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homeostasis and response (T5) Flashcards

1
Q

define homeostasis

A

the regulation of the internal conditions of a cell or organism to maintain the optimum conditions for function, in response to internal and external changes

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2
Q

why do we need to control internal conditions

A

enzymes:
- enzymes only work at their best in specific conditions (opt. temp and pH)
- enzymes control all the functions of a cell
- the functioning of a cell is vital for the tissues, organisms and organs to work

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3
Q

what internal conditions need to be controlled?

A
  • body temp
  • water content
  • blood glucose conc
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4
Q

how are the internal conditions controlled

A

detecting changes and responding to them involves automatic control systems including the nervous system and the hormonal system (endocrine system)

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5
Q

what detects changes (stimuli)

A

receptor cells

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6
Q

what decides what needs to be done (processes information)

A

coordination centre - brain/spinal cord

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7
Q

what makes the response happen

A

effectors - muscles/organs

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8
Q

where are receptor cells found

A

in sense organ

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9
Q

what are the senses and sense organs

A
  • touch - skin
  • smell - nose
  • sight - eyes
  • taste - tongue
  • sound - ears
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10
Q

what are the two communication systems + diff in response?

A
  • nervous system - produces fast, short-lasting response
  • hormonal system - produces slow long-lasting response
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11
Q

what is the nervous system responsible for

A

coordinating responses to changes in the environment

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12
Q

what are the two diff parts of the nervous system

A
  • central nervous system (CNS)
    brain and spinal cord
  • peripheral nervous system (PNS)
    nerves taking info to and from CNS
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13
Q

how do we respond to stimuli

A
  • stimuli
  • receptors in sense organs
  • sensory neurones (nerves)
  • CNS - coordinator - spinal cord and brain
  • motor neurones (nerves)
  • effectors (muscles)
  • response
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14
Q

how are nerve cells adapted to their function

A

nucleus:
- controls cell activities
nerve fibre/axon:
- long thin extension of cytoplasm that carries the nerve impulse
branched endings:
- parts that connect with the effector or other neurones
insulating sheath (myelin):
- layer to insulate the neurone and increase the speed of the impulses

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15
Q

what is a reflex action/arc

A

automatic and rapid response to a stimulus - does not involve conscious part of brain
e.g. constricting/dilating pupil based on light levels

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16
Q

how does a reflex work

A
  • stimulus detected by a receptor cell
  • nerve impulses carried along a sensory neurone
  • then passed and carried through a relay neurone in the spinal cord
  • impulse sent along a motor neurone to an effector
  • effector carries out response
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17
Q

what are synapses

A

gaps in between neurones

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18
Q

how do synapses works

A

when impulse reaches end of one neurone it causes a chemical called a neurotransmitter to be released. this neurotransmitter diffuses diffuses across the gap and binds to receptor sites on the next neurone which generates a new electrical impulse in the next neurone

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19
Q

what is the brain

A

organ that controls complex behaviour, made of billions of inter connected neurones, diff regions carry out diff functions

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20
Q

what is the function of the cerebal cortex

A

concerned w/ consciousness, intelligence, memory and language

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21
Q

what is the function of the cerebellum

A

coordinating muscular activity and balance

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22
Q

what is the function of the medulla

A

concerned w/ unconscious activities e.g. breathing, control of the heartbeat, movement of the gut

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23
Q

how have scientists been able to map out different regions of the brain

A

by studying patients with brain damage, electrically stimulating different parts of the brain and using MRI scanning techniques

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24
Q

why is treating brain injuries very difficult

A

the brain is a very complex and delicate organ so it is easy to cause extra damge.

