Responding to Changes in the Environment Flashcards
Why do organisms respond to changes?
To increase their chance of survival and ensure internal conditions are always optimum for metabolism
What is a Taxis and give an example?
Directional movement in response to a stimulus. The direction of the stimulus effects the result
For example, woodlice show a tactic response to light. They move away from a light source. This helps them survive as it keeps them concealed under stones during the day and keeps them in damp conditions
What is a Kinesis and give an example?
Nondirectional movement in response to a stimulus. The intensity of a stimulus effects a result.
Woodlice show a kinetic response to humidity in high humidity. They move slowly and turn less often, so they stay where they are. And as air gets drier, they move faster and turn more often, so they move into a new area.
How do you investigate Taxis and Kinesis?
- To investigate the effect of light intensity on woodlouse movement, cover 1/2 of the lid with black paper and put damp filter paper in both sides of the base to maintain humidity
- Place ten wood lies in the centre of the chamber and position the lid on the mesh so it’s lined up with the base
- After 10 minutes, take off the lid and record the number of wood lice on each side of the chamber
- Repeats by gently moving wood lice back to the centre. Using a soft paint brush. you should find that most wood lice end up on the dark side of the choice chamber, a tactic response to light
What’s the difference between receptors and effectors?
Receptors- Cells or proteins on cell surface membranes that detect a stimuli
Effector- Cells that bring about a response to a stimuli to produce an effect.
What are the three types of neurons?
Sensory- Transmit electrical impulses from receptors to the central nervous system
Motor- Transmit electrical impulses from the central nervous system to effectors.
Relay- Transmit impulses between sensory and motor neurons
What is a reflex arc?
This is a rapid, involuntary response to a stimulus by going through the spinal cord instead of the brain- so it happens automatically.
They help organisms avoid damage to the body because the response happens quickly.
What is a trophism?
A trophism is the response of a plant to a directional stimulus by regulating their growth.
What are the two types of trophism?
- phototropism’s
- Gravitropism’s
What is a phototropism?
This is the growth of a plant in response to light shoots. up positively phototrophic and grow towards lights, roots are negatively phototrophic and grow away from lights
What is a Gravitropism?
This is the growth of a plant in response to gravity shoots. a negatively gravitropic and grow upwards while roots are positively gravitropic and grow downwards
What is an Auxin?
Auxins are hormone like chemicals that speed up or slow down plant growth. They are produced in the growing regions of the plants and moves to where they’re needed in other parts of the plant
Give an example of an auxin and explain how it works?
Indoleacetic Acid (IAA)- IAA is an important auction that’s produced in the tips of shoots and roots in flowering plants. It’s moved around the plant to control trophism’s.
It moves to the more shaded parts of the shoots and roots, so there’s uneven growth allowing elongation and the shoot to bend towards the light.
What is a receptor?
Can be cells, or proteins specific to a type of molecule to respond to a specific stimuli
What are the three types of receptors?
MECHANORECEPTORS- pressure
PHOTORECEPTORS- light
CHEMORECEPTORS- detect certain chemicals
Talk about the Resting Potential.
When a nervous system receptor is in resting state, there is a difference in charge between the inside and the outside of the cell. The inside is negatively charged relative to the outside. This means there is a voltage across the membrane, or a potential difference.
The potential difference when a cell is at rest is called its resting potential. This is generated by ion pumps and ion channels
What is a Generator Potential
When a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell, altering the potential difference. The change in potential difference due to a stimulus is called the generator potential. A bigger stimulus excites the membrane more, causing bigger movement of ions and a bigger change in potential difference
What is an Action potential?
If the generator potential is big enough, it will trigger an action potential. an action potential is an electrical impulse along a neuron. This is only triggered if the generator potential Reaches a certain level called the threshold level.
Give the process of an action potential being made.
- there is a potential difference between inside and outside the cell
- the potential difference when cell is at rest is called the resting potential
- When a stimulus is detected, the membrane becomes more permeable causing the ions to diffuse accross and the potential difference to increase.
- This change in potential difference is known as the generator potential
- If the generator potential is large enough it triggers an action potential- an electrical impulse along a neuron
What is a Pacinian Corpuscle?
