Photosynthesis

Question 1

The balanced symbol equation for photosynthesis is:

Answer 1

6CO₂ + 6H₂O ⇒light energy + chlorophyll⇒ C₆H₁₂O₆ + 6O₂

Question 2

The simple sugars such as glucose can be:

Answer 2

• Used in respiration, releasing energy
• Converted into cellulose to make cell walls
• Converted into proteins for growth and repair
• Converted into starch, fats and oils for storage

Question 3

Why is starch used for storage?

Answer 3

Starch is used for storage since it is insoluble and does not move from storage areas. Unlike glucose, it does not affect the water concentration of cells and cause osmosis.

Question 4

Photosynthesis is a two stage process:

Answer 4

• Water is split up by light energy releasing oxygen gas and hydrogen ions.
• Carbon dioxide gas combines with the hydrogen ions producing glucose and water.

Question 5

Historical understanding of photosynthesis

Answer 5

• Greek scientists believed that plants took minerals out of the soil to grow and gain mass
• Van helmont concluded from his experiment on growing a willow tree that plant growth could not be due only to the uptake of soil minerals - it must depend on something else.
• Priestley’s experiment showed that plants produce oxygen.

Question 6

Modern photosynthesis experiments.

Answer 6

Modern experiments using a green algae called Chlorella and an isotope of oxygen, ¹⁸O, as a part of a water molecule, have shown that light energy is used to split water, not carbon dioxide. The water is split up into oxygen gas and hydrogen ions. Isotopes are different forms of the same element

Question 7

The rate of photosynthesis can be increased by the plant having:

Answer 7

• More carbon dioxide
• More light
• A higher temperature which increases enzyme action.

Question 8

.When does respiration and photosynthesis take place?

Answer 8

• Plants respire at all times by taking in oxygen and releasing carbon dioxide. Plants are living organisms they must respire and release energy at all times.
• During the day, when it is light, they also carry out photosynthesis taking in carbon dioxide and releasing oxygen:
  
  • the same gas exchange as respiration but in reverse. The rate of gas exchange in photosynthesis is more than that of respiration in terms of quantities, so respiration can only be noticed at night (in darkness).

Question 9

Limiting factors

Answer 9

Since photosynthesis depends on light, temperature and carbon dioxide, a lack of one of these factors will limit the rate of photosynthesis. They are called limiting factors.