iGCSE Biology Notes Coordination and response

[qdeck card_back=”none” ]

[h] iGCSE Biology Notes Coordination and response

[q] What is homeostasis?

What is the definition of homeostasis?

[a]

Your body is a very complex place, and for it to remain stable the conditions inside your body need to remain constant.
This includes your temperature, water levels and blood glucose concentration.
Homeostasis is the maintenance of a constant internal environment.
Homeostasis controls the internal environment within set limits.

[q] How does the nervous system work?

What is a reflex action?

[a]

A reflex action is an automatic, rapid response to a stimulus.
The signal doesn’t need to travel to your brain.
A stimulus is something in the environment that your body may detect and respond to, like a bright light, a hot surface or a bee sting.
You have a receptor that will detect that stimulus.
Your eyes detect bright light, your skin detects a hot surface, your ears detect music, your tongue detects delicious plov, etc.
You also have an effector which is either a muscle or a gland that will activate in response to the stimulus.
Your skin detects a hot surface so automatically pulls your hand away using your muscles.

[q] How does homeostasis keep things constant?

How does homeostasis work?

[a]

When there is a change in the external environment (a stimulus), this may change the bodies internal environment.
The bodies receptors will detect this, send an impulse to a coordination centre, which will then trigger a response which sets it back to the normal point again.
This is a negative feedback loop.

[q] What is the nervous system?

What is the nervous system made of?

[a]

The nervous system consists of the brain, the spinal cord, and all nerve cells in your body.
The role of the nervous system is to coordinate and regulate body functions.
The nervous system is split into two parts.
The central nervous system consists of the brain and the spinal cord.
The peripheral nervous system consists of all the nerve cells (neurones) outside of the brain and spinal cord.

[q] What is the structure of a neurone?

What is a neurone?

[a]

A neurone is a nerve cell, it carries electrical impulses along it and connects to other neurones.
This is to send signals throughout the body very quickly.
All neurones have a cell body where the nucleus and most organelle are kept.
They also have an axon, with is a very long part of the cell which the electrical impulse is carried along.
All neurones also have dendrites which are arms connecting to other cells
Some neurones also have a myelin sheath which insulates and speeds up electrical impulses.

[q] Sensory vs relay vs motor neurones

What are the differences between neurones?

[a]

Motor neurones cell body is always on the end next to the relay neurone.
An effector is on the other end.
The cell body in a sensory neurone is more separate from the axon, in the middle of it.
Relay neurones have lots of dendrites and a short axon
Sensory and motor neurones may also have a myelin sheath which speeds up electrical impulses.
Draw and label!

[q] How does homeostasis regulate the body?

Look back at the previous lesson

[a]

Can anyone look back to the previous lesson where we wrote about the body’s response to stimuli?
We always have a stimulus which is detects by a receptor.
The receptor then sends a signal along a coordination centre (usually the spinal cord).
Which then sends the signal to the effector to do a response.
The effector is always a muscle or gland.

[q] What is the reflex arc?

What is a reflex arc?

[a]

This is all well and good knowing what stimuli, receptors and effectors are, but what how does the receptor tell the effector to react?
This is where the nervous system and various neurones come in.
When a receptor detects a stimulus, the impulse is sent to a sensory neurone.
The sensory neurone would then carry that electrical impulse to a relay neurone at a coordination centre, usually the spinal cord.
The relay neurone then passes the impulse to a motor neurone which then tells the effector to respond to the stimulus.

[q] Let’s bring this all together

Using examples from before, write a paragraph for each detailing the reflex arc

[a]

Here is an example:
A hot candle is the stimulus, and the skin cells of a person’s hand is the receptor that detects this.
The impulse is transferred to a sensory neurone which sends an electrical impulse to the coordination centre which is the spinal cord and passes the impulse to a relay neurone.
The relay neurone sends the impulse to a motor neurone.
The motor neurone then sends an impulse to the effector which in this case is the muscle, to move the hand away from the hot candle to avoid damage.
This reaction is involuntary, automatic and rapid.

[q] What is the difference between voluntary and involuntary?

What do the words voluntary and involuntary mean?

