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Biology Year 13 > Chemical Control In Mammals And Plants > Flashcards

Chemical Control In Mammals And Plants Flashcards

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1
Q

What is homeostasis?

A

The maintenance of a state of dynamic equilibrium in the body despite changes in the external or internal conditions

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2
Q

What needs to be controlled for your body to be kept in dynamic equilibrium?

A
  • matching the supply of oxygen and glucose to the continually changing demands of the body while removing carbon dioxide
  • maintaining an even temperature and pH
  • water potential
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3
Q

What do the main homeostatic systems in mammals respond to?

A

• changes in both external and internal conditions

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4
Q

Why must the pH levels of the body be maintained?

A

So that the structures of protein molecules remai stable. This allows enzymes to function at their optimum activity and the structure of cell membranes to be maintained

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5
Q

Why must the core temperature of the body remain stable?

A

To maintain the optimum activity of the enzymes that control the rate of cellular reactions. A stable temperature also maintains the integrity of the membranes so they can control the movement of substances into and out of the cells

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6
Q

Why musy the water potebtual of the body fluids remain within narrow limits?

A

To avoid osmotic effects that could damage or destroy the cells

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7
Q

What are sensors/receptors?

A

Specialised cells that are sensitive to specific changes in the environment

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8
Q

What are effectors?

A

Systems (usually muscles or glands) that either work to reverse, increase or decrease changes in a biological feedback system

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9
Q

What may the communication in a feedback system be?

A
  • hormones (chemical messengers)

* nerve impulses (electrical messages)

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10
Q

What do negative feedback systems do?

A

Provide a way of maintaining a condition such as the concentration of a substance within a narrow range. A change in conditions is registered by receptors and as a result effectors are stimulated to restore the equilibrium

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11
Q

What is a positive feedback system

A

Where effectors work to increase an effect that gas triggered a response

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12
Q

What is an example of a positive feedback system?

A

Contractions of the uterus during labour:
• baby pushes against cervix. Cervix stretches
• stretch receptors in cervix send impulses to brain
• brain stimulates pituitary to release oxytocin
• oxytocin makes uterus contract harder pushing baby against cervix

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13
Q

What is the main system of coordination in plants?

A

Chemical control

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14
Q

When is chemical control usually used?

A
  • when long term stimulation of tissues is required
  • when it is necessary to send messages that have an effect on many different areas of the body simultaneously
  • when an effect is needed over a long period of time
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15
Q

What are hormones?

A

Organic chemicals produced in endocrine glands and released into the blood and carried through the transport system to parts of the body where they bring about changes which may be widespread or very targeted. They are usually either proteins, parts of proteins such as polypeptides (e.g. insulin) or steroids (e.g. the sex hormones oestrogen and testosterone

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16
Q

What do endocrine glands do?

A

Produce hormones. They do not have ducts. They release hormones directly into the bloodstream

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17
Q

What happens once a hormone enters the bloodstream?

A

It is carried around in the blood until it reaches the target organ or organs. The cells of the target organs have specific receptor molecules on the surface of their membranes that bind to the hormone molecules. This brings about a change in the membrane and elicits a response

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18
Q

What do exocrine glands do?

A

Produce chemicals (e.g. enzymes) and release them along small tubes or ducts

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19
Q

What are examples of multipurpose endocrine glands?

A
  • The ovaries that produce ova as well as hormones

* the pancreas is both an exocrine gland producing digestive enzymes and an endocrine gland producing insulin

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20
Q

What do all gland hav3?

A

A rich blood supply with plenty of tissues within the glandular tissue itself

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21
Q

How does a negaive feedback loop work?

A
  • increased level of appropriate chemical in the blood stimulates the release of the hormone from the endocrine gland.
  • as a result of the rise in the hormone levels tbe amount of stimulating chemical in the blood drops. Therefore the endocrine gland recieves less stimulation and so the amount of stimulating chemical in the blood drops. Therefore the endocrine gland recieves less stimulation and so the hormone levels drop
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22
Q

What are many hormones released from the endocrine gland in response to?

