AQA BIOL5 ~ 17th June 2013 ~ A2 Biology

nooooo! the dna probe that is made is complementary to the persons dna sequence... eg the father

the son is then considered to have the same dna as the farther so the sons dna is mixed with the probe and if the same (if the guy is the sons dad) the probe will join... the probe will have a marker and will show up under a test for example if its florescent marker the probe with show if binded under uv light

I'm really, really not looking forward to this exam. I feel like I know the content better than in any of my other subjects but the way there is no flexibility around wording in answers and that kind of thing is really worrying me. Anyone got any tips? I'm just finding it hard to work out what the question is actually asking if that makes sense!

Energy transfer within living organisms




Energy is defined as the ability to do work. It is the main substance that enables humans, animals, plants and insects to carry out most activities. The main source of energy within a biological ecosystem is the sun. However, without all the different organisms in an ecosystem, the regeneration of energy and molecules would come to a standstill.




The main type of energy used by plants and animals is ATP. ATP is an immediate source of energy that only requires a single step reaction to produce energy; ATP- ADP + Pi.




As the sun is the main source of energy, photosynthesis in plants is one of the most fundamental biological systems in energy transfer. Photosynthesis occurs in 2 stages; light dependent reaction and the light independent reaction (calvin cycle). The main substances needed for photosynthesis is water, light and carbon dioxide. In the light dependent reaction light strikes a chlorophyll molecule, making it become excited, releasing an electron to a higher energy level. Light also cause the photolysis of water, forming oxygen, hydrogen proton and an electron (that is able to replace the one lost in the chlorophyll molecule). The excited electron now passes down a series of reactions forming ATP from ADP+Pi. This is due to the fact that the electron moves from a high energy level to a lower energy level releasing energy to catalyse the reaction. When the electron reaches the final energy level it here combines with a molecule of NADP and the hydrogen proton to produce NADPH (or reduced NADP). Although the Calvin cycle doesn't require light, it does indirectly. For the Calvin cycle to proceed one molecule of ATP and NADPH is needed which is produced from the light dependent reaction. The Calvin cycle starts with one molecule of RuBP (a 5C molecule) this combines with carbon dioxide (1C). By the help of the enzyme rubisco, 2 molecules of the 3C molecule GP is produced. 2 molecules of the 3C molecule TP is produced from GP by the addition of the energy from the reaction of ATP - ADP + Pi and the reduction using hydrogen from the molecule of NADPH. TP is now able to produce useful substances in the plant such as the hexose sugar glucose, or it can be regenerated back to RuBP. Glucose can be sorted in the plant as a food source. Although this process seems very energy efficient, only 10% of the suns rays actually strike the chlorophyll molecule. Most of the suns rays are reflected back to space, absorbed by other objects or are not of the correct wavelength. In practice, only 2% on the suns energy is used in photosynthesis.




Herbivores are now able to eat these plants. Converting 10% of the plants energy, into energy they can use themselves. However, herbivores and other mammals and insects also have their own way of producing energy. The oxygen that the plants release from the photolysis of water and the glucose produced by the calvin cycle can be used in the process of respiration. Respiration is split into 4 processes: glycolysis, links reaction, Krebs cycle and the electron transport chain. EXPLAIN 4 PROCESSES. (i am able to explain all 4 processes in detail, it will just save me some time to write another essay if i leave it out). 36 molecules of ATP is produced per glucose molecule. This also seems like a large amount of energy, however only 10% of energy is transferred from each stage in the food chain to the next. This explains why food chains are usually no longer than 5 stages long due to the lack of energy at the end of the chain.




ATP is used for many different things within the mammalian body. But one of the main things it is used for is muscle contraction. ATP bound to the head of the myosin filament causes it to have the right orientation to bind to the actin filament causing an actin-myosin cross bridge to be formed. ATP is able to be split into ADP + Pi releasing energy which changes the orientation of the myosin head, causing the actin filament to be slid along with it (sliding filament theory). ATP is then regenerated by the enzyme ATPase. Therefore the process occurs over and over again until the muscle becomes unstimulated and the tropomyosin moves back to block the myosin binding site on the actin filament due to no supply of Ca2+.




Plants also need ATP for active transport. Due to active transport occurring up a concentration gradient (from a low concentration of molecules to a high concentration of molecules) the kinetic energy of the molecules is not enough to power this type of transport. The ATP is broken down into ADP + Pi supplying energy for the process. This occurs in root hair cells. The active transport of minerals such as nitrates into the roots lowers the water potential in the cells causing water to move from a high water potential in the soil to a low water potential inside the root hair cells by osmosis. This water is then moved up the cell via the apoplastic and symplastic pathway using cohesion tension. This water is used to increase the turgidity of the cells and for photosynthesis.




Essay was marked 24(23)/25 taking into account that the 4 processes of resp would have to be added in.

Thats fantastic cheers!! Great structure and depth! Good luck for tomorrow

Thank you!

Last thing, do you know if the lac repressor is part of the spec or just extra knowledge?


Posted from TSR Mobile

Wait what? So you're saying they make the DNA probes from the person they are trying to compare the DNA with? Isn't that what I originally said??

"Ok so during genetic fingerprinting, after they have separated the strands and transferred the single stranded DNA fragments onto a nylon membrane they add DNA probes to it.

My question: Where are these probes taken from? Is it from the person or animal the extracted sample is being tested against? If so then does the subsequent number of bands correspond to the chance it was the person or animal's DNA? Because I'm not really sure what the book is saying.."

Wait what? So you're saying they make the DNA probes from the person they are trying to compare the DNA with? Isn't that what I originally said??

"Ok so during genetic fingerprinting, after they have separated the strands and transferred the single stranded DNA fragments onto a nylon membrane they add DNA probes to it.

My question: Where are these probes taken from? Is it from the person or animal the extracted sample is being tested against? If so then does the subsequent number of bands correspond to the chance it was the person or animal's DNA? Because I'm not really sure what the book is saying.."

Can anyone tell me what 'neutral' means on mark schemes? I've always wondered. Really dreading this essay and how science works questions tomorrow -.-

Got 79 in C4 !! Good Luck for tomorrow, how you holding up for it?

how much points should you make in the essays??

I sent you the essay?

yeah your original post was right.. my post was more to the person you were replying to.. he got it wrong, didnt want you making the mistake of taking on what someone else said when you were right in the first place

A DNA probe is a single strand of DNA with complementary bases to the gene or region of DNA you want to find, i.e. if we were screening for a mutated gene which may cause cancer, we create, in the lab, a DNA probe with complementary bases to the mutated gene. This probe is radioactively or flourescently labelled so we can visually see the mutated genes location once the complementary bases have paired up.

Hope that helped.


Posted from TSR Mobile

yeah your original post was right.. my post was more to the person you were replying to.. he got it wrong, didnt want you making the mistake of taking on what someone else said when you were right in the first place

pH, temperature and water potential are three things that are controlled carefully by the body.

Does pressure count as something the body needs to control? (homeostasis).