Homeostasis Flashcards
What is Homeostasis
-Every reaction in a cell is catalysed by enzymes. A good example is respiration which releases energy from glucose.
-Enzymes need stable conditions to work effectively. These conditions are maintained by homeostasis.
-Homeostasis is defined as the regulation of the internal conditions of a cell or organism to maintain optimal conditions for function in response to internal and external changes.
List possible Changes to the Body’s Internal Environment
-An increase in the concentration of blood glucose due to eating a meal
-A decrease in the concentration of blood glucose due to exercise
-An increase in body temperature due to exercise
-An increase in the level of water in the blood due to having a drink of water
-A decrease in the level of water in the blood due to sweating
List possible Changes to the Body’s External Environment
-An increase in the temperature of the skin due to hot conditions
-A decrease in the temperature of the skin due to cold conditions
How do Internal Body Conditions Change During Exercise
-Blood glucose levels will decrease because more glucose is being used to release energy by respiration.
-Body temperature will increase because an increase in respiration releases more thermal energy.
-Blood water levels will decrease because sweating releases water to cool the body down.
List the Order of the Features in the Homeostatic Control System
- Stimulus (e.g. change in temperature)
- Receptor Cells
- Coordination Centre (brain or spinal cord)
- Effector (muscle or gland)
- Response (e.g. sweating to cool down)
What is the Function of Receptor Cells in Homeostatic Control
The function of receptor cells is to detect the stimulus ( a change to the body’s internal or external environment)
What is the Function of the Coordination Centre in Homeostatic Control
-The function of the coordination centre is to receive information from the receptor cells and then process the information.
-(i.e. make a decision on the response required).
-The coordination centre then sends instructions to the effectors.
What is the Function of Effectors in Homeostatic Control
The function of the effector is to bring about the response to restore the optimum levels.
Describe the Features of Neurones
-A long fibre (axon) which is insulated by a fatty (myelin) sheath. They are long so they can carry messages up and down the body.
-The myelin sheath also increases the speed of the impulses.
-Tiny branches (dendrons) which branch further as dendrites at each end. These receive incoming impulses from other neurones.
What is the Function of Neurones in Homeostatic Control
-A stimulus is detected by receptors. These send electrical impulses down sensory neurones to the central
nervous system, telling it what the receptors have detected.
-The central nervous system acts as the coordination centre. This is where relay neurones are found.
-Electrical impulses now pass through motor neurones from the central nervous system to the effectors, telling them what to do. The effectors then bring about a response.
How do Muscles and Gland Bring About a Response
-Both muscles and glands are effectors.
-To bring about a response, muscles contract and glands secrete a hormone into the bloodstream.
Match Stimuli to Their Receptors
Light- light receptors in the eye
Sound, body position- sound and balance receptors in the ear
Chemicals (in food)- chemical receptors in the mouth/ on the tongue
Chemicals (in the air)- chemical receptors in the nose
Touch, pain, pressure, and temperature- thermo and pressure receptors in the skin
Describe the Stages in the Reflex Arc
-The stimulus (heat) is detected by receptors in the skin. Electrical impulses pass down the sensory neurone and travel towards the central nervous system.
-The electrical impulses reach the synapse at the end of the sensory neurone. A chemical is released at the synapse. The chemical diffuses to the relay neurone.
-An electrical impulse is triggered in the relay neurone. At the next synapse a chemical is released. Electrical impulses are triggered in the motor neurone.
-The impulses travel away from the central nervous system. The impulses reach the effector (a muscle). The muscle contracts and the hand pulls away (the response).
Describe How Information passes Across a Synapse
-The impulse from the neurone arrives at the synapse.
-This stimulates the release of chemicals.
-Chemicals diffuse across the gap.
-These bond with a specific receptor on the next neurone.
-This triggers a new impulse.
Explain why Reflexes are Automatic and Rapid
-Reflexes are automatic and rapid. This is because although electrical impulses pass through the central
nervous system, no decision making takes place in the conscious part of the brain.
-We often find reflexes involved when there is danger. In these cases, the body needs to respond very rapidly to events.
-The response needs to be automatic. If the brain had to make a decision, then this would slow down the response and that could prove dangerous or even fatal.
Describe a Method for the Reaction Time Practical
-Person 1 sits at a table. They should have a good, upright position. Person 1 places their dominant arm on the table so their dominant hand is over the edge.
-Person 2 holds a metre ruler vertically so the 0cm mark is between person1’s thumb and index finger. Person 2 tells person 1 to prepare.
