6A Flashcards
Responding to the Environment
- Organisms increase their chances of survival by responding to changes in their external environment, e.g. moving away/towards places that are too hot/cold)
- Organisms also respond to changes in their internal environment to make sure the conditions are always optimal for their metabolism. Any change in the external or internal environment is called a stimulus
Simple Responses - Tactic response - (Taxis)
Directional movement in response to a stimulus. E.g. woodlice move away from the stimulus of light. They are innate behaviour; They don’t have to be learned
Simple Responses - Kinetic Response - (Kinesis)
Non-Directional (random) movement in response to a stimulus. The intensity of the stimulus affects the response. E.g. Woodlice move slowly and turn less often in high humidity, and when in low humidity, they move faster and turn more often until they move into a new area
What is Positive Tropism?
If an organism moves towards the stimulus
What is Negative Tropism
If an organism moves away from the stimulus
What is Phototropism
Response to light
What is Geotropism?
Response to Gravity
What is a Stimulus?
A change inside or outside an organism that borings about a response in that organism
What is a Receptor?
A structure that detects a stimulus. They communicate with effectors via the nervous system or the hormonal system, or sometimes both
What is an Effector?
A structure that carries out a response. E.g. Muscles, glands, organs and cells.
What is Hydrotropism?
Response to water
Investigating Simple Animal Responses - Light
1 - Construct a choice chamber using a petri dish, a divider and fine mesh
2 - Cover one side of the lid with black paper to make one side of the chamber dark. Then put damp filter paper on both sides of the base to make the humidity constant on both sides of the chamber
3 - Place 10 woodlice on the mesh in the centre and put the lid on
4 - Wait 10 mins and record how many woodlice are on each side
5 - Gently move the woodlice back to the centre and repeat the experiment
6 - To investigate Humidity, place damp filter paper on one side of the chamber and a drying agent on the other. Don’t cover the lid with paper and record the number of woodlice on each side of the chamber after 10 mins
Simple responses are automatic responses to a stimulus, the organism doesn’t ‘choose’ where to move
Order for a simple response
Stimulus, Receptor, Co-ordinator, Effector and Response
What do Baroreceptors detect?
Blood pressure
Neurones (Nerve cells)
It is made up of a complex network of cells called neurones, and the three main types are called:
- Sensory
- Motor
- Relay
What do Sensory Neurones do?
Transmit electrical impulses from receptors to the CNS - the brain and spinal cord
What do Motor Neurones do?
Transmit electrical impulses from the CNS to effectors
What do Relay Neurones do?
Transmit electrical impulses between the sensory and motor neurones
Order of simple response with neurones (The reface arc)
Stimulus, Receptor, Sensory neurone, CNS (Relay), Motor neurone, effectors, response
What are the chemicals called which take information across the gap from one neurone to the next
Neurotransmitters
What are the electrical impulses that are sent along the neurone called (other than nerve impulse)
Action Potentials
What does the Co-ordinator do?
It formulates an appropriate response to a stimulus before sending impulses to an effector
The nervous impulse
When an electrical impulse (Action Potential) reaches the end of the neurone, neurotransmitters (Chemical messengers) are secreted directly onto cells, so the nervous response is localised. The response is short-lived as the neurotransmitters are quickly removed. The impulses are fast, and a response is usually rapid.
What is a simple reflex?
A simple reflex is a rapid, involuntary response to a stimulus. The pathway of communication goes through the spinal cord but not through the conscious parts of the brain, so the response happens automatically. It is protective; to avoid damage to the body.
An Example of a Reflex Arc
- Stimulus - you touch a hot surface
- Receptors - Thermoreceptors in your skin detect the heat stimulus. A sensory neurone carriers the impulse the CNS
- CNS - A relay neurone in your spinal cord carriers the impulse to a motor neurone
- Effectors - The motor neurone carriers the impulse to muscle cells in your biceps
- Response - Your bicep muscles contract to pull your arm away from the heat source and stop your hand from being damaged
What happens if your brain wants to withstand heat and there’s a relay neurone involved
Your brain can override the Relay neurone and keep your hand near the heat source
What part of a plant is Positively Phototropic?
Shoots - grow towards light
What part of a plant is Negatively Phototropic?
