"Photosynthesis absorbs carbon dioxide and releases oxygen" Carbon-oxygen balance in green plants and biosphere PPT courseware 4

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"Photosynthesis absorbs carbon dioxide and releases oxygen" Carbon-oxygen balance in green plants and biosphere PPT courseware 4

ANALYSE information

A person inhales an average of 25 kilograms of air (containing about 5 kilograms of oxygen) a day and consumes about 1 kilogram of oxygen (excluding animal breathing and burning). When the oxygen content in the air drops to 7%--8 %, the person will become comatose, suffocate, or even die. But such a phenomenon does not occur in nature. Why?

1. Raw materials for photosynthesis

Priestley

Priestley's experiment

Think about it, discuss it

1. What conclusions can be drawn from Priestley’s experiment?

Plants can renew air that has become polluted by burning candles or breathing animals. Photosynthesis releases oxygen and consumes carbon dioxide.

2. When future generations repeat this experiment, some succeed but others fail. Can you help them analyze the reasons?

Poor airtightness, insufficient light, few plants, etc.

Experimental methods and procedures

① Use a glass cover of appropriate size to cover a potted green plant with normal growth and a cup of NaOH solution, making it airtight.

② Place the above-mentioned plants and devices in a dark room and starve them to consume the organic matter stored in the leaves. A green safety light is installed in the dark room.

③ After starving for a certain period of time, take it out from the dark room and illuminate it for several hours to allow it to fully carry out photosynthesis.

④ Take a leaf, put it into a beaker filled with alcohol, and heat it over water to dissolve the chlorophyll in the alcohol.

⑤ Take out the degreened leaves, lay them flat in a petri dish, and use iodine solution to detect whether there is a specific color reaction of starch.

Control group: the same method but replacing NaOH with water

Experimental proof

In the (1) device that uses sodium hydroxide solution to absorb carbon dioxide, the color of the iodine solution on the plant leaves does not change to blue, and no organic starch is produced.

In the (2) device with carbon dioxide, the iodine solution on the plant leaves turns blue, producing organic starch. Prove that plants perform photosynthesis in a device with carbon dioxide.

It proves that carbon dioxide is an essential raw material for plants to carry out photosynthesis.

1. Photosynthesis produces oxygen

Experimental phenomenon: The hygienic incense (or bamboo stick) that is about to go out will immediately burn violently when it encounters the gas released by hornwort under light (oxygen combustion-supporting characteristics)

Experimental conclusion: In addition to organic matter, the products of photosynthesis of green plants also include oxygen.

Aquatic plants perform photosynthesis and produce many bubbles in their leaves.

Application of photosynthesis in agricultural production

1. Reasonable dense planting

If planted too thinly, light will not be fully utilized, resulting in waste; if planted too densely, the leaves will block each other, affecting the photosynthesis of plants.

When planting crops, to increase yield, they should neither be too thin nor too dense, but should be planted reasonably densely.

2. Crop intercropping – interplanting

Inter-cropping is to make full use of the plant growth season, promote inter-cropping to reduce the loss of light energy in farmland, and increase the multiple-cropping index of farmland. The peak growth period of farmland intercropping crops is in spring, summer and autumn, and the multiple-cropping index can reach more than 200% so that the entire growing season can be improved. The photosynthetic efficiency in the field is in a relatively strong state; intercropping of tall and short crops coexists, which can continuously utilize light energy regardless of time and space, and at the same time increase the overall photosynthetic area.

3. Extend the lighting time

Plants can be divided into long-day plants, short-day plants and medium-day plants according to their different needs for light time. Crop rotation takes advantage of the different needs of plants for light time and strengthens the light time.

Consolidation exercises

1. External conditions that plants do not need when performing photosynthesis ( )

A. Carbon dioxide B. Water C. High temperature D. Light

2. To ensure that urban residents can get fresh air every day, effective measures that can be taken are ( )

A. Build more high-rise buildings and live in high-rise buildings

B. Expand living area

C. Don’t throw away garbage

D. Plant more lawns and a variety of types

judge

1. The energy stored in organic matter ultimately comes from solar energy ( )

2. All cells in plants can perform photosynthesis ( )

3. Cactus cannot carry out photosynthesis because its leaves turn into thorns ( )

4. The energy stored in organic matter ultimately comes from solar energy ( )

5. Organic matter necessary for green plant organisms can be absorbed from the soil by the roots ( )

6. All living cells in plants can perform photosynthesis ( )

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Update Time: 2024-09-08

This template belongs to biology courseware People's Education Edition seventh grade biology volume 1 industry PPT template

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