Biology OCR AS Level Unit 1 Notes

Biology OCR AS Level Unit 1 Notes

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  • Created on: 20-04-11 17:20
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Golgi apparatus recieves proteins from ER and modifies them.
Xerophyte -a plant that is adapted to reduce water loss so it can survive in dry conditions.
Eukaryote- an organism having cells with a nucleus and membrane-bound organelles.
Potometers measure the amount of water taken up by a plant, or the mass change in X.....they
can be affected by external factors, so mention this if improvement question comes up.
Potometer measures water uptake (not transpiration) and you have to know how to set up a
cut root underwater.
make sure apparatus is bubble free.
set up apparatus underwater.
make sure air and water tight.
let leaves dry (acclimatise).
record start position of air bubble.
and using stopwatch measure distance travelled per minute (mm/m).
Cytokinesis- The division of the cell, following nuclear division, to form two new cells.
Movement of water across root:
1. Minerals pass by active transport across cortex lowering water potential, setting up water
potential gradient.
2. Water passes by osmosis down water potential gradient across cortex via apoplast
pathway between cells.
3. Casparian strip blocks apoplast, forcing water into symplast pathway.
4. Water moves through endodermal cells into xylem.
Movement of water up plant:
1. Water is forced into xylem by osmosis creating root pressure that forces water upwards.
2. Water molecules joined together by Hydrogen-bonds. These forces of cohesion cause water
molecules to join into column. When water is lost by transpiration, tension in column forces it
3. Water molecules attached to xylem vessels by adhesion.
1. Water moves by osmosis from xylem to mesophyll cells.
2. Water is evaporated from mesophyll cells, water vapour collects in air spaces.
3. Water vapour diffuses out of stomata.
Entry of sucrose into sieve tube elements:
1. Hydrogen ions actively transported out of companion cells reducing concentration in
companion cells, setting up diffusion gradient.
2. Hydrogen ions diffuse back into companion cells via co-transporter proteins bringing in
3. Sucrose moves into sieve tube elements by diffusion via plasmodesmata.
Mitosis is needed for growth, repair and asexual reproduction in plants and animals.
Growth - Multicellular organisms produce new extra cells to grow. New cells are genetically
identical to the parent cell and can preform the same function.

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Repair - Damaged cells need to be replaced by new ones to preform the same function and
need to be genetically identical.
Asexual reproduction - Single celled organisms divide to produce two daughter cells that are
separate organisms. Some multicellular organisms produce offspring from parts of the parent.
Interphase - DNA Replicates. Cell increases in volume and size. Organelles are replicated.
Prophase - Chromosomes coil, shorten and thicken. They are now visible under a light
microscope. The nuclear envelope breaks down.…read more

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can also bind cells together in tissues.
Cardiac cycle;
1. Relaxation of Ventricles and atria.
2. Blood enters atria from veins returning to heart.
3. Atria fill with blood.
4. Atria contract (atrial systole).
5. Blood passes into ventricles.
6. Through atrioventricilar valves.
7. Atrioventricular valves shut to prevent backflow back into atria.
8. Ventricles contract (ventricular systole).
9. Blood passes out into arteries leaving the heart through open semilunar valves.
10. Semilunar valves shut to prevent backflow.…read more

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What is translocation?
Translocation is the transport of assimilates throughout the plant, in the phloem tissue.
What is a source?
A source releases sucrose into the phloem.
What is a sink?
A sink removes sucrose from the phloem.
Describe how the phloem is actively loaded at the source...
ATP is used by companion cells to actively transport hydrogen ions out of their cytoplasm and
into surrounding tissue. This sets up a diffusion gradient and hydrogen ions diffuse back into
the companion cells.…read more

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HEAD (which is hydrophilic- "water loving").
two fatty acid TAILS which are hydrophobic ("water hating").
called a BILAYER because the cytoplasm inside the cell and the fluid outside the cell
contains a lot of water. so the heads (water loving) face OUT towards the water on
either side of the membrane .
Therefore the centre of this bilayer (which is made up of the fatty acid tails- water
hating) is HYDROPHOBIC.
So as the centre is made of the hydrophobic tails(water hating).…read more

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Active transport is essentially the same concept as facilitated diffusion through a carrier
protein, (substance to be transported fits into carrier protein, carrier protein changes shape,
carrier protein releases substance on other side of membrane) however the difference is:
active transport uses ATP from energy to move (specific) substance AGAINST a concentration
gradient.…read more

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The low partial pressure of oxygen causes the adult haemoglobin to release oxygen
which the fetus picks up.
So the curve for fetus is higher than adult.
Water moves up the xylem in 3 ways
1) Root pressure/Hydrostatic pressure:
As the minerals are ACTIVELY transported into the xylem vessel, this lowers the water
potential of the xylem vessel causing water from the endodermis cells to move down
the water potential gradient and enter the xylem by osmosis. This increases the root
pressure/hydrostatic pressure.…read more

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Describe the functions of glycoproteins in cell surface membrane?
Acts as receptor sites for hormones due to its complementary shape.
Cell Adhesion- binds tissues together providing stability.
Forms OH bonds with water- again stability.
Regulates what enters and leaves (pores/channels/carrier proteins).
Cell signalling- Recognises cells as "self" so involved in the immune system.
Xylem - transport of water and dissolved minerals UP the plant
- no end walls.
- no cell contents.…read more


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