Responding to changes in environment

What is a stimulus?

Something that can be detected by an organism. It can either be internal or external

What is a receptor?

An organ or specialised cell that can detect the change that is causing the stimulus

What is a response?

A result of the stimulus that is detected by the receptor. This may be movement of the organism or a change in behaviour

What is taxis?

A response that involves movement in a specific direction

What is the difference between positive and negative taxis?

Positive taxis is towards the stimulus and negative taxis is away from the stimulus

What is kinesis?

A response that involves movement but this time in random directions.

What is affected in kinesis?

Both the speed and frequency of direction change increase

Why does kinesis occur?

The response is carried out in order to increase the chance that the organism will enter different conditions - their favoured conditions - more rapidly.

Why do plants respond to external stimuli?

Plants respond to external stimuli to increase their chance of survival.

What is tropism?

A growth response controlled by a directional stimulus

Give an example of tropism

The shoots of plants growing towards the direction of light

What is plant growth controlled by?

Plant growth is controlled by IAA which is an important auxin produced in the tips and shoots of flowering plants

What does IAA do in roots?

In roots IAA inhibits growth, therefore causing the cells on the upper side to grow faster, causing the root to bend downwards

What is a reflex?

Reflexes are rapid automatic responses.

Why is a reflex important?

This is because they protect an organism from harmful stimuli and therefore can help it to survive and avoid danger.

What is the general path of a reflex arc?

(PHOTO)

What does a sensory neurone do?

It carries the nerve impulse from the receptor to the spinal cord

What does a motor neurone do?

It carries the nerve impulse from the spinal cord to the effector which can be a muscle or gland

What does an intermediate neurone do?

Located entirely in the spinal cord, it relays the nerve impulse from the sensory neurone to the motor neurone

Where are Pacinian corpuscles located?

Pacinian corpuscles are located deep in the skin and are mostly found on fingers, soles of the feet as well as external genitalia

Describe the structure of a Pacinian corpuscle

Pacinian corpuscles have a single sensory neurone, located in the centre of connective tissue called lamellae which forms layers separated by a gel.

How is a Pacinian corpuscle stimulated?

The Pacinian corpuscle contains stretch mediated sodium channels in the cell surface membrane. Under pressure these become deformed allowing a rapid influx of sodium ion. This causes depolarisation which results in an action potential being created.

How is the amount of light entering the eye controlled?

The amount of light entering the eye is controlled by muscles in a structure called the iris

How is light focused onto the eye?

The lens of the eye focuses the light on the retina where the photoreceptors are located

Where are photoreceptors located?

Photoreceptors are located on the retina of the eye, specifically the fovea

Where do nerve impulses received by photoreceptors go?

The nerve impulses received by the photoreceptor cells are then carried via the optic nerve to the brain

What is the blind spot?

The point where the optic nerve leaves the eye is known as the blind spot as there are no photoreceptors there.

What are the two types of photoreceptors?

Rods and cones

What are cones for?

Cones are involved in colour vision

What are rods for?

Rods are for monochromatic vision

What is the pigment in cone cells?

iodopsin

What is required for cone cells to work and why?

cone cells are not sensitive to light and therefore require bright light to work

What are the three different types of cone cells?

the cone cells sensitive to each of the primary colours of light: red, green or blue

Why do cone cells have good visual acuity?

cones have good visual acuity because each cone cell has its own synapse via a bipolar neuron which connects to the optic sensory neurone

What pigment is in rod cells?

rhodopsin

Where are rod cells concentrated?

rod cells are mainly concentrated in the highest density outside of the fovea

How are rod cells stimulated?

rod cells are very sensitive to light and therefore are stimulated in low light conditions

Why do rod cells have low visual acuity?

rod cells have low visual acuity as more than one rod cell shares the same synapse with a bipolar cell. As a result multiple rods need to be stimulated to cause a generator potential

Why is the heart described as myogenic?

due to the heart's ability to initiate its own contraction

Where is the sinoatrial node located?