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25
Q

what is the eye

A

a sense organ containing receptors sensitive to light intensity and colour

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26
Q

what is the function of the ciliary muscle

A

changes the shape of the lens for focusing

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27
Q

what is the function of the lens

A

changes shape slightly to adjust the focusing of light onto the retina

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28
Q

what is the function of the pupil

A

light enters your eye through this hole

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29
Q

what is the function of the iris

A

controls the amount of light entering your eye

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30
Q

what is the function of the cornea

A

transparent part at the front of your eye, does most of the bending of the light rays

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31
Q

what is the function of the sclera

A

tough, white protective layer

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32
Q

what is the function of the optic nerve

A

carries nerve impulses to brain

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33
Q

what is the function of the suspensory ligaments

A

holds the lens in place and helps w focusing

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34
Q

what is the function of the retina

A

inner light-sensitive layer, contains rod cells that work in dim light and cone cells that detect colour and detail

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35
Q

what is the blind spot

A

the point where the optic nerve leaves the eye has no retina so there are no rod or cone cells there. this causes a blind spot, however you are unaware of this as the brain fills the gap.

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36
Q

what is accommodation

A

process of changing the shape of the lens to
focus on near or distant objects.

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37
Q

how does the lens change shape to focus on distant objects

A
  • the ciliary muscles relax
  • the suspensory ligaments are pulled tight
  • the lens is made less convex (flatter and thinner) and only slightly refracts light rays.
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38
Q

how does the lens change shape to focus on nearby objects

A
  • the ciliary muscles contract
  • the suspensory ligaments loosen
  • the lens is made more convex (rounder and thicker) and refracts light rays strongly.
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39
Q

how does the pupil change in dim light

A
  • radial muscles contract
  • causes your pupil to dilate (expand) which lets more light into your eye
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40
Q

how does the pupil change in bright light

A
  • circular muscles contract
  • causes your pupil to constrict (get smaller) which lets less light into your eye
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41
Q

what are the two common eye defects

A
  • myopia (short-sightedness)
  • hyperopia (long-sightedness
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42
Q

what ab the image on the retina

A

formed upside down but our brains interpret the image as the right way up

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43
Q

how does myopia affect sight

A
  • can clearly see objects when they are near but objects further away appear blurred
  • eyeball is too long or lens is too curved so light rays focus just in front of the retina
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44
Q

common treatments for myopia

A
  • glasses w/ a concave lens
  • spreads out the light from distant objects before it reaches the eye. this means the thicker lens can bring the rays into perfect focus on the retina
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45
Q

how does hyperopia affect sight

A
  • can focus clearly on distant objects but close objects appear blurred
  • eyeball is too short or lens is too flat so light rays focus just behind the retina
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46
Q

common treatments for hyperopia

A
  • glasses w/ a convex lens
  • bring light rays from closer objects closer together before it reaches the eye. this means the thinner lens can bring the rays into perfect focus on the retina
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47
Q

what defect can contact lenses treat

A

myopia and hyperopia

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48
Q

how do contact lenses work

A
  • lens placed on the surface of the eye that refracts light to focus it on the retina
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49
Q

what are the advantages of contact lenses

A
  • cannot be seen
  • makes life easier for playing sports + general activities
  • soft lenses are comfortable to wear
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50
Q

what are the disadvantages of contact lenses

A
  • have to be removed overnight
  • risk of eye infection
  • soft lenses do not last long
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51
Q

what defects can laser eye surgery treat

A

myopia and hyperopia

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52
Q

how does laser eye surgery work

A

lasers are used to reduce (myopia) or increase (hyperopia) the thickness of the lens to focus light onto the retina

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53
Q

what are the advantages of laser eye surgery

A
  • permanent change
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54
Q

what are the disadvantages of laser eye surgery

A
  • only available once eyes have stopped growing so not accessible for everyone
  • can be expensive
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55
Q

what defects can replacement lenses treat

A

myopia and hyperopia

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56
Q

how do replacement lenses work

A

add another lens inside the eye itself to correct the visual defect permanently
- two techniques: natural lens left in place or the faulty lens is replaced

