Biology AQA paper 1

• • Animals and plant cells are eukaryotic cells. They have a cell membrane, cytoplasm and a nucleus containing dna
• Bacterial cells are prokaryotic and much smaller. They have a cell wall, cell membrane, cytoplasm and a single circular strand of DNA and plasmids
• Structures like the cell membrane are examples of organelles
• Nucleus - contains DNA coding for a particular protein needed to build new cell walls
• Cytoplasm - liquid substance where chemical reactions occur, contains enzymes and organelles are found in it
• Cell membrane - controls what enters and leave the cell
• Mitochondria - where aerobic respiration occurs, providing energy for the cell
• Ribosomes - where protein synthesis occurs, found on a structure called the rough endoplasmic reticulum
• Chloroplasts - where photosynthesis takes place, contains chlorophyll pigment (green) which harvests the light needed for photosynthesis
• Permanent vacuole - contains cell sap, within cytoplasm, improves cell's rigidity
• Cell wall - made from cellulose, provides strength to the cell
• Cells specialize by undergoing differentiation
• Sperm cells - male DNA to egg, streamlined head and tail (flagella), many mitochondria for energy, acrosome (the top of the head) has digestive enzymes which break down the outermost layer of the egg
• Nerve cells - transmit electrical signals quickly from one place in the body to another, axon is long allowing impulses to travel far, has lots of extensions from the cell body so they can connect to other nerve cells, nerve endings have many mitochondria which supply energy to make special transmitter chemicals called neurotransmitters
• Muscle cells - specialised to contract quickly to move bones or to squeeze smooth muscle, special proteins allow them to contract, lots of mitochondria to provide energy for respiration, can store glycogen used in respiration by mitochondira
• Root hair cells - specialised to take up water by osmosis and mineral ions by active transport, large surface area, large permanent vacuole, mitochondria to provide energy from respiration for active transport
• Xylem cells - specialised to transport water and mineral ions up the plant from the roots, the cells are dead and so lose their contents and join to form tubes to transport the water and ions, lignin is deposited in spirals to help withstand pressure
• Phoem cells - specialized to carry the products of photosynthesis, cell walls allow movement of substance from cell to cell
• Stem cells are contain all genes needed and they get certain ones turned on or off based on what they are differentiating too
• Animals cell mostly differentiate at an early stage by undergoing mitosis
• Red blood cells lose their nucleus and cannot divide and are replaced by adult stem cells
• In mature animals, cell division mostly only happens to repair or replace damaged cells, as they undergo little growth
• Most plant cells only differentiate when they reach their final position in the plant
• Light microscope

  • Two lenses (objective and eyepiece)
  • Objective - magnified
  • Illuminated from underneath
  • Max magnification of x2000
  • Used for tissues and cells
• Electron microscope

  • Forms and image from the smaller electron wavelengths
  • 2d or 3d images
  • Magnification of up to x2000000
• Magnification of the eyepiece lens X magnification of the objective lens = magnification of light microscope
• Size of image / magnification = size of object