Unit 2 Biology: Homeostasis

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involves a stimulus-response model in which change in the condition of the external or internal enviornment is detected and appropriate responses occur via negative feedback

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receptor that detect changes in touch, pressure hearing and equilbrium, position and acceleration

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receptor that is sensitive for heat and cold

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receptor that detects chemical energy of substances dissolved in fluid around them - taste and smell

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receptors, detect physical and chemical damage to tissues

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receptor that detects changes in water volume

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receptor that detects change in light sensitivity

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two types of receptors

muscles and glands

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  • organic tissues that can contract in response to neural stimulation.

  • constructed of repeatedly overlapping filaments of myosin and actin. These two molecules, shuffle along each other when activated by a signal from a motor neuron.

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organs that secrete chemicals or proteins either within the body, called endocrine glands, or externally, called exocrine glands. Endocrine glands secrete substances into the bloodstream, such as insulin and adrenaline. Unlike muscles, glands can respond to both neural and chemical stimulation.

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set of metabolic pathways that break down molecules into smaller molecules

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set of metabolic pathways that build up larger molecules from smaller molecules

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why do changes in metabolic acitivity alter the optimum conditions for catalyctic activity of enzymes

  • enzymes work at optimum temps and pH

  • metabolic acitivity produces heat and CO2 that can affect pH levels

  • higher temps and extremes of pH will denature enzymes

  • an increase in metabolic activity can lower enzyme functuality

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sensory neurons

neurons that transmit information from tissues and organs to the CNS

  • soma is at centre of cell

  • cell body is in the PNS

  • dendrites at ends of axon

  • shorter axon

  • axon connects to receptor

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short neurons found in the spinal cord linking sensory and motor neurons as well as making up nerve tissue in the brain

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motor neurons

neurons that carry impulses to effectors

  • soma is at one end

  • soma is in CNS/brain/spinal cord

  • dedrites connected directly to cell body

  • longer axon

  • axon connects to effector

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soma/cell body

  • contains nucleus and granular cytoplasm containing many ribosomes

  • these ribosomes group together to form Nissl granules that are concerned with the formation of neurotransmitters

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thin extensions that carry impulses towards the soma/cell body

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  • a long membrane-covered cytoplasmic extension that transmits impulses away from the cell body

  • it divides into branches at its end, which forms synapses with other neurons

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schwann cell

  • produce the multilayered myelin sheath around neuronal axons

  • acts as an electrical insulater and speeds up the transmisssion of impulses

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nodes of ranvier

a small gap in the myelin sheath that allows action potential to take place

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axon terminals

endings that are specialised to release neurotransmitters of the presynaptic cell

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  • presynaptic ending that contains neurotransmitters, mitachondria and other cell organelles

  • a postsynaptic ending that contains receptor sites for neurotransmitters

  • a snypatic cleft or space between the presynaptic and postsynaptic endings

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resting potential

  • when a neuron is not sending a signal, it is at rest: the inside neuron is negatively relative to the outside (approx -70 mV)

  • due to 3Na+ being actively moved out of the membrane, whilst being actively transported into the axon

  • membrane is inactive and polarised

  • there are more sodium ions outside the neuron and more potassium inside

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action potential

  • when stimulated the membrane is briefly polarised

  • stimulus causes the membrane at one part of the neuron to increase in permability to Na+

  • Na voltage-gated channels open and Na+ enter the axon down their elctrochemical gradient by diffusion

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when there is a slight overshoot in the movement of K+ meaning that the inside of the axon is more negative than usual (refractory period)

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synaptic transmission

  • the incoming action potential causes depolarisation in the synaptic knob which causes the calcium channels to open and calcium ions (Ca2+) flood into the synaptic knob

  • neurotransmitters are released into the synaptic cleft by exocytosis

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  • a chemical compound that is involved in the control of various metabolic functions

  • they act as intercellular messengers to regulate cellular functions

  • they relay messages to cells displaying specific receptors for each hormone via the circulatory or lymphatic system

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cell-surface receptor

  • membrane-anchored, or intergral proteins that bind to external molecules

  • this type of receptor spans the plasma membrane and performs signal transduction, converting an extracellular signal into a intercellular signal

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their heat is produced through internal means, and not reliant on the external temp

structural features:

  • brown adipose tissue: turns food into body heat by non-shivering thermogenesis

  • increased number of mitachondria per cell: mitachondria release heat when metabolishing fats and sugars

  • insulation: insulation in vertebrates can take the form of fur, feathers or fat layers

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behavourial response: any form of thermoregulation by which an animal shares in the metabolic thermogenesis of another animal. most common form is huddling

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behavioural response: is voluntary and allows an animals metabolism slow significantly, heartbeat slows, it breathes more slowly and body temp drops.

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behavioural response prolonged torpor or dormancy of an insect, fish, or amphibian during a hot or dry period.