-Person 2 then drops the ruler at random and person 1 has to catch the ruler as quickly as possible. Person 2 records the measurement on the ruler that is level with person 1’s thumb.
-This test is repeated several times. A mean value is taken and person 1’s reaction time is determined using a conversion table.
-Person 1 and 2 switch places and person 2’ s reaction time is determined and compared to person 1’s.
Why is an Upright Posture better than a Slouched Posture in the Reaction Time Practical
-A person with good upright posture is likely to be more alert than a person who is slouched.
-A slouched person is more likely to be relaxed and not ready to catch the ruler.
Why is it Important that the Position of the Ruler Between the Fingers Doesn’t Change in the Reaction Time Practical
-The initial position of the ruler is a control variable. This must not be allowed to change.
-If the ruler was not at the zero position at the start then we would have a zero error.
Why is it Important that the Measurement is Always at the Top of Person 1’s Thumb in the Reaction Time Practical
-The final measurement position is also a control variable.
-In this case, we have decided to always measure the final position at the top of the person’s thumb.
-We need to make sure that we keep this the same between experiments
Describe How Investigating the Effect of Practice Changes the Reaction Time Practical
-To study the effect of practise, we would measure the person’s reaction time repeatedly over a large number of attempts.
-We could then see if there was any difference from the first attempt through all of the remaining attempts.
-If practise decreased a person’s reaction time then we should see them catch the ruler more rapidly as the experiment continued.
Describe How Investigating Dominant vs Non-dominant Hand Changes the Reaction Time Practical
-To study the effect of dominant versus non-dominant hand, we would ask the person to catch the ruler
with their dominant hand first and then with their non-dominant hand.
-We would need to carry out a number of repeats in order to get valid results.
-However, we would need to be careful that practise does
not affect the result (for example we could leave an interval from one experiment to another).
How does Alcohol and Caffeine Affect Reaction Time
-Alcohol is a depressant so slows the rate of release of chemicals across the synapse. This slows the response rate of an effector.
Caffeine is a simulant so increases the rate of release of chemicals across the synapse. This increases the response rate of an effector.
How does the Brain Control Complex Behaviour
-The brain can control complex behaviour because the brain contains billions of interconnected neurones.
-We can compare the brain with the simple reflex which contains only three neurones (the sensory neurone, the relay neurone and the motor neurone). This is very simple and cannot coordinate complex behaviour.
-However, the human brain contains many billions of neurones and these are connected together, forming trillions of connections. This allows the human brain to control complex behaviour
Name the Parts of the Brain and Their Functions
-The cerebrum (the outer layer is called the cerebral cortex), which is split into two hemispheres and is highly folded.
-It controls intelligence, personality, conscious thought and high-level functions, such as language and verbal memory.
-The cerebellum, which controls balance, co-ordination of movement and muscular activity.
-The medulla, which controls unconscious activities such as heart rate and breathing rate.
The hypothalamus, which is the regulating centre for temperature and water balance within the body.
How do Scientists Investigate the Brain
-It is difficult to study to brain or treat brain disease or damage. The brain is surrounded by the skull making it hard to access. It is also delicate and easy to damage.
-The brain is complex so it is difficult to work out which parts have which function. Looking at patients with brain damage can give us clues on the function of that part of the brain.
-We can also stimulate different parts of the brain with electricity and look at the effect on the person’s behaviour.
-MRI scanning can tell us which parts of the brain are most active when a person carries out certain tasks, allowing us to narrow down the function to a specific region of the brain.
Describe the Use of Electrical Stimulation in Investigating the Brain
-Scientists have stimulated different parts of the brain with a weak electrical current and asked patients to describe what they experienced.
-If the motor area is stimulated, the patient makes an involuntary movement. If the visual area is stimulated, they may see a flash of colour.
-EEGs (Electroencephalograms) can be created and studied, to observe the electrical activity in the brain.
Describe the Use of MRI Scans in Investigating the Brain
-Modern imaging methods such as MRI (Magnetic Resonance Imaging) scans, use strong magnetic fields and radio waves to show details of brain structure and function.
-Patients are asked to perform various tasks and, by looking at the scan, scientists can see which parts of the brain are active when the task is carried out.
Describe the Risks of investigating the Brain
-Brain surgery may be needed to remove a tumour or excess fluid, such as blood.
-All surgery carries a level of risk, but due to the complexity and delicacy of the brain, investigating and treating brain disorders can be very difficult.
-If surgery is undergone more damage or side-effects may be created, which could affect the patients’ quality of life.
-Serious considerations about the risks involved against the benefits need to be undertaken first.
