🌞 Photosynthesis – How Plants Make Food

Photosynthesis is the process through which green plants, algae, and some bacteria produce their own food. Using sunlight, water, carbon dioxide, and the green pigment chlorophyll, plants convert light energy into chemical energy in the form of glucose (a simple sugar).

• Raw materials:
  • Sunlight – energy source
  • Carbon dioxide – from the air
  • Water – absorbed from soil through roots
• Produced:
  • Glucose – food for the plant
  • Oxygen – released into the air

Photosynthesis mainly occurs in the leaves of green plants.

🧬 Special Modes of Plant Nutrition

While most green plants prepare food through photosynthesis, some use other methods to obtain nutrients.

🔸 1. Parasitic Nutrition

• A parasitic plant depends entirely or partially on another living plant (called the host) for food and water.
• Example: Cuscuta (dodder) – it coils around the host and sucks nutrients using special structures called haustoria.

🔸 2. Saprotrophic Nutrition

• Plants like fungi feed on dead and decaying matter.
• They release digestive enzymes to break down organic substances and then absorb the nutrients.

🔸 3. Insectivorous Nutrition

• Some plants trap insects to fulfill their nutritional needs, especially nitrogen.
• Example: Pitcher Plant – has a modified leaf shaped like a pitcher to trap and digest insects using enzymes.

🔬 Photosynthesis Process

Photosynthesis is a chemical reaction that takes place inside the plant’s cells, specifically within the chloroplasts of the leaf.

Equation:
CO₂ + H₂O + Light → Glucose (C₆H₁₂O₆) + O₂

Photosynthesis occurs in two stages:

1. Light-dependent Reactions – sunlight is used to split water molecules and generate energy.
2. Light-independent Reactions (Dark Reactions) – carbon dioxide is used to build glucose molecules.

🌱 Parasitic Plants

Parasitic plants are those that cannot make their own food. They grow on other healthy plants and extract nutrients and water.

• They lack chlorophyll and do not perform photosynthesis.
• Have special root-like structures to draw nutrients from the host.
• Examples: Mistletoe, Cuscuta, Rafflesia

🍄 Saprotrophic Nutrition

In this mode, organisms feed on dead organic material.

• Common in fungi like mushrooms and molds.
• They release enzymes outside their body to digest the matter and absorb nutrients.

This is a form of external digestion and helps in natural decomposition.

🤝 Symbiotic Nutrition

In symbiotic relationships, two different organisms live together in a way that benefits both.

• Example: Rhizobium bacteria live in the root nodules of leguminous plants (like peas).
  • Bacteria get shelter and food.
  • In return, they fix atmospheric nitrogen and make it available to the plant.

This type of relationship improves soil fertility.

🧪 Raw Materials & Their Roles in Photosynthesis

🌿 Understanding Symbiosis

A symbiotic relationship is a close and long-term biological interaction between two different species that benefits both.

• Example: Lichens – formed from an association between algae (make food) and fungi (provide shelter and moisture).

These relationships show cooperation in nature.

🌞 Steps in Photosynthesis

• Photosynthesis occurs mainly in the mesophyll cells of the leaves.
• These cells are rich in chloroplasts, where chlorophyll traps light energy.
• Stomata (tiny pores) on the underside of leaves allow carbon dioxide to enter.
• Water is transported from roots to leaves via the xylem vessels.
• After the process, oxygen is released and glucose is stored or used as energy.

🧪 What are the Raw Materials in Photosynthesis?

The four essential inputs:

1. Carbon Dioxide (CO₂)
2. Water (H₂O)
3. Light energy
4. Chlorophyll pigment

All are required for successful food production in plants.

🌾 Introduction to Parasitic Plants

Parasitic plants survive by feeding off other living plants. They have evolved mechanisms to attach to hosts and extract sap or minerals.

• Possess haustoria – specialized roots for absorbing nutrients.
• Some examples include:
  • Cuscuta
  • Mistletoe
  • Rafflesia
  • Nuytsia floribunda

These plants may be partial or complete parasites, depending on whether they can photosynthesize or not.

🌱 Nutrients from Soil

Plants absorb minerals and nutrients from the soil to support their growth. However, with continuous farming, soil becomes nutrient-depleted.

To replenish it:

• Fertilizers (chemical)
• Manures (natural)
• Rhizobium bacteria in soil fix nitrogen and improve soil fertility

Rhizobium lives in symbiosis with leguminous plants, offering a natural way to enrich soil.

🌾 What are Biofertilizers?

Biofertilizers are preparations containing beneficial microbes that increase soil fertility.

• These microbes break down organic matter and release nutrients.
• They are eco-friendly, unlike chemical fertilizers which cause pollution.
• Preferred in organic farming and sustainable agriculture.

⚖️ Chemical vs. Natural Fertilizers

🌿 Manure vs. Fertilizer – What’s the Difference?

🩸 What is Leghaemoglobin?

• Leghaemoglobin is a red pigment found in the root nodules of leguminous plants.
• It helps protect nitrogen-fixing enzymes from oxygen.
• Gives the nodule a pink or reddish color, much like haemoglobin in blood.

🌱 Root Nodules in Leguminous Plants

• Root nodules are swollen structures on roots, seen in plants like soybean, lentils, peas.
• Inside the nodules, Rhizobium bacteria live and perform nitrogen fixation.
• Help enrich the soil without chemical fertilizers.

🌿 What are Leguminous Plants?

Leguminous plants belong to the pea family (Leguminosae). They are known for their nitrogen-fixing ability and contribute greatly to soil health.

• Produce pods or seeds (e.g., beans, peas)
• Improve soil nitrogen naturally
• Examples:
  • Soybean
  • Peanut
  • Clover
  • Alfalfa

🔬 Understanding Cell, Cell Membrane, and Nucleus

• Cell: The basic unit of life in all living organisms.
• Cell Membrane: A semi-permeable boundary that protects the cell and controls what enters or exits.
• Nucleus: The command center of the cell, storing DNA and controlling growth and reproduction.
• Cytoplasm: The gel-like fluid inside the cell where most reactions take place.