Mission 4: Stayin' Alive (Part 2)

Mission 4 – page 1

Name: ______Teacher: ______

Commander Spud Goodroot is very excited about the information you will learn on Mission 4. We will continue our investigation into the 7 things that plants need to live. We have talked about water, nutrients, and air. Now we will talk about the remaining four things that plants need to grow.

Sections:

Light Me and My Shadow Why Plants are Green Heat Time Room to Grow

As we learned in Mission 1, energy travels to Earth from the Sun in the form of light and heat. We learned in Mission 2 that plants use sunlight to make the food it needs through the process of photosynthesis. So, plants need light in order to live.

What happens when light from the Sun hits an object? Some objects are transparent, like glass, and the light travels through them easily. Some objects, like paper, are translucent. This means that light does travel through but the path of the light is distorted. And, some objects are opaque. Light does not travel through these objects.

In the pictures below, Polly is holding up three different objects. One is transparent, one is translucent, and one is opaque. But which one is which? Look on the next page for answers.

Mission 4 – page 2

Polly is holding up a translucent object. Some light travels through the object, and you can still see Polly, but her appearance is slightly changed.

Polly is holding up an opaque object. No light is transmitted at all. Polly cannot be seen behind the object.

Polly is holding up a transparent object, like a pane of glass. Light travels through the glass easily and doesn't change Polly's appearance. Mission 4 – page 3

Me and My Shadow

A shadow is an area where light cannot directly shine because an opaque object lies between the area and the Sun or source of light. A shadow is also the image cast by an object that is blocking rays of light.

Sometimes we can see very special, unique events in the sky when the Sun, Moon and Earth line up in a certain way. An eclipse is a shadow cast by one large object on another. A solar eclipse occurs when the Moon passes directly in front of the Sun and casts its shadow on the Earth in the middle of the day. In a lunar eclipse, the Moon passes through the Earth's shadow. During a full moon, when a lunar eclipse occurs, you can see the Earth's shadow move over the moon. Mission 4 – page 4

Why Plants are Green

Light can be refracted, absorbed, or reflected by an object. Refraction happens when a light ray traveling through air hits a different material. When the light ray hits the new material, its speed and direction will change. This can cause some things to look strange. For example, this happens if we look at a pencil through a glass of water.

The color that we see when we look at an object is the color of light that the object reflects. Objects that are white reflect all of the colors of the spectrum and absorbing none. Objects that are black absorb all colors of the spectrum and reflect none. So what does that mean about all of the other colors we see? For example, when we look at Polly in a dark room with a flashlight, she appears to be red in color. Polly and other strawberries reflect red light and absorb the other colors of the spectrum. Mission 4 – page 5

If we put a blue light bulb in our flashlight and shine that blue light on Polly in a dark room, what color do you think she will be?

Polly will appear black. When you shine only blue light on Polly, there is no red light for her to reflect. So she appears to have "lost" her color. You can try this at home with apples and bananas using colored cellophane paper and a flashlight.

So now we know why plants appear to be green. They reflect green light and absorb the other colors of light. When we try to grow plants in space, this information can be useful for scientists. Spacecraft are not hooked up to power stations and they cannot pull up to a gas station either. Spacecraft like the space shuttle have a limited amount of energy. If we need to run lights to grow plants on these spacecraft, that takes energy. But we may be able to reduce that amount of energy by only providing the plants one or two colors of light instead of all colors. Mission 4 – page 6

Did you know that plants can also move? They usually do so by growing in a certain direction, towards light, water, gravity or even away from other plants. These movements and responses are called tropisms. Phototropism is when plants grow towards the light. Remember in Mission 2 when we learned about plants responding to gravity, or gravitropism?

Heat is another form of energy that comes from the Sun and is needed by plants to live. But, be careful…too much heat will kill plants! Plants generally like the same temperatures as humans. Temperature is a measurement of the amount of heat in or around an object. There are several temperature scales that measure heat in degrees. In North America, we typically use the Farenheit temperature scale when we talk about our local weather. Scientists in all countries use the Celsius temperature scale.

We have learned that light energy moves - its waves travel and can be reflected and bounce off of objects. Heat energy moves as well, and it moves in three different ways. Conduction is when heat is transferred from an area of high temperature to an area of cooler temperature by the movement of energy between the particles that make up those materials. When you put your hand against a cold window on a winter's day, the window sucks the heat from your hand by conduction. Another example is when a metal pot is on a hot stovetop. At first, only the bottom of the pot directly touching the stovetop is very hot. Then, the heat energy moves through the metal particles that make up the pot. Eventually the entire pot, and sometimes even the handle, becomes hot. This is conduction of heat through a material. Mission 4 – page 7

Convection occurs when a fluid, such as air or water, comes in contact with an object that is at a higher temperature. Have you ever looked at a hot cup of cocoa where the liquid meets the air? You begin to see circulation or swirled patterns appear. This circular pattern happens when the air near the surface of the cocoa gets warmed by the coffee and it rises. The surrounding cooler air falls to take its place and begins a circular motion. This convection pattern will continue until the two substances reach the same temperature.

