PLANTS

Plants are autotrophs, meaning they make their own food using sunlight, water, and carbon dioxide.

Main Parts of a Plant

• Roots – absorb water & minerals, anchor plant

• Stem – transports water, minerals, food

• Leaves – photosynthesis

• Flowers/Fruits – reproduction

WATER IN PLANTS

Functions of Water in Plants

1. Raw material for photosynthesis

2. Transport medium (minerals & food)

3. Maintains turgidity (keeps plant upright)

4. Temperature control (cooling via transpiration)

5. Chemical reactions (metabolism)

Absorption of Water

Water is absorbed mainly by root hairs through:

• Osmosis – movement of water from high to low water concentration

Path of Water

Root hair → Cortex → Endodermis → Xylem → Leaves

Transport of Water (ASCENT OF SAP)

Occurs through xylem by:

1. Root pressure

2. Capillary action

3. Transpiration pull (MOST IMPORTANT)

Transpiration

Loss of water vapor from aerial parts of plant (mainly leaves).

Types

• Stomatal (most)

• Cuticular

• Lenticular

Importance

• Creates transpiration pull

• Cooling effect

• Mineral transport

MINERAL SALTS IN PLANTS

Plants absorb mineral salts dissolved in water from soil.

Essential Mineral Elements

Divided into Macronutrients and Micronutrients

Macronutrients (Needed in large amounts)

1. Nitrogen (N)

• For proteins, enzymes, chlorophyll

• Deficiency → Yellow leaves, stunted growth

2. Phosphorus (P)

• ATP, DNA, RNA

• Deficiency → Poor root growth

3. Potassium (K)

• Enzyme activation, stomatal function

• Deficiency → Leaf edge scorching

4. Calcium (Ca)

• Cell wall formation

• Deficiency → Weak stems, dead root tips

5. Magnesium (Mg)

• Part of chlorophyll

• Deficiency → Yellowing between veins

6. Sulphur (S)

• Proteins & vitamins

• Deficiency → Poor growth

Micronutrients (Needed in trace amounts)

• Iron (Fe) – chlorophyll synthesis

• Zinc (Zn)

• Copper (Cu)

• Manganese (Mn)

• Boron (B)

• Molybdenum (Mo)

⚠️ Even though needed in small amounts, deficiency is dangerous.

Absorption of Minerals

• Passive absorption – diffusion

• Active absorption – uses energy (ATP)

PHOTOSYNTHESIS

Definition

Photosynthesis is the process by which green plants make food (glucose) from carbon dioxide and water using sunlight and chlorophyll, releasing oxygen.

Site of Photosynthesis

• Chloroplast

  • Grana → Light reaction

  • Stroma → Dark reaction

Stages of Photosynthesis

1️⃣ Light Reaction (Photochemical Phase)

• Occurs in grana

• Requires sunlight

• Water splits (photolysis)

• Produces:

  • ATP

  • NADPH

  • Oxygen (released)

2️⃣ Dark Reaction (Calvin Cycle)

• Occurs in stroma

• No direct sunlight needed

• Uses ATP & NADPH

• CO₂ converted into glucose

Factors Affecting Photosynthesis

1. Light intensity

2. CO₂ concentration

3. Temperature

4. Water availability

5. Chlorophyll content