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57
Q

what are the advantages of replacement lenses

A
  • permanent change
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58
Q

what are the disadvantages of replacement lenses

A
  • risk of cataracts
  • risk of infections
  • can be expensive
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59
Q

where is body temp monitored and controlled

A

the thermoregulatory centre in the brain

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60
Q

how are changes in body temp detected

A
  • thermoregulatory centre contains receptors sensitive to temp of blood
  • skin has temp receptors that send nerve impulses to the thermoregulatory centre
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61
Q

what happens if body temp is too high

A
  • blood vessels dilate (vasodilation)
  • sweat produced
  • both these mechanisms cause a transfer of energy from the skin to the environment
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62
Q

what happens if body temp is too low

A
  • shivering > muscles contract - more respiration - exothermic - increases temp
  • blood vessels constrict (vasoconstriction)
  • sweating stops
  • going pale - less blood closer to surface so heat can’t escape
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63
Q

what are hormones

A
  • chemicals in our body that control responses or changes that are longer-lasting
  • blood carries the hormone from where they’re made to the target organ
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64
Q

what is the endocrine system

A

system composed of glands which secrete hormones directly into the bloodstream

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65
Q

what does adrenaline do

A

speeds up the heartbeat and breathing rate

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66
Q

where is adrenaline made

A

adrenal glands (on top of kidneys)

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67
Q

what does insulin do

A

controls blood glucose conc

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68
Q

where is insulin made

A

pancreas

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69
Q

what do growth hormones do

A

control chemical reactions in body and effects growth

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70
Q

where are growth hormones made

A

thyroid

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71
Q

what does progesterone do

A

causes the body changes in puberty in females and menstrual cycle

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72
Q

where is progesterone made

A

ovaries

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73
Q

what does testosterone do

A

causes the body changes at puberty in males

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74
Q

where is testosterone made

75
Q

what is the role of the pituitary gland

A

makes hormones that control the other glands

76
Q

what is negative feedback

A

A negative feedback control system responds when conditions change from the ideal or set point and returns conditions to this set point. There is a continuous cycle of events in negative feedback.

77
Q

what is thyroxine

A
  • hormone produced by thyroid gland in neck
  • controls basal metabolic rate of body
  • important role in growth and development
  • stimulates synthesis of proteins
  • normal levels important in developing babies for brain development
78
Q

describe the negative feedback mechanism for regulating thyroxine production

A
  • hypothalamus detects low thyroxine levels
  • hypothalamus releases TRH
  • pituitary gland releases TSH
  • thyroid gland releases more thyroxine
  • thyroxine levels return to normal
  • hypothalamus detects normal thyroxine levels
  • normal thyroxine levels inhibits TRH release by hypothalamus
  • inhibition of TRH means pituitary gland stops producing TSH
79
Q

what is adrenaline

A
  • hormone produced by adrenal glands when stressed, angry, excited or frightened so body ready for action
80
Q

what does adrenaline cause and how does it help

A
  • heart rate and breathing rate to increase
  • glucose and oxygen in blood moves faster so more respiration takes place and more energy is released
  • stored glycogen in liver to be converted to glucose for respiration
  • more available for respiration so more energy released
  • pupils of your eyes to dilate to let in more light
  • can see better
  • mental awareness increases
  • reflexes more accurate and can think more clearly
  • boosts delivery of glucose and oxygen to brain and muscles to prepare body for fight or flight
  • more available for respiration
81
Q

why do we need to control blood glucose conc

A

glucose is needed for respiration

82
Q

what will effect blood glucose levels

A
  • after meals blood sugar will be high, before meals + after exercise blood sugar is likely to be low
83
Q

what happens if blood glue conc is too low

A
  • not enough for respiration so cells can shut down
84
Q

what happens if blood glucose conc is too high

A
  • affects osmosis so cells lose too much water which can lead to a coma
85
Q

what hormones control blood sugar and where are they produced

A
  • insulin and glucagon produced in the pranceas
86
Q

how does insulin control blood sugar

A

reduces blood sugar if its too high

87
Q

how does glucagon control blood sugar

A

increases it if blood sugar is too low

88
Q

what is the regulation of blood sugar an example of

A

a negative feedback mechanism

89
Q

describe the negative feedback mechanism for controlling blood glucose levels

A

IF BLOOD GLUCOSE IS TOO HIGH:
- pancreas releases insulin
- insulin increases the amount of glucose taken in by cells
- it also converts glucose into glycogen in the liver
- blood glucose falls
- blood glucose returns to a normal level