- A type of mechanoreceptor found in the skin
- contains a sensory neuron ending wrapped in lamellae
Talk about the stimulation of a Pacinian Corpuscle
- When a Pacinian Corpuscle is stimulated, the lamellae are deformed and pressed on the sensory nerve ending.
- This causes the sensory neurons cell membrane to stretch, deforming the stretch mediated sodium ion channels.
- The channels open, and sodium ions diffuse into the cell, creating a generator potential
- if the generator potential reaches the threshold, it triggers an action potential
Talk about the Retina
- Light is detected by photoreceptors in the retina, which contain light-sensitive pigments.
- Light bleaches these pigments, changing the membrane’s permeability to sodium ions.
- This creates a generator potential, which can trigger an action potential.
- The action potential is passed to a bipolar neurone, then to the optic nerve, and finally to the brain for processing.
Talk about Rods
Sensitivity to Light- High as many rods connect to 1 neurone so many action potentials can be made
Sensitivity to colour- LOW as only sensitive to light levels
Visual Acuity- LOW as many rods connect to one neuron and light from 2 points can be duistinguished and one impulse is sent
Talk about Cones
Sensitivity to Light- LOW as only 1 cone is connected to a bipolar neurone so take more light to reach a threshold
Colour- HIGH as different types of cones contain a different pigment. When stiumulated together, we ssee different colours
Acuity- seperate impulses can be sent so many action potentials can be reached.
Talk about the control of heart rate- structure.
Cardiac Muscle is myogenic- contraction is initiated by the muscle itself not via nerves
The *Sinoatrial Node (SAN) sets the frequency at which the cardiac muscle cells contract sending out regular impulses to the atrial walls causing atria to contract.
Talk about contraction of the heart
- The SAN (sinoatrial node) generates an electrical impulse, which spreads across both atria, causing them to contract at the same time.
- The septum stops the impulse from directly crossing to the ventricles.
- The impulse reaches the AVN (atrioventricular node), where there is a short delay to allow the atria to empty fully into the ventricles.
- The AVN sends the impulse down the bundle of His and then through the Purkyne fibres, which carry it to the walls of the ventricles.
- This causes the ventricles to contract from the bottom upwards, pushing blood out of the heart.
How is heart rate controlled?
- done by autonomic nervous system
- The rate of which the SAN generates impulses is controled by the brain
- It changes in response to internal stimuli alike changes in blood
Talk about the Medulla
Electrical impulses from these receptors are sent to the medulla via sensory neurons which processes info and sends to SAN via:
- Sympathetic Neurons- more for activity
- Parasympathetic Neurons- for relaxation
Talk about the resting potential of a myelinated neuron
- 3 sodium ions are actively transported out of the axon in exchange for two potassium ions via a NA/K pump
- The concentration of sodium ions builds up as channels are closed
- Outside is less negative than inside creating a potentual difference
- resting potential- -70mv
What is the first stage of action potential creation of a myelinated neuron
DEPOLARISATION- a stimulus excited a membrane on cell-surface so membrane becomes more permeable to sodium ions. Sodium ion channels open and sodium diffuses in while potassium doesnt so inside is less negative
What is the second stage of action potential creation of a myelinated neuron
REPOLARISATION- Sodium ion channels close while potassium open so potassium diffuses out of neurone and the inside becomes more negative and voltage returns to normal level
What is the third stage of action potential creation of a myelinated neuron
HYPERPOLARISATION- Voltage gated potassium ion channels are still open for a short time meaning too many ions diffuse out of neurone and voltage becomes more negative than resting potential. Potassium ion channels close restoring resting potential
How does the action potential move in an unmyelinated axon?
- In unmyelinated axons, the action potential travels continuously along the entire length of the axon membrane
- Each section of membrane undergoes depolarization and repolarization in sequence
- This results in a slower conduction of the nerve impulse compared to myelinated axons
- The action potential is regenerated at each point along the axon to maintain the signal strength
How does the action potential move in an myelinated axon?
- Action potentials can only occur at the nodes of Ranvier (gaps between myelin sheaths)
- The action potential “jumps” from node to node in a process called saltatory conduction
- This makes the transmission of nerve impulses much faster than in unmyelinated axons
- The myelin sheath acts as an electrical insulator, preventing ion movement through the membrane except at the nodes
What is the all or nothing principle?
The strength of a stimulus is not reflected in the size of the action potential, but rather in the frequency of action potentials generated
What is the process of synaptic transmission?
