Nervous and hormonal control (part 2)

Question 1

What is a stimulus?

Answer 1

Any change in the internal or external environment

Question 2

What do receptors do?

Answer 2

Receptors detect stimuli – they can be cells or proteins on cell surface membranes

Question 3

What do effectors do?

Answer 3

They bring about a response to a stimulus to produce an effect
Eg muscles cells

Question 4

How do receptors communicate with effectors?

Answer 4

Via the nervous or hormonal system

Question 5

How does the eye respond to dim light?

Answer 5

• Light receptors in the eyes detect a lack of light
• The CNS processes information
• The radial muscles in the iris are stimulated by the motor neurones
• The radial muscles contract to dilate the pupils

Question 6

How does the eye respond to bright light?

Answer 6

• Light receptors in the eyes detect bright light
• The CNS processes the information
• The circular muscles in the iris are stimulated by the motor neurones
• The circular muscles contract to constrict the pupils

Question 7

What is the hormonal system comprised of?

Answer 7

Glands and hormones

Question 8

What is a gland?

Answer 8

A group of cells that are specialised to secrete a useful substance such as a hormone
Eg the pancreas secretes insulin

Question 9

What is a hormone?

Answer 9

A ‘chemical messenger’ – many are proteins or peptides but some are steroids

Question 10

When are hormones secreted?

Answer 10

When a gland is stimulated

Question 11

How can glands be stimulated x2

Answer 11

• By a change in concentration of a substance eg another hormone
• Electrical impulses

Question 12

Describe how hormones trigger a response in target cells (use blood glucose):

Answer 12

• Receptors on pancreas cells detect low blood glucose concentration
• The pancreas releases the hormone glucagon into the blood
• Target cells in the liver detect glucagon and convert glycogen into glucose
• Glucose is released into the blood so glucose concentration increase

Question 13

Differences between nervous and hormonal system x4:

Answer 13

• Nervous uses electrical impulses, hormonal uses chemicals
• Nervous has a faster response, hormonal has a slower response
• Nervous has a localised response, hormonal has a widespread response
• Nervous has a short-lived response, hormonal has a long-lived response

Question 14

Nervous system: What are photoreceptors?

Answer 14

Light receptors in the eye

Question 15

What part of the eye controls the amount of light entering?

Answer 15

The muscles of the iris

Question 16

What part of the eye contains photoreceptors?

Answer 16

The retina

Question 17

Which part of the retina has an abundance of photoreceptors?

Answer 17

The fovea

Question 18

Name the two types of photoreceptors:

Answer 18

Rods and cones

Question 19

Where are rods found + what do they do?

Answer 19

Mainly found in the peripheral parts of the retina

They deliver information in black and white

Question 20

Where are cones found + what do they do?

Answer 20

In the fovea

They deliver information in colour

Question 21

What are the three types of cone?

Answer 21

Red-sensitive, blue-sensitive, green-sensitive

Question 22

What happens to rod cells when stimulated by light?

Answer 22

They become hyperpolarised

Question 23

What is the light-sensitive pigment found in rod cells called and what is it made of?

Answer 23

Rhodopsin is made of retinal and opsin

Question 24

What happens to rod cells in the dark?

Answer 24

• Sodium ions diffuse into the rod cells, depolarising the cell
• Neurotransmitters are released across the synapse to the bipolar neurone
• Inhibitory response occurs so the bipolar neurone does not depolarise, and no action potential is fired

Question 25

What happens to rod cells in the light?

Answer 25

- Rhodopsin absorbs light and breaks down into retinal and opsin - Opsin activated a cascade of reactions that result in the closing of cation channels - Sodium cannot diffuse into the rod cells, so the cell membrane becomes hyperpolarised - No release of neurotransmitters so there is no inhibition of the bipolar neurone, so it depolarises, delivering an action potential to the brain via the optic nerve

Question 26

What is a tropism?

Answer 26

A plants growth response to an external directional stimulus

Question 27

What is a positive/negative tropism?

Answer 27

``` Positive = grow towards the stimulus Negative = grow away from the stimulus ```

Question 28

Relationship between roots/shoots and light:

Answer 28

Shoots are positively phototropic | Roots are negatively phototropic

Question 29

Relationship between roots/shoots and gravity:

Answer 29

Shoots are negatively geotropic | Roots are positively geotropic

Question 30

How are plant responses brought about?

Answer 30

They respond using growth factors that either speed up or slow down plant growth

Question 31

Where are growth factors produced?

Answer 31

In growing regions of the plant eg shoot tips and move to where needed

Question 32

How do auxins stimulate growth in shoots?

Answer 32

By cell elongation – cells walls become lose and stretchy so get longer

Question 33

What do high concentrations of auxins do to roots?

Answer 33

Inhibit growth

Question 34

Name 4 other growth factors:

Answer 34

Gibberellins – stimulate flowering Cytokinin – stimulate cell division Ethene – stimulates fruit ripening ABA – stimulates leaf fall

Question 35

What is IAA?

Answer 35

An important auxin produced in the tips of shoots in flowering plants

Question 36

How does IAA control cell elongation and growth?

Answer 36

When IAA enters the nucleus of a cell it can regulate the transcription of genes involved in elongation and growth

Question 37

How is IAA transported over short distances?

Answer 37

Active transport and diffusion

Question 38

How is IAA transported over short distances?

Answer 38

Active transport and diffusion

Question 39

How is IAA transported over longer distances?

Answer 39

Phloem

Question 40

How do plants detect light?

Answer 40

Using photoreceptors called phytochromes

Question 41

Where are phytochromes found?

Answer 41

Leaves, seeds, roots, and stems

Question 42

What two states do phytochromes exist in?

Answer 42

Pr and Pfr

Question 43

What light + wavelength does Pr absorb?

Answer 43

Pr absorbs red light at a wavelength of 660nm

Question 44

What light and wavelength does Pfr absorb?

Answer 44

Far-red light at a wavelength of 730nm

Question 45

What is Pr converted to in red light?

Answer 45

Converted quickly into Pfr

Question 46

What is Pfr converted to in far-red light?

Answer 46

Converted quickly into Pr

Question 47

What happens to Pfr in darkness?

Answer 47

Slowly converted into Pr