What is the Function of the Sclera
The white part of the eye. This tough outer structure protects the eye.
What is the Function of the Cornea
The transparent front of the eye. This starts the focussing of the light rays.
What is the Function of the Iris
The coloured part of the eye. This adjusts the size of the pupil in response to light intensity.
What is the Function of the Pupil
This is a hole in the centre of the iris. Light passes through this before passing through the lens.
What is the Function of the Lens
This focuses the light onto the back of the eye. It changes shape when viewing far or near objects.
What is the Function of the Retina
Light is focussed here. It contains receptor cells for light intensity and light colour.
What is the Function of the Optic Nerve
Carries electrical impulses from the retina to the brain.
What is the Function of the Suspensory Ligaments
Work with the ciliary muscles to change the shape of the lens for focussing on near or distant objects.
What is the Function of the Ciliary Muscles
Work with the suspensory ligaments to change the shape of the lens for focussing on near or distant objects.
How does the Eye Adapt to Light Levels
-In dim light, the pupils dilate to allow more light in. This is because circular muscles in the iris relax and radial muscles contract.
-In bright light, the pupils contract to allow less light in. This is because circular muscles in the iris contract and radial muscles relax.
How does the Eye Change to Focus on Near Objects
-To focus on a near object, the ciliary muscles contract so they have a smaller diameter.
-This causes the suspensory ligaments to loosen so the lens becomes thicker and more curved.
-The thicker lens is more convergent so light rays are refracted strongly causing the light rays to be focused on the retina.
How does the Eye Change to Focus on Distant Objects
-To focus on a distant object, the ciliary muscles relax so they have a larger diameter.
-This causes the suspensory ligaments to tighten so the lens becomes thinner and less curved.
-The thinner lens is less convergent so light rays are refracted slightly causing the light rays to be focused on the retina.
Describe why a Person With Long Sight (Hyperopia) cannot Focus on Near Objects
-A person with hyperopia cannot focus on near objects. This can be because their eyeball is too short for the strength of the lens.
-This means that the light is focused at a point behind the retina.
-In some cases, long sight is caused when the lens becomes less elastic.
-In this case, the lens cannot become thick enough to focus on near objects.
How does a Convex Lens Adjust the Light rays to Treat Long Sightedness
-Long sight is treated with a convex lens. This partially focuses the light before it passes into the eye.
-Now the lens can complete the focusing of the light, onto the retina.
Describe why a Person With Short Sight (Myopia) cannot Focus on Near Objects
-A person with short sight cannot focus on distant objects. In many people with short sight, the eyeball is too long for the strength of the lens.
-This means that the light is focused at a point in front of the retina.
-In some cases, the lens is too thick and focuses the light too strongly
How does a Convex Lens Adjust the Light rays to Treat Short Sightedness
-Short sight is treated with a concave lens.
-This partially unfocuses the light before it passes into the eye.
How does Laser Eye Surgery Work
-Laser eye surgery reshapes the cornea surgically so it refracts light to a greater or lesser extent.
-It is common for myopia but can be used for some hyperopia conditions.
Give the Advantages and Disadvantages of Laser Eye Surgery
Advantages:
-Treats both myopia and hyperopia (permanently)
Disadvantages:
-Procedure may be expensive
-Only for adults who have stopped growing
Give the Advantages and Disadvantages of Glasses
Advantages:
-Treats both myopia and hyperopia (only while worn)
-Last a long time
Disadvantages:
-Bulky
-harder for playing sports and general activities
How do Contact Lenses Work
-Contact lenses sit on the eyeball.
-They refract the light in the same way as glasses.
Give the Advantages and Disadvantages of Contact Lenses
Advantages:
-Can’t be seen and easier for playing sports
-Soft lenses are comfortable, hard lenses last a while
Disadvantages:
-Must be removed overnight and kept sterile
-Soft lenses don’t last a while, hard lenses are uncomfortable
How do Replacement Lenses Work
-Implanting artificial lenses is a recent development.
-They can placed in front of the original lens, through a small cut in the cornea, to correct an eye defect.
Describe the Thermoregulatory Centre
-The body temperature is controlled by the thermoregulatory centre in the brain.
-The thermoregulatory centre has receptors which monitor the temperature of the blood. We also find temperature receptors in the skin.
-These send electrical impulses down sensory neurones to the thermoregulatory centre in the brain.
Explain how Sweating Reduces Body Temperature
-When the body temperature rises, sweat glands release sweat onto the skin surface.
-When the sweat evaporates, it takes energy away from the body, cooling it down.
