Stimuli and Responses Flashcards
1
Q
How do organisms respond to the environment?
A
- Organisms increase their chances of survival by responding to changes in their external environment (animals and plants respond in different ways)
- Organisms also respond to changes in their internal environment to make sure that the conditions are optimal for their metabolism
2
Q
What is a stimulus?
A
- Any change in the internal or external environment e.g. change in pressure, temperature, light intensity
- Response can be tactic or kinetic
- By detecting harmful stimulus, can move away from predators and extreme temperatures
- This increases chance of survival and the alleles being passed on
- Selection pressure that favours organisms with more appropriate responses to keep them in their favourable environment
3
Q
Tactic response (taxis)
A
- Directional movement in response to a stimulus
- The direction of stimulus affects response (woodlice move away from light so they don’t lose water- negative taxis)
4
Q
Kinetic response (kinesis)
A
- Non-directional (random) movement in response to a stimulus
- Intensity of stimulus affects response
- Woodlice example= show a kinetic response to humidity
- In high humidity, turn less often and move slowly, so that they stay where they are
- As air gets drier, they move faster and turn often, so that they move into a new area
- Response helps move woodlice to humid air to increase their chances of survival-reduces water loss and keeps them concealed
5
Q
Responses of earthworms, bacteria, single-called algae
A
- Algae (positive phototaxis) survival increased as they use light to make food
- Earthworms (negative phototaxis) survival increased as they are taken into the soil to conserve water, find food and avoid predators
- Some bacteria (positive chemotaxis) move towards glucose as they use it to make food
6
Q
Receptors
A
- Detect stimuli- can be cells or proteins on cell surface membranes
- Loads of different receptors that detect different stimuli
- Receptors are specific to one type of stimulus
7
Q
Effectors
A
- Cells that bring about a response to a stimulus, to produce an effect
- Examples include muscle cells or cells found in glands
- Receptors communicate with effectors via the nervous system or hormonal system (or both)
8
Q
The nervous system
A
Made up of a complex network of cells called neurones
9
Q
Sensory Neurones
A
- Transmit electrical impulses from receptors to CNS- the brain and spinal cord
- Have 1 dendron that is often long
10
Q
Motor Neurones
A
- Transmit electrical impulses from CNS to effectors
- Long axon, many short dendrites
11
Q
Relay Neurones
A
(intermediate) Transmit electrical impulses between sensory neurones and motor neurones
12
Q
Nervous Communication
A
- Stimulus is detected by receptor cells and an electrical impulse is sent along a sensory neurone
- When an electrical impulse reaches the end of a neurone chemicals called neurotransmitters take the information across the gap (synapse) to the next neurone, where another electrical impulse is generated
- CNS (coordinator) processes information and sends impulses along motor neurones to an effector
13
Q
Nervous response
A
- When an electrical impulse reaches the end of a neurone, chemical messengers called neurotransmitters are secreted directly onto cells- so nervous response is localised
- Neurotransmitters are quickly removed once they have done their job, so response is short-lived
- Electrical impulses are really fast, so response is rapid- allows animals to react quickly to stimuli
14
Q
Simple reflex
A
- Rapid, involuntary response to a stimulus
- Pathway of communication goes through spinal cord but not through conscious parts of the brain-so response is automatic
- Protective as they help organisms to avoid damage to the body because the response happens so quick
- Fast due to absence of decision making (brain can’t get overloaded) and short neurone pathway
15
Q
Reflex arc
A
- Pathway of neurones linking receptor to effectors in a simple reflex
- If relay neurone involved, then possible to override refelx
16
Q
Spinal cord
A
- Column of nervous tissue that runs along the back and lies inside the vertebral column for protection
- By the time the brain has recieved nerve impulses from receptors, the muscles have already moved
17
Q
Tropisms
A
- Flowering plants, like animals, increase their chances of survival by responding to changes in their environment
- Plants have no nervous system
- A tropism is the response of a plant to a directional stimulus
- Plants respond to stimuli by regulating their growth
- Positive tropism is growth towards the stimulus, whereas a negative tropism is growth away from the stimulus
18
Q
Phototropism
A
- Growth of a plant in response to light
- Shoots are positively phototropic and grow towards light (capture light for photosynthesis to survive)
- Roots are negatively phototropic and grow away from light (so roots can absorb nutrients and water for survival)
19
Q
Gravitropism
A
- Growth of plant in response to gravity
- Shoots are negatively gravitropic and grow upwards
- Roots are positively gravitropic and grow downwards so roots can be firmly anchored into the soil
20
Q
Auxins
A
- Plants respond to directional stimuli using specific growth factors- these are hormone like chemicals that speed up or slow down plant growth
- Plant growth factors are produced in the growing regions of the plant (shoot and root tips) and they move to where they’re needed in the other parts of the plant
- Some plant growth factors affect tissues that release them
- Growth factors called auxins are produced in the tips of shoots and diffuse backwards to stimulate the cell just behind the tips to elongate
- This is where cell walls become loose and stretchy, so cells get longer
- If the tip of a shoot is removed, no auxin will be available and the shoot stops growing
- Auxins stimulate growth in shoots but high concentrations inhibit growth in roots
21
Q
Indoleacetic acid (IAA)
A
- Plant growth factor that belongs to auxins
- IAA is an important auxin that’s produced in the tips of shoots and roots in flowering plants
- Moved around plants to control tropisms (by diffusion and active transport over short distances and phloem via long distances)
- Results in different parts of the plant having different concentrations of IAA
- Uneven distribution of IAA means there’s uneven growth of the plant
- Cells only elongate on young cell walls because mature cells have greater rigidity
- IAA increases plasticity by active transport of hydrogen ions from the cytoplasm into spaces in the cell wall
22
Q
IAA phototropism and gravitropism
A
23
Q
How do receptors work?
