AQA BIOL2~3rd June 2013~AS Biology (Now Closed) Watch
root pressure pushes on column of water - it would normally produce positive pressure (pushes wall of xylem outwards)
Both the water from the symplast and the apoplast end up in the final endothelial cell. Then all the water crosses the endothelial membrane into the xylem. The endothelial membrane is like a customs office in an airport. All the water has to pass through it and be checked before going into the xylem.
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DNA unravels and replicates so there are two copies of each chromosome, called chromatids.
The DNA condenses to form, double armed, chromosomes made from two sister chromatids.
The chromosomes arrange themselves into homologous pairs.
Meiosis I: the homologous pairs are separated, halving the chromosome number.
Meiosis II: The pairs of sister chromatids that make up each chromosome are separated.
Four haploid (gametes) that are genetically different from each other are produced.
The enzyme DNA helicase breaks the hydrogen bonds between two polynucleotide DNA strands.
Each original strand acts as a template for a new strand. Free floating nucleotides join to the template by specific base pairing.
DNA Polymerase enzyme joins the nucleotides together. Hydrogen bonds form between the bases on the original and new strand.
Each new DNA molecule contains one original strand and one new strand. This is SEMI CONSERVATIVE.
In Mitosis a parent cell divides to produce two genetically identical daughter cells.
Interphase: The cell carries out normal functions but also prepares to divide. The DNA is unraveled and replicated to double the DNA content.
Prophase: Proteins called centriole move to opposite ends of the cell. Forming a spindle. The nuclear envelope breaks down and the chromosomes are free in the cytoplasm.
Metaphase: Chromosomes each with two chromatids line up along the middle of the cell, and are attached to the spindle by their centromere.
Anaphase: The spindle fibre pulls chromatids apart. The chromatids are pulled to opposite ends of the cell, centromere first.
Telophase: Chromatids uncoil and become long and thin, they are again called chromosomes. A nuclear envelope forms around each group of chromosomes. The cytoplasm divides and there are now two daughter cells that are genetically identical.
Assemble the potometer.
Cut a shoot underwater.
Remove the apparatus from the water but keep the end of the capillary tube submerged in a beaker of water.
Check that the apparatus is watertight and airtight.
Dry the leaves, allow time for the shoot to acclimatise and then shut the tap.
Remove the end of the capillary tube from the beaker of water until one air bubble has formed, then resubmerge tube.
Record starting position of the air bubble, then record the distance moved by the bubble per unit time.
Knowing my luck, it will come up.