biology GCSE topic 5 homeostasis and response

What is homeostasis?

the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes

what are the three internal conditions controlled by homeostasis?

body temperature, water content of the body, blood glucose concentration

why is it important to maintain body temperature?

if its too cold chemical reactions happen too slowly and the cell won't work and if the cell gets too hot enzymes become denatured causing the cell to die

why is it important to maintain the water content of the body?

because if it cells absorb too much water by osmosis they would fill up with water and eventually burst. low levels change the shape of the cell

why is it important to control blood glucose concentration?

low blood glucose concentration will affect respiration and brain function and high blood glucose will lead to circulatory problems

what is stimuli

a change in the environment

What is a receptor?

cells that detect stimuli (a change in environment)

What are coordination centres?

areas that receive and process information from receptors and coordinate a response

What are effectors?

muscles and glands that bring about response

What does the nervous system do?

allows humans to react to their surroundings and coordinate their behaviour

how does the nervous system allow us to quickly react to our surroundings?

it uses electrical impulses

what is a receptor (part of body)

a sense organ

what is the effector (body part)

muscle or gland

what are the three types of neurones

sensory, motor and relay neurones

What are sensory neurones?

the neurones that carry information as electrical impulses from the receptors to the CNS

what are motor neurones?

The neurones that carry electrical impulses from the CNS to effectors

what are relay neurones?

Nerve cells that carry signals from sensory neurones to motor neurones. they are short neurones

what is the difference between neurones and nerves?

a neurone is a singular special cell whereas nerves are bundles of hundreds or thousands of neurons

how is a response in the nervous system carried out?

by effectors

in an experiment what is the advantage of working out the mean

it gives us an average, closer to the answer which means its more accurate

what happens in a reflex action when you touch something hot?

Receptor: when you touch an object a receptor in your skin is stimulated, an electrical impulse from the receptor passes along the sensory neurone to the CNS.

the sensory neurone arrives at the synapse where a chemical is diffused across the synapse where it sets off another electrical impulse which travels across the relay neurone.

when the impulse reaches the synapse between the relay neurone and a motor neurone returning to the arm another chemical is released which diffuses across the synapse and starts a new electrical impulse down the motor neurone to the effector

when the impulse reaches the effector organ it is stimulated to respond and the muscle contract. the action moves the hand rapidly away from pain. if the effector is a gland it will respond by releasing chemical substances

What are synapses and what do they do?

the connection between two neurones is called a synapse. the nerve signal is transferred by chemicals which diffuse across the gap

what are reflexes?

These are rapid, predictable, and involuntary responses to stimuli that dont involve the conscious part of the brain

what is an example of a reflex?

breathing, moving food through your digestive system

why cant breathing and swallowing happen in the conscious part of the brain but speaking and eating can?

they need to happen automatically and constantly even when you're asleep, you cannot rely on a conscious thought process. speaking and eating require coordination of different parts of the body and so need to be under conscious control

why could be considered unethical in the reaction time experiment?

using a drug like caffeine. you need consent

what is the independent variable in the reaction time experiment?

the hand used

how does the reaction time change in the reaction time experiment when the independent variable is changed?

In the non-dominant hand the reaction time is usually slower but if switched to dominant hand the reaction time is faster

how could you improve the precision of your results in the reaction time experiment?

measure to the nearest millimeter

What does the cerebral cortex do?

responsible for consciousness, intelligence, memory and language

What does the hypothalamus do?

controls body temperature

What does the cerebellum do?

Controls balance, equilibrium, and muscle coordination.

What does the medulla do?

it controls your unconscious activities, like breathing and your heartbeat

What does the pituitary gland do?

secretes hormones

how has brain damage helped scientists discover more about the brain?

if a small part of the brain is damaged the effect it has on the patient can tell you a lot about what the damaged part of the brain does

How has electrical stimulation of the brain helped scientists?

the brain can be stimulated electrically by pushing a tiny electrode into the tissue and giving it a small zap of electricity. by observing what stimulating different pats of the brain does, its possible to get an idea of what those parts do.

How do MRI scams help us learn about the brain?

It produces a detailed picture of the brain's structures, helping us to find out what parts of the brain are engaged when we do certain activities

what are the benefits of an mri scan?

