9 Coordination and Response

Question 1

Describe a nerve impulse

Answer 1

An electrical signal that passes along nerve cells called neurons.

Question 2

Describe the human nervous system

Answer 2

Consists of
- The central nervous system (brain and spinal cord) which processes nervous impulses from body and coordinates any response.
- Specialised receptor organs (sense organs such as eye and ear) that contain receptor cells which sense stimuli.
- Nerves (large bundles of many neurons) of the peripheral nervous system that connect the central nervous system to other parts of the body.
- Specialised effectors which produce the response to the stimulus such as contraction of muscles and secretion of hormones.

Question 3

Describe a reflex arc

Answer 3

A reflex arc is the pathway that impulses travel along during a reflex.
Stimulus detected by a receptor, sensory neuron sends electrical impulses to the spinal cord. Electrical is passed on to relay neuron in the spinal cord. Relay neuron connects to motor neuron and passes impulse on. Motor neuron carries impulse to an effector and a response is made.

Question 4

Describe a reflex action

Answer 4

A means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands).

Question 5

Difference between Voluntary response and Involuntary response

Answer 5

A voluntary response is one where you make a conscious decisions to carry out a particular action therefore it starts with your brain. An involuntary (or reflex) response does not involve the brain as a coordinator of the reaction and you are not aware until after it is carried out. They are usually essential to basic survival and are rapid.

Question 6

Role of Cornea

Answer 6

Refracts light.

Question 7

Role of Iris

Answer 7

Controls how much light enters pupil.

Question 8

Role of Lens

Answer 8

Focuses light onto retina.

Question 9

Role of Retina

Answer 9

Contains light receptors, some sensitive to light of different colors.

Question 10

Role of Optic nerve

Answer 10

Carries impulses to the brain.

Question 11

Explain the pupil reflex

Answer 11

A reflex action carried out to protect the retina from damage in bright light and protect us from not seeing objects in dim light. In dim light the pupil dilates (widens) in order to allow as much light into the eye as possible. In bright light the pupil constricts (narrows) in order to prevent too much light entering eye and damaging the retina.

Question 12

Define Accommodation

Answer 12

The function of the eye in focusing on near and distant objects.
The lens is elastic and its shape can be changed when the suspensory ligaments attached to it become tight or loose.

Question 13

Explain accomodation in the eye to near objects

Answer 13

When an object is close up the ciliary muscles contract. This causes the suspensory ligaments to loosen, stopping them from pulling on the lens which allows it to become fatter. Light is refracted more.

Question 14

Explain accomodation in the eye to distant objects

Answer 14

When an object is far away the ciliary muscles relax. This causes the suspensory ligaments to tighten, making them pull on the lens causing it to become thinner. Light is refracted less.

Question 15

Describe Hormone

Answer 15

A chemical substance, produced by an endocrine gland, carried by the blood, which alters the activity of one or more specific target organs.

Question 16

Describe Adrenaline

Answer 16

The hormone secreted in the adrenal gland during ‘fight or flight’ situation and its effects are an increased pulse rate, depth of breathing, and dilates pupils for better vision.

Question 17

Which organ regulates hormones?

Answer 17

The liver. Breaks down or transform any in excess.

Question 18

How are hormones transported around the body?

Answer 18

Endocrine glands have a good blood supply as they need to get the hormones into the bloodstream as soon as possible so they can reach the target organs and bring a response. The hormones only affect cells with target receptors they can bind to.

Question 19

Describe Insulin

Answer 19

A hormone secreted in the pancreas to lower blood glucose levels. Causes excess glucose in the blood to be taken up by the muscles and liver and converted into glycogen for storage.

Question 20

Describe Testosterone

Answer 20

A hormone secreted in the testes. It is the main sex hormone in males, for the development of the secondary sexual characteristics in males.

Question 21

Describe Estrogen

Answer 21

A hormone secreted in the ovaries. It is the main sex hormone in females, for the development of secondary sexual characteristics in females and controls menstrual cycle.

Question 22

Differences between nervous and hormonal system.

Answer 22

Nervous system:
Made up of: nerves, brain and spinal cord.
Type of message: electrical impulse.
Speed of transmission: very fast.
Length of effect: short - until nerve impulses stop.

Endocrine system:
Made up of: glands.
Type of message: chemical hormones.
Speed of transmission: slower.
Length of effect: longer - until hormone is broken down.

Question 23

Define Homeostasis

Answer 23

The maintenance of a constant internal environment.

Question 24

Role of Insulin in homeostasis

Answer 24

Insulin is secreted into the blood at times when glucose levels are high. This is most often directly after a meal. The kidneys can only cope with a certain level of glucose in the blood. If it is too high, insulin is released and converts excess glucose into glycogen to decrease blood glucose concentration.

Question 25

Role of Glucagon in homeostasis

Answer 25

Glucagon converts glycogen back several hours later when blood glucose levels have dropped due to respiration in all tissues.

Question 26

Explain the concept of control by negative feedback

Answer 26

Negative feedback is where a change in stimulus causes a response that produces the opposite change.

Question 27

How is the constant internal body temperature maintained?

Answer 27

Temperature of the blood from the core of the body is monitored by the hypothalamus. If temperature changes too much, a negative feedback occurs, making it go back to 37C. It also receives electrical impulses from the heat-receptor in the skin surfaces.

Question 28

What happens if core temperature rises too far?

Answer 28

• Sweat is released on the surface of skin from glands. When the water in sweat evaporates, the energy is removed from the skin surface cooling the skin.
• Arterioles carrying blood near the surface of the skin dilate so more blood flows through capillaries in the skin. This is known as vasodilation. Makes it easier for heat energy to be transferred to skin surface and to environment by radiation and conduction.

Question 29

What happens if core temperature falls too far?

Answer 29

• Body hair may be raised by muscles in the skin. This is called goosebumps. Air gets trapped in the hair and serves as a layer of insulation as air does not conduct heat energy well.
• Muscles may shiver, this means that they produce rapid contractions. Cellular respiration is needed to do this so energy released warms blood flowing through the muscles.
• Arterioles carrying blood near the surface of the skin constrict which reduces the amount of blood flowing through surface capillaries. This is known as vasoconstriction. As the warm blood is kept deeper in the skin, reduces rate of heat transfer.

Question 30

Define Gravitropism

Answer 30

A response in which parts of a plant grow toward or away from gravity.

Question 31

Define Phototropism

Answer 31

A response in which parts of a plant grow toward or away from directional light.

Question 32

Role of Auxins

Answer 32

They control shoot growth. They are made in the shoot tip only, spread through the plant, and is unequally distributed in response to light and gravity. It stimulates cell elongation.

Question 33

Explain the growth of shoots toward light

Answer 33

When all sides of a shoot receive light, equal amounts of auxin diffuse down all sides of the shoot, so cells all around the shoot are stimulated equally to grow longer. Makes shoot grow straight up.
When light comes mainly on one side, auxin on that side move across to the shaded side. Cells on the shaded side of the shoot will grow longer making it curve toward the light.

Question 34

Explain the growth of a root toward gravity

Answer 34

When roots are pointing down, all sides of the root receive same amount of auxin.
When roots are growing at an angle to gravity, auxin go to lower side, makes root to curve downward toward gravity.