Nutrition in Plants
Class 7 Science - Topic Wise Q&A from NCERT
Plants have different ways of obtaining their nutrition. While most plants make their own food through photosynthesis, some depend on other sources. This guide covers all important questions about plant nutrition from NCERT Class 7 Science.
Mode of Nutrition in Plants
What are nutrients?
Nutrients are components of food necessary for organisms. They include carbohydrates,
proteins, fats,
vitamins, and minerals.
How do plants prepare their food?
Plants prepare their food through photosynthesis,
using sunlight, carbon dioxide, water, and chlorophyll to produce glucose and oxygen.
Why are nutrients important for living organisms?
Nutrients enable living organisms to:
- Build their bodies
- Grow and develop
- Repair damaged parts
- Provide energy for life processes
Define nutrition.
Nutrition is the process by which organisms take in food and utilize it for growth, repair, and energy.
What is autotrophic mode of nutrition?
Autotrophic nutrition is when organisms make their own food from simple substances like carbon dioxide and water.
What does the word "trophos" mean?
The word "trophos" means nourishment.
What are autotrophs? Provide examples.
Autotrophs are organisms that make their own food. Examples include:
Autotroph Examples:
- Green plants
- Algae
- Cyanobacteria (blue-green algae)
Why can't our body make food from CO₂, water, and minerals like plants?
Humans lack chlorophyll, which is essential for photosynthesis.
Our bodies aren't designed to convert sunlight into energy like plants do.
Photosynthesis - Food Making Process
Where are the food factories of plants located?
The food factories of plants are located in the leaves.
Is food made in all parts of a plant or only certain parts?
While photosynthesis mainly occurs in leaves, some plants can perform it in green stems too.
How do plants obtain raw materials for photosynthesis?
Plants obtain raw materials as follows:
- Water & minerals: Absorbed by roots and transported via xylem
- Carbon dioxide: Taken in through stomata
- Sunlight: Captured by chlorophyll in leaves
What are stomata?
Stomata are tiny pores present on the surface of leaves surrounded by guard cells.
What are the functions of stomata and guard cells?
- Stomata: Allow gas exchange (CO₂ in, O₂ out)
- Guard cells: Control opening and closing of stomata
What is the role of chlorophyll?
Chlorophyll is a green pigment that captures sunlight energy for photosynthesis.
Why is the sun the ultimate source of energy for all living organisms?
The sun provides energy for photosynthesis, which creates food that sustains all food chains.
Why do desert plants have scale-like leaves?
Desert plants have scale-like leaves to reduce water loss through transpiration.
How do desert plants perform photosynthesis?
Desert plants perform photosynthesis through their green stems since their leaves are modified to reduce water loss.
Why can leaves synthesize food but other plant parts cannot?
Leaves contain chlorophyll and stomata which are essential for photosynthesis.
How do we test if photosynthesis has occurred?
We test for the presence of starch using iodine solution, which turns blue-black if starch is present.
Do plants with red, violet, or brown leaves perform photosynthesis?
Yes, they contain chlorophyll masked by other pigments and can perform photosynthesis.
What are algae?
Algae are simple, aquatic organisms that contain chlorophyll and perform photosynthesis.
Why are algae green in color?
Algae are green due to the presence of chlorophyll.
How do algae obtain their food?
Algae make their own food through photosynthesis.
Where do plants obtain nitrogen?
Plants obtain nitrogen from the soil in the form of nitrates, and some through symbiotic relationships with bacteria.
Other Modes of Nutrition
What is heterotrophic nutrition?
Heterotrophic nutrition is when organisms obtain food from other sources rather than making it themselves.
What are heterotrophs?
Organisms that depend on others for food are called heterotrophs (e.g., animals, fungi).
What are parasites and hosts?
- Parasite: Organism that lives on/in another organism and obtains nutrients
- Host: The organism that a parasite lives on and derives nutrients from
Provide 5 examples of parasites.
Parasite Examples:
- Cuscuta (amarbel or dodder plant)
- Mosquito
- Lice
- Tapeworms
- Bed bug
What are insectivorous plants?
Plants that trap and digest insects for nutrients are called insectivorous plants (e.g., pitcher plant, Venus flytrap).
Why do pitcher plants feed on insects despite having chlorophyll?
Pitcher plants grow in nitrogen-poor soil. Though they perform photosynthesis, they get additional nutrients from insects.
Saprotrophs
What are saprotrophs? Give examples.
Saprotrophs are organisms that obtain nutrients from dead and decaying matter. Examples include fungi and bacteria.
How do saprotrophs acquire nutrients without mouths?
Saprotrophs secrete digestive enzymes onto dead matter, break it down externally, and absorb the nutrients.
What is saprotrophic nutrition?
Saprotrophic nutrition is the process of obtaining nutrients from dead and decaying organic matter.
What conditions are required for saprotroph growth?
Saprotrophs require:
- Warmth
- Moisture
- Organic matter
How do fungi appear suddenly during rainy season?
Fungal spores in the air land on warm, moist surfaces during rains and germinate quickly.
How can we protect things from fungal spoilage?
- Keep items dry
- Store in cool places
- Use airtight containers
- Use antifungal agents
How are fungi useful and harmful?
Useful:
- Decompose organic matter
- Used in medicines (penicillin)
- Used in food (mushrooms, yeast)
Harmful:
- Spoil food and materials
- Cause plant diseases
- Cause human diseases (athlete's foot)
What is symbiosis? Provide examples.
Symbiosis is a relationship where two organisms live together and benefit each other.
Examples:
- Lichen (algae + fungus)
- Rhizobium bacteria + legume plants
- Mycorrhizae (fungi + plant roots)
Nutrient Replenishment in Soil
Why do soil nutrients need replenishment?
Plants continuously absorb nutrients from soil, depleting them. Replenishment maintains soil fertility.
How do fertilizers and manures help?
Fertilizers and manures add essential nutrients like nitrogen, phosphorus, and potassium back to the soil.
Why do crop plants deplete nitrogen from soil?
Crops absorb large amounts of nitrogen for growth, making soil nitrogen-deficient over time.
How does the legume-Rhizobium relationship help farmers?
Rhizobium bacteria convert atmospheric nitrogen into usable form for plants, reducing the need for nitrogen fertilizers.
Extra Questions
Are insectivorous plants partial heterotrophs?
Yes, because they perform photosynthesis (autotrophic) but also obtain nutrients from insects (heterotrophic).
What substances besides carbohydrates do plants make?
Plants make proteins for growth,
fats for energy storage,
and use minerals from soil to stay healthy.
Why do plants need nitrogen?
Plants need nitrogen to make
green leaves for photosynthesis,
grow properly, and build
proteins for their cells.
Where do insect-eating plants grow?
They grow in poor soil that lacks nutrients,
especially wet, swampy areas like bogs
where other plants can't survive.
How does soil replenish nutrients?
Soil replenishes nutrients in two main ways:
- Artificial method: Adding fertilizers and manure
- Natural method: Symbiotic relationships like between rhizobium bacteria and leguminous plants
What do algae and fungus provide each other?
In their symbiotic relationship (lichen):
- Algae provides food through photosynthesis
- Fungus provides water and minerals and creates a protective home
What do rhizobium and leguminous plants exchange?
In their symbiotic relationship:
- Rhizobium bacteria provide nitrogen to the plants
- Plants provide shelter and food to the bacteria
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