chapter 13 p1

Question 1

Examples of these changes:
1. External environment:

Answer 1

humidity
external temperature
light intensity
new or sudden sound

Question 2

Examples of these changes:
Internal environment:

Answer 2

blood glucose concentration
internal temperature
water potential
cell pH

Question 3

How Animals and plants respond to these changes in a variety of ways:

Answer 3

Animals react through electrical responses (via neurones), and through chemical responses (via hormones).
Plant responses are based on a number of chemical communication systems including plant hormones.
These communication systems must be coordinated to produce the required response in an organism.

Question 4

Why coordination is needed

Answer 4

As species have evolved, cells within organisms have become specialised to perform specific functions.
As a result organisms need to coordinate the function of different cells and systems to operate effectively.
Few body systems can work in isolation (apart from a few exceptions, for example, a heart can continue to beat if placed in the right bathing solution).

Question 5

Coordination in animals:

Answer 5

red blood cells transport oxygen effectively, but have no nucleus.
This means that these cells are not able to replicate - a constant supply of red blood cells to the body is maintained by haematopoietic stem cells.
In order to contract, muscle cells must constantly respire, and thus require a consistent oxygen supply.
As these cells cannot transport oxygen, they are dependent on red blood cells for this function.

Question 6

Coordination in plants:

Answer 6

In plants flowering needs to coordinate with the seasons, and pollinators must coordinate with the plants.
In temperate climates light-sensitive chemicals enable plants to coordinate the development of flower buds with the lengthening days that signal the approach of spring and summer.

Question 7

What is homeostasis:

Answer 7

In many relatively large multicellular animals, different organs have different functions in the body.
Therefore, the functions of organs must be coordinated in order to maintain a relatively constant internal environment.
This is known as homeostasis.
For example, the digestive organs such as the exocrine pancreas, duodenum, and ileum along with the endocrine pancreas and the liver work together to maintain a constant blood glucose concentration.

Question 8

, the digestive organs such as the exocrine pancreas, duodenum, and ileum along with the endocrine pancreas and the liver work together to maintain a constant blood glucose concentration. diagram

Answer 8

Question 9

Cell signalling

Answer 9

Nervous and hormonal systems coordinate the activities of whole organisms.
This coordination relies on communication at a cellular level through cell signalling.
This occurs through one cell releasing a chemical which has an effect on another cell, known as a target cell.

Question 10

What can cells do with cell signalling:

Answer 10

• transfer signals locally, for example, between neurons at synapses. Here the signal used is a neurotransmitter.
• transfer signals across large distances, using hormones.
  For example, the cells of the pituitary gland secrete antidiuretic hormone (ADH), which acts on cells in the kidneys to maintain water balance in the body.

Question 11

Coordination in plants:

Answer 11

Plants do not have a nervous system like animals.
However, to survive they still must respond to internal and external changes to their environment.
For example, plant stems grow towards a light source to maximise their rate of photosynthesis. This is achieved through the use of plant hormones.

Question 12

The nervous system:

Answer 12

The nervous system is responsible for detecting changes in the internal and external environment.
These changes are known as a stimulus.
This information then needs to be processed and an appropriate response triggered.
Both the nervous system and hormonal system play a role in reacting to stimuli, but they do so in very different ways
neuronal communication is generally a much faster and more targeted response than hormonal communication.

Question 13

Role of Neurons:

Answer 13

The nervous system is made up of billions of specialised nerve cells called neurons.
The role of neurons is to transmit electrical impulses rapidly around the body so that the organism can respond to changes in its internal and external environment.
There are several different types of neurons found within a mammal.
They work together to carry information detected by a sensory receptor to the effector, which in turn carries out the appropriate response.

Question 14

Structure of a neurone:
Mammalian neurones have several key features:

Answer 14

Cell body
Dendrons
Axons

Question 15

Cell body

Answer 15

this contains the nucleus surrounded by cytoplasm.
Within the cytoplasm there are also large amounts of endoplasmic reticulum and mitochondria which are involved in the production of neurotransmitters.
These are chemicals which are used to pass signals from one neurone to the next.

Question 16

Dendrons

Answer 16

these are short extensions which come from the cell body.
These extensions divide into smaller and smaller branches known as dendrites
They are responsible for transmitting electrical impulses towards the cell body.

Question 17

Axons

Answer 17

these are singular, elongated nerve fibres that transmit impulses away from the cell body.
These fibres can be very long, for example, those that transmit impulses from the tips of toes and fingers to the spinal cord.
The fibre is cylindrical in shape consisting of a very narrow region of cytoplasm (in most cases approximately 1 um) surrounded by a plasma membrane.

Question 18

Sensory neurones

Answer 18

these neurones transmit impulses from a sensory receptor cell to a relay neurone, motor neurone, or the brain.
They have one dendron, which carries the impulse to the cell body, and one axon, which carries the impulse away from the cell body.

Question 19

Relay neurones

Answer 19

• these neurones transmit impulses between neurones.
  For example, between sensory neurones and motor neurones.
  They have many short axons and dendrons.

Question 20

Motor neurones

Answer 20

these neurones transmit impulses from a relay neurone or sensory neurone to an effector, such as a muscle or a gland.
They have one long axon and many short dendrites.