- When an action potential reaches the presynaptic membrane, it triggers voltage-gated calcium channels to open
- Neurotransmitters (like serotonin) diffuse across the synaptic cleft
- The neurotransmitter binds to specific receptor proteins on the postsynaptic membrane
- This can trigger various responses in the postsynaptic neuron, depending on the neurotransmitter
What is summation?
Summation is the process where multiple stimuli that individually are below threshold can add together to trigger an action potential
What are the two types of summation?
Temporal summation: When multiple stimuli arrive at the same point on a neuron in quick succession, their effects can add together to reach threshold
Spatial summation: When multiple stimuli arrive at different points on a neuron simultaneously, their effects can combine to reach threshold
What is synaptic inhibition
Synaptic inhibition is when neurotransmitters cause a decrease in the likelihood of the postsynaptic neuron generating an action potential
What is synaptic excitation?
While synaptic excitation (like what happens with serotonin) makes an action potential more likely
How do inhibitory neurotransmitters work?
- Making the postsynaptic membrane more negative (hyperpolarization)
- Preventing depolarization from reaching threshold
What is a neuromuscular junction?
This is a specialised synapse between a motor neuron and a muscle cell. They use the neurotransmitter acetylcholine (ACh) which binds to cholinergic receptors.
What is the first 2 steps of synapse at neuromuscular junctions?
When an action potential reaches the presynaptic membrane of a motor neurone, calcium ions diffuse in, triggering vesicles to release acetylcholine (ACh) into the neuromuscular junction.
ACh binds to receptors on the sarcolemma, opening ion channels and allowing sodium ions to diffuse in, depolarising the membrane.
What is the last two steps in neuromuscular synapse?
The resulting action potential travels down T-tubules, causing voltage-gated calcium channels in the sarcoplasmic reticulum to open.
Calcium ions diffuse into the sarcoplasm, bind to troponin, and cause a shift in troponin-tropomyosin, exposing myosin-binding sites on actin filaments, enabling muscle contraction.
Name some ways in which drugs can affect synaptic transmission.
- Some drugs are the same shape as neurotransmitters so they mimic the action at receptors, these are called agonists. They activate more receptors. i.e. nicotine mimics acetylcholine so binds to there receptors in the brain.
- Some drugs block receptors so they cant be activated,i.e SSRI’s
- some drugs break down neurotransmitters
- some drugs stimulate the release of neurotransmitters
- some drugs inhibit the release of neurotransmitters
Name the three types of muscles
Smooth- contracts without conscious control, found in the walls of internal organs
Cardiac- contracts without conscious control, found only in the heart
Skeletal- type of muscle you use to move
What is the role of skeletal muscles?
skeletal muscles are attached to bones by tendons. Ligaments attach bones to other bones to hold them together
A pair of skeletal muscles are called antagonistic pairs and contract and relax to move bones at a joint.
Describe the basic structure of skeletal muscles.
Skeletal muscles are made of muscle fibres which contain an organised arrangement of proteins each surrounded by a cell surface membrane and contain many nuclei.
Talk about the cell surface membrane equivalent on muscle fibres.
SARCOLEMMA
Have many deep projections which fold in from its surface to increase the surface area. These are called transverse system tubules or T tubules
Talk about the cytoplasm equivalent of muscle fibres.
SARCOPLASM
- Contains many mitochondria to generate ATP required for muscle contraction.
- Contains many myofibrils- bundles of actin and myosin filaments which slide past each other during muscle contraction
Talk about the endoplasmic reticulum equivalent of muscle fibres
SARCOPLASMIC RETICULUM
- The membranes contain protein pumps which transport calcium ions into the lumen
What is the difference between actin and myosin filaments?
Myosin Filaments- these have globular heads that are hinged so they can move back and forth. Each myosin head has a binding site for actin and a binding site for ATP
Actin Filaments- these have binding sites for myosin heads called actin- myosin binding sites. another protein called tropomyosin is found between actin filaments which help myofilaments move past each other.
What are myofibrils?
Bundles of thick and thin myofilaments located in the sarcoplasm which allow muscle contraction by moving past each other. They are arranged in a particular order creating different types of lines and bands
What is the difference between thick and thin filaments?