IF BLOOD GLUCOSE IS TOO LOW:
- glucagon is released
- glucagon breaks down glycogen into glucose
- it also breaks down amino acids/fats (into glucose)
- blood glucose rises
- blood glucose returns to a normal level

90
Q

what is type 1 diabetes

A

a disorder in which the pancreas fails to produce sufficient insulin

91
Q

what are the causes/risk factors for type 1 diabetes

A
  • could be a genetic link
  • damaged pancreas
92
Q

what are the short term symptoms of type 1 diabetes

A
  • producing lots of urine
  • tired
  • thirsty
93
Q

what are the long term effects of type 1 diabetes

A

(if untreated):
- severe weight loss
- wasting away
- eventually death

94
Q

current treatments for type 1 diabetes

A
  • insulin injections
  • pancreas transplant
95
Q

what is type 2 diabetes

A

the body cells no longer respond to insulin produced by the pancreas (or not making enough)

96
Q

what are the causes/risk factors for type 2 diabetes

A
  • genetics
  • obesity
  • lack of exercise
97
Q

what are the short term symptoms of type 2 diabetes

A
  • increased thirst
  • weight loss
  • tired
    (MILDER SYMPTOMS)
98
Q

what are the long term effects of type 2 diabetes

A
  • increased risk of heart attacks and strokes
  • possible blindness
  • possible risk of amputation
99
Q

current treatments for type 2 diabetes

A
  • increased exercise
  • drugs/medicine
100
Q

how is insulin provided for diabetics today

A
  • diabetics used to have to take insulin from pigs
  • bacteria can now be genetically modified to produce human insulin
101
Q

what is the problem w/ pancreas transplants

A

it is a difficult and risky operation and there are not nearly enough pancreas donors for all type one sufferers

102
Q

what are some treatments being researched/experimented with so far to use instead of pancreas transplants

A
  • in 2005 scientists produced insulin secreting cells from stem cells and used them to cure diabetes in mice
  • in 2008 they turned mice pancreas cells that normally made enzymes into insulin producing cells
103
Q

what treatments to cure diabetes scientists hope to develop in the future

A
  • scientists hope that in the future they will be able to genetically engineer faulty human pancreatic cells so that they work properly
  • or use stem cells from humans embryos to produce new insulin-secreting pancreas cells
104
Q

what happens if water balance is low

A

blood becomes more concentrated than cell solution so water moves out of the cell by osmosis through a partially permeable membrane - shrivels up

105
Q

what happens if water balance is too high

A

blood becomes more dilute than cell solution so water into out of the cell by osmosis through a partially permeable membrane - swells until it bursts

106
Q

what organ plays an important role in maintaining the water balance in our bodies

107
Q

what are the inputs of water in our bodies

A
  • water content in food
  • water content in drinks
  • water made in respiration
108
Q

what are the outputs of water in our bodies

A
  • urine
  • sweat
  • exhalation (lost as water vapour)
  • in faeces
109
Q

how do kidneys work

A
  • your kidneys filter your blood
  • glucose, mineral ions, urea and water are all squeezed out of the blood into the nephron
  • red blood cells and proteins are too large to leave the blood during the filtering process
  • all the glucose is reabsorbed back into the blood as it passes through the nephron by diffusion and active transport
  • none of the urea is reabsorbed so that it all goes into the urine formed and is excreted
  • the amount of water and mineral ions reabsorbed into the blood varies - selective absorption in order to maintain the conc. in the body
110
Q

describe the negative feedback mechanism for controlling water balance

A

TOO MUCH SALT/SWEATING:
- water content detected by hypothalamus
- water content of the blood decreases
- pituitary gland produces more ADH
- high vol. of water reabsorbed by kidney
- urine output is low (small vol. of concentrated urine)
-water content of the blood returns to normal

TOO MUCH WATER DRUNK:
- water content detected by hypothalamus
- water content of the blood increases
- pituitary gland produces less ADH
- low vol. of water reabsorbed by kidney
- urine output is high (large vol. of dilute urine)
-water content of the blood returns to normal

