AQA GCSE Biology: Unit 1 Overview

Cell Structure

Eukaryotic Cells (Animals and Plants)

• Nucleus: Controls cell activities, contains DNA for protein synthesis.
• Cytoplasm: Site of chemical reactions.
• Cell Membrane: Controls entry and exit of substances, partially permeable.
• Ribosomes: Site of protein synthesis.
• Mitochondria: Release energy through respiration (not "produce" energy).
• Plant-specific Structures:
  • Cell Wall: Provides strength and support, made of cellulose.
  • Sap Vacuole: Contains cell sap (sugary solution).
  • Chloroplasts: Contain chlorophyll for photosynthesis.

Prokaryotic Cells (Bacteria)

• No Nucleus or Mitochondria.
• Cell Structures:
  • Cytoplasm: Site of chemical reactions.
  • Ribosomes: Make proteins.
  • Cell Membrane and Cell Wall: For strength and support.
  • Circular DNA and Plasmid: Control cell activities, carry genes.

Cell Sizes

• Animal cell: ~10 micrometers
• Plant cell: ~50 micrometers
• Prokaryotic cell: ~5 micrometers

Cell Differentiation and Specialization

Process

• Differentiation: From fertilized egg to specialized cells.
• Specialized Cells:
  • Animals: Nerve cells, muscle cells, sperm cells.
  • Plants: Xylem, phloem, root hair cells.

Specialized Cells

• Nerve Cells: Cell body, dendrites, axon, insulating sheath.
• Sperm Cells: Midpiece with mitochondria, tail for swimming, acrosome with enzymes.
• Muscle Cells: Contractile fibers, mitochondria, glycogen stores.
• Plant Cells: Xylem (dead, lignin rings for support), Phloem (companion cells for sugar transport), Root hair cells (large surface area).

Microscopy

Types

• Simple Microscope: Low magnification and resolution.
• Light Microscope: School-level.
• Electron Microscope: High magnification and resolution.

Scale and Conversions

• Millimeters to micrometers, micrometers to nanometers conversions.

Mitosis and Cell Cycle

Cell Cycle Stages

• Stage 1: Cell growth and replication.
• Stage 2 (Mitosis): Chromosomes align, divide, nucleus divides.
• Stage 3: Cytoplasm and cell membrane divide, forming identical cells.

Stem Cells

Types

• Embryonic Stem Cells: Can differentiate into any cell type.
• Adult Stem Cells: Found in bone marrow, differentiate into blood cells.
• Plant Stem Cells: Found in meristem; can differentiate throughout life.

Applications

• Therapeutic Cloning: Produces patient-specific tissues without rejection risk.

Diffusion and Active Transport

Diffusion

• Definition: Movement from high to low concentration.
• Factors Affecting Rate: Concentration gradient, temperature, surface area of membrane.

Active Transport

• Definition: Movement from low to high concentration using energy.
• Examples: Sugar absorption in intestines, mineral ion absorption in plants.

Exchange Systems

Surface Area to Volume Ratio

• Importance in single vs. multicellular organisms.

Adaptations

• Small Intestine: Villi and microvilli for absorption.
• Lungs: Alveoli for gas exchange.
• Leaves: Stomata for gas exchange.
• Gills in Fish: Filaments for gas exchange.

Osmosis

Definition

• Osmosis: Diffusion of water across a partially permeable membrane.

Examples

• Plant Cells: Turgidity provides support.
• Root Hair Cells: Absorb water from soil.

Experiment: Effect of Sugar Solutions on Plant Tissue

• Procedure: Using potatoes to measure change in mass due to osmosis.
• Variables: Concentration, mass difference, percent change.

Review these notes to reinforce understanding of cell structures, processes, and adaptations crucial for AQA GCSE Biology Unit 1.