Question 21

the electrical impulse follows the pathway in nervous responses:

Answer 21

Receptor → sensory neurone → relay neurone → motor neurone → effector cell

Question 22

types of neurones diagram

Answer 22

Question 23

Myelinated neurones:
Myelin Sheath Formation and Structure:

Answer 23

• The axons of some neurones are covered in a myelin sheath, made of many layers of plasma membrane.
• Special cells, called Schwann cells, produce these layers of membrane by growing around the axon many times.
• Each time they grow around the axon, a double layer of phospholipid bilayer is laid down.
• When the Schwann cell stops growing there may be more than 20 layers of membrane.

Question 24

Function of Myelinated Neurones:

Answer 24

The myelin sheath acts as an insulating layer and allows these myelinated neurones to conduct the electrical impulse at a much faster speed than unmyelinated neurones.
Myelinated neurones can transmit impulses at up to 100 metres per second. In comparison, non-myelinated neurones can only conduct impulses at approximately 1 metre per second.

Question 25

Nodes of Ranvier

Answer 25

Between each adjacent Schwann cell there is a small gap (2-3 um) known as a node of Ranvier.
This creates gaps in the myelin sheath.
In humans these occur every 1-3 mm.
The myelin sheath is an electrical insulator.
In myelinated neurones, the electrical impulse ‘jumps’ from one node to the next as it travels along the neurone.
This allows the impulse to be transmitted much faster. In non-myelinated neurones the impulse does not jump - it transmits continuously along the nerve fibre, so is much slower.

Question 26

structure of myelinated motor neurone

Answer 26

Question 27

Multiple sclerosis (MS)

Answer 27

is a neurological condition which affects around 100 000 people in the UK.
Most people are diagnosed between the ages of 20 and 40.
MS affects nerves in the brain and spinal cord, causing a wide range of symptoms, including problems with muscle movement, balance, and vision.
MS is known to be an autoimmune disease (where the immune system mistakenly attacks healthy body tissue)
This results in a thinning or complete loss of the myelin sheath and, as the disease advances, results in the breakdown of the axons of neurones.
It is not known what triggers this disorder but is thought to be a combination of genetic and environmental factors, such as a viral infection.

Question 28

Sensory Receptor Processing and Effector Response:

Answer 28

The body is able to detect changes in its environment using groups of specialised cells known as sensory receptors.
These are often located in the sense organs, such as the ear and eye.
Sensory receptors convert the stimulus they detect into a nerve impulse.
The information is then passed through the nervous system and on into the central nervous system (CNS) - normally to the brain.
The brain coordinates the required response and sends an impulse to an effector (normally a muscle or gland) to result in the desired response.

Question 29

All sensory receptors have two main features:

Answer 29

They are specific to a single type of stimulus.
They act as a transducer - they convert a stimulus into a nerve impulse.

Question 30

four main types of sensory receptor present in an animal:

Answer 30

Question 31

Sensory receptors role as a transducer:

Answer 31

Sensory receptors detect a range of different stimuli including light, heat, sound, or pressure.
The receptor converts the stimulus into a nervous impulse, called a generator potential.
For example, a rod cell (found in your eye) responds to light and produces a generator potential.

Question 32

What is a Pacinian corpuscle:

Answer 32

specific sensory receptors that detect mechanical pressure.

Question 33

Location of Pacinian Corpuscles:

Answer 33

They are located deep within your skin and are most abundant in the fingers and the soles of the feet.
They are also found within joints, enabling you to know which joints are changing direction.

Question 34

Structure and Function of Pacinian Corpuscles p1

Answer 34

The end of the sensory neurone is found within the centre of the corpuscle, surrounded by layers of connective tissue.
Each layer of tissue is separated by a layer of gel.
Within the membrane of the neurone there are sodium ion channels

Question 35

Structure and Function of Pacinian Corpuscles p2

Answer 35

These are responsible for transporting sodium ions across the membrane.
The neurone ending in a Pacinian corpuscle has a special type of sodium channel called a stretch-mediated sodium channel.
When these channels change shape, for example, when they stretch, their permeability to sodium also changes.

Question 36

Structure of Pacinian Corpuscles diagram

Answer 36

Question 37

Steps that explain how a Pacinian corpuscle converts mechanical pressure into a nervous impulse:
p1

Answer 37

In its normal state (known as its resting state), the stretch-mediated sodium ion channels in the sensory neurone’s membrane are too narrow to allow sodium ions to pass through them.
The neurone of the Pacinian corpuscle has a resting potential.

When pressure is applied to the Pacinian corpuscle, the corpuscle changes shape. This causes the membrane surrounding its neurone to stretch.

When the membrane stretches, the sodium ion channels present widen. Sodium ions can now diffuse into the neurone.

Question 38

Steps that explain how a Pacinian corpuscle converts mechanical pressure into a nervous impulse:
p2

Answer 38

The influx of positive sodium ions changes the potential of the membrane - it becomes depolarised. This results in a generator potential.
In turn, the generator potential creates an action potential (a nerve impulse) that passes along the sensory neurone.
The action potential will then be transmitted along neurones to the CNS.

Question 39

Steps that explain how a Pacinian corpuscle converts mechanical pressure into a nervous impulse. diagram

Answer 39