Chapter 1

• Eukaryotic cells


  Animal and plant cells have genetic material (DNA) that forms chromosomes and is contained in a nucleus
• Cell membrane


  • Controls the movement of substances in and out of a cell
• Animal cell


  • Nucleus contains DNA
  • Mitochondria where energy is released through respiration
• Plant cell


  • Cell wall made of cellulose, which strengthens the cell
  • Permanent vacuole contains cell sap
  • Chloroplasts contain chlorophyll to absorb light energy for photosynthesis
  • Ribosomes are the site of protein synthesis
• Bacteria


  • Single-celled
  • No nucleus, have a single loop of DNA
  • Have small rings of DNA called plasmids
  • Smaller than eukaryotic cells
• Cells in animals and plants differentiate to form different types of cells
• Most animal cells differentiate at an early stage of development, whereas a plant's cells differentiate throughout its lifetime
• Sperm cell


  • Tail to swim to the ovum and fertilise it
  • Lots of mitochondria to release energy from respiration, enabling the sperm to swim to the ovum
• Red blood cell


  • No nucleus so more room to carry oxygen
  • Contains a red pigment called haemoglobin that binds to oxygen molecules
  • Flat bi-concave disc shape to increase surface area-to-volume ratio
• Muscle cell


  • Contains protein fibres, which can contract to make the cells shorter
  • Contains lots of mitochondria to release energy from respiration, allowing the muscles to contract
• Nerve cell


  • Branched endings, called dendrites, to make connections with other neurones or effectors
  • Myelin sheath insulates the axon to increase the transmission speed of the electrical impulses
• Root hair cell


  • Long projection speeds up the absorption of water and mineral ions by increasing the surface area of the cell
  • Lots of mitochondria to release energy for the active transport of mineral ions from the soil
• Palisade cell


  • Lots of chloroplasts containing chlorophyll to absorb light energy
  • Located at the top surface of the leaf where it can absorb the most light energy
• Light microscope


  Uses light to form images, living samples can be viewed, relatively cheap, low magnification, low resolution
• Electron microscope


  Uses a beam of electrons to form images, samples cannot be living, expensive, high magnification, high resolution
• Electron microscopes allow you to see sub-cellular structures, such as ribosomes, that are too small to be seen with a light microscope
• Magnification


  Calculated as: image size / actual size
• Diffusion


  The spreading out of particles, resulting in a net movement from an area of higher concentration to an area of lower concentration
• Factors affecting rate of diffusion

  • Difference in concentration, temperature, and surface area of the membrane
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Active transport


  The movement of particles from a more dilute solution to a more concentrated solution using energy from respiration
• Particles move down the concentration gradient in diffusion, water moves from an area of lower solute concentration to an area of higher solute concentration in osmosis, and particles move against the concentration gradient in active transport
• Diffusion examples


  • Nutrients in small intestine diffuse into capillaries, oxygen and carbon dioxide diffuse in lungs, urea diffuses from cells into blood, oxygen and carbon dioxide diffuse in fish gills, carbon dioxide and oxygen diffuse in plant leaves
• Osmosis example


  • Water moves from soil into root hair cells
• Active transport examples


  • Sugar absorbed from small intestine, mineral ions absorbed into root hair cells
• Key terms


  • cell membrane, cell wall, chloroplast, chromosome, concentration, cytoplasm, dilute, DNA, eukaryotic, gill filaments, gradient, magnification, mitochondria, nucleus, partially permeable membrane, passive process, permanent vacuole, plasmid, prokaryotic, resolution, ribosome, root hair cell, stomata