[a]

An involuntary action is an action which you have no choice in doing.
The reflex arc does not pass through the conscious part of your brain.
This makes involuntary actions automatic and rapid.
A voluntary action however is an action you choose to do.
The impulse passes through the conscious part of your brain.
This makes voluntary actions slower.

[q] How do neurones send messages between each other?

How do neurones connect?

[a]

All neurones have a similar basic structure.
They all have a cell body where most organelles are, they have an axon along which electrical impulses travel and they have dendrites which are arms that connect to other neurones
Here is a reminder of the slight differences between neurones and which direction an electrical impulse would travel.
There is a junction between the dendrites of any two neurones, called a synapse.

[q] What is a synapse?

What is the structure of a synapse?

[a]

A synapse is a junction between two neurones.
For the electrical impulse to get from one neurone to another, the impulse is converted to a chemical signal.
Chemicals then pass through the very short space between the two neurones.

[q] What is a synapse?

What is the structure of a synapse?

[a]

Firstly, we have the synaptic gap, the space between the two neurones.
Then we have the pre-synaptic neurone before the synaptic gap and then the post-synaptic neurone after the synaptic gap.
The pre-synaptic neurone is filled with vesicles which are sacks with their own membrane
These vesicles have neurotransmitters in.
The post-synaptic neurone has receptor proteins on its cell membrane.

[q] What happens at a synapse?

Step-by-step, what happens at a synapse?

[a]

Firstly, an electrical impulse travels along the first neurone and arrives at the pre-synaptic neurone.
This trigger vesicles containing neurotransmitters to move to the cell membrane and release the neurotransmitters into the synaptic gap.
These neurotransmitters then diffuse across the synaptic gap.
They then bind to the receptor proteins on the cell membrane of the post-synaptic neurone.
This activates a new electrical impulse in the next neurone.

[q] What happens at a synapse?

More synapse structure

[a]

Discuss: How does a synapse ensure that the impulses only travel in one direction?
Because the receptor cells are only found on the post-synaptic neurone.
Discuss: what must happen after one electrical impulse gets transmitted?
The neurotransmitters need to be moved back into the pre-synaptic neurone.

[q] What are sense organs in general?

What is a sense organ?

[a]

A sense organ is a group of receptor cells that respond to a specific type of stimulus.
A sense organ could be eyes, nose, tongue skin etc.
We have different receptors for different stimuli, like eyes for light, ears for sound etc.

[q] What is the eye made of?

What are the different structures of the eye?

[a]

The eye is highly complex structure with distinct parts that have specific functions.
The retina contains the light receptors which detect light.
The optic nerve sends the information from the retina to the brain.
There is a blind spot here where no light is detected.
The cornea refracts light into the eye.
The lens focuses the light onto the retina.
The iris controls how much light gets into the eye.
The hole in the centre is the pupil.
The ciliary muscles and suspensory ligaments change the lens shape to see different distances.

[q] What is the eye made of?

What are the different structures of the eye?

[a]

The eye is highly complex structure with distinct parts that have specific functions.
The retina contains the light receptors which detect light.
The optic nerve sends the information from the retina to the brain.
There is a blind spot here where no light is detected.
The cornea refracts light into the eye.
The lens focuses the light onto the retina.
The iris controls how much light gets into the eye.
The hole in the centre is the pupil.
The ciliary muscles and suspensory ligaments change the lens shape to see different distances

[q] TRIPLE ONLY What are rods and cones?

What is the difference between a rod and cone receptor cell?

[a]

Humans have two types of light receptor cell in the retina, rods and cones.
Cones are found packed together in a space of the retina called the fovea, in the centre of vision. Rods are found on the periphery.
Cones can give colour vision (there are three cones; red cones, blue cones and green cones) but there is just one type of rod and it gives black and white vision.
Cones are less sensitive however and work better in bright light, but rods are more sensitive and work better in low light.
Let’s do a test, do we see in black and white in low light?

[q] What is the pupil reflex?

How does our pupil get bigger or smaller?

