A Level Edexcel Biology B Topic 9 Question & Answers 2024, Exams of Nursing

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Question & Answers 2024

What does homeostasis mean? - Correct Answers ✅Maintenance of a state of dynamic equilibrium What does homeostasis control? - Correct Answers ✅Constant internal environment, including constant temperature water potential and pH Why must temperature and pH be regulated? - Correct Answers ✅For optimum enzyme activity Why must water potential be regulated? - Correct Answers ✅To avoid negative osmotic effects which could damage a cell e.g lysis, shrinkage and disruption of metabolic reactions What does negative feedback do? - Correct Answers ✅Ensures that any departure from an ideal state results in a return to the ideal state Counteracts changes in internal conditions to maintain dynamic equilibrium What is the process of negative feedback? - Correct Answers ✅1. Change occurs in internal environment

2. Change is detected by receptors

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3. Receptors lead to activation of a mechanism that reverses the change
4. Conditions return to ideal and the mechanism is switched off What is the process of positive feedback? - Correct Answers ✅1. Change occurs in the internal environment
5. This change is detected by receptors
6. Receptors lead to activation of a mechanism that continues the change What does positive feedback do? - Correct Answers ✅Causes a departure from a starting condition to lead to further departure What are the two main modes of action in hormones? - Correct Answers ✅1. Hormones attach to receptor sites and trigger the release of a second messenger by a series of membrane bound reactions. The second messenger activates enzymes in the cell e.g. adrenaline
7. Hormones enter the cell through the cell membrane and bind to transcription factors e.g oestrogen and steroid hormones What do endocrine glands do? - Correct Answers ✅Secrete hormones directly into blood which signal proteins

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What are cytokines? - Correct Answers ✅Chemical messengers released by cells in the immune system that stimulate other cells in the immune system What are neurotransmitters? - Correct Answers ✅Chemicals released at the ends of neurones that stimulate their target cells What are target cells? - Correct Answers ✅Cells with receptor proteins on their cell surface membrane complimentary to the chemical What are meristems? - Correct Answers ✅Regions of actively dividing cells e.g. roots and shoots What do cytokinins do? - Correct Answers ✅promote cell division of stem and promote growth of lateral buds How do auxins cause cell elongation? - Correct Answers ✅Causes cell elongation by active transport of hydrogen ions into the cell walls, which lowers pH, making the cell walls flexible. Cells stretch to accommodate more water which leads to growth of the cell. What is Apical Dominance? - Correct Answers ✅The balance between auxins and cytokinins

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Auxin inhibits cytokinins effect on lateral growth. As the shoot grows up, the concentration of auxin decreases lower and lateral buds form What do auxins do? - Correct Answers ✅Promote cell elongation Promote growth of root laterally Suppresses growth of lateral buds What do gibberellins do? - Correct Answers ✅Promote cell elongation when auxins are present Reinforces the effect of auxins in apical dominance Stimulates germination, growth of fruit and flowering How do gibberellins stimulate seed germination? - Correct Answers ✅1. Seed absorbs water and embryo is activated

2. The embryo secretes gibberellins which diffuse to the aleurone layer
3. The aleurone layer produces amylase
4. Amylase diffuses to the endosperm layer and breaks down to glucose

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What happens when cytokinins work synergistically with ethene? - Correct Answers ✅Promotes leaves falling off What is a phytochrome? - Correct Answers ✅Plant pigment that exists in two forms What is Pr? - Correct Answers ✅Absorbs red light (sunlight), the biologically inactive form What is Pfr? - Correct Answers ✅Absorbs far red light, the biologically active form What happens when a phytochrome absorb red light? - Correct Answers ✅It converts to Pfr What happens when a phytochrome absorbs far red light? - Correct Answers ✅It converts to Pr What does Pfr do? - Correct Answers ✅It is transported from the cytoplasm into the nucleus of the plant cells where it activates transcription factors that stimulate the transcription of genes affecting photomorphogenesis

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Whats photomorphogenesis? - Correct Answers ✅Effect of light of the growth of plants What does Pfr do to long- day plants? - Correct Answers ✅Stimulates flowering when there are short nights What does Pfr do to short-day plants? - Correct Answers ✅Inhibits flowering when nights are long What is etiolation? - Correct Answers ✅When plants are grown in the dark and become tall, thin, fragile, small and yellow leaved and short rooted What happens if a plant is exposed to red light followed by far red light? - Correct Answers ✅The plant is only effected by the last light exposed to it What is the central nervous system? - Correct Answers ✅The brain and spinal cord What is the peripheral nervous system? - Correct Answers ✅Automatic:

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Sympathetic-ganglia close to CNS that coordinates flight or fight response Parasympathetic-ganglia far from the CNS that coordinates the rest and digest response Voluntary: Under conscious control/ somatic How do the sympathetic and parasympathetic nervous systems work together? - Correct Answers ✅Antagonistically What is the order of a reflex? - Correct Answers ✅Receptor Sensory neurone Relay neurone Motor neurone Effector

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What is in white matter? - Correct Answers ✅Myelinated axons of motor neurones leaving the white matter and sensory neurones entering the white matter Sensory neurones enter via a branch from a spinal nerve called the dorsal root at the back of the chord Motor neurones leave by a spinal nerve at the front of the chord- the ventral root What is in grey matter? - Correct Answers ✅Un-myelinated neurones Links sensory and motor neurones in reflex arcs Runs up and down the spinal cord What does the hypothalamus do? - Correct Answers ✅temperature regulation and osmoregulation Where is the pituitary gland? - Correct Answers ✅ Where is the hypothalamus? - Correct Answers ✅

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Where is the cerebrum? - Correct Answers ✅ Where is the medulla oblongata? - Correct Answers ✅ Where is the cerebellum? - Correct Answers ✅ What does the cerebrum do? - Correct Answers ✅Initiates movement What does the cerebellum do? - Correct Answers ✅Controls balance and coordination of movement What does the medulla oblongata do? - Correct Answers ✅Controls breathing and heart rate What's in the cell body of a neurone? - Correct Answers ✅Nucleus and cell organelles What are dendrons? - Correct Answers ✅at the end of axons and stimulated by neurotransmitters released by an adjacent neurone

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What is an axon? - Correct Answers ✅Long extension from cell body that transmits impulses What is a myelin sheath? - Correct Answers ✅Insulates axon, restricting movement of a charge jumping What are Schwann cells and Nodes of Ranvier? - Correct Answers ✅cells wrapped around axons and the gaps between them What do synaptic bulbs do? - Correct Answers ✅release neurotransmitter onto cell What does a motor neurone look like? - Correct Answers ✅ What does a sensory neurone look like? - Correct Answers ✅ What does a relay neurone look like? - Correct Answers ✅ What speeds up the speed of transmission in a neurone? - Correct Answers ✅Myelination-prevents electrical impulses jumping Thicker diameter of nerve fibre

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Saltatory conduction What is saltatory conduction? - Correct Answers ✅Rapid conduction of action potentials in myelinated axons as they jump between nodes of Ranvier What is a resting potential? - Correct Answers ✅When an axon is polarised when it is not transmitting an impulse There is a difference in charge between cytoplasm and external medium The membrane potential is -70mV How is a resting potential maintained? - Correct Answers ✅1. Na+ is actively transported out of the neurone

2. K+ is transported into the neurone
3. For every 3 Na+ ions pumped out, 2 K+ ions are pumped in (by a sodium-potassium pump) so cytoplasm is more negative
4. K+ also diffuses out of the cell by facilitated diffusion through open K+ channels
5. Na+ diffuses into the cell through open Na+ channels

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What is an action potential? - Correct Answers ✅When a receptor or neurone secretes neurotransmitter across an excretory synapse it causes the membrane potential of the receiving cell to change momentarily to about +40mV What are the steps of depolarisation and repolarisation? - Correct Answers ✅1. All the voltage-gated Na+ channels and voltage-gated K+ channels are closed

2. Some voltage-gated Na+ channels open allowing Na+ ions to diffuse into the axon. This makes the membrane potential less negative
3. The membrane potential reaches -55mV which is the threshold level and more voltage-gated Na+ channels open and Na+ ions rapidly diffuse into the axon
4. The membrane potential reaches +40mV and two events are stimulated: -voltage-gated Na+ channels close -voltage-gated K+ channels open to let K+ ions diffuse out of the axon and resting potential is restored
5. Often too many K+ ions diffuse out causing hyperpolarisation of about -80mV What does an action potential graph look like? - Correct Answers ✅

