AQA June 2017 - Past Paper 7402/01 Guide with the Markscheme

AQA released the June 2017 Biology papers - they are all available at 

http://www.aqa.org.uk/subjects/science/as-and-a-level/biology-7401-7402/assessment-resources

I combined the 7402/01 paper with the mark-scheme to make it easier to follow and interpret. If you find it useful then please like and share.

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AQA June 2017 - Past Paper 7402/02 Guide with the Markscheme

AQA released the June 2017 Biology papers - they are all available at 

http://www.aqa.org.uk/subjects/science/as-and-a-level/biology-7401-7402/assessment-resources

I combined the 7402/02 paper with the markscheme to make it easier to follow and interpret. If you find it useful then please like and share.

Please like and share (and click on a advert to help with the hosting costs !)

AQA June 2017 - Past Paper 7402/03 Guide with the Markscheme

AQA released the June 2017 Biology papers - they are all available at 

http://www.aqa.org.uk/subjects/science/as-and-a-level/biology-7401-7402/assessment-resources

I combined the 7402/03 paper with the markscheme to make it easier to follow and interpret. If you find it useful then please like and share.

Please like and share (and click on a advert to help with the hosting costs !)

Common Mistakes and misconceptions with Cells and Membranes

A few common mistakes with molecules and cells and membranes 

1. Ions are polar….. - NO - Ions are charged hence they cannot pass through the hydrophobic inside of the Cell Surface Membrane.

2. The nucleolus contains rRNA - NO - the nucleolus synthesizes rRNA (which forms part of ribosome), but it itself is made of DNA (coiled around histones)

3. Fatty acid/ hydrocarbon tails interact with hydrophobic bonds - NO Fatty acid/ hydrocarbon tails interact with hydrophobic interactions

4. Ribosomes have one membrane - NO -  Ribosomes do not have membranes

5. Facilitated diffusion uses only channel proteins. Active transport uses only carrier proteins. NO - Facilitated diffusion uses both channel proteins and carrier proteins. The carrier protein can change conformation without ATP hydrolysis. Active transport uses only carrier proteins which can change conformation only upon ATP hydrolysis

6. Exocytosis is the same as active transport - NO.- Exocytosis is a type of bulk transport requiring vesicles (and ATP to move the vesicles) , while active transport uses carrier proteins.

7. Mitochondria carry out respiration - NO - Mitochondria carry out aerobic respiration

A-level Biological Molecules - 11 basic points to help you learn

1. 99% of life is Carbon, Hydrogen, Oxygen and Nitrogen (and a bit of Phosphate)

2. Mono is one, Di (and Bi) is two, Tri is three, oligo is a few, poly is many.

3. Anything ending in -ose is a sugar, -ol is a lipid. - ase is an enzyme and all enzymes are proteins

4. Beta glucose is only in Cellulose - everything else is Alpha glucose

5. A condensation reaction makes water and joins two monomers together - glycosidic bond is a condensation reaction

6. A hydrolysis reaction breaks a bond (lysis means split) - with the addition of water (hydro)

7. A Glycosidic bond joins 2 monosaccarides together 

8. A peptide bond joins 2 amino acids together (many-poly, by peptide bonds...=polypeptide)

9. A lipid is made from a glycerol joined by an ester bond to 3 (tri) fatty acids - hence triglyceride

10. Carbohydrates and lipids are just C,H,O. Amino acids are C,H,O,N (ok, and a bit of Sulphur with 2 of the R groups), Nucleic acids (DNA, RNA, ATP) have C,H,O,N,P. Phospholipids are C,H,O,P.

11. Large or non-polar molecules are insoluble in water hence Starch, Glycogen and Fats are osmotically inactive which means they are good energy storage molecules

How to Understand the Cardiac Cycle - Now with a Quiz and Questions

There are many concepts in A level Biology where a small adjustment in thought process and understanding can lead to sudden clarity. This is certainly true of the cardiac cycle.

Start with simple concepts and build upon them.

Don’t start with looking at the human heart, four chambers, four valves and a great deal of plumbing.

Begin with drawing a single flexible tube, filled with fluid, now imagine you squeeze the middle. The volume decreases, therefore the pressure increases and the fluid will move to where the pressure is lower. Remember this principle.

Now consider how we could increase the efficiency by preventing flow in one direction?

Introduce two flaps of flesh on the inside of the pipe. These are pushed open and pushed closed by the flow of blood, we call these valves.

The valves in your circulatory system are completely passive (they are pushed open by the flow of blood).

Now let’s go back to the valve we have added to create two regions of the pipe. On one side of the valve we have a chamber called the atrium, on the other we have a chamber called the ventricle.

As blood flows into the atria from the vein (vena cava or pulmonary vein), the atria fill with blood and the pressure increases (because there is more blood !!), when the pressure is higher in the atria than in the ventricle the blood pushes open the valve and falls into the ventricle.

After the valve has been pushed open by the flow of blood from atria into ventricle, then the atria contract to push the rest of the blood through the already open valve into the ventricle

Then the muscle (cardiac) surrounding the chamber (ventricle) contracts then volume of the chamber decreases, which increases the pressure (remember the principle) and the blood moves back toward the atrium which pushes the valve between the atrium and the ventricle closed.

Blood leaving the ventricle pushes open the valve between the ventricle and the aorta. The blood flowing through the valve into the aorta increases the pressure and pushes the walls of the aorta outwards. As the ventricle relaxes, the recoil of the aortic walls pushes blood back to the ventricle, which pushes the valve closed.

Think of the four-chambered human heart as two, two-chambered hearts joined back to back, as they pump blood round two completely separate systems (the systemic and the pulmonary).

Remember, as volume decreases, pressure increases. Blood pushes valves open, and pushes them closed. Blood flows to the lowest pressure. Stick to those principles and when you understand them, apply the knowledge to the human heart.