[a]

This is an example of an involuntary reflex arc, so it is an automatic, rapid response that by-passes the brain.
Bright light can damage the retina, so the iris has two muscles, the radial muscles and the circular muscles to change the size of the pupil.
These muscles work as an antagonistic pair.
In bright light, the circular muscles contract (so the radial muscles relax), making the pupil smaller/constrict.
In dim light, the radial muscles contract (so the circular muscles relax), making the pupil wider/dilate.

[q] What is accommodation?

How does our eye see objects both near and far?

[a]

This is another example of a reflex action, but this time only one muscle is involved, the ciliary muscles.
To look at near objects, the ciliary muscles contract, which slackens the suspensory ligaments, making the lens fatter and refract light more.
To look at far objects, the ciliary muscles relax, which tightens the suspensory ligaments, making the lens thinner and refract light less.

[q] What is a hormone?

What is the definition of a hormone?

[a]

Before we get the definition, can you name any hormones?
Hormones include well known substances like insulin, adrenaline, oestrogen, serotonin, testosterone and auxin.
A hormone is a chemical produced by glands, carried in the blood to alter the activity of a specific organ(s).

[q] TRIPLE ONLY What makes up the endocrine system?

What are the different organs of the endocrine system?

[a]

Every organ in the endocrine system contains glands which produce a substance, like a hormone.
The pituitary gland is in the brain and often acts as a master gland, controlling all the others.
The pancreas produces the hormones insulin and glucagon.
The adrenal glands sit on top of the kidneys and produce adrenaline.
The ovaries produce oestrogen in females.
The testes produce testosterone in males.

[q] What is adrenaline?

What does adrenaline do to the body?

[a]

Adrenaline is a hormone produced by the adrenal glands which sit on top of the kidneys.
Adrenaline causes a ‘flight or fight’ response.
It is often produced when you are stressed, excited or are in a dangerous situation.
Adrenaline causes your heart rate and breathing rate to increase
This provides the body with more blood flow, so it has more oxygen for aerobic respiration.
Adrenaline also causes your pupils to dilate (become wider).

[q] Adrenaline gives you a sugar rush? (supplement)

How does adrenaline increase blood glucose levels?

[a]

We already know that adrenaline causes the heart to contract faster and with more force.
This increases blood flow, so more oxygen and glucose gets to the body including the muscles where aerobic respiration occurs in large amounts.
Adrenaline also causes the liver to break down the glycogen stores to release even more glucose, which increases blood glucose level for even more energy.

[q] How do we maintain constant body temperature?

How do we stay at the same temperature?

[a]

The average human body temperature is 37C, and it never varies more than 1C or 2C.
Let’s first recap the structure of a reflex action. Discuss in your table the order of a reflex action.
This time, change in temperature from 37 C will be the stimulus.

[q] How do we maintain constant body temperature?

How do we stay at the same temperature?

[a]

Mammals, like humans, have both skin and blood temperature receptors to detect a change in temperature.
These receptors will then send an impulse along a sensory neurone to the brain, through a relay neurone, then along a motor neurone to an effector which will trigger a response.
This response will try to get the temperature back to normal

[q] How do we maintain constant body temperature?

How do we stay at the same temperature?

[a]

Let’s first look at the skin and see it’s structure so we can understand what it can do to return body temperature back to normal.
Our skin has hairs.
These hairs have hair erector muscles which can make then stand up or lay flat.
We have sweat glands which can release sweat.
There are receptors with sensory neurones attached to detect stimuli.
There are also arterioles which lead to capillaries which provide the skin with oxygen.
Finally, there is a layer of fatty tissue.

[q] How do we reduce body temperature?

What do we do if our body temperature gets too high?

[a]

Discuss: What might the body do in response to a rise in temperature?
The sweat glands will secrete more sweat.
As sweat evaporates, it cools the skin.
The hair erector muscles relax so the hairs lie flat.
This means there is no trapped air, so heat is lost more easily
The arterioles dilate (get wider) so more blood flows through the capillaries nearer the surface of the skin.
This means heat is more easily lost from the blood.
This is called vasodilation.

[q] How do we increase body temperature?

What do we do if our body temperature gets too low?