A

Another hormone or chemical in the blood

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23
Q

What is the pituitary gland?

A

A small gland in the brain that had an anterior lobe and a posterior lobe and produces and releases secretions that affect the activity of most of the other endocrine glands in the body

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24
Q

What is the hypothalamus?

A

A small area of brain directly above the pituitary gland that controls the activities of the pituitary gland and coordinates the automatic (unconcious) nervous system

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25
Q

How is the hypothalamus anatomically linked to the pituaitary gland?

A

As the embryo forms the posterior pituitary lobe develops as an outgrowth of the hypothalamus itself, whilst the anterior lobe grows out from the roof of the mouth. The two parts then fuse and the connection with the root of the mouth is lost

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26
Q

What are neurosecretory cells?

A

Nerve cells that produce secretions from the end of their axons. These secretions either stimulate or inhibit the release of hormones from the anterior pituaitary (neurosecretory cells 1). They are known as releasing factors or releasing-inhibiting factors. Or they are stored in the posterior pituitary and then later released as hormones (neurosecretory cells 2)

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27
Q

What hormones does the pituitary gland produce and which are from the anterior and posterior lobe?

A 
Anterior pituaitary:
• thyroid stimulating hormone
• growth hormone (GH)
• Adrenocorticotrophic hormone (ACTH)
• follicle stimulating hormone (FSH
• Luteinising hormone (LH)
• prolactin

Posterior lobe:
• oxytocin
• ADG (antidiuretic hormon

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28
Q

What does thyroid stimulating hormone do?

A

Controls the secretion of thyroxin and triuodothyronine from the thyroid gland

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29
Q

Growth hormone (GH)

A

Stimulates the growth of body cells and increases the build up of proteins

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30
Q

What does ACTH do?

A

Controls the secretion of some of the hormones of the adrenal cortex of the adrenal glands

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31
Q

What does FSH do?

A

In females it stimulates the ovaries to produce oestrogen and also stimulates the development of ova in the menstrual cycle. In males it stimulates the testes to produce sperm

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32
Q

What does LH do?

A

Stimulates ovulation and the formation of the corpus lutem in females. It prepares the uterus for implantation. In males it stimulates the testes to produce testosterone

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33
Q

What does prolactin do?

A

Stimulates and maintains the production of milk by the mammary glands

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34
Q

What does ADH do?

A

Decreases the urine volume by affecting the tubules of the kidney, and also causes the arteries to constrict after haemorrhage, preventing excess blood loss and raising blood pressure

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35
Q

What does oxytocin do?

A

Stimulates the muscles of the uterus to contract during labour and also stimulates the contraction of cells in the mammary tissue so that milk is squeezed out when an infant suckles

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36
Q

How does ‘release of a second messenger’ with hormones have an effect?

A

Some hormobes such as adrenaline, glucagon and fsh are not lipid soluble and cannot cross the cell membrane. This triggers a series of membrane-bound reactions that result in the formation of a second chemical inside the cell. This second messenger then activates a number of different enzymes within the cell, altering the metabolism. The most common second messenger is a substance called cyclic AMP (cAMP), which is formed from ATP. Cyclic AMP triggers a number of responses in the cell including increased cellular respiration, increased contraction of muscle cells, relaxation of smooth muscle in blood vessels and so on

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37
Q

How does ‘the hormone entering the cell’ work?

A

A lipid soluble hormone passed through the membrane and acts as the internal messenger itself. Inside the cell the hormone binds to a receptor and the hormone-receptor complex passes through the pores of the nuclear membrane into the nucleus. The hormone bound to the receptor acts as a transcription factor, regulating gene expression and switching sections of DNA on or off. This is the mode of action of the lipid-soluble steroid hormones such as oestrogen and testosterone

38
Q

What stimuli do plants respond to?

A 
• light
   - the direction it comes from 
   - the intensity of the light
   - daily exposure of light
• gravity
• water
• temperature 
• sometimes touch and chemicals 
• internal chemical signals
39
Q

What are most of the responses of plants concerned with?

A

Either directly or indirectly maximising opportunities for photosynthesis and respiration

40
Q

What are tropisms?

