PAPER 1

• This video is for paper one of GCSE biology and combined science
• You can get extra help with this exam by downloading my revision workbooks and my maps from Emma DT ChiCom the link is in the description below
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• GCSE these are tough but the fact that you're watching this means that you care and are putting effort in and that always pays off good luck for your exams and thanks again for watching
• Microscopy


  The study of small objects using a microscope
• Light microscope


  • First developed in the mid 17th century
  • Uses light to form an image
  • Can be used to view live specimens
  • Relatively cheap and easy to use
  • Can magnify up to 2,000 times
• Resolution


  The ability to see two things as separate objects
• Light microscope


  • Has a low resolution with a resolving power of around 200 nanometers
• Electron microscope


  • Developed by scientists in the 1930s
  • Uses electrons to form an image
  • Specimens must be dead first
  • Very expensive and has many conditions
  • Can magnify up to 2 million times
  • Has a high resolution of 0.2 nanometers
• The electron microscope is much better than the light microscope in terms of magnification and resolution
• The high magnification and resolution of the electron microscope allows scientists to see and understand lots more about the subcellular structures of cells
• Animal cell


  Contains the following organelles: nucleus, cell membrane, cytoplasm, mitochondria, ribosomes
• Nucleus


  Controls the cell's activities and contains genetic material (DNA)
• Cell membrane


  Responsible for controlling the passage of substances in and out of the cell
• Cytoplasm


  Liquid gel that fills the entire cell and is where chemical reactions occur
• Mitochondria


  Where aerobic respiration occurs, releasing energy for the cell
• Ribosomes


  Site of protein synthesis
• Plant cell


  • Contains the following organelles in addition to those in animal cells: chloroplasts, permanent vacuole, cell wall
• Chloroplasts


  Contain chlorophyll and are the site of photosynthesis
• Permanent vacuole


  Filled with cell sap, helps keep the cell rigid
• Cell wall


  Made of cellulose, strengthens and supports the plant cell
• Animal and plant cells are both eukaryotic cells
• Eukaryotic cells


  Have a cell membrane, cytoplasm, and genetic material enclosed in a nucleus
• Prokaryotic cells


  Lack a true nucleus, have genetic material as a single loop of DNA in the cytoplasm, may have plasmids and a cell wall, but lack organelles like mitochondria and chloroplasts
• Specialized animal cells


  • Sperm cell: has a tail for movement, acrosome to break down egg, large nucleus
  • Muscle cell: has many mitochondria for energy, special proteins for contraction
  • Nerve cell: has a long axon to carry electrical impulses, dendrites to connect to other cells, nerve endings to release chemical messengers
• Specialized plant cells


  • Root hair cell: has a large surface area, large permanent vacuole, many mitochondria
  • Xylem cell: forms long hollow tubes, has spiral lignin to strengthen and support
  • Phloem cell: has sieve plates to allow movement of dissolved food, companion cells with mitochondria to provide energy
• Diffusion


  The spreading out of particles in a solution or gas from an area of higher concentration to an area of lower concentration
• Factors affecting rate of diffusion

  • Temperature: higher temperature increases rate
  • Concentration gradient: steeper gradient increases rate
  • Surface area: larger surface area increases rate
• Osmosis


  The diffusion of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane
• Osmosis is important in animal cells to maintain the right internal solute concentrations
• Left side of the membrane

  Has more water molecules
• Right side of the membrane

  Has less water molecules and more sucrose or solute molecules, therefore it is the concentrated side
• Osmosis


  1. Occurs down a concentration gradient or from a dilute solution to a more concentrated solution

  2. Net movement of water is from the left side to the right side

  3. Water concentration will eventually be equal on both sides

  4. Water molecules will continue to move back and forth across the partially permeable membrane but there's no further net movement of water, the water is balanced on both sides
• Importance of osmosis in animal cells

  • Ensures solutes like glucose and salts are at the right concentration inside the cell
  • The internal environment needs to be kept just right for the cell to work
  • The difference in concentration between the cell's internal environment and the external solution determines how much osmosis occurs
• What happens when a red blood cell is put into a hypotonic solution

  Water moves into the cell, stretching it, and the cell may even burst if a lot of water moves in, killing the cell
• What happens when a red blood cell is put into an isotonic solution


  Nothing happens, as the two solutions are the same concentration, so there is no net movement of water (no osmosis)
• What happens when a red blood cell is put into a hypertonic solution

  Water moves out of the red blood cell and into the beaker, as the red blood cell solution is more dilute, the cell will shrink and not function properly
• Required practical A by osmosis looks at the effect of concentration of salt or sugar on the mass of plant tissue
• Active transport


  Substances move from a low concentration to a high concentration, against the concentration gradient, requiring energy from respiration