B1

• electron microscopes have a higher magnification and resolution than light microscopes, they let you see things like cells - however light ones can view living samples but electron ones cannot
• microscopes: terms to know include ocular lens, objective lens, stage, slide, coarse adjustment knob, fine adjustment knob, and light source/lamp
• Cytoplasm - liquid gel where most chemical reactions take place, including anaerobic respiration
• Nucleus - controls the cell and surrounded by nuclear membrane, average size is 10 micrometres (μm)
• Cell membrane - controls the passage of substances such as glucose and mineral ions into the cell, as well as controlling urea and hormones leaving the cell
• Mitochondria - where aerobic respiration takes place
• Ribosomes - where protein synthesis takes place
• Cell wall - made of cellulose that strengthens the cell and gives it support
• Chloroplasts - green because they contain chlorophyll which absorbs light, making food by photosynthesis
• Vacuole - space in cytoplasm filled with cell sap which helps to keep the cell rigid, supporting the plant
• When cells become specialised through differentiation:

  • their shape/structure changes
  • more of some organelles - e.g. more mitochondria for more respiration = more energy
  • genes are turned on or off
• Prokaryotic cells (bacteria) replicate by binary fission and eukaryotic (animal and plant cells) replicate by mitosis
• examples of specialised animal cells - nerve, sperm, muscle
• root hair cells - take up water and mineral ions through active transport
• photosynthetic - photosynthesize and look like a classic plant cell
• xylem - transports water and minerals and also supports the plant
• phloem - transports plant’s food made by photosynthesis
• sperm cell - fertilises the egg; has a tail to swim
• red blood cell - transports oxygen around body; no nucleus to carry more oxygen
• muscle cell - contracts and relaxes to allow movement; contains protein fibres
• nerve cell - carries electrical movements around body; branched endings (dendrites) to make connections
• Diffusion:

  • net movement of a substance from an area of high concentration to an area of low concentration
• • higher the concentration gradient, faster the rate of diffusion
  • higher the temperature, more kinetic energy particles will have, so faster rate of diffusion
  • the larger the surface area of membrane, the faster the rate of diffusion
• Active transport:

  • movement of particles against a concentration gradient and uses energy released from respiration, requiring a cell membrane
• Osmosis:

  • diffusion of ONLY water molecules from a dilute solution to a concentrated solution across a partially permeable membrane
• REQUIRED PRACTICAL in Osmosis:

  • finding change in mass and change in length of potato cylinders in different sugar OR salt solutions
  • the potato in distilled water increases in mass and length
  • the potato in the lowest level of sugar solution loses a little mass and length
  • the potato in the highest level of sugar solution loses more mass and length
  • this is because the volume of water in the potato changes according to the volume of water outside it, to balance it out