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behavioural response: like hibernation, it involves a lowwr body temp, breathing rate, heart rate, and metabolic rate but only for short periods of times

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vasomotor control

control of peripheral blood vessels causes vasoconstriction or vasodilation, allowing thermoregulation to occur

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evaporative heat loss

both sweating and pantinb aids in thermoregulation as evaporation of sweat from the skin surface takes away heat too

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countercurrent heat exchange

physiological response: a circulatory adaptation that allow heat to be transferred from blood vessels containing warmer blood to those containing cooler blood

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thyroid hormones (homeostastic mechanisms)

affect basal metabolic rate and have also been found to affect how blood vessels dilate

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may be inhibited if the need for glucose arises to supply the increased rate of cellular respiration when trying to therm

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  • match the salinity of their environment not changing their owninternal osmotic balance

  • synthesise substances upon a rise in external salt concentration to keep internal and external osmolaters

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  • actively control the amount of salt in their bodies and what is happening in water around them.

  • must be able to get rid of excess salts or actively promote the uptake of salts from the enviornment

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structural features (excretory system)

animals have differing lengths of loop of Henle, depending on their enviornment

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behavioural responses

drink more water when dehydrated or move to the shake when its hot

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physiological mechanisms

  • specialised cells in gills that can actively absorb or secrete salts

  • these cells can switch between booth modes in fish such as some salmon species that start their life in feshwater before swimming to the ocean the migrating back to freshwater

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homeostatic mechanisms (antidiuretic hormone (ADH) and the kidney)

ADH causes more water is reabsorbed into the blood, therefore urine becomes more concentrated

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  • live with their roots submerged in the mud at the bottom of a pond and have floating leaves on the surface due to large air spaces present in both stem and leaf tissue

  • they have little need for support or transport tissues; have little or no cuticle and stomata only on the upper surface of their leaves

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  • cellular sequestration: can isolate toxic ions and salts within cell wall and vacuoles

  • tissue partitioning: can concentrate salts in certaim leaves which then drop off

  • root level exclusion: roots may be structured to exclude 95% of the salt found in soil

  • salt excretion: certain parts of the plant may contain salt glands to actively remove salts

  • altered flowering schedule: may flower at particular times such as during the wet season to minimise salt exposure

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they need to survive unfavourable times of the year

  • shed their leaves before winter

  • the aerial parts may die off, but bulbs can survive underground, or survive winter as dormant seeds

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rolled leaves, sunken stomata and leaf hairs to maintain humid air around stomata

stomata on inside of leaf decreases exposure to wind minimising concentration gradient → lower transpiration rates

thick wavey cuticle as a barrier to evaporation

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order of feedback system

stimulus → receptor → control centre → effector

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recall the threshold limit


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the process in how blood glucose concentration can be controlled by negative feedback

through a process involving the hormone insulin. When blood glucose levels rise, the pancreas releases insulin into the bloodstream. Insulin promotes the uptake of glucose by cells, which lowers blood glucose levels. As blood glucose levels decrease, the release of insulin decreases.

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the process by which neurotransmitters leave the presynaptic membrane

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activation of postsynaptic receptors

the process by which neurotransmitters travel across the synaptic cleft

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how an increased number of mitachondria can help cell thermoregulation

mitachondria generate heat as a by-product of oxidative metabolism in most tissues, and as the primary product in the case of thermogenic tissues

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Antidiuretic hormone helps regulate the amount of water in your body. It works to control the amount of water your kidneys reabsorb as they filter out waste from your bl

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hormones as chemical messengers

they relay messages to cells via the circulatory system or lymphatic system - the pituary gland is responsible for

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how the loop of Henle assists desert mammals in preventing excessive water loss

  • more sodium and chloride ions pumped out the ascending limb

  • increases water potential/concentration gradient

  • allows more water to be absorbed from collecting dust

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how abscisic acid (ABA) can help maintain water balance in plants

  • produced in the roots when soil is dry

  • translocated to the leaves and changes osmotic potential of guard cells

  • causes stomata to close, reducing water loss

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hydrophobic hormones

can move straight through the cell membrane and bind to intercellular receptors in the cytoplasm or the nucleus → binding changes shape of receptor protein

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hydrophilic hormones

cannot pass through the cell membrane because of their size, so they bind to the extracellular receptors that are on the cell membrane

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ion channel protein

an extracellular protein that opens so that ions can be transported across the cell membrane. this response is fast because of concentration gradients

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G protein-coupled receptors

these extracellular receptors have a protein called G-protein attatched to them. when a hormone binds, the receptor changes conformation and the G protein is released to activate other proteins in the signal transduction pathway

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tyrosine kinase receptors

this extracellular receptor mediates cell-to-cell communication and controlling a wide range of complex biological functions, including cell growth, motility, differentiation and metabolism

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  • helps the organism maintain internal body temp by for eg. polar bears, their fur aids thermoregulation bu trapping an insulating layer of air close to the skin

  • in hot temps, fir can insulate animals from the radient heat or hot air around them

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vasomotor control in hot environments

their nerve impulses stimulates the arteolies in the skin to dialate (vasodialation) which allows a lot of blood to flow close the skins surface → results in red and warmer skin

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vasomotor in cold environments

nerve impulses cause the skin arterioles to constrict (vasoconstriction). decreases the diameer of blood vessels

