Feb march 2026 9700 variant 22 solved

Added: 2026-05-12

[00:00:02]Hello students, this is Dr. Faizan Mirza. In this video, I'm discussing with you the expected answers because the MS is not yet out of Feb-March 2026 paper. Variant two, biology AS.

[00:00:15]The first question they have simply asked you to put a tick or cross for the animal and the plant cell regarding the feature of 80S ribosome.

[00:00:22]We know they are present in both. The cell wall is composed of peptidoglycan, neither. Large permanent vacuole, no for animal cell, yes for plant cell. The next part shows to you phloem sieve tube and a cell A, and you can see the this this this sieve sieve plate is there. They are showing to you a part of the cell surface membrane of cell A. We know cell A is the companion cell. So, this companion cell is having the plasmodesmas, various plasmodesmas that allow sucrose to enter into the sieve tube. This particular cell membrane is having a proton pump. We know the proton pump can push the H+ ions out into the apoplast pathway, and the cotransporter protein then allow the same H+ ion together with the sucrose to enter back into the companion cell by the secondary active transport. And the H+ can then go back again by active transport. So, H+ goes out by active transport via using ATP breakdown.

[00:01:15]Uh the energy released from ATP breakdown and the sucrose H+ cotransporter brings it back. So, if there are more cotransporters, so a lot of uh uh sucrose can get moved in like quickly. Describe and explain how the structure of cell A is related to its function of transporting sucrose into the phloem sieve tube. So, we will just just mention all this thing. The cell is companion cell. Proton pump in its membrane used to pump plus push the H+ ions out into the apoplastic pathway cell wall by active transport. This establish the electrochemical gradient across the cell surface membrane, and the H+ ions the cotransport protein uses the electrochemical gradient to transport sucrose back into the companion cell against the gradient where the H+ ions are moving down the gradient. So, this becomes a very important point that one of the things is moving down the gradient, the other is moving against the gradient. That's sucrose being actively pumped in, like pushed in, like pulled in. Sorry, not pumped in.

[00:02:04]Sucrose enters into the sieve tube element by crossing the plasmodesmata down the gradient while the H+ ion moves out again with the same proton pump.

[00:02:12]We can add another point of many co-transporters being there and many plasmodesmata being there, so this this process occurs like uh at a fast pace because it is shown to us in the diagram. Two of them are shown to you, so you will use this as a hint.

[00:02:26]Multiple plasmodesmata are shown to you, so we use this as a hint.

[00:02:30]Explain how the sucrose that enters into the phloem sieve tube from cell A is transported to the sink. So, we know that sucrose lowers the water potential of the sieve tube, so water enters by osmosis down the water potential gradient from the xylem to the sieve tube element. The hydrostatic pressure gets raised in the sieve tube element and the mass flow occurs to the sink.

[00:02:46]Moving into the sink, sucrose water solution moves in one direction along sieve tube. We mentioned this that it goes along one direction crossing sieve plates through the sieve pores. Upon reaching sink, the sucrose is removed at the sink during unloading and this maintains the gradient.

[00:03:02]Question two deals with blood transports many substances including gases. Explain how water The properties of water allow this to function in the mammalian circulatory system. So, we know that water acts as a solvent because water is polar. It's able to It's able to dissolve polar substances such as glucose, amino acids. It's able to dissolve uh The property allows the water to form hydrogen bond with positively They are charged substances as well as negatively charged ones such as sodium ion, hydrogen carbonate ions, chloride ions.

[00:03:31]We give example wherever possible because the command word is explain.

[00:03:36]Then cohesion between water molecules allow blood to flow as a continuous column within vessel without breaking and incompressibility helps maintain pressure in the liquid state allow the blood to flow. High latent heat of vaporization allow blood to lose heat near the surface of skin cooling the body.

[00:03:51]Although the last point is not very relevant transportation, but yes, uh I will do that as well.

[00:03:56]Um state two different ways in which carbon dioxide is transported in blood.

[00:04:00]So, we include 10% of carbon dioxide transported as carbon monohemoglobin inside RBC bound to the amine group of hemoglobin. And carbon carbon dioxide is transported as 5% solution plasma. We can go for the bicarbonate ion as well.

[00:04:12]So, mentioning the percentage and all.

[00:04:14]So, let's move the next question. The next part.

[00:04:18]Here uh uh the ribbon diagram is shown to you of a myoglobin. They're saying myoglobin is found in the muscle tissue. You can see that this is one protein made from one amine end and one carboxylate. It means this is one polypeptide chain. There's an alpha helix. So, this is alpha helix and there are the beta strands as well.

[00:04:37]And and there are some random coils and there's just one prosthetic group with the iron ion. So, only a single oxygen molecule can attach to it.

