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January 26, 2024
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Exploring Photosynthesis with Microgreens

Exploring Photosynthesis with MicrogreensPea microgreen drawingcorn microgreens

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All living things need food to live. Plants are living things so they need food. Where does the food that plants need to grow come from? Learn about the process plants use to make food for themselves, and how that process affects you. Explore hands-on photosynthesis activities with pea and corn microgreens. This lesson is adaptable to additional grade levels.

Lesson Title: Exploring Photosynthesis with Microgreens

Grade Level: 4th -7th Grade

Objective: By the end of this lesson, students will be able to

  • Define photosynthesis and its importance to plants and life on Earth
  • Describe the basic requirements for photosynthesis
  • Understand how microgreens can be used to study photosynthesis.

Words to know:

Chloroplast: a part of a cell found in plants that converts light into sugar. 

Chlorophyll: the pigment that allows a plant to absorb sunlight and makes a plant green. (https://en.wikipedia.org/wiki/Chlorophyll  for more information)

Thylakoid: the flattened disk-shaped compartments filled with chlorophyll inside the chloroplast. They are composed of protein and lipids and are where the photochemical reactions of photosynthesis happen.

Photo– light  Synthesis– put together.    Photosynthesis means to put together with light.

Hypothesis – A hypothesis is an idea that is proposed so that it can be tested to see if it might be true. In the scientific method, the hypothesis is an educated guess based on the knowledge you already have. You ask a question and form a hypothesis. Then you research to see if your hypothesis is correct.

Thinking

Question– how do you think a plant eats?

Ask this question and allow students to answer, using their current understanding, to judge their level of knowledge about the subject. Have them write their answer down in their science journal. It is important to assure the student that there is no right or wrong answer- they are making a hypothesis, which is a guess that is made based on information you already have. The purpose of this lesson is to gain new knowledge. Not knowing the answer is an opportunity to learn.

How does a plant make its food?

Plants make their food using nature’s food factories: the leaves. They take water from the ground through their roots. They take a gas called carbon dioxide from the air. Using sunlight and the chlorophyll in the chloroplasts,  they turn the water and carbon dioxide into glucose (food) and oxygen.  

Plants take in sunlight through their leaves and other green parts. There are little green structures inside the cells of a plant called chloroplasts. Chloroplasts are tiny factories inside the cells that take energy from the sun and use that energy to make food for the plant.

  • drawing of Chloroplasts containing stacks of thylakoidsChloroplasts contain stacks of thylakoids
  • Thylakoids contain chlorophyll.
  • Chlorophyll is what makes plants green, and is what absorbs the energy from the sunlight and where the energy is used for photosynthesis.  
  • Carbon dioxide is absorbed from the air.
  • Text Box: Why is photosynthesis important? Review what is produced during photosynthesis. Can the students make the connection between oxygen production by plants and our need for oxygen? Encourage discussion.Oxygen is released into the air as the plant makes its own food.

People and animals need oxygen to live.  We breathe in oxygen, and we breathe out carbon dioxide.  

Where does the oxygen come from, and where does the carbon dioxide that we breathe out go?

photosynthesis drawingCarbon dioxide is exhaled by most animals as a waste product- each animal and human exhales carbon dioxide. Human activities also lead to carbon dioxide emissions. *

Plants need carbon dioxide to make their own food. The carbon dioxide is absorbed into the leaves through tiny pores called stomata at the same time as water is absorbed through the roots. Inside the plant cells, in the chloroplasts, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This chemical reaction turns the water into oxygen and the carbon dioxide into glucose, or sugar.

But how does the water and carbon dioxide change?

Enter the sun! The chloroplasts inside plant cells are tiny factories that use light as energy to combine water and carbon dioxide into glucose. Glucose is used by the plants to grow. During the process of photosynthesis, the extra oxygen molecules from H20 and C02 are sent back out through the stomata as waste.

  • The ‘waste’ of our breathing is carbon dioxide, which plants need to grow
  • The ‘waste’ of photosynthesis is oxygen, which humans and other animals need to grow and live.

So, what does that mean for us?

The oxygen in our air, that we need to live, is made by plants- a good reason to grow more plants! (Note: up to 70% of our oxygen comes from marine plants).

The glucose that the plants make through photosynthesis is the food that helps the plant grow and develop seeds and fruit.

The sugar that plants produce is important to humans too.  Because we cannot make our own energy from sunlight and water, we rely on eating plants that make energy or on eating animals that eat plants.  

cartoon drawing of sunflower microgreen proud of making glucoseA cartoon child eating a sunflower microgreen Photosynthesis in plants is responsible for feeding nearly all life on Earth. Because green plants are the only living organisms capable of producing their own food, all other living organisms (including humans) depend on them either directly or indirectly for survival.

The chemical equation for photosynthesis is:

CO2  +  6 H2O  + Light Energy   —>   C6H12O6 +  6 O2

Carbon dioxide + water  + energy from light—–turns into—-     glucose              + oxygen

Let’s Explore!

Q- Can plants grow without light?

Q- How does light change the way that plants grow?

Before beginning these experiments, come up with 2 hypotheses based on what you know and basic research.


