Biology Notes

Organisation of Living Things

  • Organisms:
    • Unicellular: Single cell (e.g., bacteria, protozoa).
    • Colonial: Cells working together but can survive alone (e.g., volvox).
    • Multicellular: Many cells (e.g., plants, animals).
  • Similarities: All composed of cells with cell membranes, cytosol, ribosomes, and genetic material.

Cell Structure and Specialization

  • Cell Specialization: Cells acquire specific structures and functions through differentiation.
    • Undifferentiated Cells (Stem Cells):
      • Embryonic: Differentiate into all cell types.
      • Multipotent: Differentiate into a limited range of cell types.
  • Differential Gene Expression: Determines cell's specific structure and function.
  • Cell structure and specialization are related to function.

Cells Working Together

  • Interdependence: Specialised cells rely on each other.
  • Communication:
    • Animals: Chemical secretions (hormones), nerve cells (neurons).
    • Plants: Chemical signals, physical contact (plasmodesmata).

Structural Organization

  • Hierarchy: Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Multicellular Organisms.
  • Increasing levels of organisation allow for greater complexity and efficiency.

Animal Tissues

  • Epithelial: Covers surfaces, protects organs, forms glands.
  • Connective: Support, binding, protection, transport (e.g., fibrous, loose, adipose, cartilage, bone, blood).
  • Nervous: Communication via neurons.
  • Muscle: Contraction for movement (skeletal, cardiac, smooth).

Plant Tissues

  • Meristematic: Cell division and growth.
  • Dermal: Protection (epidermis, cuticle, bark).
  • Vascular: Transport (xylem, phloem).
  • Ground: Storage, support, photosynthesis.

Levels of Organisation (Plant)

  • Specialised Cells → Tissues → Organs → Organ Systems.
  • Shoot System: Leaves, stem, reproductive organs.
  • Root System: Roots, root hairs.
  • Vascular System: Xylem, phloem.

Nutrient Requirements

  • Essential Nutrients: Inorganic and organic substances.
  • Organic Nutrients: Glucose, amino acids, fatty acids, glycerol, nucleotides, vitamins.
  • Inorganic Nutrients: Minerals, water.
  • Heterotrophs: Obtain nutrients from external sources.
  • Autotrophs: Produce own organic nutrients (photosynthesis).

Autotroph Structure and Function

  • Vascular Plants: Transport system (xylem, phloem).
  • Non-Vascular Plants: Nutrient absorption via diffusion and osmosis.
  • Root System: Anchors, absorbs water and nutrients.
    • Root Hair Zone: Increases surface area for absorption.
  • Shoot System:
    • Stems: Support, transport.
    • Leaves: Photosynthesis, gas exchange.
    • Thin, Flat Structure: Large surface area for light capture
    • Transparent Epidermis: Allows light penetration to mesophyll
    • Mesophyll Layers (Photosynthetic Tissue). palisade and Spongy Cells
    • Epidermis (Upper & Lower): Protective outer layer
    • Guard Cells & Stomata: Guard cells are bean-shaped cells that control the opening (stoma - pore) for gas exchange

Vascular Tissue

  • Xylem: Transports water and minerals.
  • Phloem: Transports sugars.

Imaging Technologies

  • 3D Imaging: External structure.
  • MRI: Internal structures (non-destructive).
  • Micro-CT: High-resolution internal images (non-destructive).
  • Radioisotopes: Track movement of substances.

Gas Exchange

  • Requirement: Constant supply of O2 and removal of CO2.
  • Respiratory Surfaces:
    • Large Surface Area: For faster diffusion.
    • Moist, Thin Surface: Gases dissolve for easier diffusion.
    • Proximity to Transport System: Efficient delivery and removal.
    • Maintenance of Concentration Gradient.