Roots - Grow downwards, away from light
What part of a plant is Positively Geotropic?
Roots - They grow downwards, towards gravity
What part of a plant is Negatively Geotropic?
Shoots - They grow against gravity
What are Auxins?
They are hormone-like chemicals that speed up or slow down plant growth. Plant growth factors are produced in the growing regions of the plant (shoots/root tips) and move where they’re needed in other parts of the plant. If the tip of the plant is removed, no auxins can diffuse down and the shoot stops growing
The role of IAA (Indoleacetic Acid)
It is an Auxin, which diffuses backwards to stimulate cell growth by making the cell walls loose and stretchy, elongating them. It moves by Diffusion and Active Transport, and via the phloem over long distances.
IAA and Positive Phototropism
IAA moves to the shaded part of the shoots, increasing the shaded side to elongate, causing the shoot to bend towards the light stimulus. The elongation is possibly due to hydrogen ions being secreted into the cell walls, weakening the bonds between the cellulose microfibrils, allowing the cell wall to expand when it takes up water
IAA and Negative Phototropism
IAA moves to the shaded side of the roots and inhibits the growth of the cells, so the root bends and grows downwards, away from the light stimulus.
What is the Meristem?
The growth region of the shoots/roots. Where rapid cell division occurs
What is Orthokinesis?
Rate of Movement
What is Klinokinesis?
Rate of Turning
How Receptors work
Receptors are specific, only detecting a particular stimulus. Receptors in the nervous system convert the energy of the stimulus into the electrical energy used by neurones
The Resting Potential
When the nervous system receptor is in its resting state (not stimulated) theres a different in charge between the inside and the outside of the cell - the inside is negatively charged relative to the outside. This means there’s a voltage across the membrane. Voltage is also known as Potential Difference. The Potential Difference when the cell is at rest is called its Resting Potential.
The 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 is Potential Difference due to a stimulus is called the Generator Potential. A bigger stimulus excites the membrane more, causing a bigger movement of ions and a bigger change in Potential Difference - so a bigger Generator Potential is produced.
The Action Potential
If the Generator Potential is big enough, it’ll trigger an Action Potential (AP) An electrical pulse along a neurone. AP’s are all one size, so the strength of a stimulus is measured by the frequency of the AP’s. If the Stimulus is too weak, The Generator Potential won’t reach the threshold, so there won’t be an AP
Pacinian Corpuscle
They are mechanoreceptors, which detect mechanical stimuli (E.g. vibration, pressure etc.) found in the skin. They contain a sensory neurone ending, wrapped around layers of connective tissue called Lamellae. Within each layer is a viscous gel with a high conc. of Sodium ions. When it is stimulated, the lamellae deform, and press on the Sensory nerve ending, causing the membrane to stretch. This deforms the intrinsic proteins called the stretch-meditated-sodium-ion channels to open and allow sodium ions to diffuse into the cell, causing a Generator Potential. If the Generator Potential reaches the threshold, an AP will be triggered.
Photoreceptors
Receptors in the eye which detect light. Light enters through the pupil and the amount of light that enters is controlled by the muscles of the iris. Light rays are focused by the Lens onto the retina, which lines the inside of the eye. The retina contains lots of photoreceptor cells. The Fovea is an area of the retina where there the most Photoreceptors. Nerve impulses are carried from the retina rot the Brain by the Optic nerve. Where the optic nerve leaves the eye is called the blind spot.
How Photoreceptors work
Light enters the eye, and hits the Photoreceptors. It is absorbed by light-sensitive optical pigments, which are bleached by the light, causing a chemical change and altering the membrane permeability to sodium ions. A generator potential is created, and if it reaches the threshold, an Action potential is created. The nerve impulse is sent along a bipolar neurone, where it connects to the Optic nerve, which takes the impulse to the brain.
Rods
- They contain the pigment Rhodopsin, which doesn’t distinguish the different wavelengths of light, so produces a black and white image.
