WELCOME..... TO .....HIGH SCHOOL BIOLOGY BLOG !!!

Tuesday, April 26, 2011

Breathing process

1. Breathing control centre are:
  • located in two major regions (medulla oblongata + pons).
  • in medulla - sets the basic rhythm,
  • in pons - moderates it smoothing out the transition between inhalation + exhalation.
  • send impulses to the diaphragm + external intercostals muscle.

2. The central chemoreceptors (lies near the breathing control centers):
  • detet the changes in pH of the cerebospinal fluid (CSF).
  • stimulate the breathing centre
  • slow down or speed the rhythmic discharge of nerve impulses













3. Carotid bodies are
  • found in the carotid artery in the neck.
  • chemoreceptor with nerve endings in the wall of carotid artery
  • monitors the changes of blood pH in the carotid artery.
















4. Aortic bodies are
  • found in aorta.
  • chemoreceptors that monitor the changes of blood pH.
  • nerve endings in the wall of aorta.















5. Aortic and carotid bodies:
  • also called peripheral chemoreceptors.
  • impulses are relayed to the breathing control centres.
  • change of CO2 conc. in the blood triggers a series of chain reactions.
  • blood CO2 conc. back to normal,
  • negative feedback loop.

6. In the blood plasma:
  • CO2 released by cellular respiration 
  • reacts with H2O to form carbonic acid (H2CO2)
  • dissociates to form hydrogen carbonate ions (HCO3+) and hydrogen ions (H+).
  • increase in hydrogen ions (H+) conc.
  • increase the acidity of the blood plasma,
  • decreasing the pH.













7. In the region of medulla
  • CO2 diffuses into CSF from the surrounding capillary.
  • then reacts with H2O in the fluid to form carbonic acid (H2CO3).
  • dissociates to form hydrogen carbonate (HCO3+) and hydrogen ions (H+).
  • The acidity in the CSF increases
  • resulting in the decreases in the pH.


8. When blood flows through Peripheral Chemoreceptors (from aortic + carotid bodies) + Central Chemoreceptor












à detect increase in H+ conc
à send impulses to breathing control centre (in medulla oblongata)
à sends impulses to diaphragm + external intercostals muscles to contract faster
à breathing rate increases (to expel excess CO2)
à lungs expand (for faster breathing)
à stimulates stretch receptors (in lungs)
à send impulses to the breathing control centre
à sends impulses (via parasympathetic nerve) to the diaphragm + external intercostals muscle
à to slow down the contraction
à breathing rate returns to normal
à negative feedback reaction.



Tuesday, April 19, 2011

Anaerobic Respiration (Fermentation)

1. Anaerobic respiration (fermentation):
    - respiration takes place in the absence of O2
    - occurs only in the cytoplasm.
    - produces: pyruvate, 2 NADH + 2 mol ATP 
    - pyruvate + NADH accumulate in cytoplasm








2. - pyruvate + NADH accumulate in cytoplasm
       --> causes tissues to run out of H acceptor (NAD+) - limited supply.
       --> glycolysis may not occur.
       --> need for an alternative H acceptor.
       --> pyruvate or acetaldehyde becomes the H acceptor.
       --> pyruvate can undergo both aerobic and anaerobic respiration.

3. In plants:
    - pyruvate undergoes alcohol fermentation --> produce ethanol,
    - occurs in roots of the plants (water logged conditions).












4. In animals:
    - pyruvate undergoes lactic acid fermentation --> produce lactic acid
    - occurs in the muscles during vigorous activity + strenuous exercise.











7. Fermentation products are used commercially.
    - Wine, methanol and formic acid are formed by alcohol fermentation.
    - Yogurt, cheese and soy sauce are formed by lactic acid fermentation.

Saturday, April 16, 2011

Aerobic Respiration - Electron Transport System

1. Electron transport system = chain of e- acceptors (embedded in the inner membrane of the mitochondrion).




















2.  e- transferred from NADH + FADH2 via several e- acceptors --> final e- acceptor (molecular O2).
3.  energy produced = ATP (thru oxidative phophorylation).
4.  inhibitors = cyanide + CO - inhibit the function of ETC.
5.  Cyanide + CO --> block activity of cytochrome oxidase --> inhibit the ETS --> no production of H2O --> no activation of ATP synthase --> no ATP production.














6.  ETS:
  • accepts e- from energy carriers (NADH + FADH2) from glycolysis + Krebs cycle.
  • consists of mostly cytochromes (proteins with prosthetic groups).
  • produces H2O from O2 at the end
  • NADH produces 3 ATP
  • FADH2 produces 2 ATP.
  • net energy gain = 34 ATP molecules.

 

Aerobic Respiration - Krebs cycle

1. Krebs cycle:
  • biochemical reactions occurring in all living cells,
  • in the inner membrane of mitochondria.
  • involves a metabolic pathway (pyruvate --> CO2 + H2O) to generate energy.
  • also called citric acid cycle or trycarboxilic acid (TCA) cycle.

2.  Acetyl CoA initiates the Krebs cycle (by combining with oxaloacetate (4C) --> citrate).
3.  Citrate is decarboxilated and dehydrogenated.
4.  Energy stored = NADH, FADH2 and GTP.
5.  2 mol of CO2 are released (as waste product).
6.  NAD + FAD = H acceptors.
7.  1 mol of  ATP is gained.
8.  provides H for use in ETC (as energy for formation of ATP).

Friday, April 15, 2011

Aerobic Respiration - Glycolysis

Aerobic respiration is a process:
  1. which sugars are broken down - to release energy - in the presence of O2.
  2. occurs in three stages: glycolysis, Krebs cycle, electron transport system.










Glycolysis:
  1. takes place in cytoplasm of a living cell,
  2. glucose --> 2 mol of pyruvate.
  3. series of reactions catalysed by specific enzymes
  4. involves two phases: energy investment phase and energy pay off phase.
5. Energy investment phase:

  • glucose is broken down into 2 mol of PGAL
  • 2 mol of ATP are utilized in this phase.
  










6.   Energy pay off phase:
  • 2 mol of PGAL --> 2 mol of pyruvate.
  • 4 ATP is formed by substrate level phosphorylation.
  •  The net = 2 ATP + 2 NADH.

Experiment 14: Structure of flowers


Investigating...the flowers...and friends.
 
Must... must finish....must finish today!

Delonix regia in half.......










Hey!...Where's the ovary???



  
Concentrate....concentrate.........ohm..

<>
draw....draw.....draw....z z z z!

The orchid is cut into equal halves.



 
 


Thursday, April 14, 2011

Alternative mechanism of C fixation occurs in C4 and CAM plants

C4 plants:
1. occurs both in mesophyll + bundle sheath cells.
2. CO2 fixation is catalyzed by PEP carboxilase in mesophyll cells and sugar formation by RUBISCO in bundle sheath cells via Calvin cycle.
3. First product of CO2 fixation is a 4C compound oxaloacetate in C4 plants.

CAM plant:
1. live in hot climatic conditions
2. both C3 and C4 cycles occur.
4. fix CO2 during the night + synthesise sugar during the day.
5. G3P produced = used for the synthesis of sugars, amino acids and fatty acids.
6. Sugars formed = glucose, sucrose, starch + cellulose.
7. Lipids:
·  formed from glycerol + fatty acids.
·  Glycerol = formed directly from G3P
·  fatty acids = built from acetyl coenzyme A.
8. Protein formed by: conversion of G3P --> acetyl Co A (enters Krebs cycle) --> α-glutarate --> glutamate --> transamination --> form amino acids + proteins.