Thick- They are made of myosin molecules with a globular head and fibrous part
Thin- made of actin molecules which are globular. two actin chains twist together to form one. A fibrous protein known as tropomyosin is twisted around two actin chains. Another protein called troponin is attached to the chains at regular intervals
Distinguish between the types of bands in muscles.
H band- only thick filaments are present
I band- only thin actin filaments are present
A band- contain areas where only myosin filaments are present and areas where myosin and actin filaments overlap.
Distinguish between the two types of lines in muscles.
M line- attachment for myosin filaments
Z line- attachment for myosin filaments
What is a sarcomere?
The section of myofibril between two z lines, muscles contract by shortening sarcomeres.
Describe the process of the sliding filament model.
Action potential reaches the neuromuscular junction, triggering calcium ion release from the sarcoplasmic reticulum.
Calcium binds to troponin, causing troponin-tropomyosin to shift and expose myosin-binding sites on actin filaments
Myosin heads bind to actin, forming cross-bridges, and bend, pulling actin towards the sarcomere center (power stroke), releasing ADP + Pi.
ATP binds to myosin, causing it to detach from actin. ATP hydrolysis returns myosin to its original position (recovery stroke).
The cycle repeats as long as calcium remains bound and ATP is available, leading to further contraction.
Talk about the role of ATP in muscle contraction
- ATP is essential for muscle contraction, providing energy for myosin head movement and actin filament sliding.
- Active transport of Ca²⁺ back into the sarcoplasmic reticulum also requires ATP.
- Stored ATP in resting muscles lasts ~3-4 seconds of intense exercise.
- Aerobic respiration produces ATP but is slow; anaerobic respiration is faster but takes ~10 seconds to generate ATP.
Talk about the role of phosphocreatine PCr in muscle contraction.
- Phosphocreatine (PCr) provides a rapid ATP source by donating a phosphate to ADP:ADP + PCr → ATP + Creatine
- Different muscle fibre types store varying amounts of PCr, allowing short bursts of contraction (e.g., 100m sprint).
- Once PCr is depleted, ATP production must rely on aerobic and anaerobic respiration.
Talk about slow twitch muscle fibres
- Contract more slowly, suited for endurance activities (e.g., walking, posture maintenance).
- Rely on aerobic respiration → fatigue-resistant due to lower lactate production.
- Dense capillary network → short diffusion distance for oxygen and glucose.
- High myoglobin, haemoglobin, and mitochondria → efficient oxygen supply and aerobic respiration.
- Appear dark red due to high myoglobin content.
- Common in migratory animals (e.g., geese wings, wolf legs) and human postural muscles (e.g., back muscles).
Talk about fast- twitch muscle fibres
- Contract rapidly due to faster myosin-actin interactions.
- Require high Ca²⁺ levels for rapid contraction-relaxation cycles.
- Fewer capillaries → slower oxygen and glucose supply.
- Low myoglobin content → reduced oxygen storage, making them appear paler.
- Rely on anaerobic respiration → suited for short bursts of intense activity (e.g., cheetah legs, robin wings, human eyelids).
- Fatigue quickly due to lactate accumulation.
What is homeostasis?
Homeostasis is the maintenance of the body to have a constant internal environment despite fluctuations in the activity of the external environment. This includes factors like temperature, water potential, pH and blood glucose levels.
Talk about the importance of homeostasis in the functioning of organisms.
Organisms with the ability to maintain constant internal environments are more adapted to changes in the external environment meaning they have a greater chance of finding food and shelter etc.
Talk about the importance of homeostasis in Enzymes
Enzymes that control metabolic reactions are sensitive to changes in pH and temperature, any change could cause denaturing chaning their tertiary structure and meaning they can’t carry out ther roles effectivley
Talk about the importance of homeostasis in water potential
Changes to water potential can cause cells to shrink and expand causing water to leave via osmosis. This means cells cant effectivley work. A constant blood glucose concentration is essential for this.
Talk about negative feedback and homeostasis and how it works
This is achieved with the help of negative feedback. This means all changes are reversed to restore optimum conditions. This is achieved by:
Sensory receptors, i.e. temperature receptors, to detect changes in internal conditions. When conditions change, the receptors pass the message either by the nervous or hormonal system to the effectors like the liver or muscles. i.e. blood glucose falls, insulin increased, convert glycogen to glucose.