Many weather patterns occur because of convection. Sea breezes are a good example. During the day, the land warms up faster than the sea. The air above the ground is hot, the air above the water is cold. The hot air above the land rises, and the cold air above the sea swoops in to take its place. This causes a wind to blow from the ocean toward the land, a sea breeze. At night, the situation reverses. The land cools down faster than the sea, so the air above the ground is colder than the air above the water. The hot air above the water rises, the cold air from the land rushes in, and you have a land breeze.

The third way that heat energy moves is through radiation, energy carried from the Sun to us by electromagnetic waves. To scientists, radiation means any kind of light ray, whether visible or invisible (like ultraviolet or infrared light). Hot things glow and give off light which carries the heat away, and that is just how the Sun heats the Earth. Radiation can be harmful in high amounts, and solar radiation is largely absorbed by the stratosphere, a layer of the Earth's atmosphere. The ozone layer is located in the stratosphere.

One neat thing about light and heat energy is that they can be changed into one another. Light from the sun can also warm our bodies when we are standing outside in the sunlight. And, heat from a fireplace also provides light in the flames. Mission 4 – page 8

There are two more things that plants need to live and grow which may seem pretty obvious to us. One of those things is time. Plants live, grow, flower, and die in different time frames. Annuals are plants that complete their life cycles in one growing season. Biennials need two growing seasons to complete their life cycles. A perennial is a plant that lives for three of more years. It may grow new stems if it is herbaceous, or it may just live for many years (trees.)

Room to Grow

And last but not least, plants must also have room to grow both above and below ground so they can carry out the process of making food for themselves. If plants do not have enough room to grow, they begin to compete with each other for resources like nutrients and water. The stronger plants will take the nutrients and the other plants will wither and die. Unscramble the words below to find four things plants need that we learned about in this mission. Make sure to write these four things in the table in your Agronaut Log (Entry 17.)

1) thilg ______

2) meerptrauet ______

3) meit ______

4) moro ot wgro ______Mission 4 – page 9

Light and Heat Report

Look back at the information you have learned in Mission 4 and write a report on the following page to Commander Spud Goodroot answering the following questions:

1. What are the four things you learned in this Mission that plants need in order to live?

2. Which one of these things do you think will be most challenging to address when we try to grow plants on the Moon? Why?

3. Which one of these things do you think will be easiest to address when we try to grow plants on the Moon? Why?

Congratulations! You have completed Mission 4! Mission 4 – page 10

Mission 4 Glossary absorb to take in something annual a plant that finishes its life cycle in one growing season and dies in the winter biennial a plant that takes two years to complete its life cycle (dies after 2 years) circulation movement in a circle or in a circuit conduction the act of energy from heated particles moving from an area of high temperature to an area of cooler temperature. This happens by the transfer of energy between the particles that make up those materials convection the act of a fluid, such as air or water, coming in contact with an object that is at a higher temperature. This contact causes convection currents to form as fluid of higher temperature moves to areas of cooler temperature. eclipse a shadow cast by one very large object on another electromagnetic relating to magnetism which is developed by the passage of an electric current gravitropism the response of plants to gravity; roots move towards the pull of gravity and shoots move away from the pull of gravity image an object as seen in a mirror or lens (When looking in a mirror, we see an image of ourselves) infrared invisible wavelengths of the spectrum, just longer than the color of red lunar eclipse occurs when the Moon passes through the Earth's shadow. The Moon then appears to be red in color. opaque does not let light pass through it ozone layer a part of the Earth's atmosphere, almost 20 miles up in the sky, that contains ozone. Ozone blocks harmful radiation from the Sun so that it will not reach the Earth. Mission 4 – page 11

perennial a plant that lives for many years and comes back after resting each winter, such as grass and trees phototropism the response and movement of plants towards light radiation energy radiated or transmitted as rays, waves, in the form of particles reflect to throw or bend back light from a surface refract when a light ray traveling through air hits a different material. When the light ray hits the new material, its speed and direction will change. This can cause some things to look strange. For example, this happens if we look at a pencil through a glass of water. shadow an area where light cannot directly shine because an opaque object lies between the area and the source of light. A shadow is also the image cast by an object that is blocking rays of light. solar eclipse occurs when the Moon passes in front of the Sun during the day and casts its shadow onto the Earth stratosphere region of the atmosphere above the troposphere. The stratosphere is the region which contains the ozone layer. translucent able to transfer some light, but the light is distorted (paper is an example) transparent easily seen through; light can go through these objects with little distortion tropism the movement and response of plants as a result of light, gravity, water, or other causes ultraviolet invisible wavelengths of the spectrum, just beyond the color of violet