EP 07 Do plants need light?
In this lesson, we are going to find out the most suitable light intensity range for plant growth, and get to know the relationship between plant growth and light.
NGSS - NEXT GENERATION SCIENCE STANDARDS - MIDDLE SCHOOL (MS)
From Molecules to Organisms: Structures and Processes MS-LS1-4, MS-LS1-5
Ecosystems: Interactions, Energy and Dynamics MS-LS2-1, MS-LS2-4, MS-LS2-5 MS-ESS3
Earth and Human Activity MS-ESS3-3
Engineering Design MS-ETS1-1, MS-ETS1-3
If someday, human activities make the extreme weather more frequent, and in a place, the
sunshine hasn't been seen for a very long time. Guess, which kind of plant in the following
will suffer more? Which of them will live longer?
●Explore this question by taking a poll of students in your class.
●Copy the chart below into your notebook.
●When completed, discuss the poll results with students sitting near you.
●Why do you choose these plants?
●List a few reasons from your discussion which support the results of the poll.
In this activity, your group will use a light sensor to detect intensity of light, and set up controlled experiments to explore the effect of light intensity on plant growth.
Activity Procedure Setup:
1.Connect the Battery Pack to the MainBoard-110. Ensure the MainBoard-110 is turned OFF.
2.Use a short BOSON Cable to connect the Display Module with the MainBoard-110.
3.Use a long BOSON Cable to connect the Light Sensor with the MainBoard-110.
4.Set the BOSON equipment aside.
5.Use a permanent marker to label the three plastic cups as A, B, and C.
1.Fill each plastic cup 1/2 full with potting soil. Pat the soil down gently.
2.Divide the pothos into three parts and plant them in three pots.
3.Put the three parts of pothos at different positions of a room.
Tips: light intensity value from the light sensor Low(0-50) intermediate(450-600) high(900-1000)
4.Water plants with the same amount of water at regular intervals.
5.Read the value of the light sensor.
6.Observe the leaf quantity, color, and growth situation.
7.Repeat steps 4 to 6 in two weeks and record what you observed.
Copy the Data Table below into your notebook.
Making Sense of the Data:
Summarize the collected data in the line chart below.
1.Plot date on the X-axis
2.Plot the numbers of green leaf, yellow leaf on the Y-axis respectively
3.Use three colors to represent plants in pot A, B and C
Observe and think:
1.Will plants grow differently under different light intensities?
2.What’s the most suitable light intensity range for plant growth?
Light is something we all take for granted unless you live in the arctic circle or something! But if you get into gardening, or more specifically, indoor hydroponics, you start to appreciate how valuable sunlight truly is.
You cannot grow anything in the darkness. Mushrooms and fungi are an exception of course, but for any plants with green chlorophyll coursing through their leaves, light is mandatory.
Why Plants Need Light?
Let's refresh that memory with a few basic concepts. Asking why plants need light is like asking why we need fire or heat to cook our food.
Plants are autotrophs, which means that they are capable of creating nutrition (read carbs, proteins, and fats) in their bodies. To create these foods they absorb the following ingredients from the environment:
●Nutrients and Minerals from the soil via routes
●Water, again through the roots
●Carbon Dioxide, through the pores in the leaf.
To combine these ingredients and cook up some food, plants need energy. This they derive from the sunlight, using the green chemical called chlorophyll in their leaves.
The recipe reads something like this:
Carbon Dioxide and water, in the presence of Chlorophyll & Sunlight, combine to produce Glucose and Oxygen molecules. The glucose is used by the plants for growth and bearing fruit, while the oxygen is released into the atmosphere as a by-product.
This is a simple definition of the process of photosynthesis that happens in a plant leaf in the presence of chlorophyll and sunlight. You may have noted the absence of any minerals in the equation.
But minerals like magnesium and phosphorus are essential for photosynthesis. Without magnesium, plants cannot create chlorophyll in the leaves. And phosphorus is essential for creating proteins.
How Does Light Affect Plant Growth?
Direction of Growth
The survival of a plant is entirely dependant on the source of light. In the case of all outdoor plants, the sun is the only source of light.
When the first leaves appear on the plant, it will try to grow towards the light source, to ensure that maximum light is received by the leaves for photosynthesis.
Some plants take this to its extreme and follow the sun as it traverses the sky in the day. The sunflower is the most famous example of these plants, called heliotropic by botanists.
The rest of the plants are called phototropic, which means that they respond to light. The stems of these plants try to grow towards the direction of the source of the light.
Consider a garden plant which is partially in the shade. When light shines on a part, it stimulates the secretion of growth hormones called auxins in that area of the stem.
These auxins cause that part of the stem cells to elongate, forcing the stem to grow towards the sunlight. These are changes that occur continuously through the life cycle of a plant.
If there is one disadvantage to sunlight, it is the fact that it is not constant all through the year. The duration and intensity of sunlight received fluctuate with the changing seasons.
So plants have adapted to these changing seasons as well. In the summer and spring, with light being plentiful, most plants focus on growth, blooming of flowers, and bearing of fruit.
When the light intensity and duration reduces as winters approach, the plants put more emphasis on conserving energy and reducing growth.
Photosynthesis is reduced in the fall, and leaves start losing chlorophyll. This is why leaves tend to turn brown, yellow, or red in autumn.
Consider the following questions:
1.After reading the above material, please explain why plants grow differently in different light level.
2.Do plants grow better with higher light intensities?