists are developing artificial cannabinoids that can enter neuromuscular junctions but cannot enter brain tissue.
Suggest why these artificial cannabinoids would be better to use than cannabis when treating someone with MS.
They wont affect synapses in the brain
They won't cause problems with the brain's function / won't damage brain;
A myelinated axon conducts impulses faster than a non-myelinated axon. Explain this difference.
1.(In myelinated) action potential / depolarisation only at node(s);
2. (In myelinated, nerve impulse) jumps from node to node / saltatory;
3. (In myelinated) action potential / impulse does not travel along whole length;
It is important that a neurotransmitter such as serotonin is transported back out of synapses. Explain why.
1. (If not removed) keeps binding (to receptors);
2. Keeps causing action potentials / depolarisation (in post-synaptic membrane);
Describe how the resting potential is established in an axon by the movement of ions across the membrane.
active transport / pump of Na+ out of axon;
diffusion of K+ out of axon / little diffusion of Na+ into the axon;
Explain the importance of reflex actions.
1. automatic (adjustments to changes in environment) / involuntary;
2. reducing / avoiding damage to tissues / prevents injury / named injury e.g. burning;
3. role in homeostasis / example;
4. posture / balance;
5. finding / obtaining food / mate / suitable conditions;
6. escape from predators;
One form of muscle disease is caused by a mutated allele of a gene. This leads to production of myosin molecules that are unable to bind to other myosin molecules.
If myosin molecules are unable to bind to other myosin molecules, this prevents muscle contraction.
Use the diagram and your knowledge of how muscles contract to suggest why.
1. Can't form myosin / thick filaments;
Neutral: prevents actin and myosin sliding filament action
2. Can't pull / can't move actin / slide actin past / (myosin) have to be joined / fixed to pull actin;
Accept: myosin can't pull on each other
3. Myosin moves / if attached doesn't move;
4. Can't move actin towards each other / middle of sarcomere / between myosin / can't shorten sarcomere / can't pull Z lines together.
Accept: contract for shorten
The stain used reacts with an ATPase enzyme. Muscle fibres containing a lot of this ATPase stain brown. Fibres containing little ATPase stain yellow.
The tissue in the diagram came from muscle with a high proportion of brown-staining fibres. Was the tissue removed from slow or fast skeletal muscle?
Explain your answer.
Fast because (lots of) ATPase allows rapid hydrolysis of ATP OR
Slow because (lots of) ATPase allows rapid synthesis of ATP.
Use information from the table to suggest and explain one advantage of:
(i) the high glycogen content of fast muscle fibres
1. (Glycogen broken down) gives (lots of) glucose for glycolysis / anaerobic respiration;
2. Glycolysis / anaerobic respiration not very efficient / only yields 2 ATP per glucose;
(ii) the number of capillaries supplying slow muscle fibres.
1. (Many capillaries) give high concentration / lots of oxygen / shorter diffusion pathway for oxygen / large surface area for oxygen exchange / diffusion / good glucose supply with little glycogen present;
2. Allows high rate of / more aerobic respiration OR prevents build-up of lactic acid / (muscle) fatigue;
Diabetes can damage the nervous system. The response of the rats with diabetes is different from the response of the healthy rats. Use your knowledge of the control of heart rate by the nervous system to suggest an explanation for these results.
1. Damage to autonomic (nervous) system in diabetic rats; /carotid body) don't work as well;
2. (Could be) pressure receptors/baroreceptors (in arteries/aorta
3. Damage to medulla
Change in (number of) impulses to/from medulla;
4. (When pressure drops damage to) sympathetic system, so
doesn't speed up (enough);
5. (When pressure rises damage to) parasympathetic system, so
doesn't slow down (enough);
Some drugs inhibit the transmission of nerve impulses to the heart. Explain how these drugs reduce high blood pressure.
1. inhibit impulses in sympathetic nerves / from cardio-acceleratory centre;
2. SAN not stimulated / noradrenaline not released so heart rate lowers / does not increase;
Give two ways in which people with type 1 diabetes control their blood glucose concentration.
1. Treat with insulin (injection/infusion);
2. (Control) diet/control sugar intake;
Explain why the events shown in the diagram can be described as an example of negative feedback.
A change to the normal level initiates a response which reduces the effect / reverses / acts against the change;
Describe the role of the hormone glucagon in the control of blood sugar concentration.
Binds to (specific) receptor; On muscle / liver cell;
Activation of enzymes (in liver);
Hydrolysis of glycogen;
(Facilitated) diffusion of glucose out of (liver cells) cells; Increases blood glucose levels;
Describe how urea is removed from the blood.
Hydrostatic pressure / description of pressure / description of how pressure generated; Causes ultrafiltration (Allow description of ultrafiltration) at Bowman's capsule / glomeruli / renal capsule;
Through basement membrane;
Enabled by small size urea molecule;
Some people who have diabetes do not secrete insulin. Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin.
1. High concentration of glucose in blood;
2. High concentration in tubule / in filtrate;
3. Reabsorbed by facilitated diffusion / active transport; 4. Requires proteins / carriers;
5. These are working at maximum rate / are saturated; 6. Not all glucose is reabsorbed / some is lost in urine;
Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH). Explain how these two features are adaptations to living in desert conditions.
For general principle, applied to either example:
1. More water (from filtrate) reabsorbed / returned to blood / less lost in urine;
2. By osmosis;
3. From collecting duct / from end of second convoluted tubule;
4. Due to longer loop of Henle;
For loop of Henle, maximum 2 marks:
5. Sodium / chloride ions absorbed from filtrate in ascending limb;
6. Gradient established in medulla / concentration of ions increases down medulla;
For ADH, maximum 2 marks:
7. Acts on collecting duct / distal convoluted tubule / second convoluted tubule;
8. Makes cells more permeable / inserts aquaporins in plasma membranes;
A high blood glucose concentration could cause glucose to be present in the urine of a diabetic person. Suggest how.
Large amount / high concentration of glucose in filtrate;
Cannot all be reabsorbed / 1st convoluted tube too short to reabsorb all of glucose / saturation of carriers;
If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why.
Glucose in filtrate lowers water potential;
Ignore 'urine'. Accept increase solute potential
Lower Ψ gradient / less difference in Ψ filtrate − Ψ plasma; Ignore 'concentration'
Less water reabsorbed by osmosis;
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