bio p1

• 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
• Types of microscopes

  • Light microscope
  • Electron 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
  • 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 more about the subcellular structures of cells
• Animal cell


  Contains a nucleus, cell membrane, cytoplasm, mitochondria, and ribosomes
• Plant cell

  Contains a nucleus, cell membrane, cytoplasm, mitochondria, ribosomes, chloroplasts, permanent vacuole, and cell wall
• Animal and plant cells are both eukaryotic cells
• Eukaryotic cells

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


  Have a cell membrane and cytoplasm, but their genetic material is not enclosed in a nucleus
• Features of prokaryotic cells

  • Cell membrane
  • Cytoplasm
  • Ribosomes
  • Cell wall (not made of cellulose)
  • Single loop of DNA
  • Plasmids
  • Slime layer
  • Flagella
• Prokaryotic cells do not have chloroplasts or mitochondria
• Specialized cells


  Cells that have developed different subcellular structures to carry out a particular function
• Sperm cell


  • Has a tail to help it swim
  • Has many mitochondria in the mid-piece to provide energy
  • Has an acrosome containing enzymes to break down the egg
  • Has a large nucleus to contain DNA
• Muscle cell


  • Has many mitochondria to release energy for contraction
  • Has special proteins that cause contraction by sliding across each other
  • Can store glycogen to be broken down for respiration
• Nerve cell

  • Has a long axon to carry electrical impulses
  • Has dendrites to connect to other nerve cells
  • Has nerve endings that release chemical messengers
• Root hair cell


  • Has a large surface area for absorption
  • Has a large permanent vacuole to speed up osmosis
  • Has many mitochondria for active transport of mineral ions
• Xylem cell


  • Forms long hollow tubes to allow easy movement of water and minerals
  • Has spirals of lignin to strengthen the cell walls and support the plant
• Phloem cell


  • Has sieve plates with holes to allow easy movement of dissolved food
  • Has adjacent companion cells with many mitochondria to provide energy for food transport
• Diffusion


  The spreading out of particles in a solution or gas from an area of higher concentration to an area of lower concentration
• Diffusion is a passive process that does not require additional energy
• Factors affecting rate of diffusion

  • Temperature
  • Concentration gradient
  • Surface area
• Osmosis


  The diffusion of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane
• Osmosis is a passive process that occurs down a concentration gradient
• Osmosis is important in animal cells to maintain the right internal environment
• 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. Eventually the water concentration will 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 will determine how much osmosis occurs
• Effect of different solutions on a red blood cell

  1. Hypotonic solution: Water moves into the cell, it stretches and may burst

  2. Isotonic solution: No net movement of water, no osmosis occurs

  3. Hypertonic solution: Water moves out of the cell, it shrinks and won't function properly
• Osmosis is a required practical that looks at the effect of concentration of salt or sugar on the mass of plant tissue
• Active transport

  • Moves substances from a more dilute solution to a more concentrated solution, against the concentration gradient
  • Requires energy from respiration