A

Plant growth responses to environmental cues

41
Q

How do plants grow by cell wall elongation?

A

The main areas of cell division in plants are known as meristems and occur just behind the tip of the root or shoot. The regions of cell division and cell elongation are particularly sensitive to plant growth substances. These chemical messages act in a number of ways - e.g. they can make it easier for the cellulose cell walls to be stretched, in turn making it easier for the cells to expand and grow

42
Q

What are auxins?

A

Plant hormones that act as powerful growth stimulants and are involved in apical dominance, stem and root growth, and trophic respinses to unilateral light

43
Q

Where are auxins produced?

A

In young shoots

44
Q

In which direction do auxins always move?

A

Down the plant from the shoots to the roots

45
Q

What do auxins do in low concentrations?

A

Promote root growth

46
Q

How do auxins affect the ability of the plant cells walls to stretch?

A

IAA is made in the tip of the shoot and diffuses back to the zone of elongation. The molecules in IAA bind to specific recpetor sites on the cell surface membranes, activating the active pumping of hydrogen ions into the cell wall spaces. This changes the hydrogen ion concentration, providing the optimum pH of around 5 for enzymes that breaks bonds between adjacent cellulose microfibrils. This allows the microfibrils to slide past each other very easily, keeping the walls very plastic and flexible. The cells absorb water by osmosis and as a result of turgor pressure, the very flexible cell walls stretch allowing the cells to elongate and expand. Eventually as the cells mature the IAA is destroyed by enzymes, the pH of the cell wall rises, the enzyme is inhibited and bonds form between the cellulose microfibrils so the cell becomes rigid and can no longer expand

47
Q

How does the distribution of auxin work in plants? (Not well phrased, sorry)

A

The light on one side of the plant is usually stronger than the other. The side of a shoot exposed to light contains less auxin than the side that is not illuminated. Light causes the auxin to move laterally across the shoot, producing a greater concentration on the uniliminated side. This movement means the shoot tip acts as a photoreceptor. More of the hormone diffuses down to the region of cell elongation on the dark side. This stimulates cell elongation and therefore growth on the dark side, resulting in the shoot bending towards the light

48
Q

What are gibberllins?

A

Plant hormones that act as growth regulators, particularly in the internodes of stems by stimulating elongation of the growing cells; they also promote the growth of fruit and are involved in breaking dormancy in seeds and in germination as they stimulate the formation of enzymes in seeds.

49
Q

How does gibberllin help with germination?

A

Gibberellin stimulates the aleurone layer in the embryo to produce amylase that diffuses into endosperm and breaks down food stores to provide the embryo with materials for respiration and growth

50
Q

What are cytokins?

A

Plant hormones that act as growth regulators by promoting cell division in the apical meristems and the cambium through interactions with auxins. They promote lateral bud development which can overcome apical dominance if the leading shoot is removed or damaged. Cytokins work synergistically with ethene in the abscission of leaves, flowers and fruits

51
Q

What is an abscission?

A

The shedding of leaves, flower parts or fruits from a plant after the formation of an abscission zone across the stem attaching the organ to the plant

52
Q

What is synergy?

A

When growth regulators work together, complementing each other and giving a greater response that would otherwise be the case.

53
Q

What is an example of synergy?

A

Auxins and gibberellins work synergistically in the growth of stems

54
Q

What is antagonism?

A

If substances have opposite effects, for example one promoting growth and the other inhibiting it, the balance between them will determine the response of the plant

55
Q

What is an example of antagonism in plants?

A

Auxins and cytokins work antagonistically on the maintenance of apical dominance

56
Q

What is an example of antagonism in plants?

A

Auxins and cytokins work antagonistically on the maintenance of apical dominance

57
Q

What is apical dominance?

A

One lead shoot in a young plant grows bigger anf faster than all the others and the greoth of all the other lateral buds is inhibitted as a result of the high auxin levels produced by the first shoot to emerge. The auxin acts antagonistically with cytokinin, which stimulate the development of the lateral buds

58
Q

What happens in the natural growth of the plant to do witb apical dominance?

