Grade 10 Biology: Lesson 9
Lesson 9: Plant control systems
Lesson 9: plant control systems
Plant Control Systems
Animals have the ability to sense and then respond to their environment by thinking and acting
Plants cannot think, however, they do Respond to their environment as well
These responses to the environment are called Tropisms in plants
Phototropism
The growth of a plant toward a light source
Phototropism allows the plant to maximize the amount of light that is absorbed by the leaves which in turn maximizes the amount of Photosynthesis within the leaves
Since the plant can not move, Phototropism is accomplished in an interesting way In order to bend towards the light a plant will have the cells of its stem grow at different rates
Cells on the side of the stem that is further from the light will grow longer than the cells on the side of the stem that are closer to the light
The Darwin's' Experiment
In 1880 Charles Darwin and his son Francis performed experiment to prove that plants will grow toward a light source
In their experiment they not only proved that plants respond to a light source, they also proved that it was the tip of the plant that would sense, respond and then send
The Boysen-Jensen Experiment
Decades after the Darwin's' Experiment a Danish scientist named Peter Boysen-Jensen continued on with Darwin's idea
He was interested in the actual signal that was sent from the tip of the plant in response to light
He cut the tip of a plant off and replaced it with both Gelatin and Mica
The Gelatin-tipped plant grew toward the light as the signals were able to diffuse through it
However, the signal could not diffuse through the Mica and the plant grew straight up and did not respond to the light proving that the signals are sent from the tip of the plant to the rest of it
Auxins: Plant Growth Chemicals
Fritz Went's Avena Experiment:
In 1926 a Dutch Scientist named Fritz Went confirmed the hypothesis that a growth chemical signal is produced in the plant tips and are sent to the rest of the plant
He extracted the chemical by removing the tips from young stems and then placing the tips in Agar (a growth material)
The chemical signal diffused into the Agar
He then took the chemical filled Agar and put them onto the cut tips of small Oat seedlings
Fritz Went's Results:
Went found that the plants grew in different ways! Plant tip Completely covered by chemical soaked Agar = Plant Grew Straight Up
Plant tip Partially covered by chemical soaked Agar - Plant Grew Away from the Side with the Chemical Soaked Agar
Plant tip Completely covered by Non-chemical soaked Agar - Plant Did Not Grow At All
Went concluded that the chemical produced in the plant tips stimulated Growth
This chemical was called Auxin (Greek for "To Grow")
Action of Auxins:
Auxins are produced in the tip of the plant as it responds to a light source
After Auxin is produced in the tip of the plant it travels to the shaded side of the stem
Active transport moves the Auxin into the cells of the shaded side of the plant
The Auxin then causes the cells on the shaded side of the plant to grow longer than those cells on the lighted side causing the plant to bend toward the light
Gravitropism
Gravitropism is a plant growth response to Gravity (an environmental stimulus)
Positive Gravitropism:
Positive Gravitropism occurs in the Roots of plants which the roots will grow downwards with gravity
Negative Gravitropism:
Negative Gravitropism occurs in the Stems of plants in which the stem will grow upwards against gravity
Gravitropism and Auxin
Gravitropism also relies on the ability of the plant signal Auxin to elongate the cells on one side of the stem or the roots
This is accomplished in opposite ways in the Stem vs. The Roots
Gravitropism in the Stem:
A plant will respond to gravity by releasing Auxin from its tip (ex. If a plant was on its side)
The Auxin will be sent to the lower side of the stem stimulating the cells on that side of the stem to elongate
The stem will bend to grow upwards against gravity
Gravitropism in the Roots:
A root will respond to Auxin in the opposite way
The Auxin will be sent to the lower side of the roots inhibiting the cells on that side of the root from elongating
The roots will bend to grow downwards with gravity
Nastic Response
Some plants have the ability to respond to Touch Ex. Venus's-Flytrap and the Mimosa Plant
Cells and Complex Responses in Plants
Imagine how difficult it must have been for ancient scientists to solve the questions about life works without some of the modern technologies we take for granted today
The invention of the microscope and the discovery of the cell has allowed modern scientists to explain and even predict observable events such as the closing of a Venus's-flytrap!
