Topic 1 covers the fundamental unit of life: the cell. Students learn cell theory, compare prokaryotic and eukaryotic cells, understand membrane structure and transport, and study cell division.
Three principles: all living things are made of cells; cells are the basic unit of life; cells come from pre-existing cells. Exceptions: muscle fibres (multi-nucleate), fungi (no true cells), viruses (non-cellular). Prokaryotes (bacteria): no membrane-bound nucleus, 70S ribosomes, naked DNA, cell wall. Eukaryotes: membrane-bound nucleus, 80S ribosomes, organelles (mitochondria, ER, Golgi, etc.).
Fluid mosaic model: phospholipid bilayer with embedded proteins (integral/peripheral), cholesterol (fluidity), glycoproteins (recognition). Simple diffusion: small non-polar molecules down concentration gradient. Facilitated diffusion: via channel or carrier proteins. Osmosis: water through partially permeable membrane. Active transport: against gradient, requires ATP.
Mitosis: one cell → two genetically identical daughter cells. Stages: prophase (chromosomes condense), metaphase (align at equator), anaphase (chromatids separate), telophase (nuclei reform) + cytokinesis. Purpose: growth, repair, asexual reproduction. Cell cycle includes interphase (G₁, S phase — DNA replication, G₂) and mitotic phase.
Undifferentiated cells with the capacity to differentiate into specialised cell types. Totipotent (can form any cell type), pluripotent (most cell types), multipotent (limited range). Therapeutic uses: treating leukaemia (bone marrow transplant), potential for Parkinson\'s, diabetes. Ethical considerations around embryonic stem cell research.
Diffusion is the net movement of particles (molecules, ions) from high to low concentration. It applies to any substance. Osmosis is specifically the movement of water across a partially permeable membrane from a region of lower solute concentration to higher solute concentration. Osmosis is essentially diffusion of water, governed by solute concentration differences.
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