Gas Exchange in Plants

  • Leaves: Primary site (stomata, air spaces).
    • Stomata: Pores for O2 and CO2 movement; regulated by guard cells.
      • Opening/Closing Factors: Light, water availability, temperature, CO_2 concentration, humidity.
  • Lenticels: Pores in woody stems for slow gas exchange.

Gas Exchange in Animals

  • Mammals: Lungs (alveoli).
    • Alveoli: Thin-walled air sacs surrounded by capillaries.
    • Adaptations: Large SA, thin lining, moist surface, proximity to capillaries, concentration gradients.

Mammals Digestive System - Heterotrophs

  • Heterotrophs: Must obtain nutrients by consuming other organisms.
  • Digestion: Breakdown of large food molecules into smaller, absorbable forms.
    • Mechanical: Physical breakdown.
    • Chemical: Enzymatic breakdown.

Pathway through the Digestive System

  1. Mouth: Mechanical and chemical digestion (salivary amylase).
  2. Oesophagus: Peristalsis.
  3. Stomach: Mechanical and chemical digestion (HCl, pepsin).
  4. Small Intestine: Duodenum, jejunum, ileum; absorption.
  5. Liver: Regulates nutrients, detoxifies, produces bile.
  6. Large Intestine: Absorbs water, salts, vitamins; forms faeces.

Absorption in Small Intestine

  • Villi and microvilli increase surface area.
  • Products absorbed: glucose, amino acids, fatty acids, glycerol, water.
  • Rich capillary network and lacteals.

Fate of Digestive Products

  • Transported by blood to cells.
  • Used for building materials, energy storage (glycogen, adipose tissue).

Transport Systems in Animals

  • Need: Multicellular organisms need transport systems due to low surface area-to-volume ratio.
  • Functions: Nutrient delivery, gas exchange, waste removal, heat regulation.

Open Circulatory System

  • Transport fluid: Hemolymph (mixture of blood and tissue fluid)
  • Structure: Heart, open-ended vessels, sinuses.
  • Function: Slow, low-pressure flow; nutrient and waste exchange (not gases).
  • Limitations: Inefficient for large, active organisms.

Closed Circulatory System

  • Transport fluid: blood
  • Structure: Heart, arteries, veins, capillaries.
  • Function: Transports nutrients, gases, hormones, wastes; high-pressure system.

Blood Composition and Function

  • Plasma: Fluid component carrying dissolved substances.
  • \text{Red Blood Cells (RBCs)}: Oxygen transport (haemoglobin).
  • \text{White Blood Cells (WBCs)}: Defence and immune response.
  • \text{Platelets}: Blood clotting.

Lymphatic System

  • Returns excess tissue fluid to blood.
  • Immune function: transports white blood cells.

Blood Vessels

  • Arteries: Carry blood away from the heart (thick walls, high pressure).
  • Veins: Carry blood towards the heart (thin walls, low pressure, valves).
  • Capillaries: Exchange between blood and cells (one-cell-thick wall, slow flow).

The Heart – The Driving Force of the Circulatory System

  • The heart is a muscular organ that pumps blood throughout the body
  • In mammals, the heart is four-chambered and functions as a double pump, maintaining unidirectional blood flow via valves.
  • It is made of cardiac muscle, capable of rhythmic, involuntary contractions to produce a heartbeat.
  • Right Atrium: Receives deoxygenated blood from the body
  • Right Ventricle: Pumps deoxygenated blood to the lungs
  • Left Atrium: Receives oxygenated blood from the lungs
  • Left Ventricle: Pumps oxygenated blood to the rest of the body

Change in Composition of Transport Medium

  • Purpose of the Transport System in Animals. Transports oxygen and nutrients to body cells. Removes carbon dioxide and metabolic wastes
  • Lungs: O2 ↑, CO2 ↓.
  • Body Tissues: O2 ↓, CO2 ↑, glucose ↓, amino acids ↓, wastes ↑.
  • Small Intestine: Glucose ↑, amino acids ↑.
  • Lymphatic System: Fatty acids, lipids ↑.