A
- Specific-detect one type of stimulus
- Some receptors are cells while others are proteins on cell-surface membranes
- Receptors in the nervous system convert energy of stimulus into electrical energy used by neurones
24
Q
Resting Potential
A
- When nervous sytem is in it’s resting state, there’s a difference between inside and outside of cell (inside is more negatively charged)
- Means their is a voltage across the membrane (potential difference)
- Potential difference at resting state is resting potential
- It is generated by ion pumps and ion channels
25
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**
* Change in 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
26
Action Potential
* If generator potential is **big enough** it'll trigger an **action potential**-an electrical impulse along a neurone
* An action potential is only triggered if the **generator potential** reaches a certain level called the **threshold level**
* Action potentials are all **one size**, so the strength of the stimulus is measured by the **frequency** of action potentials
* If stimulus is too **weak** the generator potential won't reach the threshold, so there's **no action potential**
27
Pacinian Corpuscles
* **Mechanoreceptors** (detect mechanical stimuli like pressure and vibrations, found in skin)
* They contain a **sensory nerve ending** wrapped in loads of layers of **connective tissue** called **lamellae**
* When stimulated (tap on the arm), lamellae are **deformed** and **press** on sensory nerve ending
* This causes sensory neurone's cell membrane to **stretch**, **deforming** the **stretch-mediated sodium ion channels**
* Channels open and sodium ions diffuse into the cell, creating a **generator potential**
* If generator potential reaches threshold, it triggers an **action potential**
28
Cone cells
* Made of **iodopsin** pigment which is only broken down at high **light intensity**
* **One cone cell** connects to **one bipolar neurone** which connects to **one sensory neurone** (therefore no summation of light can take place so only detects **high light intensity** as threshold isn't that easy to reach)
* But because one cone cell connects to one bipolar neurone which connects to one sensory neurone, each stimuli can be distinguished as **two separate action potentials** go to the brain= **high visual acuity**
* Mainly found in **fovea**
* Contain **different optical pigments**- **red**, **green** and **blue** sensitive (colour vision)
29
Rod cells
* made of **rhodopsin** pigment which can be broken down at **low light intensity**
* a **few rod cells** connect to **one bipolar neurone** which connects to **one sensory neurone** (therefore summation of light can take place so can detect **low light intensity**)
* This is due to combining **weak generator potentials** to trigger an action potential
* but because a few rod cells connect to one bipolar neurone which connects to one sensory neurone, the **stimuli** will be **merged together** = **low visual acuity**
* Found in **peripheral parts** of the **retina**
* Can't distinguish between different wavelengths of light so **monochromatic vision**
30
Photoreceptors
* Receptors in the eye that **detect light**
* Amont of light entering pupil is controlled by the **muscles** of the **iris**
* Light rays are **focused** by the **lens** onto the **retina**
* Retina contains photoreceptor cells (most in **fovea**)
* Nerve impulses from the photoreceptor cells are carried from the **retina** to the **brain** by the **optic nerve**, which is a bundle of neurones
* Where the optic nerve leaves the eye is called the **blind spot**- no photorecptor cells
31
How photoreceptors work?