Talk about positive feedback and homeostasis (give an example)
It is also less commonly controled by positive feedback, where it increases the original change in conditions i.e. the dilation of the cervix during childbirth.
Talk about the correct blood glucose concentration and why this is important.
The correct range is 70-99mg/dl
This is needed to ensure all essential processes are maintained like for respiration to generate ATP for energy
What is the difference between glyconesis, glycogenolysis and gluconeogenesis?
glyconesis- making glycogen from glucose removed from the blood
glycogenolysis- breaking down stored glycogen into glucose which can be released into the blood.
Gluconeogenesis- synthesis of glucose from other molecules like amino acids
What happens when the glucose concentration is too high?
- The rise in glucose concentration is detected by beta cells found in the Langerhans in the pancreas.
- Insulin is secreted by beta cells inhibiting the action of alpha cells
- This travels in the blood to target cells known as hepatocytes in the liver, fat and muscle cells
- Binding of insulin to the receptors on the plasma membrane causes vesicles with glucose transport proteins to fuse with the membrane
- This increases the permeability of the cells to glucose increasing the rate of glucose uptake into the cell. This is then converted to glycogen or fats and subsequently used for respiration.
What happens when glucose is too low?
- Alpha cells in the islets of Langerhans in the pancreas detect a fall in glucose and secretes the hormone glucagon
- Glucagon secretion inhibits beta cell action
- glucagon stimulates hepatocytes to convert glycogen to glucose
- Glucose diffuses out of hepatocytes into the blood
- cells use fatty acids and amino acids for respiration insted
Talk about how adrenaline breaks down glucose
- Adrenaline fuses to a receptor on the cell surface membrane of liver cells and causes the receptor to change shape on the inside of the membrane
- the changing shape on the inside of the membrane activates the enzyme adenyl cyclase converting ATP to cAMP which acts as a second messenger.
- The cAMP then changes shape and activates the protein kinase enzyme which catalyses the converson of glycogen into glucose.
Talk about Type 1 Diabetes: what happens? what causes it? How to control?
Type 1 is insulin dependent diabetes and occurs early in life caused by the immune system attacking insulin producing beta cells reducing insulin prodcution.It causes rapid fluctuations due to insulin lack leading to dangerously high or low levels.
It is normally caused by genetic vulnerability or autoimmune conditions.
Diet can be used to control it using low sugar and balanced carbs, but insulin injections and careful blood glucose monitoring is still needed
Talk about Type 2 Diabetes: what happens? what causes it? How to control?
This is not insulin dependent and often appears later on in life due to lifestyle choices. It is called by decreased insulin production or by glycoprotein receptors on target cells becoming unresponsive to insulin. It cases blood glucose levels to stay high for long periods leading to damage of tissues
This is often caused by obesity, poor diet, age and a lack of exercise.
Diet control plays a major role with low sugar and high fiber diets as well as lifestyle changes like exercise.
Talk about Hypoglycemia and when a diabetic may experience it
When blood glucose levels drop too low, a person may experience dizziness, shaking and sweating. A diabetic may experience this after overusing insulin, skipping meals excessive exercise and alcohol consumption.
Talk about hyperglycemia and when a diabetic may experience it
When blood glucose levels are too high, a person may experience thirst and fatigue. A diabetic may experience this if they missed insulin, have a nigh carb or sugar intake or during environmental issues like stress and illness.
What is the fasting oral glucose tolerance test and how do you carry it out?
This is a way of testing blood sugar levels overtime in order to see weather they have diabetes.
1. Fast for 8 hours
2. A sample of your blood is taken and blood sugar levels are measured.
3. Drink 100g if sugar in a glucose solution
4. Blood sugar is taken again after 1 hour, 2 hours and 3 hours.
What is the difference between diabetics and non diabetics on the fasting oral glucose tolerance test?
both groups show a rise in glucose levels initially with the diabetic levels being increasingly higher, the normal persons levels return to normal a lot faster than diabetic levels and also return to near the original level when a diabetic remains higher for longer and only slowly decreases showing the body of a diabetic cant efficiently regulate glucose levels.
What are the two functions of the Kidney?
- Regulating the water content of blood- essential for maintaining blood preassure.
