Plant Orientation Responses Flashcards
What are all the abiotic and biotic factors that might affect the growth of a plant?
Environmental Factors
What is the prefix for light?
Photo
What is the prefix for chemicals?
Chemo
What is the prefix for gravity?
Geo or Gravi
What is the prefix for touch?
Thigmo
What is the prefix for water?
Hydro
What is the prefix for temperature?
Thermo
What is the prefix for current?
Rheo
Define a tropism
A plant growth response towards or away from an environmental factor coming from one direction only
The name of the type of tropism in which a plant grows towards the direction of an environmental stimulus
Positive
Name this tropism - A pea plant tendrils grow around a climbing frame
Positive thigmotropism or heliotropism
Name this tropism - A seed germinates underground and grows upwards
Negative geotropism
Name this tropism - A pollen tube grows towards the ovule in response to the chemical it secretes
Positive chemotropism
The name of the hormone that controls many plant tropic responses
Auxin
What does auxin promote or inhibit in cells?
Cell elongation
Explain how auxin encourages cell elongation
It releases the tension of the cellulose in the cell wall of plant cells
Does a high concentration of auxin in root cells promote or inhibit cell elongation?
Inhibits cell elongation
Does a high concentration of auxin in shoot/stem cells promote or inhibit cell elongation?
Promotes cell elongation
What is the name of the root that emerges from a seed?
Radicle
Why do radicles bend downwards once they germinate?
Auxin accumulates on the lower side on the radicle due to the pull of gravity. A high concentration of auxin on the lower side inhibits cell elongation in root cells. A low concentration of auxin on the upper side promotes cell elongation causing the root to bend downwards.
Name three reasons why roots bend downwards linked to biological processes.
Towards a greater source of water for photosynthesis.
Towards nutrients that are used in cell division, respiration and photosynthesis
To increase the stability of the plant in the ground
What is the name of the shoot that emerges from a seed?
Plumule
Why do plumules bend upwards once they germinate?
Auxin accumulates on the lower side on the plumule due to the pull of gravity. A high concentration of auxin on the lower side promotes cell elongation in shoot cells. A low concentration of auxin on the upper side inhibits cell elongation causing the shoot to bend downwards.
Name two reasons why shoots bend upwards linked to biological processes.
To emerge quickly from the soil so they can produce flowers, get pollinated and reproduce.
To emerge and capture sunlight for a faster rate of photosynthesis.
Name the response of a plant that grows towards the sun.
Positive phototropsim
Explain the mechanism behind why positive phototropism occurs
The photoreceptor at the tip of the shoot detects the direction of the sunlight. Auxin is produced and moves across and down the ‘dark side’ of the shoot (opposite side to where light is coming from). A high concentration of auxin on the dark side promotes cell elongation in shoot cells. A low concentration of auxin on the ‘light side’ inhibits cell elongation causing the shoot to grow towards the sun.
Why do plants grow towards the sun?
To receive a higher light intensity for a faster rate of photosynthesis.
What is the mechanism behind positive thigmotropism/ heliotropism?
The touch inhibits auxin and causes it to move to the non-touch side. A low concentration of auxin on the touch side inhibits cell elongation. The opposite side of the touch has a high concentration of auxin promoting cell elongation. This causes the plant to grow around the touching object.
Why would a growing plant grow around a climbing frame?
To provide support for a plant so it can dedicate cell division to grow upwards quicker rather than outwards. This means it can outcompete other plants for light for photosynthesis.
Define a nastic response.
A plant growth response to a change in the intensity of an environmental stimulus, not its direction
Name this response - Mimosa folds its leaflets inwards when touched.
A thigmonastic response
Why would Mimosa fold its leaflets in response to touch?
To reduce the chances of its leaves being grazed
What is the mechanism that causes Mimosa leaves to fold inwards?
Turgor pressure - the leaves pump ions out of the leaf in response to touch by active transport (energy cost). This causes water to leave the vacuoles inside the cells and the leaves go limp and fold inwards.
Name this response - Leaves droop at night and rise up and open during the day.
A photonastic response/nictonasty
Why do leaves show a photonastic/nictonastic response during the day?
Lifting up and opening out during the day increases the surface area exposed to the sun so it can capture more light energy for photosynthesis.
Why do leaves show a photonastic/nictonastic response during the night? Give two reasons
Drooping leaves are less likely to be grazed.
Hanging reduces surface area exposed to the cold night and frost damage.
