AQA GCSE Biology - Topic 1: Cell Biology

Cell Structure

Eukaryotic Cells

• Animal and Plant Cells: Contain structures such as nucleus, cytoplasm, cell membrane, ribosomes, and mitochondria.
  • Nucleus: Controls cell activities and 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: Releases energy by respiration (not "produces" energy).
• Plant Cells: Have additional structures like cell wall (made of cellulose), sap vacuole, and chloroplasts.
  • Cell Wall: Provides strength and support.
  • Chloroplasts: Contain chlorophyll for photosynthesis.

Prokaryotic Cells

• Bacterial Cells: Lack a nucleus and mitochondria.
  • Circular DNA: Controls cell activities.
  • Plasmid: Small DNA ring with extra genes.
• Size Comparisons: Animal cell (~10 μm), Plant cell (~50 μm), Prokaryote (~5 μm).

Cell Differentiation and Specialization

Differentiation Process

• Animals: Sperm cell fertilizes egg, leading to undifferentiated cells that specialize (nerve, muscle, sperm cells).
• Plants: Pollen fertilizes egg, similar differentiation.

Specialized Cells in Animals

• Nerve Cells: Conduct impulses, have dendrites and axon.
• Sperm Cells: Have mitochondria for energy, tail for movement.
• Muscle Cells: Have fibers for contraction, store glycogen.

Specialized Cells in Plants

• Xylem Cells: Dead, transport water, supported by lignin.
• Phloem Cells: Transport nutrients, have end plates with pores.
• Root Hair Cells: Large surface area for absorption.

Microscopy

Development of Microscopes

• Simple Microscopes: Low magnification and resolution.
• Electron Microscopes: High magnification and resolution, allow viewing of subcellular structures.

Units and Conversions

• Conversions: Millimeters to micrometers (×1000), micrometers to nanometers (×1000).

Magnification Calculations

• Formula: Magnification = Size of Image / Real Size of Object.
• Ensure units are consistent.

Mitosis and the Cell Cycle

Cell Division

• Purpose: Growth, repair, and replacement.
• Stages:
  1. Cell growth and DNA replication.
  2. Mitosis: Chromosomes align and are separated into two new nuclei.
  3. Cytoplasm divides, forming two genetically identical cells.

Stem Cells

Types and Uses

• Embryonic Stem Cells: Differentiate into most cell types, used for research and treatments.
• Adult Stem Cells: Found in bone marrow, differentiate mainly into blood cells.
• Plant Stem Cells: Found in meristem tissue, can differentiate throughout the plant's life.

Therapeutic Cloning

• Produces tissues not rejected by the patient.
• Potential issues include viral infections and ethical concerns.

Diffusion and Active Transport

Diffusion

• Definition: Movement from high to low concentration.
• Examples: Oxygen and carbon dioxide movement in blood.
• Factors: Concentration gradient, temperature, surface area.

Active Transport

• Definition: Movement from low to high concentration, requires energy.
• Examples: Sugar absorption in intestines, mineral ion uptake in roots.

Exchange of Substances

Surface Area to Volume Ratio

• Smaller organisms have a higher ratio, facilitating diffusion.

Adaptations in Organisms

• Intestines: Villi and microvilli increase surface area.
• Lungs: Alveoli provide large surface area for gas exchange.
• Leaves: Flat, thin leaves with air spaces for efficient gas exchange.
• Gills: Large surface area and good blood supply for gas exchange.

Osmosis

Definition

• Osmosis: Water movement from dilute to concentrated solution through a partially permeable membrane.

Practical Investigation

• Investigating effects of different concentrations on plant tissue mass.

Key Points

• Turgid Cells: Result from water uptake, support plants.
• Animal Cells: Risk of bursting without a cell wall.

Summary

• Understanding cell biology principles is crucial for topics including cell structure, functions, differentiation, division, and transport mechanisms.