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What is the refractory period of an action potential? - Correct Answers ✅The period of time after an action potential where another action potential can't take place What is the absolute refractory period? - Correct Answers ✅Periods of depolarisation and repolarisation What is relative refractory period? - Correct Answers ✅Period of hyperpolarisation and time when resting potential is restored What is a synapse? - Correct Answers ✅Junction between two neurones What is in the synaptic knob? - Correct Answers ✅Surface membrane with gated Ca2+ channels Cytoplasm with many mitochondria Vesicles containing a neurotransmitter e.g. acetylcholine or noradrenaline

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What is the synaptic cleft? - Correct Answers ✅The gap between two cells What does the dendrite on the post-synaptic neurone have? - Correct Answers ✅A cell surface membrane with neurotransmitter receptors that act as gated Na+ and K+ channels What does an excitory synapse do? - Correct Answers ✅Stimulates an impulse in the post-synaptic cell What does the inhibitory synapse do? - Correct Answers ✅Inhibits an impulse in the post-synaptic cell What happens at an excitory synapse? - Correct Answers ✅1. Action potential arrives at the pre-synaptic membrane

2. The pre-synaptic membrane depolarises so the Ca2+ channels open and Ca2+ rapidly diffuses from the synaptic cleft into the pre-synaptic neurone
3. Entry of Ca2+ ions cause vesicles to fuse with the pre-synaptic membrane and release a neurotransmitter into the synaptic cleft
4. The neurotransmitter diffuses across the synaptic cleft and fuses with receptors in the post-synaptic membrane
5. Gated Na+ channels open in the membrane and Na+ rapidly diffuse into the post-synaptic cell

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6. The cytoplasm of the post-synaptic cell becomes more positively charged and the action potential continues What happens at an inhibitory synapse? - Correct Answers ✅1. Action potential arrives at the pre-synaptic membrane
7. The pre-synaptic membrane depolarises so the Ca2+ channels open and Ca2+ rapidly diffuses from the synaptic cleft into the pre-synaptic neurone
8. Entry of Ca2+ ions cause vesicles to fuse with the pre-synaptic membrane and release a neurotransmitter into the synaptic cleft
9. The neurotransmitter diffuses across the synaptic cleft and fuses with receptors in the post-synaptic membrane
10. Gated K+ channels and gated Cl- channels open in the membrane letting K+ and Cl- to rapidly diffuse into the post-synaptic cell
11. The cytoplasm of the post-synaptic cell is more negatively charged, preventing an action potential What is the effect of nicotine? - Correct Answers ✅Mimics the effect of acetylcholine and triggers the release of dopamine What is the effect of lidocaine? - Correct Answers ✅Blocks voltage gated Na+ channels in post-synaptic membranes Used as anaesthetic

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What is the effect of cobra venom? - Correct Answers ✅Blocks acetylcholine receptors in post-synaptic membranes Deadly What is the structure of the retina? - Correct Answers ✅Outer segment-light sensitive and contains flattened membranous vesicles with photosensitive pigments Constriction- a narrow region between segments Inner segment- packed with mitochondria and ribosomes Synaptic region What is the difference between rod and cone cells? - Correct Answers ✅Cone found at centre, rod found at periphery Cone has iodopsin, rod has rhodopsin

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Iodopsin degrades with high intensity light, rhodopsin degrades with any light Cone sensitive to red, green or blue light, rod is insensitive to light What happens when Rhodopsin is stimulated by light? - Correct Answers ✅1. The pigment within rods is degraded into opsin and retinal

2. Opsin stimulates a series of enzyme-catalysed reactions that cause the cell surface membrane of the rod cell to become hyperpolarised
3. Rod cells no longer release neurotransmitters
4. The cell surface membrane of the bipolar cell becomes depolarised and release neurotransmitters
5. The ganglion cell becomes depolarised and transmits an impulse to the optic nerve
6. Rhodopsin is resynthesised in the dark What happens when Rhodopsin is not stimulated by light? - Correct Answers ✅1. Cell surface membrane is depolarised
7. Rod cells release a neurotransmitter onto the bipolar cell
8. This has an inhibitory synapse so a neurotransmitter is not released to the ganglion cell
9. No impulses are sent from the ganglion cell to the optic nerve

