B1

• What is differentiation?

  The process by which a cell changes to become specialised for its job
• How does differentiation work?

  As cells change they develop different subcellular structures and turn into different type of cells. This allows them to carry out specific functions

  
  

  Mostly occurs as an organism develops

  
  

  Animal cells lose ability to differentiate in early stages after being specialised whereas plants don't lose it
• What are the main reasons for cells that differentiate in mature animals?

  For repairing and replacing cells, like skin or blood cells
• What are stem cells ?

  Undifferentiated cells
• What are the 5 examples of specialised cells?

  Sperm cells, nerve cells, muscle cells, root hair cells, phloem and xylem cells
• How are sperm cells specialised?

  For REPRODUCTION

  long tail and streamline head to help it swim to the egg

  Lot of mitochondria in the cell to provide the energy needed

  Carries enzymes in its head to digest through the egg cell membrane
• How are nerve cells specialised?

  For RAPID SIGNALLING

  To carry electrical signals

  Long - cover more distance

  Branched connections at their ends to connect to other nerve cells and form a network throughout the body
• How muscle cells specialised ?

  FOR CONTRACTION

  Cells are long (space to contact) and contain lots of mitochondria for energy
• How are root hair cells specialised?

  For absorbing WATER and MINERALS

  Long - big surface area to absorb these from soils
• How are phloem and xylem cells specialised?

  For TRANSPORTING SUBSTANCES

  Form tubes which transport food and water around the plants

  The cells are joined end to end

  Xylem cells are Hollow

  Phloem cells have Very few subcellular structures so stuff can flow through them
• What are chromosomes?

  Contain genetic information, nucleus contains genetic material in form of chromosomes

  
  

  They are coiled up length of DNA molecules

  
  

  They carry large number of genes which control development of characteristics. Body cells have 2 copies of each chromosome one "mother" and one "father"
• What's the cell cycle ?

  Makes new cells for growth, development and repair

  
  

  Body cells in multicellular organisms divide to produce new cells. These organisms use mitosis to grow or replace damaged cells

  
  

  End of cycle results in 2 new cells identical to original cell with same number of chromosomes
• What are the 2 main stages of cell cycle ?

  Growth and DNA replication and mitosis
• What is growth and DNA replication ?

  1).DNA is spread out in long strings

  2).Before it divides cell grows and increases amount of subcellular structures like mitochondria and ribosomes

  3). Then duplicates DNA so there is 1 copy for each cell, this forms x-shapes chromosomes (each arm is exact duplicate)
• What is mitosis?

  After DNA is copied cell is ready for mitosis

  1). Chromosomes line up at centre of cell and cell fibres pull them apart. The 2 arms go to opposite ends

  2). Membranes form around each sets of chromosomes which become nuclei of 2 new cells (nucleus has divided )

  3). Then cytoplasm and membrane divide

  Cell has now produced 2 new daughter cells
• What are daughter cells ?

  Daughter cell contains exactly the same DNA, they are identical
• What can embryonic stem cells do?

  Turn into any type of cell
• What are undifferentiated cells called?

  stem cells, they can divide to produce more undifferentiated cells. They can differentiate into different types of cells depending on instructions they are given.
• Where are stem cells found?

  In early human embryos or the bone marrow of adults

  
  

  Human embryos can turn into any kind of cell

  
  

  Bone marrow can't turn into any cell type, only certain ones like blood vessel

  
  

  These stem cells can be grown in a lab to produce clones and made to differentiate into specialised cells to use in medicine or research
• How can stem cells be used in medicine?

  Stem cells transferred from bone marrow of a healthy person can replace faulty blood cells.

  
  

  Embryonic stem cells used to replace faulty cells, you could make insulin- producing cells for people with diabetes and nerve cells for people paralysed by spinal injuries
• What is therapeutic cloning?

  Embryo can be made to have same genetic information as the patient. Which means stem cells produced from it contains same genes and so wouldn't be rejected by patients body
• What are the risks using stem cells in medicine ?

  Stem cells grown in the lab may become contaminated with a virus which could be passed on to the patient and make them sicker
• Reason why people are against stem cell research?

  Feel that human embryos is a potential human life and others believe curing existing patients who are suffering is more important than rights of embryos

  
  

  People argue that the embryos in experiments are unwanted ones from fertility clinics and would be destroyed anyway

  
  

  Some believe scientists should find other sources of stem cells.

  
  

  Its banned in some countries but allowed in the uk following strict guidelines
• How do stem cells produce identical plants ?

  The stem cells in a plant are found in the meristems, cells in the meristem can differentiate into any plant cell.

