Biology DNA, mitosis etc.

• Chromosome


  a strand of DNA found inside the nucleus, containing hundreds of genes, 46 chromosomes in each human cell (23 pairs)
• Gene


  a section of DNA that determines a characteristic
• DNA


  deoxyribonucleic acid, a chemical that genes and chromosomes are made of
• Stem cell


  unspecialised cell that can differentiate into a new cells that are specialised
• Differentiation


  the specialisation of cells to carry out a particular job
• Genes during differentiation


  when a cell differentiates, some of the genes have been switched on and others have been switched off
• Adult stem cells


  produce the same sort of cell from division and exist to replace the dead or damaged cells
• Plant stem cells


  plants differentiate all throughout their lives and unspecialised cells are found in the meristems (near the stems and roots)
• Redifferentiation


  when a cell undergo mitosis and forms a completely different type of plant cell when it moves from one part of the plant to another
• Nucleus


  controls cell activities, contains the DNA
• Gamete


  has only 23 chromosomes and once fused, they add up to make a total of 46
• Mitosis


  cell grows, replicates DNA to form two copies of each chromosome (held together in an x shape), increases other organelles ready for the cell to divide, chromosomes line up on the Equator/middle, cell fibres pull the chromosomes and copies to opposite ends/poles and the nucleus divides, cytoplasm and cell membranes then divide (cytokinesis) forming two genetically identical daughter cells
• Mitois reasons


  growth and replacement of worn cells
• Cloning


  clones can be formed from a tiny piece of leaf tissue

  in the right conditions, a plant cell will become unspecialised and undergo mitosis many times, forming different tissues and finally forming an identical plant
• Using embryonic stem cells

  from the early stages of embryo formation, ability to become any type of body cell, divide rapidly, used for research, medical treatment, could be rejected and may cause cancer, uses extra embryos from IVF, ethical objections because it is a potential life
• Using adult stem cells

  form particular cell types, for regrowing specific cell types to replace damaged tissues for organs, limited, virus may be transmitted from donor to patient and also risk of rejection, less ethical objections because donors give permission
• Reason against ESCs


  money is better spent on treating people now than on research that might be unsuccessful, expensive
• Reasons for ESCs


  research into treating chronic illnesses in the future, IVF embryos will be thrown away anyway if they aren't used
• Therapeutic cloning


  -adult cell from patient is removed and nucleus is taken out

  -egg cell from donor is removed and nucleus is taken out

  -nucleus from patient is inserted into the egg cell

  -egg cell divides creating cloned embryonic stem cells identical to the patients cells

  -specific tissues or organs are grown and used to treat patient with 0 rejection risk, however not a solution for genetic disorders/diseases
• Flower


  reproductive part of the plant, containing pollen and the egg
• Epidermal


  single layer of cells, (upper epidermis is transparent) forms a boundary and often secretes a waxy substance that waterproofs the surface (waxy cuticle)
• Palisade mesophyll


  under epidermis, contains many chloroplasts for photosynthesis
• Xylem


  transports water and mineral ions, substances move in one direction (up), xylem vessels are made from dead cells, they lose their end walls to from a continuous, hollow tube, strengthened and waterproofed by lignin
• Phloem


  transports sugars and amino acids dissolved in water, substances move up and down the plant (translocation), phloem is made up of living cells with sieve tubes so the cytoplasm of one cell connects with the next, and companion cells which provide the energy required for transportation
• Spongy mesophyll


  big air spaces for easier diffusion of CO2 inside and O2 outside
• Stomata


  small pores mainly found on the underside of leaves, allow gas exchange and transpiration, has guard cells that open and close the stomata (2 each pore)
• Transpiration


  water loss from plant, involves evaporation of water and then diffusion of the vapour, lost from stomata. water moves up through the xylem to replace water lost
• Transpiration stream


  the constant movement of water through a plant
• Transpiration factor- light intensity


  the brighter it is, the greater the transpiration rate because stomata are opened more to let in CO2 for photosynthesis, so more water is lost from the stomata
• Transpiration factor- temperature


  when it is warmer, water particles have more energy so evaporate quicker, then diffuse out of the stomata, therefore transpiration is faster
• Transpiration factor- humidity


  if the air is humid, the conc. gradient is less steep than when the air is dry because there is more water vapour in the air so diffusion and transpiration is slower
• Transpiration factor- air flow

  if it is windy, the water vapour that has diffused out of the leaves, will be blown away and so a steep conc. gradient is maintained, increasing transpiration