Key Concepts in Biology

• Cell types


  • Eukaryotic (animals and plants)
  • Prokaryotic
• Eukaryotic cell


  Contains a nucleus and membrane-bound organelles
• Prokaryotic cell


  Does not contain a nucleus or membrane-bound organelles
• Components of plant and animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Genetic information storage in eukaryotic cells

  Within the nucleus, arranged in chromosomes
• Function of the nucleus

  Controls cellular activities
• Cytoplasm


  Fluid component of the cell containing organelles, enzymes and dissolved ions and nutrients
• Function of the cytoplasm

  Site of cellular reactions e.g. first stage of respiration
• Function of the cell membrane


  Controls the entry and exit of materials into and out of the cell
• Function of the mitochondria

  Site of later stages of aerobic respiration in which ATP is produced
• Simple diffusion


  The net movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient
• Function of the ribosomes


  Joins amino acids in a specific order during translation
• Molecules that enter and leave cells via simple diffusion through the cell membrane


  • Small molecules e.g. oxygen, water, glucose, amino acids
• Factors that affect the rate of diffusion

  • Temperature
  • Concentration gradient
  • Surface area of cell membrane
• Organelles found in plant cells only

  • Large, permanent vacuole
  • Cell wall
  • Chloroplasts
• Osmosis


  The net movement of water molecules from an area of high water concentration to an area of low water concentration through a partially permeable membrane
• Function of the cell wall

  • Provides strength
  • Prevents the cell bursting when water enters by osmosis
• Active transport


  The movement of molecules across a cell membrane from an area of low concentration to an area of high concentration, against the concentration gradient, using energy
• Permanent vacuole contents


  A solution of salts, sugars and organic acids
• Function of the permanent vacuole

  Supports the cell, maintaining its turgidity
• Function of the chloroplasts

  Site of photosynthesis
• Appearance of chloroplasts under a light microscope


  Appear green due to containing chlorophyll, a green pigment
• Organelles found in prokaryotic cells

  • Chromosomal DNA
  • Plasmid DNA
  • Cell wall
  • Cell membrane
  • Ribosomes
  • Flagella
• Genetic information storage in prokaryotic cells

  Found free within the cytoplasm as chromosomal DNA (single large loop of circular DNA) and plasmid DNA
• Plasmids


  Small, circular loops of DNA found free in the cytoplasm and separate from the main DNA, carrying genes that provide genetic advantages e.g. antibiotic resistance
• Flagellum


  Long, rotating, 'whip-like' protrusion that enables bacteria to move
• Haploid cell


  A cell that contains a single copy of each chromosome (half the number of chromosomes)
• Diploid cell


  A cell that contains two copies of each chromosome (full set of chromosomes)
• Gametes


  Reproductive cells (e.g. egg and sperm cells) that are haploid cells
• Sexual reproduction in terms of chromosome number

  1. Two haploid gametes fuse

  2. Resulting embryo has two chromosomes for each gene and two copies of each allele ∴ diploid
• Egg cell adaptations


  • Haploid nucleus contains genetic material
  • Mitochondria in cytoplasm produce energy for the developing embryo
  • Cytoplasm contains nutrients for the developing embryo
  • Cell membrane hardens after fertilisation, preventing the entry of other sperm and ensuring the zygote is diploid
• Sperm cell adaptations


  • Haploid nucleus contains genetic information
  • Tail enables movement
  • Mitochondria provide energy for tail movement
  • Acrosome contains enzymes that digest the egg cell membrane
• Diploid


  Having two copies of each gene and two copies of each allele
• Egg cells are adapted to their function
• Egg cells


  • Haploid nucleus contains genetic material
  • Mitochondria in cytoplasm produce energy for the developing embryo
  • Cytoplasm contains nutrients for the developing embryo
  • Cell membrane hardens after fertilisation, preventing the entry of other sperm and ensuring the zygote is diploid
• Simple diffusion


  The net movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient
• Sperm cells


  • Haploid nucleus contains genetic information
  • Tail enables movement
  • Mitochondria provide energy for tail movement
  • Acrosome contains enzymes that digest the egg cell membrane
• Molecules that enter and leave cells via simple diffusion through the cell membrane


  • Small molecules e.g. oxygen, water, glucose, amino acids
• Ciliated epithelial cells are found lining the surface of structures such as the respiratory tract and uterus
• Factors affecting the rate of diffusion

  • Temperature
  • Concentration gradient
  • Surface area of cell membrane