AQA GCSE Biology - Unit 1 Overview

Cell Structure

Eukaryotic Cells

• Animal and Plant Cells
  • Both contain a nucleus: controls cell activities, contains DNA for protein synthesis.
  • Cytoplasm: site of chemical reactions.
  • Cell Membrane: controls what enters and exits, partially permeable.
  • Ribosomes: site of protein synthesis, too small for light microscopes.
  • Mitochondria: release energy by respiration, not producing energy.
• Plant Cells Specific
  • Cell Wall: made of cellulose, provides strength and support.
  • Vacuole: contains cell sap, a sugary solution.
  • Chloroplasts: contain chlorophyll for photosynthesis.

Prokaryotic Cells

• Bacterial Cells
  • No nucleus or mitochondria.
  • Cytoplasm: site for chemical reactions.
  • Ribosomes: protein synthesis.
  • Cell Membrane & Cell Wall: not made of cellulose, provides strength and support.
  • Circular DNA & Plasmids: control cell activities and genetic material.

Cell Sizes

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

Cell Differentiation and Specialization

Differentiation Process

• Animals: nerve cells, muscle cells, sperm cells.
• Plants: xylem, phloem, root hair cells.
• Animal cell specialization usually limits further differentiation.
• Plant cells maintain potential for differentiation.

Specialized Cells

• Nerve Cells: cell body, dendrites, axon, insulating sheath, axon terminals.
• Sperm Cells: midpiece with mitochondria, tail for movement, acrosome with enzymes, nucleus with 23 chromosomes.
• Muscle Cells: fibers for contraction, mitochondria for energy, glycogen storage.
• Xylem Cells: dead, no end plates, lignin reinforcement.
• Phloem Cells: have cytoplasm, companion cells for energy, end plates with pores.
• Root Hair Cells: large surface area, mitochondria for active transport.

Microscopy

Types of Microscopes

• Simple Microscopes: low magnification and resolving power.
• Electron Microscopes: high magnification and resolving power, reveal subcellular structures.

Measurement Conversions

• Millimeters to Micrometers: multiply by 1000.
• Micrometers to Nanometers: multiply by 1000.
• Reverse by dividing by 1000.

Magnification Calculations

• Formula: Magnification = Image Size / Real Size
• Convert units to be the same before calculation.

Mitosis and Cell Cycle

Cell Cycle Stages

• Stage One: cell growth, increase in subcellular structures, DNA replication.
• Stage Two (Mitosis): chromosomes align and separate, nucleus divides.
• Stage Three: cytoplasm and membrane divide, form identical cells.

Stem Cells

Types

• Embryonic Stem Cells: undifferentiated, can become most cell types, used for cloning and medical research.
• Adult Stem Cells: found in bone marrow, differentiate into blood cells.
• Plant Stem Cells: in meristem tissue, can differentiate into any plant cell.

Therapeutic Cloning

• Process: patient body cell nucleus inserted into egg cell, cloned to produce tissues for treatment.
• Advantages: tissues not rejected by patient.
• Disadvantages: risk of viral infection, ethical concerns.

Diffusion and Active Transport

Diffusion

• Definition: movement of particles from high to low concentration.
• Examples: oxygen from blood to cells, CO2 from cells to blood.
• Factors Affecting Rate: concentration gradient, temperature, surface area.

Active Transport

• Definition: movement from low to high concentration, requires energy.
• Examples: sugar absorption in intestines, mineral ions in root hair cells.

Exchange of Substances

Surface Area to Volume Ratio

• Larger organisms have smaller ratios, require exchange systems.

Adaptations for Exchange

• Small Intestine: villi and microvilli increase surface area, thin walls.
• Lungs: alveoli increase surface area, good blood supply, thin walls.
• Leaves: flat, wide, thin for gas diffusion, air spaces, stomata.
• Gills: large surface area, thin walls, good blood supply, water flow.

Osmosis

Definition

• Water diffusion from dilute to concentrated solution through a partially permeable membrane.

Examples

• Plant Cells: water in, cells become turgid.
• Root Hair Cells: water from soil into cells by osmosis.

Investigating Osmosis

Experiment Steps

1. Prepare solutions of different concentrations.
2. Cut and weigh plant tissue.
3. Place in solutions, reweigh after set time.
4. Calculate percentage change in mass.

Analysis

• Graph percent change versus concentration.
• Explain mass changes via osmosis.

Conclusion

• Reviewing the complete Unit 1 for AQA GCSE Biology, covering fundamental cell biology, processes, and experimental methods.