in the wall of the right atrium

What is the accelerator nerve?

a nerve that is a part of the sympathetic nervous system that delivers a higher frequency of impulses to the SAN to increase heart rate

What is the vagus nerve?

a nerve that is part of the parasympathetic nervous system that delivers a slower frequency of impulses to slow down the heart rate

Which factors affect heart rate?

changes in pH and blood pressure

How does pH affect heart rate?

changes in pH, caused by CO₂ conc., are detected by chemoreceptors located in the carotid arteries, aorta and brain. The receptors send impulses to the medulla oblongata more frequently, via the sympathetic pathway. As a result, more frequent impulses are sent to the SAN, which increases heart rate. This increases blood flow to lungs where CO₂ can be expelled

How does blood pressure affect heart rate?

changes in blood pressure are monitored by baroreceptors in the sinus. If blood pressure increases then an increased frequency of impulses are sent from the medulla oblongata via the parasympathetic pathway to the SAN. This causes heart rate to decrease, lowering blood pressure.

What enables neurones to carry out electrical impulses called action potentials?

The polarised nature of the neurone membrane in the resting state enables the neurone to carry electrical impulses

How is the resting potential maintained?

With the help of the sodium-potassium pump which moves sodium ions out of the axon, creating an electrochemical gradient

How does a myelin sheath speed up the passage of an action potential down an axon?

The presence of a myelin sheath means no action potential can be generated. Therefore, the action must jump between the nodes of Ranvier - saltatory conduction

What 3 factors affect the speed of a nerve impulse?

Presence or absence of a myelin sheath, diameter of axon, temperature

How does diameter of the axon affect the speed of a nerve impulse?

The greater the diameter of the axon the faster the conduction

How does temperature affect the speed of a nerve impulse?

As temperature increases, ions diffuse more rapidly. It also affects the rate of respiration and therefore the production of ATP needed in the sodium-potassium pump

What is the refractory period?

A short period during which the neurone membrane cannot be excited as the sodium channels enter a recovery stage.

Why is the refractory period important?

it ensures that an action potential can only pass in one direction as discrete signals.

What is the all-or-nothing principle?

A threshold value must be reached in order for an action potential to be created, with all action potentials being of the same strength.

What are synapses?

Junctions between two neurones

What are the roles of a synapse?

Preventing action potentials from going in the wrong direction, amplifying the effects of Low frequency action potentials using summation, transmitting signals

How do synapses amplify a low frequency action potential?

It can either be temporal - a single presynaptic neurone releases neurotransmitters many times over a short period of time - or spatial - multiple presynaptic neurones release neurotransmitters - causing the threshold potential to be reached in the post-synaptic neurone

What the 2 types of synapses?

Inhibitory or excitatory

How does an action potential move across a synapse?

An action potential arrives. Presynaptic membrane depolarises causing calcium ion channels to open and calcium ions to enter. Calcium ions in the neurone cause the fusion of synaptic vesicle, filled with a neurotransmitter, with the presynaptic membrane. Neurotransmitters are released into the synaptic cleft and then diffuse across and bind to the receptors on the postsynaptic membrane. This stimulates the opening of sodium ion channels in the postsynaptic neurone causing sodium ions to enter the postsynaptic neurone leading to depolarisation

What is a tendon?

Non-elastic tissue which connects muscles to bones

What is a ligament?

Elastic tissue that join bones together and determines the amount of movement possible at a joint

What is a joint?

The area where two bones are attached, allowing body parts to move. They are made of fibrous connective tissue and cartilage

What are antagonistic muscle pairs?

Pairs of muscles which pull in opposite directions - as one muscle contracts the other relaxes.

What are myofibrils made of?

Thick filaments made of myosin and thin filaments made of actin

How is an actin filament made?

Two actin molecules are twisted together to make the filament

What are slow twitch fibres specialised for?

They are specialised for slow contractions and are adapted to long periods of exercise and therefore do not fatigue quickly

How are slow twitch fibres adapted?