111
Q

how are excess amino acids removed from body

A
  • the digestion of proteins from the diet results in excess amino acids which need to be excreted safely
    -in the liver these amino acids are deaminated to form ammonia
  • ammonia is toxic and so it is immediately converted to urea for safe excretion.
112
Q

what are the consequence of kidney damage or disease

A
  • damage from accidents or disease can lead to a build-up of poisonous wastes in the body
  • humans can survive with one kidney, but for people who suffer from total kidney failure this would be fatal if not treated.
113
Q

what is dialysis

A

acts as an artificial kidney to remove most of the urea and restore/maintain the water and ion balance of the blood

114
Q

how does a dialysis work

A
  • inside the machine the blood and dialysis fluid are separated by a partially permeable membrane – the blood flows in the opposite direction to dialysis fluid, allowing exchange to occur between the two where a conc gradient exists
    -the dialysis fluid has no urea in it, there is a large conc gradient - meaning that urea moves across the partially permeable membrane, from the blood to the dialysis fluid, by diffusion. this is very important as it is essential that urea is removed from the patients’ blood.
  • as the dialysis fluid contains a glucose conc equal to a normal blood sugar level, this prevents the net movement of glucose across the membrane as no conc gradient exists. this is very important as the patients’ need to retain glucose for respiration.
  • as the dialysis fluid contains an ion conc similar to the ideal blood plasma conc, movement of ions across the membrane only occurs where there is an imbalance.
  • if the patient’s blood is too low in ions, they will diffuse from the dialysis fluid into the blood, restoring the ideal level in the blood.
  • if the patient’s blood is too high in ions, the excess ions will diffuse from the blood to the dialysis fluid.
115
Q

advantages of dialysis

A
  • greatly reduced levels of urea – it is ‘cleaned blood’
  • no overall change in blood glucose levels
  • the correct water and ion balance maintained or restored (with only excess ions removed)
116
Q

disadvantages of dialysis

A
  • they are expensive
  • the patient must have his or her blood connected to the machine for several hours every week
  • patients must follow a very rigid diet to avoid complications
  • they only work for a limited time for a patient
117
Q

what is a kidney transplant

A

involves implanting a kidney from an organ donor into the patient’s body to replace the damaged kidney

118
Q

advantages of a kidney transplant

A
  • patients can lead a more normal life without having to watch what they eat and drink
  • cheaper for the NHS overall.
119
Q

disadvantages of a kidney transplant

A
  • must take immune-suppressant drugs which increase the risk of infection
  • shortage of organ donors
  • kidney only lasts 8-9 years on average
  • any operation carries risks
120
Q

what is the main reproductive hormone in males

A

testosterone - produced by testes

121
Q

what does rising levels of testosterone do

A

trigger development of the secondary sex characteristics
- stimulates sperm production

122
Q

what are the secondary sex characteristics in males

A
  • increased growth of testes and penis
  • deepening voice
  • growth of facial and underarm hair
  • growth of pubic hair
  • growth spurt
  • increased muscle mass
123
Q

what is the main reproductive hormone in females

A

oestrogen - produced in ovaries

124
Q

what does oestrogen trigger the development of

A

secondary sex characteristics

125
Q

what are the secondary sex characteristics in females

A
  • growth spurt
  • growth of underarm and pubic hair
  • breasts develop
  • fat is deposited on hips and thighs
  • mature ova (eggs) develop every month
  • menstruation begins
126
Q

describe the menstrual cycle

A
  • days 1-5: uterus lining breaks down and menstruation occurs
  • day 6-10: uterus lining begins to thicken again
  • days 11-18: ovulation occurs (an egg is released from the ovary)
  • days 19-28: uterus lining continues to thicken in preparation to recieve the egg
127
Q

how do hormones control the menstrual cycle

A

1) pituitary gland in the brain produces FSH
2) FSH causes an egg in the ovary to mature
2a) FSH stimulates the ovaries to produce oestrogen
-> i) oestrogen causes the pituitary gland to releases LH - triggers the release of the egg from the ovary
-> ii) oestrogen prevents more FSH being secreted so no more eggs mature
-> iii) oestrogen also stimulates the ovary to make progesterone which maintains the uterus lining

