Tropisms and IAA Flashcards
What you should already know!
What are plants sensitive to?
What do shoots respond to?
What do roots respond to?
What do plants produce to coordinate and control growth?
What is a plant’s response to light called?
What is a plant’s response to gravity called?
Why do shoots grow towards the light?
Why do roots grow towards gravity?
What are plants sensitive to? Light moisture gravity
What do shoots respond to? Towards light against gravity
What do roots respond to? Towards moisture towards gravity
What do plants produce to coordinate and control growth? (Hormones)– growth factors
What is a plants response to light called? phototropism
What is a plants response to gravity called? gravitropism
Why do shoots grow towards the light? Unequal distribution of auxin because it diffuse to the dark side where it increases growth rate
Why do roots grow towards gravity? Unequal distribution of auxin, with higher concentration on lower side where it decreases growth rate
A tropism is a growth response of a plant to an ________ ________ _______ The direction of the stimulus determines the direction of the growth response. A _______tropism is growth towards the stimulus, whereas a ________tropisms is growth away from the stimulus. Common stimuli in plants include light, gravity, water, touch and chemicals. The tropisms get their names from the stimuli involved photo-_____, gravi- ______, hydro – water, thigmo-______and chemo -chemicals
A tropism is a growth response of a plant to an external directional stimulus. The direction of the stimulus determines the direction of the growth response. A positive tropism is growth towards the stimulus, whereas a negative tropisms is growth away from the stimulus. Common stimuli in plants include light, gravity, water, touch and chemicals. The tropisms get their names from the stimuli involved photo-light, gravi- gravity, hydro – water, thigmo-touch and chemo -chemicals
Phototropism is the growth of a plant in response to _____. Young shoots & leaves are ____tively phototropic and grow towards the light which maximises light absorption for ___________. Roots are _________phototropic and grow _____from the light.
Phototropism
Phototropism is the growth of a plant in response to light. Young shoots & leaves are positively phototropic and grow towards the light which maximises light absorption for photosynthesis. Roots are negatively phototropic and grow away from the light.
What is the link between more light & photosynthesis and more growth?
More photosynthesis means more _______which can be used as a respiratory substrate to produce ___ providing the energy for cell _______& the synthesis of polymers such as proteins and _________for cell walls as the cells _______/get larger
More photosynthesis means more glucose which can be used as a respiratory substrate to produce ATP providing the energy for cell division & the synthesis of polymers such as proteins and cellulose for cell walls as the cells expand/get larger
Gravitropism
Gravitropism is the growth of a plant in response to ________________. Shoots are ______________________ gravitropic and grow upwards. Roots are _____________________ gravitropic and grow downwards, they also display positive hydrotropism to reinforce the appropriate growth behaviour
Gravitropism is the growth of a plant in response to gravity. Shoots are negatively gravitropic and grow upwards. Roots are positively gravitropic and grow downwards, they also display positive hydrotropism to reinforce the appropriate growth behaviour
What is an auxin?
Auxins are plant _______ _______ involved in the plant’s response to the __________and differential ______
Auxins are plant growth factors involved in the plant’s response to the environment and differential growth
What is a plant growth factor?
Plants respond to _______ ______ using specific _____ _______- these are hormone like chemicals that speed up or slow down plant growth. Plant growth factors are produced in the growing regions of the plant eg ______and _____tips and they move away from the tip by _________ diffusion (away from the tip), a_______ ________ (to a particular side of a shoot in response to the direction of light)or by ____ ____ in the phloem (over longer distances). Growth factors called _______ are produced in the tips of shoots and ________ backward to stimulate the cells just behind the tip to elongate – this is where the cell walls become stretchy and elongate so the cell gets longer as water enters by ________.
Plants respond to directional stimuli using specific growth factors- these are hormone like chemicals that speed up or slow down plant growth. Plant growth factors are produced in the growing regions of the plant eg shoot and root tips and they move away from the tip by facilitated diffusion (away from the tip), active transport (to a particular side of a shoot in response to the direction of light)or by mass flow in the phloem (over longer distances). Growth factors called Auxins are produced in the tips of shoots and diffuse backward to stimulate the cells just behind the tip to elongate – this is where the cell walls become stretchy and elongate so the cell gets longer as water enters by osmosis.