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What changes in the blood does the heart respond to? - Correct Answers ✅CO2 concentration -detected by chemoreceptors in the aorta and carotid arteries Blood pressure -detected by baroreceptors in aorta and carotid arteries Where do receptors for heart rate send impulses to? - Correct Answers ✅The medulla oblongata where the cardiac centre is located What happens when blood pH decreases (high CO2)? - Correct Answers ✅Impulses are passed down sympathetic nerves from the acceleratory centre of the cardiac centre to the SAN causes an increase in heart rate by releasing noradrenaline How is heart rate decreased? - Correct Answers ✅Impulses are passed down parasympathetic nerves and release acetylcholine at the SAN What is the structure of the kidneys? - Correct Answers ✅ What is the structure of a nephron? - Correct Answers ✅

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What happens at the Bowman's capsule and glomerulus? - Correct Answers ✅Ultrafiltration What happens in the proximal convoluted tubule? - Correct Answers ✅Selective reabsorption of filtrate What happens in the loop of Henle? - Correct Answers ✅Water conservation What happens in the distal convoluted tubule? - Correct Answers ✅pH adjustment and ion reabsorption What happens in the collecting duct? - Correct Answers ✅Water reabsorption What is ultrafiltration? - Correct Answers ✅Water, ions and small molecules are forced out of capillaries of the glomerulus and into the Bowman's capsule (in a similar process to tissue fluid being forced out of capillaries) What happens in the first process of selective reabsorption? - Correct Answers ✅Some water, all glucose and amino enzymes (co-

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transported with Na+ ions), ions and some urea is reabsorbed into the blood How does the loop of Henle conserve water? - Correct Answers ✅1. Cells in the upper part of each ascending limb actively secretes Na+ ions and Cl- ions from the ultra filtrate into the tissues of the medulla

2. Cells in the upper part of the descending limb, are permeable to these ions and diffuse in from the ascending limb
3. This greatly increases the concentration of Na+ and Cl- in the tissues of the medulla
4. This results in the tissues of the medulla having the negative water potential
5. Water passes from the collecting ducts into the medulla and into the vasa recta capillaries around the loop of Henle
6. The ultra filtrate is more concentrated than the blood and therefore urine is more concentrated What happens in the second process of selective reabsorption? - Correct Answers ✅Some ions and some water diffuse back into the blood Controlled by hormones

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What happens during water reabsorption? - Correct Answers ✅ADH regulates water diffusing back into the blood How is urea produced? - Correct Answers ✅By deamination:

1. Hepatocytes (liver cells) deaminate excess amino acids
2. Amino acids are removed and converted into ammonia
3. This is further converted to urea which is less toxic
4. Urea is secreted by the kidneys What is osmoregulation? - Correct Answers ✅Maintenance of a constant osmotic pressure in tissues of a living organism by controlling water and salt concentrations How does ADH effect the amount of urine produced? - Correct Answers ✅1. When water is in short supply, the concentration of inorganic ions in the blood rises and the water potential becomes more negative
5. The change is detected by osmoreceptors in the hypothalamus and nerve impulses are sent to to the posterior pituitary which releases ADH
6. ADH is picked up by receptors in the kidneys and reduces permeability of the distal tubule and collecting duct to let water back into the blood

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What makes kangaroo rats special? - Correct Answers ✅They never drink as they live in the desert. They do this by: Staying cool in burrows Generating water by oxidative reactions Get water from their food Producing very concentrated urine -have many juxtamedullary nephrons, long loops of Henle, high concentrations of ions in the medulla and more infoldings in cell membranes of epithelial cells lining tubules to increase diffusion What is an ectotherm? - Correct Answers ✅A cold-blooded animal that relies entirely on behavioural methods to gain or lose heat What is an endotherm? - Correct Answers ✅A warm blooded animal that uses physiological mechanisms as well as behavioural methods to gain or lose heat

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How do endotherms regulate temperature? - Correct Answers ✅They have a thermoregulatory centre in the hypothalamus that has a heat gain and heat loss centre How does the heat loss centre react to an increase of temperature? - Correct Answers ✅Behavioural: Seek shade Remove clothing to reduce insulation Physiological: Vasodilation of skin arterioles Increased sweating to increase heat loss by evaporation How does the heat gain centre react to a decrease in temperature? - Correct Answers ✅Behavioural: Move around to create extra muscle contractions to generate heat

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Put on clothing to increase insulation Physiological: Vasoconstriction of skin arterioles Sweating reduced Hairs stand up to produce an isolation layer