Overview
This lecture covers key concepts in cell biology for GCSE Paper 1, including cell types, organelles, specialized cells, microscopy, transport processes, cell division, and stem cells.
Cell Types and Organelles
- Prokaryotic cells lack a nucleus; found in bacteria.
- Eukaryotic cells have a nucleus; found in plants and animals.
- Eukaryotic cells have membrane-bound organelles; prokaryotic cells do not.
- Animal cells have nucleus, cytoplasm, cell membrane, ribosomes, and mitochondria.
- Plant cells have all animal cell organelles plus cell wall, chloroplasts, and a large permanent vacuole.
- Bacterial (prokaryotic) cells have circular DNA, plasmids, cell wall (peptidoglycan), capsule, flagella, and small ribosomes.
Specialized Cells
- Animal: nerve cells transmit impulses; muscle cells contract; sperm cells carry genetic material and swim.
- Plant: root hair cells absorb water; xylem transports water and minerals; phloem transports food; photosynthetic cells have chloroplasts for photosynthesis.
Microscopy and Orders of Magnitude
- Light microscopes use light, are easy to use, and provide color images but have low resolution/magnification.
- Electron microscopes use electrons, provide high detail (subcellular structures), but only black/white images.
- Magnification = image size รท object size (units must match).
- Orders of magnitude compare cell sizes by dividing their values (ensure same units).
Movement of Substances
- Passive transport (no energy needed) includes diffusion (movement from high to low concentration) and osmosis (movement of water through a semi-permeable membrane).
- Factors affecting diffusion: surface area, concentration gradient, diffusion distance, and temperature.
- Examples: alveoli in lungs, villi in intestines, stomata in leaves, root hair cells.
- Osmosis: hypertonic solution causes plasmolysis (cell shrinks); hypotonic causes turgid cells (swelling); isotonic results in no net water movement.
- Active transport requires energy to move substances against the concentration gradient; found in root hair cells and some animal cells.
Cell Division and Stem Cells
- Cell cycle: interphase (growth and DNA replication), mitosis (nuclear division), cytokinesis (cytoplasm division).
- Mitosis produces two genetically identical daughter cells; important for growth and repair.
- Stem cells are undifferentiated cells that can become any cell type; found in embryos and some adult tissues.
- Stem cells can be used for therapeutic cloning, organ regeneration, and treatment of diseases, but raise ethical and medical concerns.
Key Terms & Definitions
- Cell โ basic unit of life.
- Mitochondria โ site of aerobic respiration.
- Nucleus โ controls cell activities; contains genetic material.
- Cytoplasm โ jelly-like fluid where chemical reactions occur.
- Ribosomes โ site of protein synthesis.
- Prokaryotic cell โ cell without nucleus/membrane-bound organelles.
- Eukaryotic cell โ cell with nucleus/membrane-bound organelles.
- Cell wall โ supports plant cells; made of cellulose in plants.
- Cell membrane โ controls substance movement in/out of cell.
- Vacuole โ contains cell sap; keeps plant cell turgid.
- Microscope โ device for viewing small objects.
- Resolution โ ability to distinguish two close objects.
- Magnification โ enlarging an object.
- Xylem โ transports water/minerals in plants.
- Phloem โ transports food in plants.
- Diffusion โ movement from high to low concentration.
- Osmosis โ water movement across a semi-permeable membrane.
- Plasmolysis โ plant cell shrinkage in hypertonic solution.
- Turgid โ swollen plant cell in hypotonic solution.
- Mitosis โ cell division producing identical cells.
- Differentiation โ process of cells becoming specialized.
- Stem cell โ undifferentiated cell type.
- Therapeutic cloning โ creating embryonic stem cells from adult cells.
Action Items / Next Steps
- Review and understand all key terms listed above.
- Check your exam specification to ensure all topics are covered.
- Practice exam questions on cell biology.
- Convert units and calculate magnification/order of magnitude as needed.