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Photosynthesis 3 – Grade 7 Science Worksheets

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Photosynthesis

Photosynthesis is the process by which light energy is tapped and changed into chemical energy in the form of the food sugar. Carbon dioxide is taken in by the plants and oxygen is given out.

Sunlight + carbon dioxide + water = sugar + oxygen

 

Carbon dioxide and water are combined and their atoms bonds to form a sugar molecule. The bonds of the sugar molecule store the energy gained from light.

The following is the chemical reaction for photosynthesis:

Photosynthesis

Where does photosynthesis occur?

Photosynthesis is carried out by chloroplasts within the cells of plants. Chloroplasts contain chlorophyll (green color). Chlorophyll absorbs sun’s energy that is sunlight. The photons in light (i.e., the light particles) hit with the electrons in the chlorophyll, which transforms the energy.

A group of bacteria called cyan is originally the chloroplast. This is one of the examples of symbiosis. Here, the cyan bacteria were passed onto upon the host cells as eukaryotic host cells millions of years ago and the method of photosynthesis began. Not only are these ancient symbionts, cyan bacteria which are spread all over the plant in the oceans (three-fourth of the earth’s surface) are responsible for most of the photosynthesis occurring on Earth today.

(Note: A eukaryote is an organism with complex cells, or a single cell which has a complex structure.  These cells have the genetic material in the chromosomes in the nucleus of the cell.)

Photosynthesis1-768x432

Photosynthesis and the properties of energy

In photosynthesis, light energy is converted to chemical energy and stored in the form of food sugars. The law of conservation of energy is followed that is the amount of light that energy input equals the amount of chemical energy that is the output.

 Photosynthesis requires CO2+ Water H2O and sunlight. The processes by which plants and some other organisms like algae capture light energy and use it to make food from carbon dioxide and water. 

Photosynthesis2

Chemical equation for Photosynthesis

Photosynthesis3

Glucose is a type of sugar that provides us with energy.

Glucose is needed by all forms of life to produce energy.  It is an essential part of the stored food.

The process by which glucose is broken down is called respiration –

During respiration, the chemical energy stored in glucose is converted into other forms of energy, such as mechanical energy or thermal energy.

Plants use some of this energy to grow, reproduce, and perform other life functions. Unused energy is stored as food by the plants.

Plants go through both photosynthesis and respiration.

Check Point

I. Fill in the blanks – 

  1. Photosynthesis refers to the process by which …………… …………… is tapped and transformed into chemical energy in the form of the ………… ………….
  1. The bonds within the sugar molecule store the energy obtained from ……………
  1. Chloroplasts contain ………………….., a lipid that gives plants their …………….. Color.
  1. The chloroplast is actually derived from a group of bacteria known as………. bacteria.
  1. The process by which …………… is broken down is called respiration.

 

 II. State True or False –

  1. Oxygen from water is released as a by-product in this process of photosynthesis.
  2. light energy + CO2+ H2O -> CH2O + O2
  3. Photosynthesis is carried out by chromoplasts within the cells of plants.
  4. The photons in light collide with the neutrons in the chlorophyll molecule, which starts the process of energy transformation.
  5. Plants only go through photosynthesis.
Answer Key
I.Fill in the blanks – 

  1. Light energy, food sugar
  2. Light
  3. Chlorophyll, green
  4. Cyan
  5. Glucose

II.True or False –

  1. True
  2. True
  3. False
  4. False
  5. False

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