[00:04:45]They're asking you to describe the similarities and differences between the structure of myoglobin molecule shown in figure 2.1 with the structure of hemoglobin. Recall this hemoglobin. So, both hemoglobin and myoglobin have alpha helices and beta pleated strands. They both contain heme groups, prosthetic groups. They both have carboxyl and the NH terminals on opposite ends. Myoglobin is having one polypeptide chain.

[00:05:03]Hemoglobin is having four. And there is one heme group in myoglobin. There are four in a hemoglobin. Myoglobin is having one oxygen molecule that can binding site. Whereas hemoglobin have four oxygen binding sites.

[00:05:15]Contracting muscles have a higher requirement of oxygen which is supplied to the muscle cell by hemoglobin in the RBC. Myoglobin has a higher affinity of oxygen than hemoglobin. So, a higher affinity of oxygen for hemoglobin suggests why it's important for the muscle function that myoglobin has a higher affinity, why not lower affinity?

[00:05:30]Because if it had lower affinity, it would lose oxygen before hemoglobin could lose. So, this ensures he oxygen is transferred hemoglobin to myoglobin and then to the muscle and not the other way around. Uh like hemoglobin passes on the oxygen to the muscle and not myoglobin. Myoglobin acts as a store of oxygen and can provide additional oxygen only when the contracting muscle is respiring at a very high rate and needs a lot of supply of oxygen beyond which the aerobic capacity can deliver. So, myoglobin release unloads oxygen only at very low partial pressures when the demand of oxygen is not being met by oxyhemoglobin alone.

[00:06:03]The next question deals with raffinose, a sugar found in many plants. They are saying this is a structure of raffinose.

[00:06:09]It is formed by three different monosaccharide, one of which is glucose.

[00:06:12]On the figure, draw a part with that can that can be hydrolyzed to form glucose.

[00:06:16]So, we know that this part can be hydrolyzed to form glucose. So, we just encircle it. It needs to be terminal.

[00:06:21]This cannot form glucose because it's not the six-carbon sugar. It is a six-carbon sugar sugar, but the but there are like four carbons in the ring and two carbons outside the ring. So, we need to have a ring which is having five carbons in the ring and a sixth outside the ring, which is glucose.

[00:06:39]So, which type of glucose form? We know alpha glucose form the glycosidic bonds here.

[00:06:45]Number of glycosidic bonds in one molecule, reducing sugar, non-reducing sugar. So, glucose is having no glycosidic bond. We know that it's a reducing sugar. Maltose is having one bond because made from two glucose units. It's a reducing sugar. Raffinose, it's having two glycosidic bonds and it's a non-reducing sugar.

[00:07:02]Some bacteria in human digestive system has an enzyme known as alpha gal which breaks down raffinose. So, this is a breakdown of alpha gal by alpha gal shown to you. So, again, the Vmax can be read from here. Half Vmax can be tabulated like just just calculated by dividing that by two and you can just drop it down on X axis to read the value of KM. Again, you know how to read the axis. You can just do a simple conversion. How many squares represent how many units and come up with the value here. You need to make sure that you don't miss on to the unit when mentioning the this this particular KM value. So, this will be the KM value here. And Uh, by mistake I've not I mentioned arbitrary unit. These are not arbitrary unit. This is mole dm cubed.

[00:07:47]Okay.

[00:07:48]One molecule is formed by breakdown of raffinose as mentioned to you and which is this? This is a fatty acid. We know it's a fatty acid because of the carboxylic end and there's a term three three carbons there.

[00:08:00]The molecule shown in figure 3.3 can be used to make a triglyceride. Describe how this molecule becomes part of a triglyceride molecule. The fatty acid can react with glycerol. Glycerol we know is a a water molecule removed by condensation reaction. OH is lost from the carboxylic acid and fatty fatty acid and H is lost on the OH of glycerol.

[00:08:17]These both are joined together by ester linkage. So, glycerol is having three of these. So, a total of three fatty acids can attach including this one. So, a total of three water three water molecules will be removed.

[00:08:28]RSV is a virus that can infect human gaseous system. Explain why this disease caused by RSV is an example of infectious disease. This disease is caused by a pathogen and a pathogen gets transferred among different individuals.

[00:08:40]So, this must be having its own transmission cycle. That's why it's said this is an infectious disease. This diagram shows you the structure of RSV.

[00:08:47]So, if you look closely, protein subunits are shown here and there is a strand of RNA. So, this is the typical thing that a virus is having. Then there is an outer envelope. If there's an outer envelope, we know that envelope is made up of phospholipids. We have studied them in HIV as well. So, they're asking about Q. So, Q is the lipid envelope. The structure in figure 4.1 composed of protein subunits is capsid.

[00:09:09]This is the region in the bronchus shown as X. Y is the ciliated epithelial lining. So, X must be the smooth muscles.

