OCR A A-Level Biology Biological Processes [7th June 2023] Exam Chat

please could someone explain ultrafiltration and selective reabsorption in the excretion topic! i have never got my head around it and I’m really stressing out!! thank-you

Here’s a brief overview:

Ultrafiltration:

Blood arrives at glomerulus (bundle of capillaries in the nephron) through afferent arteriole (Afferent = Arriving)

The afferent arteriole has wider lumen than efferent arteriole which causes increased hydrostatic pressure in glomerulus.

This then causes water, salts, glucose and urea to be pushed out of capillary into Bowman’s capsule (passes through 3 layers - the capillary wall, the basement membrane and the epithelium of the bowman’s capsule) down a pressure gradient. This is now called glomerular filtrate. The glomerular filtrate then goes to the PCT (proximal convoluted tubule)

Note that proteins and blood cells are too big to be filtered out of the glomerulus so they stay in the blood.

Selective Reabsorption:

Lots of the solutes in the filtrate are needed by the body so they are reabsorbed. This happens at the PCT and the loop of Henle. Useful solutes (such as glucose and amino acids) are reabsorbed along the PCT by active transport. It’s called selective reabsorption as only the useful solutes are reabsorbed.

At the loop of Henle water and salts are reabsorbed. Which is Na+, Cl- and water that are reabsorbed depending on the water potential gradient.

Hope I explained this right and it was okay to understand. I really like this topic but I only understood it by going over it a couple of times with diagrams and speaking out loud to explain it to myself.

Here’s a more in depth PowerPoint I made on this topic: https://1drv.ms/p/s!AnDsLmM_5hzmjFGoLcdvTUAWcmcz

And here’s some videos of people explaining it much better than I could:

Biorach:
https://youtu.be/Vcrd9r62qWU
https://youtu.be/6HsdCxmv6BI

Miss Estruch:
https://youtu.be/6HsdCxmv6BI

Hope this helps!

i was just doing a past question and it was talking about HDLs LDLs (biological molecules) carrying cholestrol - is that something we need to know?? i've never even heard of it before

Nah, those questions are from the old spec. The only thing you need to know about cholesterol is how its properties and structure link to its function.

Does anyone have predictions for the papers?

Does anyone have predictions for the papers?

Here’s a brief overview:

Ultrafiltration:

Blood arrives at glomerulus (bundle of capillaries in the nephron) through afferent arteriole (Afferent = Arriving)

The afferent arteriole has wider lumen than efferent arteriole which causes increased hydrostatic pressure in glomerulus.

This then causes water, salts, glucose and urea to be pushed out of capillary into Bowman’s capsule (passes through 3 layers - the capillary wall, the basement membrane and the epithelium of the bowman’s capsule) down a pressure gradient. This is now called glomerular filtrate. The glomerular filtrate then goes to the PCT (proximal convoluted tubule)

Note that proteins and blood cells are too big to be filtered out of the glomerulus so they stay in the blood.

Selective Reabsorption:

Lots of the solutes in the filtrate are needed by the body so they are reabsorbed. This happens at the PCT and the loop of Henle. Useful solutes (such as glucose and amino acids) are reabsorbed along the PCT by active transport. It’s called selective reabsorption as only the useful solutes are reabsorbed.

At the loop of Henle water and salts are reabsorbed. Which is Na+, Cl- and water that are reabsorbed depending on the water potential gradient.

Hope I explained this right and it was okay to understand. I really like this topic but I only understood it by going over it a couple of times with diagrams and speaking out loud to explain it to myself.

Here’s a more in depth PowerPoint I made on this topic: https://1drv.ms/p/s!AnDsLmM_5hzmjFGoLcdvTUAWcmcz

And here’s some videos of people explaining it much better than I could:

Biorach:
https://youtu.be/Vcrd9r62qWU
https://youtu.be/6HsdCxmv6BI

Miss Estruch:
https://youtu.be/6HsdCxmv6BI

Hope this helps!

I posted this earlier. I made a document that has key topics that came up in previous papers from 2017 to 2022. I have predictions from Primrose Kitten as well.
https://docs.google.com/document/d/11KaMWppCA0RTdBy_TUJj7obqzOhzT9iIlbUWnZS9ys4/edit

ur powerpoint are so good omds do u have them for other topics???

So I looked at papers from 2017 to 2022 and I have made a document that contains all of the major topics that came up. I only focused on Section B, as that is literally 85% of the entire paper. I have also added the prediction topics made by Primrose Kitten. Yes, I bought paper 1 only to experiment, just to see if her predictions are accurate because so many people are saying they are good and some say that they are dead. Anyway, I'm going to drop the link to the document below. Just remember to focus on everything, especially topics like action potential and excretion because there will always be a question about identifying the structure from the insert. You can use this website to get exam questions. These questions are from Save My Exams but there are model answers as well so you don't have to waste time finding the question online or buy the £25 subscription:
https://chemistryonlinetuition.com/ocr-a-level-biology-topic-questions/

The link to the document:
https://docs.google.com/document/d/11KaMWppCA0RTdBy_TUJj7obqzOhzT9iIlbUWnZS9ys4/edit?usp=sharing

Anyways happy revising

Thankyou so much
could you do the same for paper 2 / paper 3 please

Thank you so much! Unfortunately I only started making them this year so only made them for topics I either really struggled with or really liked. Here are the links to ones I’ve made:

Plant Transport: https://1drv.ms/p/s!AnDsLmM_5hzmjFfOJX008Q7TByzz

Homeostasis: https://1drv.ms/p/s!AnDsLmM_5hzmjFUiXzgoACCvCVHT

Excretion: https://1drv.ms/p/s!AnDsLmM_5hzmjFGoLcdvTUAWcmcz

Ecosystems:
https://1drv.ms/p/s!AnDsLmM_5hzmjFZaYKD6N1w0lbKk

Patterns of Inheritance:
https://1drv.ms/p/s!AnDsLmM_5hzmjFj_06EZqEs2sLtY

They are not the most detailed PowerPoints and I’ve not included absolutely everything you need to know, I just made them to help my understanding of the topics. Also, I do OCR A so it follows that spec. Hope this helps!

how prepared is everyone feeling

how prepared is everyone feeling