IF EGG ISN’T FERTILISED:
- progesterone levels drop and the uterus lining breaks down and passes out of the body as the period

IF THE EGG IS FERTILISED:
- progesterone levels remain high and the uterus lining remains so that the baby can develop

128
Q

what does FSH do (follicle stimulating hormone)

A

causes the egg to mature in the ovary

129
Q

what does LH do (luteinising hormone)

A

causes the egg to be released from the ovary

130
Q

what does oestrogen and progesterone do

A

involved in maintaining the uterus lining

131
Q

how is fertility controlled

A

by a variety of hormonal and non-hormonal methods of contraception

132
Q

what are some hormone based contraceptive methods

A
  • contraceptive pill
  • contraceptive injections
  • contraceptive implant
  • contraceptive patch
133
Q

how do hormone based contraceptive methods work

A
  • release hormones (oestrogen and/or progesterone) to stop FSH being produces
  • stops eggs maturing and uterus lining developing
134
Q

what are the advantages of hormone based contraceptive methods

A
  • easy to use
  • mostly effective
  • very reliable
135
Q

what are the disadvantages of hormone based contraceptive methods

A
  • raised blood pressure
  • thrombosis
  • breast cancer
  • not always effective
  • may have to take at specific time of day
136
Q

what are some barrier methods of contraception

A
  • condom
  • diaphragm
137
Q

how do barrier methods of contraception work

A
  • prevent sperm reaching egg to prevent fertilisation
138
Q

what are the advantages of barrier methods of contraception

A
  • no side effects
  • does not need medical advice
  • easy to get a hold of
  • offers some protection against STDs
139
Q

what are the disadvantages of barrier methods of contraception

A
  • can get damaged and let sperm through - less reliable
  • diaphragm must be fitted by a doctor - if not fitted correctly it will not work
140
Q

what are some examples of IUDs (intrauterine devices)

A
  • coils
    can contain hormones
141
Q

how do IUDs work

A
  • small structures inserted into the uterus by a doctor
  • prevents the implantation of an embryo in the uterus lining
142
Q

what are the advantages of IUDs

A
  • can be removed if you want to get pregnant
  • very effective
  • lasts 3-5 years
143
Q

what are the disadvantages of IUDs

A
  • can cause period problems/infections
  • has to be inserted by a medical professional
144
Q

what is abstinence

A

not having sex

145
Q

how does abstinence work

A
  • not having sex= can’t get pregnant
  • abstaining from sex during/around ovulation means sperm can’t fertilise egg
146
Q

what are the advantages of abstinence

A
  • no side effects
  • no costs
147
Q

what are the disadvantages of abstinence

A
  • if not 100% abstinence it is a very unreliable method
148
Q

what are some examples of surgical methods of contraception

149
Q

how do surgical methods of contraception work

A
  • people can be surgically sterilised
  • males: sperm ducts cut and tied
  • females: oviducts cut/ties
150
Q

what are the advantages of surgical methods of contraception

A
  • effective permanent contraception
151
Q

what are the disadvantages of surgical methods pop contraception

A
  • permanent method
  • women need general anaesthetic
152
Q

what can be used to treat infertility in women

A
  • giving FSH and LH in a ‘fertility drug’ to a woman -can become pregnant the normal way
  • IVF - in vitro fertilisation
153
Q

describe the IVF process

A

1) mother is given FSH and LH to cause her ovaries to mature and release several eggs
2) ova (eggs) are removed form the mother in a small op.
3) eggs are fertilised by sperm in the lab and allowed to develop into embryos
4) one or two healthy embryos are implanted in the mother’s uterus lining

154
Q

benefits of IVF

A
  • couples who are infertile can have the chance to have children
  • embryos can be checked for genetic disorders before being implanted
  • IVF can increase the chance of having multiple pregnancies
155
Q

problems with iVF

A
  • mature eggs may be stored until later for use which may raise ethical problems if the relationship breaks up
  • the use of fertility drugs can have health risks for the mother
  • IVF is expensive and not always successful
  • excess fertilised eggs may be destroyed which come people think is unethical
  • IVF can increase the chance of having multiple pregnancies (can be risk for baby and mother)
156
Q

why do plants produce hormones

A

control aspects of their growth and development such as;
- growth of roots and shoots
- flowering
- ripening of fruits

