Across the curriculum.0:02
Exercise 3A, page 76.0:04
Photosynthesis, the circle of life.0:11
Energy moves along the food chain from one life form to another.0:23
Some animals eat plants to get energy.0:28
Other animals then eat these animals.0:31
Plants form the foundation of the food chain by producing their own food using energy from the sun through a process called photosynthesis.0:35
Photosynthesis is very ancient.0:48
Before there were plants, tiny creatures called bacteria carried out photosynthesis.0:52
In fact, this was happening more than 3 billion years ago.0:59
Now for the technical bit.1:07
Photosynthesis uses energy from the sun to change carbon dioxide and water into carbohydrates and oxygen gas.1:09
Carbohydrates are chemicals that contain hydrogen, carbon, and oxygen.1:22
The chemical reaction can be summarized by this equation.1:29
The raw materials to start the process.1:34
The plant absorbs carbon dioxide through tiny holes in its leaves and sucks up water from the soil through its roots.1:38
A green substance in the plant's leaves, called chlorophyll, absorbs energy from the sun.1:47
The plant now has all it needs for photosynthesis to begin changing the form of energy.1:54
There are two stages to the photosynthesis process.2:02
In the first stage, called the light reaction, light energy from the sun is converted into chemical energy.2:06
This energy is stored in a chemical called ATP, adenosine triphosphate in the dark.2:14
The second stage does not require sunlight to take place.2:24
This part of the process is called the dark reaction.2:28
In this stage, the plant uses ATP to convert the carbon dioxide and water into carbohydrates.2:32
Carbohydrates provide the plant with the energy it needs in order to grow, making life possible.2:41
Clearly, photosynthesis is very important for every living thing.2:49
As well as providing food for the plant from the sun's energy, it indirectly provides food for every other living creature.2:54
Not only that, it also produces the oxygen that animals need to breathe.3:04
Without photosynthesis, our planet could not support life as we know it.3:10
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