- Excrete toxic waste products of metabolism (like urea) and substances in excess (like salts)
Talk about the structure of the Kidney
The Kidney itself is surrounded by a fairly tough outer layer called the fibrous capsule
It is made of 3 main areas:
- The Cortex- contains the glomerulus, bowman’s capsule, both convoluted tubules.
- Medulla- contains the loop of Henle and collecting duct
- Renal Pelvis- where ureter joins the Kidney
What are the three functions of the nephrons?
ultrafiltration of the blood- happens in the glomerulus
Selective Tubular Reabsorption happens in the proximal convoluted tubule
Tubular Secretion- The secretion of substances from capillaries into the kidney tubules.
What is the order of processes for urine formation?
- ultrafiltration
- selective reabsorption
- water and salt reabsorption
Talk about ultrafiltration
Small molecules are filtered out of the blood into the Bowman’s capsule, forming glomerular filtrate, this contains: amino acids, water, glucose, urea and inorganic ions
Glomerulus: A network of capillaries with high blood pressure, forcing small molecules into the Bowman’s capsule.
Large molecules (e.g., blood cells & proteins) remain in the blood as they are too large to pass through.
Talk about selective reabsorption
Useful molecules are reabsorbed from the filtrate into the blood.
Reabsorbed substances: Water, salts, glucose, amino acids
Occurs mainly in the proximal convoluted tubule (PCT), some in the loop of Henle & collecting duct.
Talk about adaptations of the proximal convoluted tubule for selective reabsorption
Microvilli → Increase surface area
Co-transporter proteins → Help reabsorb molecules
Many mitochondria → Provide energy for active transport
Tightly packed cells → Efficient transport
What is the process of selective reabsorption
1️⃣ Sodium-potassium pumps actively transport Na⁺ from PCT cells into blood.
2️⃣ Low Na⁺ concentration inside PCT cells causes Na⁺ to diffuse in from filtrate.
3️⃣ Co-transporter proteins move Na⁺ + glucose/amino acids into PCT cells.
4️⃣ Glucose & amino acids diffuse into blood down concentration gradient.
5️⃣ Water leaves by osmosis (due to low water potential in surrounding tissues).
6️⃣ Urea leaves by diffusion and enters nearby capillaries.
Talk about the process of water and salt reabsorption in the loop of Henle
🔹 Ascending limb: Pumps Na⁺ & Cl⁻ into medulla, lowering water potential.
🔹 Ascending limb is impermeable to water, so water stays inside.
🔹 Descending limb is permeable to water, so water leaves by osmosis due to medulla’s low water potential.
🔹 Filtrate water potential decreases as it moves down the descending limb (water leaves, ions stay).
🔹 Water reabsorbed from the collecting duct by osmosis into nearby capillaries.
Why is controlling blood water potential needed?
Water is essential to keep the body functioning so the amount of water in the blood needs to be kept constant. Mammals excrete urea in solution meaning water is lost. Its also lost in sweat. The kidneys regulate the water potential of the blood to have just the right level of water- osmoregulation
Talk about the process of osmoregulation in the loop of henle?
- Near the top of the ascending limb, sodium ions are activley pumped out into the medulla, the asending limb is impermeable to water so the water stays in the tubule. This creates a low water potential in the medulla.
- As theres a lower water potential in the medulla than in the desending limb so water moves out of the desending limb into medulla via osmosis making the filtrate more concentrated. The water in the medulla is reabsorbed innto the blood.
- near the bottom of the desending limb, sodium ions diffuse out onto medulla, lowering the water potential in the medulla, further lowering water potential.
- Water moves out of the distal convuluted tubule by osmosis and is reabsorbed into blood.
- The first three stages massively increase the ion concentration in the medulla lowering water potential so water moves out of the collecting duct via osmosis- water is reabsorbed by the blood.
Talk about the negative feedback systems of water potential (water potential decreasing)
Water potential of the blood is monitored by cells called osmoreceptors in the hypothalamus. When the water potential of the blood decreases, watermoves out via osmosis causing cell volume to decrease. This sends a signal to the posterior pituitary gland to release a hormone called antidiuretic hormone (ADH) into the blood. These increase the number of protein channels called aquaphorins increasing the permeability of cells membranes. This means more water is reabsorbed creating a small volume of concentrated urine so less water is lost.
This happens in reverse if an increases in water potential.