These responses. Performed by many co-ordinated cells, combine to create a fantastic whole: a living, respiring, moving, multicellular organism/
Grade 10 Biology: Lesson 9
Lesson 9: Plant control systems
Lesson 9: plant control systems
Plant Control Systems
Animals have the ability to sense and then respond to their environment by thinking and acting
Plants cannot think, however, they do Respond to their environment as well
These responses to the environment are called Tropisms in plants
Phototropism
The growth of a plant toward a light source
Phototropism allows the plant to maximize the amount of light that is absorbed by the leaves which in turn maximizes the amount of Photosynthesis within the leaves
Since the plant can not move, Phototropism is accomplished in an interesting way In order to bend towards the light a plant will have the cells of its stem grow at different rates
Cells on the side of the stem that is further from the light will grow longer than the cells on the side of the stem that are closer to the light
The Darwin's' Experiment
In 1880 Charles Darwin and his son Francis performed experiment to prove that plants will grow toward a light source
In their experiment they not only proved that plants respond to a light source, they also proved that it was the tip of the plant that would sense, respond and then send
The Boysen-Jensen Experiment
Decades after the Darwin's' Experiment a Danish scientist named Peter Boysen-Jensen continued on with Darwin's idea
He was interested in the actual signal that was sent from the tip of the plant in response to light
He cut the tip of a plant off and replaced it with both Gelatin and Mica
The Gelatin-tipped plant grew toward the light as the signals were able to diffuse through it
However, the signal could not diffuse through the Mica and the plant grew straight up and did not respond to the light proving that the signals are sent from the tip of the plant to the rest of it
Auxins: Plant Growth Chemicals
Fritz Went's Avena Experiment:
In 1926 a Dutch Scientist named Fritz Went confirmed the hypothesis that a growth chemical signal is produced in the plant tips and are sent to the rest of the plant
He extracted the chemical by removing the tips from young stems and then placing the tips in Agar (a growth material)
The chemical signal diffused into the Agar
He then took the chemical filled Agar and put them onto the cut tips of small Oat seedlings
Fritz Went's Results:
Went found that the plants grew in different ways! Plant tip Completely covered by chemical soaked Agar = Plant Grew Straight Up
Plant tip Partially covered by chemical soaked Agar - Plant Grew Away from the Side with the Chemical Soaked Agar
Plant tip Completely covered by Non-chemical soaked Agar - Plant Did Not Grow At All
Went concluded that the chemical produced in the plant tips stimulated Growth
This chemical was called Auxin (Greek for "To Grow")
Action of Auxins:
Auxins are produced in the tip of the plant as it responds to a light source
After Auxin is produced in the tip of the plant it travels to the shaded side of the stem
Active transport moves the Auxin into the cells of the shaded side of the plant
The Auxin then causes the cells on the shaded side of the plant to grow longer than those cells on the lighted side causing the plant to bend toward the light
Gravitropism
Gravitropism is a plant growth response to Gravity (an environmental stimulus)
Positive Gravitropism:
Positive Gravitropism occurs in the Roots of plants which the roots will grow downwards with gravity
Negative Gravitropism:
Negative Gravitropism occurs in the Stems of plants in which the stem will grow upwards against gravity
Gravitropism and Auxin
Gravitropism also relies on the ability of the plant signal Auxin to elongate the cells on one side of the stem or the roots
This is accomplished in opposite ways in the Stem vs. The Roots
Gravitropism in the Stem:
A plant will respond to gravity by releasing Auxin from its tip (ex. If a plant was on its side)
The Auxin will be sent to the lower side of the stem stimulating the cells on that side of the stem to elongate
The stem will bend to grow upwards against gravity
Gravitropism in the Roots:
A root will respond to Auxin in the opposite way
The Auxin will be sent to the lower side of the roots inhibiting the cells on that side of the root from elongating
The roots will bend to grow downwards with gravity
Nastic Response
Some plants have the ability to respond to Touch Ex. Venus's-Flytrap and the Mimosa Plant
Cells and Complex Responses in Plants
Imagine how difficult it must have been for ancient scientists to solve the questions about life works without some of the modern technologies we take for granted today
The invention of the microscope and the discovery of the cell has allowed modern scientists to explain and even predict observable events such as the closing of a Venus's-flytrap!
These responses. Performed by many co-ordinated cells, combine to create a fantastic whole: a living, respiring, moving, multicellular organism/