Experiment #1:  Light Effects on Pea Seeds Germination and Growth

You will need:

  • 6 paper drink cups, approx. 8 oz
  • Sharpened pencil, or other safe, sharp tool
  • 12 speckled pea seeds
  • Planting soil- enough for the 6 cups
  • Measuring spoons for watering

Directions:

  • Poke 3 small holes in the bottom of 6 paper drink cups.
  • Fill the cups using the same soil at the same depth for each cup.
  • Soak the pea seeds for 6 hours before planting
  • Plant two Microgreen Speckled Pea seeds in each cup at the same depth, ½ inch.
  • Water using exactly the same amount of water for each cup.
  • Put 3 cups in a dark place and 3 cups in a light area out of direct sunlight.
  • Give each cup exactly the same amount of water every other day until the end of the experiment.

Observations

After 5 days, note the germination rate of each set of cups. Do you think that light made a difference in the germination of pea seeds?

Continue watching the seed growth with the 3 cups remaining in a dark area without light, and the other 3 in a bright area. Be sure the plants are not directly in the sun to avoid drying out the soil.

Each day, measure the growth of each plant and make notes on your observations.

After 12 days, what have you noticed?

1. is there a difference in the color of the plants?

2. Is there a difference in the length or thickness of the stems?

3. Review your hypotheses. What have you learned?

4. Research: are there seeds that do not germinate in the absence of light?

More information:

Plants grown with less light might grow taller than plants grown with more light due to a phenomenon called etiolation. Etiolation is a process where a plant elongates its stem to increase the chance of reaching more light. Etiolation happens when a plant receives insufficient light for photosynthesis. The plant allocates more of its resources towards stem growth instead of growing more leaves as a survival mechanism to reach light before the nutrients from the seed and soil are used up.

It’s important to note that while plants grown with less light may appear taller, they may also have weaker and thinner stems compared to plants grown with optimal light conditions. This may make the plant less healthy.


Experiment # 2   The Importance of Light in Photosynthesis

This experiment helps students understand what happens to leaves when they do not receive enough light.

You will need:

  1. Dark-colored paper, or foil
  2. Paper clips
  3. Scissors
  4. A small outside plant or an indoor plant that can be placed in a sunny location

Directions:

-Choose a small, healthy plant for this experiment.

– Write down a hypothesis of what you think will happen during this experiment. Take a photo, if possible, of the leaves that you will cover.

-Cut a piece of paper or foil into small pieces to cover 5 of the plants leaves. Note that the leaves covered should be ‘expendable’.

– Secure the pieces of paper or foil to several leaves.

– Be sure the plant is in a sunny or very bright spot.

– Each day uncover one of the leaves and examine the leaf. Make notes or take a photo of each one as you uncover it.

Are the leaves changing? What do you think is happening

More Information:

The covering blocked all of the light from the leaf. Without light, the leaf can not participate in photosynthesis and begins to die. Removing the covering allows the leaf to restart its photosynthesis ‘factory’. If left too long, however, the leaf begins to yellow and then dies so that the plant can put its energy into healthier leaves.


Experiment #3   Corn Microgreens and photosynthesis

Materials:

  1. 1 cup popcorn seeds, divided
  2. 4 Coco soil discs, rehydrated
  3. Jar or bowl to soak seeds
  4. 4 grow trays with water trays
  5. 4 cover trays
  6. Sticky notes or masking tape to label trays
  7. Age-specific Science journal page (download and print from educational resource page)
  8. Ruler to measure growth

Directions:

Step 1.

Soak only ½ cup of the popcorn seeds in a bowl or jar of cool water. The other ½ cup of seeds will not be soaked before use. The soaking seeds should be completely covered, with two inches of water above the seeds. Soak the seeds for at least 4 hours, or overnight. Drain the seeds after soaking, and rinse for 30 seconds with cool, running water.

Step 2.

Place each grow tray on top of a water tray. Dump one rehydrated cocoa soil disc in each grow tray.

Step 3.

Place ½ of the soaked seeds in each of two trays. Put ½ of the unsoaked seeds in each of the last two trays. Label each tray “soaked” or “Not Soaked”

LESSON INCOMPLETE- to be completed in Feb/2024


Next Generation Science:

NGSS 5-LS1-1. support an argument that plants get the materials they need for growth chiefly from air and water (grow seeds hydroponically in a baggie to show that it is not the soil that promotes growth)

NGSS 5-PS1-4: ‘Conduct an investigation to determine whether the mixing of two or more substances results in new substances.’ photosynthesis is a chemical change.

NGSS 5-PS3-1, describe how energy for animals’ food originally came from the Sun.” Knowledge of photosynthesis helps students understand food chains.”

NGSS LS1.C: Organization for Matter and Energy Flow in Organisms The process of photosynthesis converts light energy to stored chemical energy by converting carbon dioxide plus water into sugars plus released oxygen.

Follow Up:

  • Potential energy- the chemical energy stored in plants.
  • Explore producers, consumers, and decomposers. Explain how the energy flows from the Sun to plants to animals, and entire ecosystems.
  • Learn more about plant structures. Do all functions of a plant directly support photosynthesis?
  • *Besides breathing, human activities also lead to carbon dioxide emissions. Research how carbon dioxide is produced around the world, and consider the connection between plants and forests, and carbon dioxide.

Additional resources: https://scied.ucar.edu/image/where-does-carbon-dioxide-go#:~:text=Some%20of%20the%20additional%20carbon,is%20making%20seawater%20more%20acidic. (visual for where C02 goes)

Understanding how plants use sunlight- https://energy.mit.edu/news/understanding-how-plants-use-sunlight/#:~:text=Plants%20rely%20on%20the%20energy,excess%20can%20damage%20critical%20proteins  (older students- 14+)

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