157
Q

what is a tropism

A

a plant response to a stimulus (by growing in diff. directions)

158
Q

what is the stimuli for phototropism

159
Q

how do the shoots and roots respond to phototropism

A

shoots = towards
roots = away

160
Q

what is the stimuli for geotropism

161
Q

how do the shoots and roots respond to geotropism

A

shoots = against
roots = towards

162
Q

what is the stimuli for hydrotropism

163
Q

how do the shoots and roots respond to hydrotropism

A

shoots = no response
roots = towards

164
Q

which plant growth substance (hormone) is involved in phototropism

165
Q

where is auxin produced

A

tip of the shoot

166
Q

where does auxin have an effect

A
  • growing region - just below the tip
167
Q

how do plants grow when light is coming from all around the plant

A

1) when plants are exposed to sunlight they produce auxins in the tip of the shoot
2) auxin moves from the tip to the growing region below. when sunlight comes from all around, the conc. of auxin is equal on both sides of the stem
3) auxin causes the stem to grow. if the conc. of auxin is equal on both sides, both sided of the stem will grow at the same rate
4) if a plant continues to receive light from all around the stem will grow straight

168
Q

how does a plant grow when light comes from only one side

A

1) when plants are exposed to sunlight they produce auxins in the tip of the shoot
2) auxin moves from the tip to the growing region below. when sunlight comes from one side, there will be a higher conc. of auxin moving down the shaded part of the stem
3) auxin causes the stem to grow. if the conc. of auxin is higher on the shaded side, it will cause the shaded side of the stem to grow more than the light side
4) this causes the stem to bend
5) if a plant continues to receive light from one side the stem will grow/bend towards that side

169
Q

what plant growth substance (hormone) controls geotropism

170
Q

what effect does auxin have on shoot and root cells

A

shoot = stimulates growth
roots = inhibits growth

171
Q

describe geotropism in plants

A

1) auxin is produces by the seed and gravity causes it to collect at the base of the shoot and the root
2) in the shoot auxin stimulates growth so the base of the shoot (where the auxin is) will grow more than the other side so it will grow/bend upwards
3) in the root auxin inhibits growth so the top of the root (where there isn’t any auxin) will grow more than the base of the root (where the auxin is) causing it to grow/bend downwards

172
Q

what hormone can be used to control seed dormancy

A

gibberellins

173
Q

how do gibberellins control seed dormancy

A

used to stop seeds staying dormant and so promote germination

174
Q

why is controlling seed dormancy useful

A
  • seed dormancy must be broken for seeds so be able to germinate so it promotes plant growth
  • hormones can be used to remove dormancy so it can germinate at all times of the year
175
Q

what hormone is responsible for fruit ripening

176
Q

why is fruit ripening useful

A
  • used in the food industry to ripen fruits e.g. bananas
  • fruits picked unripe to prevent over-ripening during journey - ripened during storage
177
Q

what hormone is used to make seedless fruits

A

auxins and gibberrellins

178
Q

why are seedless fruits useful

A
  • hormones stimulate the growth of fruit w/o need for pollination
  • some ppl prefer eating fruits w/o seeds
  • easier to grow fruit
179
Q

what hormones can be used as weedkillers

180
Q

how does auxin work as a weedkiller

A

makes broad leaf plants such as dandelions grow too fast and die but does not affect narrow leaf plants such as grass

181
Q

uses of auxin as a specific weedkiller

A
  • useful for getting rid of dandelions in a lawn w/o killing the grass
  • can get rid of weeds that compete w/ crops like wheat
182
Q

what plant hormones can be used t control plant growth (as root powders)

183
Q

how is auxin used as a rooting powder

A

plant cuttings can be dipped into hormones to encourage new roots to grow

184
Q

why are rooting powders/cuttings useful

A

used by gardeners to help cuttings taken from plants to grow into new plants

biology (7 decks)

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