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Microalgae: Tiny Helpers in Water
- Microalgae are tiny plant-like organisms in water and soil.
- They make their own food using sunlight.
- They release oxygen as they do this.
- They make more than half of the Earth's oxygen.
- They are also food for many water animals.
Example 1 — Spirulina
- Spirulina is a microalga rich in protein.
- People use it as a health supplement.
- So microalgae help human health.
Example 2 — Cleaning Water
- Microalgae grow in dirty water.
- They help clean it and can make biofuel.
- So they are useful to the environment.
Important Points
- Pollution and climate change threaten microalgae.
- We should conserve them to keep the oxygen balance.
Definition — Microalgae
Microalgae are microscopic plant-like organisms that make their own food using sunlight and release oxygen.
🏭 Ever Heard Of — Spirulina, a Superfood
Spirulina is a microalga called a superfood for its health benefits.
It is more than 60 per cent protein and a good source of vitamin B12. It can be grown in a glass tank with pond water and harvested after a few weeks. Growing it can be a useful livelihood.
🧠 Test Yourself — Section 2.4
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How do microbes help clean the environment?
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They break down plant and animal waste into nutrient-rich manure. -
What gas does yeast release to make dough rise?
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Carbon dioxide. -
Which bacterium turns milk into curd?
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Lactobacillus. -
What does Rhizobium do for plants?
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It traps nitrogen from the air and makes it useful for the plants. -
Why are microalgae important?
View Answer
They make over half the Earth's oxygen and are food for water animals.
📋 NCERT Question 2 — Yeast and the balloon
Yeast is added to sugar solution in test tube B with a balloon on top. Why does the balloon inflate, and what is found by attaching it to lime water?
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📋 NCERT Question 3 — Wheat vs bean farmer
One farmer adds nitrogen fertiliser for wheat; another grows beans without it. Explain the reason.
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📋 NCERT Question 4 — Two compost pits
Snehal mixes peels with dried leaves in pit A but not in pit B. What is she trying to test?
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📋 NCERT Question 5 — Identify the microorganisms
Identify the microbe that: lives everywhere and in your gut; makes bread soft and fluffy; lives in pulse roots and provides nutrients.
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📋 NCERT Question 6 — Conditions for microbe growth
Devise an experiment to test that microorganisms need the right temperature, air, and moisture to grow.
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📋 NCERT Question 7 — Bread on the counter vs fridge
One bread slice is kept near the sink and one in the fridge. Compare them after three days and give reasons.
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📋 NCERT Question 8 — Curd turning sour
Curd left out for a day becomes more sour. Give two possible explanations.
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📋 NCERT Question 9 — Yeast and lime water setup
For the warm sugar-yeast flask connected to lime water: what happens in the flask, what is seen in the lime water, and what if no yeast is added?
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