Nutrition in Plants

• Why plants need nutrition and what nutrients they need.
• How photosynthesis works — the most important chemical reaction on Earth.
• Other modes of plant nutrition — parasitic, insectivorous, symbiotic.
• Why plants are called autotrophs (self-feeders).

Why do plants need nutrition?

• All living things need nutrients (food) to:
  • Grow and repair cells.
  • Release energy for life processes.
  • Make proteins, fats, and other molecules.
• Plants need: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulphur (and trace minerals).

Autotrophs vs Heterotrophs

• Plants are autotrophs — they make food using sunlight, water, and CO₂.
• Animals (including humans) are heterotrophs — they eat plants or other animals.

Photosynthesis

Photosynthesis = the process by which green plants make glucose using sunlight.

The equation

6CO₂ + 6H₂O + Light energy → C₆H₁₂O₆ (glucose) + 6O₂

Carbon dioxide + Water + Sunlight → Glucose + Oxygen

Where does it happen?

• In chloroplasts — organelles in plant cells containing chlorophyll.
• Chlorophyll: green pigment that absorbs sunlight (mainly red and blue wavelengths; reflects green — that's why plants look green).
• Mainly in leaves (broad, flat surface to catch light; stomata for gas exchange).

What does each ingredient do?

Products

Leaf structure and photosynthesis

• Stomata: tiny pores (mostly on underside of leaf); open during day for gas exchange; close at night.
• Guard cells: control opening/closing of stomata.
• Veins (vascular bundles): bring water to leaf cells (xylem) and carry glucose away (phloem).
• Mesophyll cells: packed with chloroplasts; most photosynthesis here.

Factors affecting photosynthesis

How plants get minerals from soil

• Glucose provides carbon + energy, but plants also need minerals (nitrogen, phosphorus, etc.).
• Minerals dissolved in soil water are absorbed by root hair cells (greatly increase surface area).
• Nitrogen is needed to make proteins and chlorophyll.
  • Plants can't use atmospheric N₂ directly.
  • Nitrogen-fixing bacteria in soil convert N₂ → ammonia/nitrates → absorbed by roots.
  • Some plants (legumes — peas, beans, lentils) have Rhizobium bacteria in root nodules that fix nitrogen directly.

Other modes of nutrition in plants

Not all plants use only photosynthesis:

Parasitic plants

• Parasite: depends entirely on another organism (host) for food.
• Cuscuta (Dodder/Amarbel): yellow, leafless vine; wraps around host plant; sucks nutrients through haustoria (sucking organs); contains no chlorophyll.
• Orobanche: parasitises roots of crops (tomato, carrot) — causes agricultural damage.

Insectivorous (Carnivorous) plants

• Grow in nitrogen-poor soils (bogs, swamps); can't get enough nitrogen from soil.
• Trap and digest insects to get nitrogen.

Symbiotic nutrition

• Symbiosis: two different organisms living together, both benefiting.
• Lichens: partnership between fungus + algae (or cyanobacteria).
  • Algae photosynthesise and provide food.
  • Fungus provides shelter and absorbs water/minerals.
  • Neither could survive alone in harsh conditions.
• Mycorrhizae: fungi on plant roots; fungus gets glucose; plant gets more water and minerals from soil.

Saprophytic nutrition

• Saprophytes: feed on dead and decaying organic matter.
• Examples: fungi (mushrooms, moulds), some bacteria.
• Not technically plants, but covered here since fungi were once classified as plants.
• Role: decompose dead material → recycle nutrients back into soil → essential for ecosystems.

• Write the equation for photosynthesis in words and symbols.
• Where does photosynthesis take place in a plant cell? What is chlorophyll?
• Name three factors that affect the rate of photosynthesis.
• What is a parasitic plant? Give one example.
• What is a carnivorous plant? How does the Venus Flytrap catch insects?

Open the Practice tab for graded questions on Nutrition in Plants.