  Can be used for:

  • produce clones of a whole plant quick and cheap

  • to grow more plants of rare species

  • grow crops of identical plants that have desired features for farmers
• What is osmosis?

  The movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of lower water concentration
• What is a partially permeable membrane ?

  A membrane that has very small holes that only small molecules such as water can pass through them and bigger molecules such as sugar molecules cant.
• How does osmosis work?

  Water can pass through both ways, there are more water molecules on one side so there is a steady net flow of water into the region with fewer

  
  

  This means that the stronger sugar solution gets more dilute it will become as water tries to "even up" concentration both sides
• Equipment needed for Practical for osmosis ?

  Potato

  Cork borer

  Ruler

  10cm^3 measuring cylinder

  Labels

  3 boiling tubes

  Test tube rack

  Paper towels

  Sharp knife

  White tile

  Range of sugar solutions

  Distilled water

  Top pan balance
• Steps for osmosis practical ?

  1). Use cork borer to cut 3 potato cylinders of same diameter

  2). Trim cylinders so they are all the same length

  3). Accurately measure and record length and mass of each potato

  4). Measure 10cm^3 of 0.5M sugar solution and put into first boiling tube. Label tube as 0.5M sugar

  5). Measure 10cm^3 of 0.25M sugar solution and put into second boiling tube. Label tube as 0.25M sugar

  6). Measure 10cm^3 of distilled water and put into 3rd boiling tube. Label as water

  7). Add one potato cylinder to each tube. Make sure u know the length and masses of each potato cylinder

  8). Record this into a table

  9). Leave potato overnight in test tube rack

  10). Remove cylinders from tube and carefully blot dry them with paper towel

  11). Re-measure length and mass of each cylinder, record into table the calculate changes in length and mass of each cylinder

  12). Then plot graph
• How do root hair cells take in minerals ?

  Each root covered in millions of microscopic hairs

  
  

  Gives plant large surface area for absorbing water and mineral ions

  
  

  Plant needs these for healthy growth

  
  

  Concentration of minerals is usually higher in too hair cells then soil.
• How do root hair cells use active transport?

  -take up mineral ions from dilute solution against a concentration gradient, this is essential for growth, but active transport needs energy from respiration to make it work
• How does active transport work in humans ?

  Used in the gut when there's a lower concentration of nutrients in the gut but a higher concentration in blood.

  
  

  Sometimes there is a lower concentration of nutrients in the gut than blood meaning the concentration gradient is the wrong way. So we use active transport.

  
  

  Which means glucose can be taken into bloodstream when concentration is higher in the gut, then transported to cells where it's used for respiration
• How do organisms exchange surfaces ?

  With their environment
• How do cells use diffusion ?

  To take in substances they need and get rid of waste products for example:

  • oxygen and carbon dioxide are transferred between cells and environment during gas exchange

  • in humans urea diffuses from cells into blood plasma for removal from the body by the kidneys

  
  

  How easy it is for an organism to exchange surfaces with environment depends on organisms surface area to volume ratio ( SA:V)
• How to compare surface area to volume ratio?

  Area of surface is found by length x width and the volume of a block is found by length x width x height and is then written in the ratio (SA:V) and simplified if needed
• How do single-celled organisms exchange substances?

  Gases and substances can diffuse directly into or our of the cell across the cell membrane because they have a large surface area compared to their volume so enough substances can be exchanged across the membrane to supply volume of the cell
• How do multicellular organisms exchange surfaces ?

  They have smaller surface area compared to volume so not enough substances can diffuse to supply volume. This means they need gas exchange for efficient diffusion. The exchange surface structures have to allow enough substances to pass through
• How have exchange surfaces adapted to maximise effectiveness?

  - They have a thin membrane, so substances only have a short distance to diffuse.

  
  

  - They have a large surface area so lots of a substance can diffuse at once.

  
  

  - In animals, they have lots of blood vessels, to get stuff into and out of the blood quickly.

  
  

  - gas exchange surfaces in animals are often ventilated too, air moves in and out
• How does gas exchange happen in the lungs ?

  1).Job of lungs is to transfer oxygen to blood and remove waste CO2

  
  

  2).For this the lungs contain lots of little air sacs called alveoli where gas exchange takes place

  
  

  3). The alveoli are specialised to maximise diffusion of O2 and CO2 such as: massive surface area, moist lining for dissolving gases, thin walls, good blood supply
• What are villi ?

  Inside small intestine it is covered in lots of villi, they increase surface area so digested food is absorbed much more quickly into the blood. They have: single layer of surface cells, very good blood supply to assist quick absorption