They are adapted to aerobic exercise by having a large store of myoglobin, a rich supply of blood vessels and numerous mitochondria

What are fast twitch fibres specialised for?

they are specialised for rapid release of energy during intense exercise such as sprinting - with the contractions being intense and in short bursts

How are fast twitch fibres adapted?

they have thick and numerous myosin filaments, a high concentration of glycogen, a high concentration of enzymes needed for anaerobic respiration and also a store of phosphocreatine so that ATP can be rapidly generated

What is homeostasis for?

homeostasis ensures that a constant internal environment is maintained despite changes in the external environment of the organism.

What is negative feedback?

When the body counteract any change in internal environment conditions, meaning all changes are reversed to restore the optimum conditions

What is positive feedback?

It increases the original change in conditions

Give an example of negative feedback?

Hormones being released to convert glycogen to glucose when blood glucose falls

Give an example of positive feedback?

The dilation of the cervix during childbirth

What is the correct range of blood glucose?

70-99mg/dl

Why is it important to ensure that correct blood glucose is maintained?

To ensure that all the essential processes such as respiration of brain cells is maintained

How does the liver regulate blood glucose?

Through glycogenesis, glycogenolysis, gluconeogenesis

What is glycogenesis?

Making glycogen from glucose removed from the blood

What is glycogenolysis?

Breaking down stored glycogen into glucose, which can then be released into the blood

What is gluconeogenesis?

Synthesis of glucose from other molecules such as amino acids

What happens if the blood glucose concentration is too high?

The rise in glucose concentration is detected by beta cells in the islets of Langerhans in the pancreas. Insulin is secreted by the beta cells, inhibiting the action of alpha cells. Insulin 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 membranes of these cells causes vesicles containing glucose transport proteins to fuse with the cell membrane. This increases the permeability of the cells to glucose, increasing the rate of glucose uptake into the cell. The glucose is then converted to glycogen or fats and then used in respiration

What happens if blood glucose concentration is too low?

Alpha cells in the islets of Langerhans detect a fall in blood glucose and secrete the hormone glucagon. Glucagon then inhibits beta cell action and stimulates hepatocytes to convert glycogen into glucose. Glucose diffuses out of the hepatocytes into the blood

How else can glycogen be broken down into glucose?

Using the secondary messenger adrenaline

How does adrenaline break glycogen into glucose?

Adrenaline fuses to a receptor on the membrane of a liver cell and causes the receptor to change shape on the inside of the membrane. The changing of the shape on the inside of the membrane activates the enzyme adenyl cyclase which converts ATP to cyclic AMP (cAMP). This acts as a secondary messenger. The cAMP then changes shape and activates protein kinase enzyme which catalyses the conversion of glycogen into glucose

What is type 1 diabetes?

Insulin dependent diabetes. It results in loss of insulin production - in some cases the immune system destroys beta cells in the pancreas.

What is type 2 diabetes?

Can be caused by decreased insulin production or lack of insulin sensitivity. This is often cause by obesity and diet.

What are the 4 step for water being reabsorbed by the kidneys?

Ultrafiltration, selective reabsorption, loop of Henle, distal convoluted tubule and the collecting duct

Describe ultrafiltration?

Blood enters the kidney via the renal artery. It is under high hydrostatic pressure causing water and all soluble plasma components, e.g. glucose, ions or urea, out of the glomerulus through small pores in the capillary endothelium and through the capillary basement membrane

Describe selective reabsorption?

All glucose in the glomerular filtrate must be reabsorbed into the blood however waste products like urea don't need to be.

How can the permeability of the collecting duct be altered?

The permeability can be altered by hormones

How does ADH increase the permeability of the collecting duct and distal convoluted tubule?

ADH is released from the posterior pituitary gland and bind to receptors on the surface of the collecting duct which activates phosphorylase. This causes vesicles containing aquaporins to be embedded into the cell surface membrane. This increases water permeability