12a2 Revision - Groby Bio Page

12a2 Revision - Groby Bio Page

12a2 Revision Tissue Fluid Formation What is meant by these three key terms? Blood Tissue Fluid Lymph

Tissue Fluid Formation Tissue Fluid Formation Capillaries are narrower than other blood vessels creating hydrostatic pressure causing ultrafiltration Tissue Fluid Formation Exchange of metabolic materials with cells

Tissue Fluid Formation Tissue fluid moves back into capillary as lower hydrostatic pressure in the capillary Tissue Fluid Formation Lower water potential in capillary so water moves back in by osmosis

Lymph Formation Not all tissue fluid returns to capillaries, some is drained into the lymphatic system. Lymph has less oxygen and nutrients than tissue fluid more carbon dioxide more fatty material absorbed

from the intestines. presence of lymphocytes produced in lymph nodes Bohr Shift Haemoglobin

Protein 2 alpha chains 2 beta chains Each with haem group to bind to oxygen molecule Carbon Dioxide

Released by respiring cells Some dissolved in plasma, some combines with Hb Carbon dioxide will reduce Hbs affinity for oxygen, so Hb will release oxygen where it is needed Bohr Effect CO2 + H2O H2CO3 H+ + HCO3

carbonic acid hydrogen ions + hydrogen carbonate ions Caused by enzyme carbonic anhydrase in RBCs Hb + H+ Haemoglobinic acid H+ cause acidity that promotes oxygen release Bohr Effect: Oxygen Dissociation Curve shifts to right

Transpiration Transpiration The loss of water vapour from aerial parts of a plant due to evaporation Transpiration Movement of water from the roots, up the stem and

out of the leaves Push: by water moving into the roots Pull: by evaporation from the leaves Water evaporates from internal surfaces of the leaves and collects in the air spaces, when the concentration of water is higher inside the leaf than out the water moves out of the stomata by osmosis Factor

Number of leaves How to increase water loss More surface area Number, size & position of stomata Cuticle

More, bigger and on under surface Absent Light Present

Temperature Higher Humidity Lower Air movement

Fast Water availability Lots Translocation

Define key terms: source, sink & translocation (Grade E-D) Translocation Definition: Transport of assimilates throughout the plant, in the phloem tissue

State examples of source and sinks (Grade E-D) Define key terms: source, sink & translocation (Grade E-D) What is a source? Examples: Leaf Cell

What is a sink? Examples: Root Cell Source & Sink Interpret the mechanism of active loading (Grade C-A) Active Loading at the Source

Companion cells Have lots of mitochondria to make ATP ATP used to pump out protons (H+ ions) This causes a diffusion gradient

Protons diffuse back in through cotransporter proteins, bringing sucrose in with them This leads to a high concentration of sucrose Sieve Tube Elements Sucrose moves in through plasmodesmata Sucrose lowers the water potential, so water moves in by osmosis

This increases the hydrostatic pressure Interpret the mechanism of active loading (Grade C-A) Removal at the Sink Sink Uses up sucrose in respiration or it is stored as starch Lowers sucrose concentration

Sucrose moves in by diffusion, lowering the water potential Water moves into the sink by osmosis This lowers the hydrostatic pressure This high hydrostatic pressure near the source and low hydrostatic pressure near the sink creates movement in the phloem called mass flow Evaluate evidence for this

mechanism (Grade C-A) Evidence Active loading and movement of sucrose in the phloem is a theory Evidence supports this theory Radioactive labelling of carbon dioxide (for

photosynthesis) Labelled carbon observed in the phloem Movement of labelled sucrose is faster than it would be by diffusion Sucrose is moved to all parts of the plant at the same rate, rather than going quicker to areas of low concentration Tree Ringing

Removal of bark in a ring all around the tree trunk, which removes the phloem but leaves the xylem intact Tree swells above the ring, where sugar collect Mitochondria Companion cells have large amounts of mitochondria

Aphids Feed by inserting mouth parts into phloem Analysis of fluids collected from aphids contain lots of sugars pH Companion Cells pH have a higher than surrounding cells

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