A

As the first shoot grows away the inhibition of the auxin is reduced and the cytokinin becomes dominant so the lateral buds lower down the plant begin to grow

59
Q

What happens if the apical bud is removed?

A

The auxin inhibition on tbe lateral buds is removed and the cytokinin can have it’s full effect and many lateral byds grow rapidly

60
Q

What happens if auxin is artificially added to the cut apical stem?

A

The antagonisitic effects return and lateral shoot growth slows again

61
Q

What is photomorphogenesis?

A

The process by which the form and development of a plant is controlled by the levels and type of light

62
Q

What is the environmental cue that determines changes such as bud development, flowering, fruit ripening and leaf fall?

A

Day length or night length

63
Q

What is red light?

A

Light with a wavelength of 580-660’ nm, which is detected by plants using phytochromes

64
Q

What is far red light?

A

Light with a wavelength of 700-730 nm which is detected by plants using phytochromes

65
Q

What are phytochromes?

A

Phytochrome is a plant pigment that reacts with different types of light and in turn affects the response of the plant

66
Q

What colour is the phytochrome pigment?

A

Blue-green

67
Q

What are the two interconvertible forms phytochromes exist in and what do the different forms do?

A

Pr (P660) absorbs red light and Pfr (P730) absorbs far red light

68
Q

What happens when one form of the phytochrome pigment absorbs light?

A

It is converted reversibly into the other form

69
Q

How do both of the forms of phytochromes end up exisiting in the plant?

A

As the seedling germinate it makes Pr. As soon as it breaks through the surface of the soil and is exposed to red light, some of the new pigment is converted into Pfr and from the on the two forms exist in the plant

70
Q

What does the length of time it takes for one form of the phytochrome pigment to be converted into the other depend on?

A

The light intensity

71
Q

Which is the more stable firm of the phytochrome and which is the more biologically active?

A

Pr is the more stable form of the pigment and Pfr is biologically active

72
Q

Why do varying periods of light and dark affect plant metabolism? (Phytochromes)

A

Because the balance between the two forms of phytochrome is affected by varying periods of light and dark which in turn affects the plant metabolism including flowering patterns. As normal sunlight contains more red light than far red light the usual situation is for most of the phytochrome to be in the Pfr form during daylight hours and then all converted back to Pr form during the night. This is why germination happens during the day with the biologically active Pfr form

73
Q

What is the photoperiod?

A

The amount of time that an organism is exposed to light during a 24 hour period

74
Q

What are short day plants (SDPs)?

A

Plants flowering when days are short and nights are long

Including strawberries and the tobacco plant

75
Q

What are long day plants? (LDPs)

A

Plants flowering when days are long and nights are short

Including snapdragons and cabbages

76
Q

What are day neutral plants? (DNPs)

A

Plants where flowering is not affected by the length of time they are exposed to light or dark. E.g. pea plants and cucumbers

77
Q

How comes DNPs are day neutral?

A

They usually evolved in tropical regions where the day length is the same all year round. As a result they are adapted to different cues shch as the amount of available water, as the triggers for flowering

78
Q

Is it the period of light or darkness that is the environmental cue affecting flowering?

A

Darkness.

79
Q

What is the current hypothesis about flowering in short-day plants?

A

The biologically active molecule Pfr inhibits flowering and a lack of Pfr allows flowering to occur. During long periods of darkness the levels of Pfr fall as it is almost all converted to Pr. This allows flowering to take place.

80
Q

What is the hypothesis for flowering in long day plants?

A

High levels of Pfr stimulate flowering. The nights are short so relatively little Pfr is converted back to Pr. As a result relatively high Pfr levels are maintained all the time, stimulating flowering

81
Q

What is florigen?

A

A hypothetical plant hormone which is involved in the photoperiodic response. It may be FTmRNA

82
Q

Mikhail Chaulakhyan the russian plant physiologist saw that the detection of the photperiod seems to take place in the leaves of the plant and hypothesised the presence of florigen. What was his evidence for this hypothesis?

