ocr as level biology

• Diffusion


  Net movement of molecules from an area of high concentration to an area of low concentration. This continues until particles are evenly distributed. Particles diffuse down a concentration gradient and its a passive process
• Fish opens its mouth lowering the floor of the buccal cavity, the volume increases


  How are fish gills ventilated?
• Molecules that are able to diffuse


  Small, non-polar molecules (oxygen, co2). Waters able as its small enough even though it's polar (osmosis)
• Factors affecting rate of diffusion


  Concentration gradient- higher= faster

  Thickness-thinner=shorter

  Surface area- larger=faster

  Temperature- warmer=faster as more kinetic energy
• Investigating diffusion


  Make agar jelly with phenolphthalein and dilute sodium hydroxide making it pink

  Fill a beaker with hydrochloric acid. Using a scalpel cut cubes and put them into beakers

  If you leave them they will turn clear as the acid diffuses into agar jelly and neutralises the sodium hydroxide

  Surface area- cut the jelly into different sizes work out surface area to volume ratio, time how long it takes to turn colourless

  Concentration gradient- prepare test tubes with different concentrations of hydrochloric acid put equal sized cubes into each and time how long it takes to go colourless

  Temperature-put test tubes into varying temperatures of water baths put equal sized cubes in and time how long it takes to go colourless
• Facilitated diffusion


  Larger molecules, ions, polar molecules can't diffuse directly through. Instead the diffuse through carrier/ channel proteins (facilitated diffusion) it goes down concentration gradient. It's passive so doesn't use energy
• Carrier proteins


  Diffuses large molecules in/out of cell down concentration gradient

  Molecule attaches do the protein changes shape it's releases the molecule on the opposite side
• Channel proteins


  They form pores in the membrane for charged molecules to diffuse down concentration gradient
• Active transport


  Uses energy to move molecules/ ions across plasma membranes against concentration gradient. Involves carrier proteins.
• The process of active transport


  Molecules attach to a carrier protein which changes shape moving the molecule across the membrane

  ATP is required
• Endocytosis


  For molecules too large for diffusion. The cell surrounds the substance with a section of plasma membrane then detaches forming a vesicle inside the cell containing the ingested substance requires ATP
• Exocytosis


  Some substances produced inside the cell need to be released vesicles detach from the Golgi apparatus. Vesicles fuse to the plasma membrane and release the contents outside the cell. It requires ATP
• Osmosis


  Diffusion of water molecules down a water potential gradient form an area of high concentration to an area of low concentration
• Water potential


  Likelihood of water molecules to diffuse in/out of a solution
• Investigating water potential


  Prepare different concentrations of sucrose solution

  Use a cork borer to cut potato into the same size

  Divide into groups of 3 and find the average mass

  Leave them for at least 20 minutes

  Remove chips and dry gently

  Weigh each group and calculate % change in mass plot results on graph
• Interphase


  Cell carries out normal function but prepares to divide. The DNA and organelles are replicated. Contains G1, G2 and synthesis
• Prophase, metaphase, anaphase, telophase

  What's the order of mitosis/meiosis?
• Prophase


  Chromosomes condense, centrioles move move to opposite sides of cell forming spindle fibres. Nuclear envelope breaks down
• Spindle fibres


  Network of protein fibres
• Metaphase


  Chromosomes line up along equator and become attacked to spindle fibres
• Anaphase


  Centromeres divide separating each pair of chromatids pulling them to opposite sides of the cell
• Telophase


  Chromatids reach opposite sides of cell they uncoil and can be called chromosomes again. Nuclear envelope reforms there are now 2 nuclei
• Cytokinesis


  Cytoplasm divides. In animal cells a cleavage furrow forms to divide the membrane. There are now 2 daughter cells genetically identical to each other
• Cell cycle


  Involves- interphase and M phase
• Meiosis


  Reproduction of 2 gametes at fertilisation forming a zygote. Involves reduction division so the hamsters produced have half the number of chromosomes (haploid cell). They're genetically different as they all have a different combination of chromosomes
• Crossing over


  Homologous pairs come together and pair up, twist around each other, bits of chromatids swap over. They still contain the same genes but now have different combinations of alleles
• Independent assortment


  Each homologous pair is made of one chromosome from each parent. When they line up in metaphase 1 and are separated in anaphase 1 it's completely random, so the 4 daughter cells have different combinations of both chromosomes leading to genetic variation
• Stem cells


  Unspecialised cells that differentiate into different types of cells. They can replace damaged cells or for growth
• Bone marrow/embryo


  Where do animal stem cells come from?
• Meristems


  Where do plant stem cells come from?
• Parkinson's

  Alzheimer's


  What 2 diseases could stem cells cure?
• Nerve cells in the brain die resulting in memory loss. Regrowing healthy nerve cells could cure people

  How could stems cells cure Alzheimer's?
• Suffer tumours because of a loss of nerves cells in the brain which release dopamine which controls movement. Transplanted cells can help regenerate dopamine-producing cells


  How could stem cells cure Parkinson's?
• Neutrophils

  Erythrocytes

  Epithelial cells

  Sperm cells


  What are 4 types of specialised animal cells?
• Palisade mesophyll cells

  Root hair cells

  Guard cells


  What are 3 types of specialised plant cells?
• Neutrophils


  Defend the body against disease. Flexible allowing them to engulf pathogens. Lysosomes in their cytoplasm contain digestive enzymes to break down pathogens (type of white blood cell)
• Erythrocytes (red blood cell)

  Carry oxygen in the blood. Biconcave shape provides large surface area for gas exchange, have no nucleus so more room for haemoglobin
• Epithelial cell


  Cover surfaces of organs. Joined by interlinking cell membranes. Some have cilia that beat to move particles away. Some (squamous) are very thin to allow efficient diffusion of gases
• Sperm cell


  Have flagellum to swim. Mitochondria for energy. The acrosome contains digestive enzymes to penetrate the surface of the egg
• Palisade mesophyll cells


  In leaves do most of the photosynthesis contain chloroplasts for absorbing sunlight, the walls are thin so CO2 can easily diffuse into the cell