Lesson 2 – Part A (for juniors): HOW PLANTS GROW
Lesson 2 – Part A (for seniors): HOW PLANTS GROW
Lesson 2 – Part B – Experiment: WATCH HOW PLANTS GROW
Lesson 2 – Part C: WHAT WILL YOU GROW?
Lesson 2 – Part A – for juniors
After seeds have germinated, they need more than water for growth. As well as water, they need light, and minerals that they soak up from soil through their roots.
As you saw in the seed germination experiment, the tiny, yellowish seed leaves became green when they were uncovered and exposed to light.
The green colouring in leaves is called chlorophyll (claw-row-fill) and has an important function in plants. It lets plants absorb and use sunlight. Most of the cells that contain chlorophyll are found in the leaves of plants.
Even though plants do need minerals from soil to be healthy (and to make chlorophyll), plants get their energy for growth from the sun. Plants are, in fact, solar-powered, and green leaves are their solar panels.
The process that allows plants to grow, and produce seed and food we can eat, is photosynthesis, which simply means making things with light.
Chlorophyll cells in leaves are able to combine carbon dioxide (from the air) with water that is soaked up by plant roots, and use the energy from sunlight to change the carbon dioxide and water into glucose (a type of sugar), at the same time as releasing oxygen into the air. Glucose is energy in the form of a simple carbohydrate that the plant can use immediately, or store as starch to make cells for new growth. Did you know that people and animals breathe in oxygen and breathe out carbon dioxide? Plants help clean the air for us by taking carbon dioxide out of the air and replacing this with oxygen.
- Return to top of page
Lesson 2 – Part A – for seniors
After seeds have germinated, they need more than water for growth. As well as water, they need light and minerals that they absorb from soil through their roots.
As you saw in the seed germination experiment, the tiny, yellowish seed leaves became green when they were exposed to light.
The green colouring in leaves is called chlorophyll (claw-row-fill) that has an important function in plants. It allows plants to absorb and use sunlight. Most of the cells that contain chlorophyll are found in the leaves of plants. Even though plants do need minerals from soil to be healthy (and to make chlorophyll), plants get their energy for growth from the sun. Plants are, in fact, solar-powered, and green leaves are their solar panels.
The process that allows plants to grow, and produce seed and food we can eat, is photosynthesis, which simply means making things with light.
Chlorophyll cells in leaves are able to combine carbon dioxide (that plants absorb from the air) with water (that is absorbed by plant roots), and use the energy from sunlight to change the absorbed carbon dioxide and water into glucose (a sugar), and release oxygen into the air. Glucose is a simple carbohydrate that the plant can use immediately, or store as starch to manufacture cells for new growth.
Plants help clean the air for us by taking carbon dioxide out of the air and replacing with oxygen which people and animals need to breathe.
The symbol for a carbon dioxide molecule is CO2 because it contains 1 atom of carbon and 2 atoms of oxygen. The symbol for a water molecule is H2O because it has 2 atoms of hydrogen and 1 atom of oxygen.
The symbol for a glucose molecule is C6H12O6 because it has 6 atoms of carbon, 12 atoms of hydrogen and 6 atoms of oxygen. The symbol for an oxygen molecule is O2 because it has 2 atoms of oxygen.
For every 6 molecules of carbon dioxide and water used in photosynthesis, the process produces 1 molecule of glucose and 6 molecules of oxygen. You can see from the equation below that no atoms have been lost, merely converted to different molecules.
- Return to top of page
Lesson 2 – Part B – Experiment
Today's experiment will show how the tops and roots of plants grow after seeds germinate. It will show the difference in growth between sweet corn seeds and pea or bean (legume) seeds. Corn belongs to the grass family of plants that only produce one seed leaf. Legumes, like most vegetable seeds, produce two seed leaves.
Over the next few weeks, this experiment will show you the changes that take place above and below ground level as plants start to grow.
For this experiment, you will need:
-
2 pots made from PET
bottles filled with growing
mix
-
A few sweet corn seeds
-
A few legume seeds
-
2 waterproof plant labels
-
2 sheets brown paper
-
2 large elastic bands
-
A pencil
-
A tray or 2 plant saucers
Using the blunt end of the pencil, poke a hole in the mix at the outer edge of each bottle to the depth that each seed is to be sown, so that the seeds rest against the wall of the bottle. (Corn is sown 3 cm deep, and legumes 2.5 cm deep.)
Choose a good-looking corn seed, and sow it in the hole in one of the bottles. Use the point of the pencil to guide it up against the bottle wall at the bottom of the hole. Then choose a plump legume seed and sow it the same way in the other bottle.
Carefully fill the holes with growing mix, and water gently to remove air pockets around the seeds. You should still be able to see the seeds through the bottle walls.
Empty any excess water from the plant saucers or tray, and label each bottle with the name of the seed.
Fold each sheet of brown paper lengthwise and wrap each sheet of paper around a bottle so that it covers the seed and growing mix. Fix the paper in place with an elastic band.
Place the top part of each bottle inside the base to make a small greenhouse to keep the seeds warm and damp until they germinate. Now place the bottles in a well-lit place out of direct sunlight and watch what happens after 8 – 10 days.
As soon as growth appears above the growing mix surface, you can unscrew the bottle tops to allow air to reach the seedlings. You will notice that one plant has two small leaves folded together, and the other seems to have only a stem because the seed leaf is hidden in the stem. Unwrap the brown paper to see the start of root growth. Then re-wrap the bases to keep the root area dark.
When the seedlings are 5 cm high, you can remove the top section of the bottles to allow good airflow around the seedlings.
Note the differences in root growth between the two types of plants. Give the seedlings enough water to keep the growing mix damp, and remember to re-wrap the bases with the brown paper after checking on the amount of root growth.
You may notice the corn plant start to produce some roots from its stem above the growing mix surface. These roots provide extra support for large plants that grow quickly. They also allow the plants to absorb more water and nutrients if soil is hilled-up around these extra roots.
- Return to top of page
Lesson 2 – Part C
After the first gardening lesson, did you think about what you would like to grow in your school garden? Now is the time to order seeds for your first crop! There are also things you can bring from home to use in your garden. Ask your parents and family for any plant pots they don't need.
What to collect:
-
Seedling punnets with
divisions
-
Very small plastic pots 
and plant tubes
-
A few very large plastic
pots
-
Waterproof plant labels
Rescue from your recycle bin:
-
Small containers for
seedlings (e.g. single serve
yoghurt and Petit Miam)
-
Straight-sided 750 ml PET
bottles with lids
-
Large plastic drink
containers with recycling
code number '2' or '5'
-
Egg cartons
- Return to top of page