Week 9 - Introduction, Moving Water, Life Cycles, Structural Adaptations, and Plant Needs

Exercise 1.2

Lesson 1.2: Plant Processes

ACTIVITY A: Moving Water - It All Starts in the Roots

Required Readings

Science in Action 7
pages 102 - 108
or
Science Focus 7
pages 107 - 111

Did You Know?

More than 90% of the water that goes into a plant is lost through transpiration!

In this lesson we will be investigating the major activities that go on inside
a plant. Some of the processes are only found in plants. For example, photosynthesis allows plants to make their own food. Other activities,
such as cellular respiration are found in all living things. In this unit, we
will start in the ground and work our way up the plant.

Humans have a pump, called the heart that pushes materials around our

body. But you can tear a plant apart and not find any pumps. So how can

the plant get water all the way to the top of the plant?

Roots have the function of getting water and nutrients from the surrounding soil into the plant. Nutrients are drawn through the cell membrane in the root cells by a process called diffusion.

The movement of water molecules across the cell membrane is called osmosis.

Diffusion is the gradual mixing of substances from an area of high concentration into an area of low concentration.

Osmosis is the diffusion of water across a differentially permeable membrane (like a cell membrane).

That means that only water can freely pass through the membrane and all other materials

can't go through.

Once water is in the plant roots, it must be transported to all the rest of the plant. That may not seem like a big deal in a dandelion, but what about a big tree. I mean a really big tree!

A Process called transpiration delivers
water from the roots to every leaf on the
tree. Under every leaf there are thousands
of tiny holes called stomata. They are there
to allow air to enter the leaf - more about
that later! Because of these holes, water is continuously evaporating from the plant.
This creates a sucking action that continues
to draw water up from the roots. And that's called transpiration!

But what holds the water molecules

together? Read page 103 'Moving Water

Up from the Roots' in the Science in Action

Text.

Exercise 1.2 - Celery Lab

Try it for Yourself: Transpiration in Action

Materials:

A piece of celery, about 15 - 20 cm long, that still has some leaves
on it.
Some food colouring. (Blue works very well.)
A drinking glass half filled with water.

Procedures: 1. Mix some food colouring in with the water. (Make it fairly dark)
2. Cut the bottom off of the celery - about 2 to 3 cm would be fine.
3. Now place the celery into the coloured water so that the leaves are
at the top.
4. Now all you have to do is wait a few hours. Hint: the longer you leave it in
the glass the more the colour will show up in the celery. The leaves will begin to
take on the colour of the food colouring.
5. If you have a magnifying glass look at the underside of the leaves.
6. Next, cut the celery stalk and look at the cross-section inside the
celery. Here you will see the part of the plant transport system that
moves water, because it is now stained by the food colouring.

Complete the assignment below:

ACTIVITY B: Making Food - The Colour Green is the Clue

Required Readings

Science in Action 7
pages 104 - 107
or
Science Focus 7
pages 110 - 111

Diffusion at Work

Earlier in the lesson, we learned that diffusion works when there is a difference in concentration.

The carbon dioxide is at a higher concentration outside of the leaf than inside it so the molecules of carbon dioxide move through the stomata and into the cells of the leaf.

Since the carbon dioxide molecules are always being used up in the food making process, the carbon dioxide gas is always diffusing into the leaves.

Oxygen is diffusing out of the leaves because its concentration is higher inside the leaf. Oxygen is actually a waste product of photosynthesis.

Leaves are the food factories of the plant. The colour green is the clue to look for. A green chemical called chlorophyll is used in the food making process. This process is called photosynthesis. Leaf size is determined by the amount of light the plant gets. For example, plants in deep forest shade tend to have large broad leaves, while those out in the sun tend to be small or thin. Examine the cross section of the leaf on page 111 in Science Focus, notice that there are air spaces between the cells of the leaf. To understand why this is necessary we must first understand the process of photosynthesis. We will use a word equation to understand the process.

The stem on a dandelion and the trunk of a tree perform the same job.

Plants in a forest setting are sometimes in competition for the sun's light. Those plants that can grow the fastest and highest will capture more of the sun's energy than those below them.

The stem, of trunk, is the portion of the plant that lifts the rest of the plant skyward.

Inside each stem or trunk there is a network of vessels that transports water and food throughout the plant.

Photosynthesis
is the name of the process that plants use to make food.

Wouldn't it be wonderful when we were hungry if we could just go outside and lay in the sun? Animals can't get their energy directly from the sun, but plants can. Plants make the food they need by a process called photosynthesis.

Have you ever wondered why plant leaves are green? Its because they have a special chemical in them called chlorophyll. Carbon dioxide, a gas, is part of our atmosphere. It enters the leaf through a stoma and travels through the air spaces to reach each cell that produces food. The water is transported up from the roots and moves through the veins in the leaf to the plant cells. When sunlight passes through the leaf the chlorophyll captures some of it and, along with the water and the carbon dioxide it is converted into food.

Scientists have developed shorthand ways of writing and what you see above is called a word equation. You should be able to write out the word equation for photosynthesis.

Transportation in Plants

So far in our learning adventure, we have found out how water, carbon dioxide and oxygen move around, but how does the plant get the food it makes to every cell in it body? Diffusion and osmosis are activities that occur naturally and normally in nature. The plant doesn't need to use up any energy in these processes. But moving food is a different story. The plant makes a food molecule called glucose. Glucose is a sugar molecule and is too big to get through the cell membrane and into the plant's cells. The plant must use a process called active transport to get the glucose into the cells, and that takes energy. Plants must use up some of its energy to move the food around to all the parts like the stem or root or flowers.

Cellular Respiration - Putting the Food to Work

So far, we have discovered that only plants can make their own food. But the next process is common to all living things - including you, me, whales, birds, grass, trees and bacteria. This common process to all living things is called cellular respiration.

By now, in our studies in grade 7 science, we know the plants can make their own food, and that even though animals can't make their own food, they can capture and kill other organisms to get the food they need. So what do all these living organisms do with this food? It is sent to every cell in their body and converted back into energy. This process is called cellular respiration. Look at the word formula for cellular respiration below. Is it different from the photosynthesis formula? Are there any similarities?

The formulas are opposites of each other! The whole wonderful world of living things cycles water, carbon dioxide and oxygen around and around between plants and animals. That is why we are constantly talking about the need for balance in the living world around us.

So, what have we learned?

1. Only green plants can make their own food through a process called photosynthesis.
2. The green part of the plant has a chemical called chlorophyll and it puts together the carbon dioxide, water and the sun's energy to make food.
3. All organisms, including plants and animals, use food for energy in a process called cellular respiration.
4. These processes take place at the cellular level.
5. The plant does not use up any energy in the processes of diffusion and osmosis.
6. Food molecules are too big to move by diffusion so the plant must use what is called active transport to move the food around its body, and this uses up some of the plants energy.