- enables us to see different part of the brain when doing different activities
- less risk-factors as is non-invasive
-can see how the brain works

what are the risks of an mri?

-No radiation or contrast- no tissue damage
-No pregnant women
-ethical consideration when working on healthy people so need consent

what are the benefits of electrical stimulation?

-no sensory nerve endings in the brain so electrical stimulation is painless
-people can be conscious during the procedure

what are the risks of electrical stimulation?

-damage to brain as brain is delicate
-brain not fully understood so can cause damage easily
-risk of infection as skull has to be cut off to get to the brain

what is the role of the suspensory ligaments and ciliary muscles?

holds the lens in place which change the shape of the lens

What is the role of the iris?

It contains muscles that allow it to control the diameter of the pupil and how much light enters the eye

What does the pupil do?

allows light to enter the eye, it changes shape based how light it is, in bright light it shrinks in order to protect to the delicate light-sensitive cells at the back of the eye

What is the sclera of the eye?

the tough supporting wall of the eye ( white outer layer and is difficult to damage)

What is the cornea?

the sclera has a transparent region at the front called the cornea that lets light in and refracts light toward the retina

what is the role of the lens of the eye?

it 'fine-tunes' the focusing of light rays, changing their direction to produce a clear image on the retina

what does the retina do?

it is made up of light-sensitive cells that send impulses impulses to the brain via sensory neurones

What does the optic nerve do?

carries impulses from the receptors to the brain

What is the blind spot of the eye?

point where optic nerve leaves the eye; there are no receptor cells located here

what does the iris do in bright light?

when light receptors in the eye detect bright light a reflex is triggered that makes your pupil smaller. the circular muscles in the iris contract and the radial muscles relax.

what does the iris do in dim light?

the radial muscles contract and the circular muscles relax which makes the pupil wider.

what happens when you look at near objects?

the ciliary muscles contract which slackens the suspensory ligaments. the lens becomes fat ( more curved). the increases the amount by which it refracts light

what happens when you look at distant objects?

the ciliary muscles relax which allows the suspensory ligaments to pull tight. this makes the lens thin. it refracts light by a smaller amount.

What is myopia?

short-sightedness

What is hyperopia?

long-sightedness

why can someone with myopia see close objects in clear focus but distant objects are blurred?

the light is focused in front of the retina so images that land of the retina are out of focus

what causes myopia?

eyeball is too long

How is myopia corrected?

with a concave lens so that light rays focus on the retina

for people with hyperopia why are far away objects blurred

the lens cannot refract light enough so the light is focused behind the retina. the image that lands on the retina is out of focus

what causes hyperopia?

eyeball is too short

how can you correct hyperopia?

with a convex lens

what are contact lenses?

contact lenses are thin lenses that sit on the surface of the eye and are shaped to compensate for the fault in focusing.

Why are contact lenses popular?

they are lightweight and almost invisible. they are more convenient than glasses for activities like sports.

what are the differences between soft and hard contact lenses?

hard contact lenses are made of relatively rigid material and last a long time whereas soft lenses are more flexible and comfortable but dont last as long. soft lenses carry higher risk of infection.

how does laser surgery correct eye defects?

a laser can be used to vaporise tissue, changing the shape of the cornea.

how does laser surgery correct myopia?

lasers are used to treat myopia by reducing the thickness of the cornea so it refracts light less strongly so light is now focused on the retina rather than in front of it.

how does laser surgery correct hyperopia?

lasers are used to change the curve of the cornea so it refracts light from close objects more effectively

what are the risks of lens replacement?

damage to the retina, cataracts developing and infections

what are lens replacements?

the addition of another lens inside the eye itself. a permanent contact lens is implanted inside the eye and the natural lens is left in place. alternatively the lens is replaced by an artificial lens

what does core body temp mean and why is it so important to keep it at 37 degrees C

it is the temperature at which enzymes work best, a few degrees above or below enzymes do not function properly

list the main causes of change in internal temperature

-transfer of energy from your muscles during excercise
-fevers caused by disease
-external temperature rising or falling

What is the thermoregulatory centre?