IAA molecules & the Sun
Indoleacetic acid (IAA) is an important auxin that is produced in _______ and ____of flowering plants and is involved in controlling tropic responses.
Indoleacetic acid (IAA) is an important auxin that is produced in shoots and tips of flowering plants and is involved in controlling tropic responses.
Phototropism in shoots and roots
1. Cells at the tip produce IAA which diffuses _____ away from the tip.
- Light from one direction (unilateral light) causes IAA to be _______ transported to the dark/shaded side of the shoot – behind the tip
- High concentrations of IAA in shoots stimulates cell elongation – more IAA ___________on the shaded side, so there is more cell elongation on the shaded side than on the light side
- The shoot grows faster on the ______ side causing the shoot to bend/grow towards the light.
- High concentrations of IAA inhibit cell elongation in roots – the shaded side of the root grows ______than the light side and the root grows ____from the uni-directional light.
Phototropism in shoots and roots
1. Cells at the tip produce IAA which diffuses evenly away from the tip.
- Light from one direction (unilateral light) causes IAA to be actively transported to the dark/shaded side of the shoot – behind the tip
- High concentrations of IAA in shoots stimulates cell elongation – more IAA accumulates on the shaded side, so there is more cell elongation on the shaded side than on the light side
- The shoot grows faster on the shaded side causing the shoot to bend/grow towards the light.
- High concentrations of IAA inhibit cell elongation in roots – the shaded side of the root grows slower than the light side and the root grows away from the uni-directional light.
Changing auxin concentrations
Why has a logarithmic scale been used for the x axis?
What does 0% stimulation mean?
At what concentration of auxin does cell elongation begin to occur in (a) a root and (b) a shoot
At what concentration of auxin inhibits cell elongation in shoots?
What conclusions can be drawn from the graph about (a) root growth and (b) shoots growth?
Why has a logarithmic scale been used for the x axis?
To allow a wide range of concentrations to be plotted on the same graph
What does 0% stimulation mean?
The root or shoot will grow at it’s normal rate
At what concentration of auxin does cell elongation begin to occur in (a) a root and (b) a shoot
(a) above 10-3 ppm (b) above 10-2ppm
At what concentration of auxin inhibits cell elongation in shoots?
Above 100ppm
What conclusions can be drawn from the graph about (a) root growth and (b) shoots growth?
(a) very low concs of auxin stimulate root growth with higher concentrations inhibiting root growth
(b) high conc of auxin stimulate shoot growth with very high concentrations inhibiting it
What does this investigation tell you about how plants respond to the stimulus of light from one side?
1 The first investigation suggests that it is the tip of the plant that is _______ to light. In the ________of light, the shoot keeps growing, but does not grow ________the light.
1 The first investigation suggests that it is the tip of the plant that is sensitive to light. In the absence of light, the shoot keeps growing, but does not grow towards the light.
2 What does this tell you about how the tip of a plant shoot controls growth?
2 This tells us that the ___is important in keeping a plant growing. Cutting off the tip stops ______. But replacing it starts _______ happening again. If there was an electrical connection (like a nerve impulse) between the tip and the rest of the shoot, cutting it off and replacing it would probably break the connection. So, the message from the tip is likely to be a _________message (like a hormone) not an electrical message.
2 This tells us that the tip is important in keeping a plant growing. Cutting off the tip stops growth. But replacing it starts growth happening again. If there was an electrical connection (like a nerve impulse) between the tip and the rest of the shoot, cutting it off and replacing it would probably break the connection. So, the message from the tip is likely to be a chemical message (like a hormone) not an electrical message.
How would you explain this result?
5 This tells us that something from the ______ tip can make a shoot grow unevenly if it is put on one side of the shoot only. So, if a chemical messenger is at a ______concentration on one side of the shoot than the other, the shoot will grow more on one side and bend. It could bend towards a stimulus (such as _____). Perhaps, somehow, light changes the __________of the chemical messenger and this is how the shoot responds to the stimulus
5 This tells us that something from the shoot tip can make a shoot grow unevenly if it is put on one side of the shoot only. So, if a chemical messenger is at a higher concentration on one side of the shoot than the other, the shoot will grow more on one side and bend. It could bend towards a stimulus (such as light). Perhaps, somehow, light changes the concentration of the chemical messenger and this is how the shoot responds to the stimulus