- Mainly found in the peripheral parts of the retina, none at the fovea
- They are sensitive to light as many Rods (15-45) join to one Bipolar neurone, so many weak Generator Potentials to reach a threshold
- Give Low Visual Acuity as many Rods join to one Bipolar neurone, therefore the brain cannot distinguish two points of light close together
Cones
- They contain 3 different types of pigments (Different forms of Iodopsin) absorbing different wavelengths of light - Red, Blue and Green sensitive
- Concentrated at the Fovea, with few in the periphery
- One cone cell is joined to one Bipolar neurone, so higher Visual Acuity as the brain can distinguish where two points go light close together came from
- Low sensitivity to light as a stronger stimulus is needed to reach the threshold for an AP to be generated
The Nervous System Structure
- CNS - Made up of the Brain and Spinal Cord
- The Peripheral System is made up of neurones that connect the CNS to the rest of the body.
The Peripheral System has two different Neurones: The Motor (CNS to muscles and glands) and The Sensory Neurones (Sensory organs to CNS) The Motor then has two systems, the Somatic (Controls voluntary movements) and Autonomic (Controls involuntary movements)
The Autonomic Nervous system has two other systems, the Parasympathetic (Rest or Digest) and the Sympathetic (Fight or Flight)
What does ‘Myogenic’ mean?
It can contract and relax without receiving signals from nerves. This pattern of contractions is what controls the regular heartbeat
Control of Heart Rate - Speed up
Cardioacceleratory Centre (CAC) (present in the medulla, and are stimulated by chemoreceptors and pressure receptors) sends impulses to the Sinoatrial Node of the heart by the Sympathetic Nervous System, so increases Heart rate
Control of Heart Rate - Slow down
Cardioinhibitory Centre (CIC) (present in the medulla, and are stimulated by chemoreceptors and pressure receptors) sends impulses to the Sinoatrial Node of the heart by the Parasympathetic Nervous System so decreasing Heart Rate
What is the Sinatrial Node (SAN)?
A small mass of tissue in the wall of the right Atrium of the heart. It is like a pacemaker - it sets a rhythm of the heartbeat by sending out regular waves of electrical activity to the Atrial walls, causing the left and right Atria to contract at the same time. Instead of the impulse travelling down directly from the Atrium to the Ventricles, a band of non-conducting collagen tissue prevents the wave of impulse and transfers the impulse to the AVN
What is the Atrioventricular Node (AVN)?
It is a mass of tissue which is responsible for passing the wave of Electrical activity from the SAN to the Bundle of His. But there is a slight delay before the AVN reacts, to make sure the Atria have emptied of blood before the ventricles contract. The Bundle of His are groups of muscle fibres responsible for conducing the impulse between the ventricles to the apex (Bottom) of the heart, splitting into finer muscle fibres in the right and left ventricle walls, called the Purkyne Tissue. This then carries the impulse into the muscular walls of the right and left ventricles, causing them to contract simultaneously, from bottom up
Controlling Heart rate in response to different stimuli - High Blood pressure
Baroreceptors (Pressure receptors) detect high blood pressure, and sends an impulse along the sensory neurone to the medulla, where an impulse along the parasympathetic neurone. This secretes Acetylcholine, a neurotransmitter which binds to receptors on the SAN, causing the heart rate to slow down in order to reduce blood pressure
Controlling Heart rate in response to different stimuli - Low Blood pressure
Baroreceptors (Pressure receptors) detect low blood pressure, and sends an impulse along the sensory neurone to the medulla, where an impulse along the sympathetic neurone. This secretes Noradrenaline, a neurotransmitter which binds to receptors on the SAN, causing the heart rate to increase down in order to reduce blood pressure
Controlling Heart rate in response to different stimuli - High blood O2, low Co2 - High blood pH
Chemoreceptors detect chemical changes in the blood and send impulses along sensory neurones to the medulla, which sends impulses along the Parasympathetic neurones. These secrete Acetylecholine, a neurotransmitter which binds to receptors on the SAN, causing the heart rate to slow down to decrease the levels of O2 and Co2
Controlling Heart rate in response to different stimuli - High blood Co2, low O2 - Low blood pH
Chemoreceptors detect chemical changes in the blood and send impulses along sensory neurones to the medulla, which sends impulses along the Sympathetic neurones. These secrete Noradrenaline, a neurotransmitter which binds to receptors on the SAN, causing the heart rate to speed up to return the levels of O2 and Co2 back to normal