[a]

Discuss: What might the body do in response to a drop in temperature?
The sweat glands will secrete less sweat.
This is so sweat does not cool the skin any further.
The hair erector muscles contract, so the hairs stand up.
This means there is a layer of trapped insulating air, preventing heat loss.
The arterioles constrict (get thinner) so less blood flows through the capillaries in the surface of the skin, so heat is less easily lost.
This is called vasoconstriction.
We can also shiver, where muscles contract in spasms where heat is released from respiration.

[q] What is blood glucose level?

What is blood glucose level?

[a]

Your body glucose level is the concentration of glucose in your blood.
You body need to glucose to carry out respiration to provide cells with energy.
However, it needs to be kept within set limits, so it is controlled by homeostasis.

[q] What makes blood glucose concentration change?

Why do we have to control blood glucose concentration?

[a]

When you eat a meal, especially one high in starch/carbohydrates or sugar, blood glucose concentration will increase as it is digested and absorbed into the blood.
If you fast and not eat for a while or do lots of exercise which uses up glucose for respiration, blood glucose concentration will decrease.

[q] How do we lower blood glucose concentration?

How does the body change blood glucose concentration back to normal after a meal?

[a]

You eat a meal and so your blood glucose concentration increases.
The pancreas receptor cells detect this increase, and the pancreas releases insulin.
Insulin tells the muscles and the liver to remove and store this excess glucose as glycogen, an insoluble storage molecule.
This then lowers the blood glucose concentration back to normal levels.

[q] How do we increase blood glucose concentration?

How does the body change blood glucose concentration back to normal during a fast?

[a]

You haven’t eaten so your blood glucose concentration decrease.
The pancreas receptor cells detect this decrease, and the pancreas releases glucagon.
Glucagon tells the muscles and the liver to break down the glycogen stores to release glucose.
This then increases the blood glucose concentration back to normal levels.

[q] TRIPLE ONLY What is type 1 diabetes?

What is the cause of type 1 diabetes?

[a]

Type 1 diabetes is where the pancreas does not produce insulin.
This means blood glucose concentration can not be controlled.
Discuss: how do you think we treat type 1 diabetes?
We treat it will insulin injections, often after mealtimes.
People with type 1 diabetes also must not eat too many sugary foods and do regular exercise to remove glucose from their blood.

[q] What is a tropism?

What is the definition of a tropism?

[a]

A tropism is the growth of a plant in response to a stimulus.
It is not a movement, like our hands moving away from a hot surface, but an actual growth of the plant in the response to a stimulus.
A positive tropism is where the plant grows towards the stimulus.
A negative tropism is where the plant grows away from the stimulus.

[q] What types of tropism are there?

What types of tropism do you need to know?

[a]

Phototropism is where a plant grows in response to light.
Gravitropism or geotropism is where a plant grows in response to gravity.
Discuss: How do the shoots/leaves of plants use these tropisms? Positive or negative?
Shoots exhibit positive phototropism and negative gravitropism.

[q] What types of tropism are there?

What types of tropism do you need to know?

[a]

Discuss: What about roots, how to roots grow in respond to light and gravity?
Roots show positive gravitropism and negative phototropism.

[q] What causes the shoots to grow in response to stimuli? (supplement)

What makes tropisms work?

[a]

The tip of the shoot produces a hormone called auxin, the most important hormones in plants.
Auxin stimulates cell growth and elongation.
Auxin diffuses from the tip and is distributed unequally in the shoot, depending on the stimulus.

[q] What causes the shoots to grow towards light? (supplement)

How does positive phototropism work?

[a]

For phototropism, the auxin accumulates on the shaded side of the shoot.
This means the shaded sides grows faster, making the shoot bend towards the light.

[q] What causes the shoots to grow away from gravity? (supplement)

How does negative gravitropism work?

[a]

For gravitropism, the auxin accumulates on the side of the shoot closer the gravity.
This means the side closer to gravity grows faster so the shoot bend up against gravity.

[x] Exit text
(enter text or “Add Media”; select text to format)

[/qdeck]

iGCSE Biology Notes Coordination and response

iGCSE Biology Notes – All Topics