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  • while many responses to low temps conserve heat, some responses generate heat

  • shivering increases metabolic processes, and also increases heat production but it has a high energy cost and is a short term adaptation

  • non-shivering → increased metabolic activity by mitachondria

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thyroid hormones at low temps

  • at low temps the hypothalamus releases a hormone, thyropin releasing hormone (TRH)

  • this activates the piturary gland to release thyroid stimulating hormone

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this pathogen injects its nucleic acid into the host cell when inside The nucleic acid tells the host cell to make multiple copies of the viral protein coat and nucleic acid → released when host cell undergoes lysis (cell bursting)

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this pathogen does not posess any genetic material (neither DNA nor RNA) they exist in our bodies normally play important roles in memory & learning and cell-to-cell signals → found at the surface of neurons

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this pathogen was the first life form on earth and still most adundant. only a small no. them cause disease and they reproduce very quickly through binary fission

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  • this pathogen can include yeast and mould. they are eukaryotes that reproduces by spores and have cell wall made of chitin

  • secrete enzymes into host which makes them digest their food externally

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  • this pathogen produces symptoms like nausea, fatigue, diahorea

  • produce cysts that are passed in faeces of a host and passed on through driking

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how do pathogens (bacterial & viral) both cause physical and chemical changes in host cells that stimulate the hosts immune responses

  • introduction of foreign chemicals via the surface of the pathogen triggers a host immune response

  • self-markers label body cells as ‘self’, so they are not attacked by the immune system

  • antigens present on the pathogen allow the immune system to recognise them as ‘non-self'‘

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innate immune responses

general or non-specific, occuring either immediately or within a few hours → does not recognise every antigen

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adaptive immune response

specific ad takes a number of days to become protective. this immunity is developed through life

  • involves cell mediated immune and memory responses

  • antigens present on the pathogen activates B lymphocytes and T lymphocytes

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physical defences

  • waxy cuticle

  • bark/wood stems

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chemical defences

  • production of toxins that are harmfulto pathogens

  • production of defensins which have antimicrobial properties that inhibit pathogen growth

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surface barriers

these barriers aim to keep pathogens out of your body or limit their ability to spread and move throughout the body

  • physical barriers: skin; mucus membranes in GI tract, respitory tract, eyelashes

  • defence mechanisms: secretions, mucus, bile, gastric acid, saliva, sweat, tears

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internal barriers

  • complement system: made of a variety of proteins that, when inactive circulate in the blood

  • opsonisation: marking pathogens so phagocytes can easily find them

  • neutralisation: blocking adhesion of pathogens to cells

  • cell lysis: cause damage the plasma membranes of pathogen

  • inflammation: activation of inflammatory response

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the response actively brings immune cells to the site of an infection by increasing blood flow to the area

  • mast cells secrete histamine and prostaglandins that cause vasodilation allowing increased blood flow to area

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histamine (continuing from inflammation)

also increases permeability of the capillaries, allowing blood plasma, proteins and white blood cells (such as phagocytes) into the area

  • phagocytes engulf pathogens

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humoral response

involves B lymphocytes and results in the producion of antibodies that act against the pathogen → memory B cells are produced

  • effector B cells (plasma cells) secrete antibodies

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memory B/lymphocytes

once activated by antigens, divide rapidly to produce plasma cells that can secrete large amounts of antibody into the blood if there is another infection

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cell-mediated response

involves T lymphocytes which destroy infected cells → memory T cells are produced

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helper T cells

help activate B cells, phagocytes and cytotoxic T cells

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cytotoxic T cells

destroy infected host cells

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regulatory T cells

distinguish between self and non-self

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memory T cell/lymphocyte

survive for many years and very quickly create cytotoxic T cells and helper T cells when the person is exposed to the pathogen again, producing a faster stronger immune response

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passive immunity

antibodies gained via the placenta or breastfeeding (natural and via antibody serum injection (artificial)

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active immunity

acquired via natural exposure to a pathogen (natural) or through the use of vaccines (artificial)

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tolerance limit

the highest and lowest values of a particular factor (eg. temp, blood glucose levels) an organism can tolerate

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continuual maintenance

  • conditions in the body are constantly flucating, negative feedback is constantly working to support homeostasis

  • receptors continually scan internal environment to ensure a narrow range of appropriate conditions are met

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the sequence of events following the arrival of an action potential at the presynaptic knob until the neurotransmitters has been released.

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work by recieving outside info and converting it to chemical or electrical signal that then can be related within the body

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receive signals from within the body’s internal environment, which is composed of interstitial fluid that bathes the cells, and the blood plasma.

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process of the passage of a nerve impulse in terms of transmission of an action potential and synaptic transmission.

Depolarization, Repolarization and Recovery. A nerve impulse is transmitted to another cell at either an electrical or a chemical synapse .

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what happens to sodium and potassium ions during the rising and falling phases of an action potential.

After approximately 1 msec, the sodium channels inactivate. The channel becomes blocked, preventing ion flow. At the same time, the voltage-gated potassium channels open

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More receptors on the outside

more sensitive to hormone

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