[00:09:18]State the function of labeled structure Y. These are the the the cilia. So, they they move the mucus over the surface of lining of the bronchus.

[00:09:26]Then they have mentioned two forms in which this can be treated in immunity.

[00:09:30]So, injection of monoclonal antibody provide artificial passive immunity whereas vaccination provide artificial active immunity.

[00:09:36]Active immunity is where you know that the memory cells get get produced. And passive is when you receive antibodies.

[00:09:42]Outline how monoclonal antibody to protect person from RSV produced using hybridoma method. So, you inject the RSV antigen to the mice and isolate the isolate the B lymphocytes and plasma cells.

[00:09:54]Uh fuse these cells with myeloma cell calling fusion using fusion or electrical current. A hybridoma cell forms. Select the desired anti-SRV antibody producing cells. Allow the hybridoma cells to grow into uh tissue culture in lab.

[00:10:06]These clone of cells produce monoclonal antibody that can be used to protect people against RSV.

[00:10:12]State one advantage of using vaccine instead of monoclonal antibody. So, vaccine is having antigen. So, it provides long-term protection. Memory cells of B and T are produced. These are long-lived cells, so they provide lasting protection. Monoclonal antibody is not an antigen, so it's just providing uh there's no immune response being evoked. So, it's a short-term protection only.

[00:10:31]Phagocytes can remove cells from the body that have been infected by a virus such as this. Outline the event that that lead to the formation of phagocytic vacuole.

[00:10:39]Uh so, upon recognition of infected cell, the cell surface membrane wraps around the infected cell forming pseudopodia. Pseudopodia are those structures that form like this is the pseudopodia. So, it literally this is the this is the thing it need to uh like phagocytize. The cell produces a mouth part and it engulfs it and pulls it in.

[00:10:59]So, it it produces pseudopodia. Uh the cell around it encloses it invaginates the vesicle pinches inward, the cytoskeleton moves in the phagocytosis uh vacuole enters the cytoplasm of the phagocyte.

[00:11:11]Which cell will be used to destroy the lysosome because it's having the hydrolytic enzymes?

[00:11:16]Next question dealing with DNA replication. Describe the role of DNA enzyme DNA polymerase in DNA replication. So, DNA polymerase allow activity nucleotide to bind to the exposed base of the DNA strand being recopied by the complementary base pairing. It ensure that adenine paired with thymine making two hydrogen bond, guanine paired with cytosine using three hydrogen bond. This enzyme allow new strands to elongate in 5' to 3' direction both. Uh one nucleotide is joined by the complementary base pair.

[00:11:39]DNA polymerase allow phosphodiester bonds to form along the sugar phosphate backbone. So, we have to follow DNA polymerase only. We will not discuss DNA ligase here.

[00:11:49]They are saying the two strands of DNA molecule are described as antiparallel.

[00:11:51]Explain how the Explain the consequences of having antiparallel arrangement. The consequence is that one strand continues on reading, the other goes lagging. So, since DNA polymerase can add nucleotide in 5' to 3' direction of the new strand, the antiparallel arrangement of DNA strand is DNA molecule being copied results in new strand being synthesized as a continuous strand called the leading strand. They are complementary to the 3' to 5' end, whereas the other strand, which is the lagging strand, is complementary to 5' to 3' end. This lagging strand is having Okazaki fragment, which are then later joined by DNA ligase. The telomeres shorten at each end of the lagging strand.

[00:12:26]Then they are saying after separation of complementary strand during DNA replication, the separated strand of DNA can become twisted coil together to form tangles.

[00:12:34]Topoiso- Topoiso- Topoiso- Not topoiso-. This is topoiso- is able to remove these tangles by two steps. Step one, topoiso- form a complex with the tangled DNA catalyzes cutting of both strands. Then topoiso- catalyzes repairs on the cuts being made.

[00:12:50]Ectoposide is a chemical that can bind to this DNA complex at step one, which means here. This makes the complex very stable and prevents step two from occurring, which means the cut will be there and the cut will not be repaired.

[00:13:01]Suggest how this might explain why this can be used in treatment of diseases such as tumors. So, this ectoposo- ectoposide as a drug in treatment tumors prevent DNA repair from after cutting.

[00:13:13]So, DNA damage accumulates in tumor cells. This stops cell division in the tumor cell and removes Question six. It deals with the fill in the blank. So, it simply asks for the transport protein that include uh that are allowing facilitated diffusion to occur. So, those are channel protein. Uh fluidity is maintained by cholesterol.

[00:13:32]And the fatty acid tails, uh they are uh they are like merged together and held together by hydrophobic interactions.

[00:13:40]I hope this uh this wasn't easy paper, by the way. So, I hope this video was helpful for you.

[00:13:45]Uh um that's it from my side. Thank you