* Light enters eye, hits **photoreceptors** and is **absorbed** by **light sensitive optical pigments**
* Light **bleaches** the pigments, causing a **chemical change** and altering the **membrane permeability** to **sodium ions**
* **Generator potential** is created and if it reaches the **threshold**, a nerve impulse is sent along a **bipolar neurone**
* Bipolar neurones connect **photoreceptors** to the **optic nerve**, which takes impulses to the **brain**
32
Structure of the nervous system
* **CNS**= brain and spinal cord
* **Peripheral NS**= neurones that connect the CNS to the rest of the body
* Peripheral NS split into **somatic** (controls conscious activities) and **autonomic** (controls unconscious activities)
* Autonomic split into **sympathetic** (fight/flight, ready for action, helps cope with stress) and **parasympathetic** (rest and digest that calms the body, slows down activities and conserves energy)
33
Control of heart beat
* **Cardiac muscle** is **myogenic** (contract and relax without recieving nerve signals)
* **Sinoatrial node** (SAN) which is a small mass of tissue in the wall of the right atrium is a **pacemaker**
* Sets out rhythm of heartbeat by sending out **regular waves** of **electrical activity** to the atrial walls
* Causes left and right atria to contract at the **same time**
* A band of **non-conducting collagen tissue** prevents waves of electrical activity from being passed directly from the **atria** to the **ventricles**
* Waves of electrical activity are transferred from SAN to **atrioventricular node** (AVN)
* AVN responsible for passing waves of electrical activity to **bundle of His**
* **Slight delay** before AVN reacts, to make sure **atria** have **emptied** before ventricles contract
* bundle of His is a group of muscle fibres responsible for conducting waves of electrical activity between **ventricles** to the **bottom** of the **heart**
* bundle of His splits into **finer muscle tissues** in the right and left ventricle walls, called **purkyne tissue**
* Purkyne tissue carries waves of electrical activity into the **walls** of the **ventricles**, causing them to **contract simultaneously**, from the bottom up
* Involves **autonomic** nervous system
34
Medulla oblongata
* Unconsciously controls rate at which SAN fires
* M.O contains cardiovascular centre
35
Communication between heart and brain
* Animals need to **alter** their **heart rate** to respond to **internal stimuli**
* Internal stimuli is detected by **pressure/chemical receptors**
* **Pressure**= baroreceptors in the aorta and carotid arteries (stimulated by high and low blood pressure)
* **Chemical**= chemorecptors in the aorta, carotid arteries and medulla (monitor oxygen levels, CO2 and pH)
* **Electrical impulses** from receptors are sent to the medulla along **sensory neurones**
* **Medulla** processes information and sends impulses to the **SAN** along **sympathetic** or **parasympathetic** neurones
36
High blood pressure
* **Baroreceptors** detect high blood pressure and send impulses along **sensory neurones** to the **medulla**, which sends impulses along **parasympathetic neurones**
* These secrete **acetylcholine**, which **binds** to **receptors** on the **SAN**
* This causes the **heart rate** to **slow down** in order to reduce blood pressure back to normal
37
Low blood pressure
* Baroreceptors detect low blood pressure and send impulses along **sensory neurones** to the **medulla**, which sends impulses along **sympathetic neurones**
* These secrete **noradrenaline**, which binds to **receptors** on the **SAN**
* Causes heart rate to **speed up** in order to increase blood pressure back to **normal**
38
Transducer
Convert energy by the stimulus to nerve impulses that can be understood by the body
39
CO2 in control of heart rate
* CO2 forms an acid that lowers pH
* CO2 dissolves to form carbonic acid
40
High blood O2, low CO2 or high blood pH levels
* **Chemoreceptors** detect chemical changes in the **blood** and send impulses along **sensory neurones** to the **medulla**, which sends impulses along **parasympathetic neurones**
* These secrete **acetylcholine**, which binds to receptors on the SAN
* This causes the heart rate to **decrease** in order to return oxygen, CO2 and pH levels back to normal
41
Low blood O2, high CO2 or low blood pH levels
* Chemoreceptors detect chemical changes in the blood and send impulses along **sensory neurones** to the **medulla**, which sends impulses along **sympathetic neurones**
* These secrete **noradrenaline**, which binds to receptors on the SAN
* Causes the heart rate to **increase** in order to return oxygen , CO2 and pH levels back to normal
42
Control by chemoreceptors during exercise
* Increased **muscular/metabolic activity**
* More **CO2 produced** by tissues from **increased respiration**
* Blood **pH** is **lowered**
* **Chemoreceptors** in the carotid arteries **increase frequency** of impulses to the **medulla oblongata**
* Centre in medulla **speeds heart rate**, increases frequency of impulses to **SA node** via **sympathetic N.S**
* SA node **increases heart rate**
* Increased blood flow **removes CO2 faster** (from lungs)
* CO2 concentration turns back to normal
