krit.club logo

Life Processes in Plants - Photosynthesis: in a nutshell

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Photosynthesis is the process by which autotrophic plants prepare their own food using CO2CO_2 and H2OH_2O in the presence of sunlight and chlorophyll.

•

The green pigment called chlorophyll is essential for capturing solar energy; it is found inside specialized organelles called chloroplasts.

•

Carbon dioxide (CO2CO_2) is taken in from the atmosphere through tiny pores on the underside of leaves called stomata, which are regulated by guard cells.

•

Water (H2OH_2O) and minerals are absorbed from the soil by roots and transported to the leaves through a network of vessels called xylem.

•

The primary product of photosynthesis is Glucose (C6H12O6C_6H_{12}O_6), which is often converted and stored as starch for future use.

•

Oxygen (O2O_2) is released as a by-product into the atmosphere, which is vital for the survival of all aerobic organisms.

📐Formulae

6CO2+6H2O→ChlorophyllSunlightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} C_6H_{12}O_6 + 6O_2

Carbon Dioxide+Water→ChlorophyllSunlightGlucose+Oxygen\text{Carbon Dioxide} + \text{Water} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{Glucose} + \text{Oxygen}

💡Examples

Problem 1:

A student covers a part of a green leaf with black paper and leaves the plant in sunlight for 48 hours. What will happen when the leaf is tested with iodine solution?

Solution:

The part of the leaf covered with black paper will not turn blue-black, while the exposed part will turn blue-black.

Explanation:

The covered part did not receive sunlight, so photosynthesis could not occur and no starch was formed. The iodine test detects starch; since only the exposed part produced starch, only that part changes color.

Problem 2:

Why is it said that all living organisms directly or indirectly depend on solar energy?

Solution:

Plants capture solar energy via photosynthesis to produce food; herbivores eat plants, and carnivores eat herbivores.

Explanation:

Solar energy is converted into chemical energy (C6H12O6C_6H_{12}O_6) by plants. This energy flows through the food chain. Without the sun, plants cannot make food, leading to the eventual collapse of all life forms.

Problem 3:

If a plant has 120120 units of glucose and uses 14\frac{1}{4} of it for immediate energy, how much is left to be converted into starch?

Solution:

120−(14×120)=90 units120 - \left(\frac{1}{4} \times 120\right) = 90 \text{ units}

Explanation:

First, calculate the energy used: 120÷4=30120 \div 4 = 30. Then subtract the used amount from the total: 120−30=90120 - 30 = 90 units remaining for storage as starch.