It's found in the hypothalamus in the brain and contains receptors that are sensitive to the temperature of the blood flowing into the brain

what is the role of temperature sensors in the skin?

they send impulses to the thermoregulatory centre giving information about skin temperature. they can detect a change of 0.5 degrees c.

if you're too hot how does your body cool you down

- blood vessels that supply your skin capillaries dilate si blood flow through them increases and more energy is lost to the environment (more blood near surface so go red causing heat to radiate)
-hairs lie flat to reduce insulation so energy can escape
-sweat production increases and as the water evaporated energy is lost

when cold how does the body warm you up

-blood vessels that supply your blood capillaries constrict to reduce blood flow through capillaries, the vasoconstriction reduces energy transferred by radiation through the skin.
-sweat production is reduced or stop so less water from sweat evaporates so less energy lost to environment
-skeletal muscles rapidly contract and relax causing you to shiver. the energy transferred from exothermic reactions raises body temp until shivering stops

why are death rates high in a heatwave (i.e paris heatwave 2003)

-when conditions are hot enzymes cant work properly, their optimum temp is 37 degrees C and any higher or lower they cannot work properly. if too hot they can become denatured and cause cells to die
-if hot and humid sweat cannot evaporate meaning you become dehydrated and cant sweat to cool down.
-elderly, young children and ill people cant regulate body temp as well
-excercise in high temp causes heating from respiration in muscles.
-sunstroke

what detects blood temperature?

the hypothalamus

Explain what happens after a meal

- high glucose levels are detected
- insulin released from pancreas
- insulin causes glucose to be converted to glycogen
- glycogen is stored in the liver
- blood glucose levels decrease

explain what happens when glucose levels fall to a low level e.g at night

the pancreas secretes a hormone called glucagon which makes you'd like break down glycogen converting it back into glucose. the stored glucose is then released back into the blood

What is type 1 diabetes?

where the pancreas produces little to no insulin

what are symptoms of type 1 diabetes

frequent urination, unusual thirst, extreme hunger, unusual weight loss, extreme fatigue

why do people with untreated type 1 diabetes feel tired and lack energy

because without insulin glucose cannot get into the cells of your body therefore rate of respiration decreases and less energy is released

what does injected insulin do

allows glucose to be taken into your body cells and converted into glycogen in the liver. this stops the concentration of glucose in the blood getting too high. then as the blood glucose levels fall the glycogen js converted back to glucose

if you have type 1 diabetes what else should you do to control your blood sugar levels?

the levels of carbohydrates eaten, need to have regular meals and exercise

why aren't pancreas transplants often used to treat diabetes

operations are difficult and risky. not enough pancreas donors are available. patient exchanged medicine (insulin) for another (immunosuppresants)

what causes type 2 diabetes

Obesity, lack of exercise

What is glucose?

a simple sugar used for respiration, carbohydrate

what is glycogen

carbohydrate storage molecule

what is glucagon

A hormone secreted by the pancreas when blood glucose is low.

why is it important your blood glucose levels are kept within narrow limits

- glucose levels need to be high enough to allow cellular respiration to take place
- too high glucose levels can lead to eye and circulatory problems
-too low glucose levels means cells wouldn't have enough blood glucose to respire

how is type 2 diabetes without treatment?

eating a balanced diet
losing weight
regular exercise

how is type 2 diabetes treated if lifestyle changes don't make a difference?

there are drugs to:
- help insulin work better on the body cells
-reduce the amount of glucose you can absorb from your gut
- help your pancreas make more insulin

What is urea?

the main waste product of the body formed when the excess protein is broken down

why must urea be excreted?

because it is poisonous and if the levels build up in your blood this will cause damage to cells

What is deamination?

removal of an amino group

how does a healthy kidney produce urine

- a healthy kidney filter your blood
- small molecular ( glucose, mineral ions, urea and water) all move out of the blood and into the kidney
- all of the glucose is reabsorbed back into the blood by diffusion and active transport
- the amount of water and mineral ions absorbed varies (selective reabsorption)
- the amount of water reabsorbed into the blood is controlled by a sensitive feedback mechanism that makes sure the water balance of the body is kept within narrow limits
- all the blood in your body passes through your kidneys
- the filtered solution trickles into the bladder where it js stored before its emptied

What releases ADH?

pituitary gland

what monitors the water content of the blood

brain

what happens when water content is too high

the brain detects this and the coordination centre jn the brain receives this information and coordinates a response. the pituitary gland releases less ADH so less water is reabsorbed by the kidney tubules