Class 9 Biology Notes

Chapter 1: Introduction to Biology

Biology

The study of living organisms (from Greek: bios = life, logos = study).

Fields of Biology

• Botany: Study of plants
• Zoology: Study of animals
• Microbiology: Study of microorganisms
• Genetics: Study of heredity
• Biochemistry: Chemical processes in living organisms
• Ecology: Study of environment

Characteristics of Living Organisms

1. Movement (self-initiated)
2. Nutrition (food intake)
3. Respiration (energy release)
4. Growth
5. Reproduction
6. Excretion (waste removal)
7. Response to stimuli (irritability)

Chapter 2: Solving a Biological Problem

Scientific Method

1. Observation: Collecting data through senses
2. Hypothesis: Proposed explanation
3. Prediction: Testable statement
4. Experiment: Testing hypothesis
5. Analysis: Interpreting results
6. Conclusion: Supporting or rejecting hypothesis

Variables

• Independent: Changed by researcher
• Dependent: Measured outcome
• Controlled: Kept constant

Chapter 3: Biodiversity

Classification

Hierarchy: Kingdom → Phylum → Class → Order → Family → Genus → Species

Five Kingdoms

• Monera: Bacteria, Blue-green algae (prokaryotic)
• Protista: Amoeba, Paramecium (unicellular eukaryotic)
• Fungi: Mushrooms, Yeast (heterotrophic, multicellular)
• Plantae: Plants (autotrophic, multicellular, cell wall)
• Animalia: Animals (heterotrophic, multicellular, no cell wall)

Chapter 4: Cells and Tissues

Cell Theory

1. All living things are made of cells
2. Cell is the basic unit of life
3. All cells come from pre-existing cells

Cell Structure

• Nucleus: Control center, contains DNA
• Cytoplasm: Gel-like fluid
• Cell Membrane: Semi-permeable
• Cell Wall: Plant cells only (cellulose)
• Mitochondria: Energy production (ATP)
• Chloroplast: Photosynthesis (plant cells)
• Vacuole: Storage (large in plant cells)

Difference: Plant vs Animal Cells

• Plant: Cell wall, Chloroplast, Large vacuole
• Animal: Centrioles, Lysosomes, Small vacuoles

Tissues

Group of similar cells performing same function.

• Plant Tissues: Meristematic (growth), Permanent (parenchyma, collenchyma, sclerenchyma, vascular)
• Animal Tissues: Epithelial, Connective, Muscular, Nervous

Chapter 5: Cell Cycle

Interphase

• G1: Cell growth, protein synthesis
• S: DNA replication
• G2: Preparation for division

Mitosis

Division of nucleus (Prophase → Metaphase → Anaphase → Telophase)

Cytokinesis

Division of cytoplasm → Two daughter cells

Chapter 6: Enzymes

Enzymes

biological catalysts (proteins) that speed up reactions without being consumed.

Lock and Key Model

Specific enzyme fits specific substrate.

Factors Affecting Enzyme Activity

• Temperature: Optimum ~37°C (human enzymes)
• pH: Specific for each enzyme
• Substrate concentration: Increases rate until saturation
• Inhibitors: Block enzyme activity

Chapter 7: Nutrition

Nutrients

• Carbohydrates: Energy (glucose, starch)
• Proteins: Growth & repair (amino acids)
• Lipids: Energy storage, insulation
• Vitamins: Co-factors (A, B, C, D, E, K)
• Minerals: Iron, Calcium, Potassium, etc.
• Water: Solvent, transport, temperature regulation
• Fiber: Digestion aid

Malnutrition

• Undernutrition: Deficiency diseases (Marasmus, Kwashiorkor)
• Overnutrition: Obesity, heart disease