Chapter Six - Nervous System and Hormones

Question 1

Draw and explain the components of the nervous system

Answer 1

Receptor is stimulated—>Information is sent from the receptor
- We have receptors to the central nervous system (brain
Sensitive to sight, and spinal cord) which is a
Sound, touch etc coordinator and determines what
response is required; info is then
Effector (usually a

Question 2

Label diagram of structure and function of the eye

Answer 2

1. conjunctiva - thin transparent protective outer covering
2. Iris - controls how much light enters eye
3. Lens - refracts/bends light
4. Pupil - space in iris through which light passes
5. Cornea - transparent front part of eye, allows light to enter; causes some refraction
6. Retina - inner coat of eye where light sensitive cells are found
7. Optic nerve - contains neurones carrying info to the brain

Question 3

Explain the two humours in the eye

Answer 3

The clear fluid found in the front of the eye (aqueous humour) and in the back of the eye between the lens and the retina (vitreous humour) are needed to provide support to the eye and to allow light to pass through the retina

Question 4

Explain the iris

Answer 4

Coloured part of the eye, consists of two types of muscle: radial muscles which are like the spokes of a bicycle wheel, and circular muscle which forms rings around the pupil

Question 5

Iris muscles in bright light

Risk, action, effect on pupil and amount of light entering eye

Answer 5

Risk - bright light can damage the cells of the retina leading the blindness

Action of Iris muscles
Circular - contract
Radial - relax

Effect on pupil diameter - decreased

Amount of light entering eye - decreased

Question 6

Iris muscles in dim light

Risk, action, effect on pupil and amount of light entering eye

Answer 6

Risk - low light levels can result in not enough light reaching retina to form an image

Action of Iris muscles
Circular - relax
Radial - contract

Effect on pupil diameter - increased

Amount of light entering eye - increased

Question 7

What is accommodation?

Answer 7

Light is focused on the retina by changing the shape of the lens. This allows near and far objects to be seen clearly

Question 8

Label eye focused on distant object

Answer 8

• lens thin
• light rays arrive parallel; cornea refracts rays; lens is thin as little additional refraction is necessary to focus light on the retina

Question 9

Label diagram of eye focused on near object

Answer 9

• lens think
• light rays diverge; cornea refracts rays; lens is thicker as additional refraction is necessary to focus light on retina

Question 10

Explain focusing on a near image

Answer 10

To focus on a near object a ring of muscle surrounding the lens (ciliary body) contracts. This allows the suspensory ligaments to become loose and the lens bulges out as it is not under pressure

Question 11

Explain focusing on a distant object

Answer 11

The ciliary body relaxes. This causes suspensory ligaments to become taut, pulling the lens into a thinner, flattened shape

Question 12

Adaptions of nerve cells

Answer 12

Nerve cells (neurones) are specially adapted to carry electrical impulses through the nervous system. These include;

1. long length - to carry impulses long distances
2. Insulating sheath - to allow rapid transmission of impulses
3. Branching ends - to receive or pass impulses from of to many other nerve cells

Question 13

What is a synapse?

Answer 13

The tiny gaps between nerve cells. For impulses to pass from one nerve cell to the next a transmitter chemical must diffuse across the synapse at a high enough concentration to trigger an impulse in the next cell.

Question 14

Label diagram in a synapse

Answer 14

• synapse
• vesticles containing chemical transmitter
• direction of impulse
• chemical transmitter

Question 15

Explain voluntary and reflex actions

Answer 15

Our nervous system allows two basic types of response. The first first of these are the voluntary actions - we have conscious control over these.

The second type of responses is reflex actions - we are not conscious of these actions. Reflex actions tend to be much faster as they use a special pathway of nerves called the reflex arc that does not include ‘thinking time’. The rapid nature of reflex actions means many are used by the body for protection.

Question 16

Label diagram of the reflex arc

Answer 16

• association (connector) neurone - joins the sensory and motor neurones
• White matter
• grey matter
• sensory neurone - carries info from receptors for example a burn on the hand, to the spinal cord
• motor neurone - carries info from spinal cord back to muscle (effector) causing a response, for example moving the hand

The three neurones link in the grey matter (butterfly shaped part) of the spinal cord; the outer part is the white matter.