A
  • if the whole plant is kept in the dark apart from one lead which is exposed to the appropriate periods of light and dark flowering occurs as normal. A plant kept in total darkness does not flower
  • using the same experimental set up if the photoperiodically exposed lead is removed immedietly after the stimulus the plant does not flower. If it is left in place for a few hours the plant does flower
  • if two or more plants are grafted together and only one exposed to appropriate light patterns all the plants will flower
  • in some species if a light stimulated leaf from one plant is grafted onto another plant the new plant will flower
83
Q

Why are scientists starting to think that FTmRNA is florigen?

A

Because recently scientists have started to show that when a leaf is exposed to a given amount of light and dark a particular form of mRNA is produced in the leaf, linked with a gene associated with flowering (the FT gene). It is called FTmRNA. Before scientists thought that it was too large a molecule to leave the cell. But now scientists have shown that FTmRNA can move from cell to cell to the transport tissue through the plasmodesmata. They have also shown that FTmRNA travels from the leaves where it is made to the shoot where other genes associated with flowering are activated

84
Q

What does the term etiolated describe?

A

The form of plants grown in the dark. They grow rapidly using up food reserves in attempt to reach the light. As a result the plants end up tall and thin, with fragile steme, long internodes and small, pale, yellowish leaves as no chlorophyll is formed

85
Q

The early seedling emerging from the seed has a cotyledon or a hooked apical shoot and shows typical characteristics of etiolation. What do these include?

A
  • rapid stem lengthening but very little thickening - the seedling grows as tall as possible as fast as possible to reach the light
  • relatively little root growth - just enough to act as an anchor and obtain water
  • no leaf growth - the leaves remain furled so no energy is wasted producing leaf tissue that is useless underground
  • no chlorophyll - no energy is wasted producing chlorophyll that is useless in the dark
86
Q

What happens once the tip of the new shoot breaks through the soil surface into the light?

A
  • the elongation of the stem slows down
  • the stem straightnens
  • the cotyledons and/or first leaves open
  • chlorophyll forms and the seedling begins to photosynthesise
87
Q

How are the changes of photomorphogenesis controlled by phytochrome interconversion?

A

In the seed there is plenty of Pr but not Pfr. Without Pfr the internodes grow but the leaves do not and no chlorophyll forms. Once the plant is exposed to light Pr is rapidly converted to Pfr and levels of Pfr build up quickly. Pfr inhibits the lengthening of the internodes (stem between the leaf nodes) so internode growth slows. It stimulates leaf development and the production of chlorophyll. The seedling turns green and begins to photosynthesise. These changes begin even before the seedling breaks through the surface of the soil and begins the transformation. As a result the chloroplasts are maturing and the seedling is often green and ready to photosynthesise as it breaks through the soil

88
Q

What is green fluorescent protein? (GFP)

A

The product of a gene often used as a marker in the production of recombinant DNA

89
Q

What is the evidence that Pfr acts as a transcription factor?

A

Researchers produced recombinant DNA linking the genes for the production of phytochrome to a gene for the production of green fluorescent protein. By inserting these hybrid genes into plant cell scientists produced plants with fluorescent phytochrome.

If seedling were kept in the dark the fluorescence linked to the inactive Pr was spread evenly through the cytoplasm. When the seedlings were exposed to red lugbt and therefore converting labelled Pr to labelled Pfr scientists observed the fluorescence moved into the nucleus. In the nucleus the fluroscence appeared as specks linked to the chromosomes

90
Q

What is the current model of phytochrome as a transcription factor?

A
  • when Pr is converted into Pfr in the presence of light it moves into the nucleus through the pores in the nuclear membrane
  • in the nucleus it binds to a nuclear protein known as the phytochrome-interacting factor 3 (PIF3)
  • PIF3 is a known transcription factor
  • PIF3 only binds to Pfr not to Pr
  • PIF3 only activates gene transcription and the formation of mRNA when it is bound to Pfr

The hypothesis is that by binding to PIF3, Pfr activates different genes and so controls different aspects of growth and development in plants.

Biology Year 13 (16 decks)

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