Question 17

What are hormones?

Answer 17

Chemicals produced by special glands in the body that can travel through the blood to target specific organs in order to produce changes in the way the cells in the organ function

Question 18

The role of insulin?

Answer 18

They key hormone in the control of blood glucose levels is insulin. Although glucose is needed for respiration, high blood glucose levels can result in damage to cells.

Question 19

Diagram of how blood glucose levels are controlled by negative feedback

Answer 19

Pancreas releases insulin Blood glucose level increases
| /\
| | normal blood glucose level
Glucose by - increasing rate of
respiration in liver and muscles
- converting glucose to glycogen
for storage in liver

Question 20

How are nerves and hormones similar as well as different

Answer 20

They are both involved in sensing and responding to changes in the environment (stimuli). The actions of nerves is faster and more short-lived than the action of hormones, which don’t act as quickly and have long lasting effects on the body.

Question 21

Explain negative feedback

Answer 21

The mechanism insulin uses to control blood glucose levels. The action of insulin in reducing blood glucose levels means that less insulin is needed. When normal blood glucose levels are restored due to the action of insulin the pancreas no longer releases insulin.

Question 22

The role of glucagon

Answer 22

Involved in increasing blood sugar levels during exercise or when blood glucose levels fall. Glucogen acts on the cells of the liver, causing them to convert glycogen back into glucose.

Question 23

What is diabetes?

Answer 23

The condition where people fail to produce enough insulin or their cells fail to respond correctly

Question 24

Symptoms of diabetes;

Answer 24

• high blood glucose levels

- glucose in the urine, excessive thirst, lethargy (tiredness) and a frequent need to urinate

Question 25

Long term dangers of diabetes;

Answer 25

If left untreated

• kidney damage
• eye damage
• stroke
• heart disease

Question 26

Why is the no. of people with diabetes increasing?

Answer 26

Varies reasons including;

• poor diet
• obesity
• lack of exercise

Question 27

How is diabetes controlled?

Answer 27

People with diabetes must test their blood glucose levels and may need to inject insulin to correct them if levels are too high. If too much insulin is taken or enough food is not eaten at regular intervals, blood glucose levels can fall too low resulting in a ‘hypo’ (hypoglycaemic attack) and unconsciousness

Question 28

Explain what phototropism is.

Answer 28

Parts of the plant above ground most often grow towards the light as this should increase their rate of growth as more photosynthesis can occur. This effect is known as phototropism.
The hormone responsible for phototropism is auxin. It is caused by auxin accumulating on the shaded side of a shoot and this causes more growth on that side.

Question 29

Explain the action of auxin if light is hitting the shoot from all directions

Answer 29

• there will be even distribution of auxin
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  Due to the even distribution all cells will elongate at a similar rate
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• the shoot will grow vertically

Question 30

Explain the action of auxin when light is shining from one side

Answer 30

• there will be accumulation of auxin on the shaded side of the shoot
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• cells on the shaded side elongate more rapidly than those on the illuminated side
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• the increase of length on one side of the shoot causes it to bend towards the light

Question 31

Commercial uses of plant hormones

Include: use, how it works and benefits

Answer 31

Selective weedkillers
How it works - hormone stimulates such a high rate of uncontrolled growth that plants disintegrate
Benefits - hormones used only act on broadleaved plants (weeds) but not on narrow leaved grasses and cereals

Rooting powder
How it works - hormone stimulates certain cells to develop features of root cells
Benefits - can be used in horticulture to allow growth of new plants from cuttings

Promoting flower and fruit formation
How it works - action of hormone causes flowers to develop - these flowers can be pollinated to allow development of seeds and fruit
Benefits - allows more fruit to be produced e.g if there are adverse weather conditions. Can also be used to produce seedless fruits

Tissue culture
How it works - hormones can stimulate growth of all types of plant cell from a mass of cells called callus
Benefits - allows species of plant that are very rare or difficult to breed to be produced more rapidly