OCR A- Level Biology 2023

Hey, do we need to know about innate behaviour and habituation for the OCR A spec?? I was doing a past paper and it came up. Thanks in advance

What past paper did it come up in?

2016 unit 5
2016 is past 2015 for the new spec but the format was in the old spec (so they had more than 3 papers and it was layer out in units)

What do we actually need to know for biotechnology, the textbook has so much stuff and I can’t distinguish between what’s necessary and what isn’t

same honestly like how vital is knowing the entire production of cheese making and yogurt

hiii Im doing this question but got a bit confused on one of the steps: "Every four hours a pipette was used to transfer a sample of the culture to agar growth medium in a petri dish."
I don't really understand what the question means by transferring the bacteria every 4 hours?? I thought you only have to transfer it once but not every 4 hours? can anyone please help if u get it
Thanks so much!!

The question:
A student was asked to measure the population density of bacteria in a broth. The student was supplied with a broth culture of the bacterium Bacillus subtilis. The teacher suggested that the student should measure the population by transferring a sample of the broth to an agar plate then incubating the plate for 24 hours. The bacterial colonies could then be counted.

* Once the student had mastered the procedure to estimate population size, they decided to investigate the effect of temperature change on the rate of population growth.

The student used the following procedure:

A broth culture was incubated at 20°C.

Every four hours a pipette was used to transfer a sample of the culture to agar growth medium in a petri dish.

The sample was spread over the surface of the agar by tilting and swirling the dish.

The petri dish was incubated at 30°C for 24 hours.

After 24 hours the petri dish was labelled and stored in a refrigerator until all results were complete.

The procedure was repeated with broth cultures incubated at 10°C, 30°C and 40°C.

Once all the agar plates had been collected the student removed them from the refrigerator and estimated population size by counting the visible colonies.

Finally the student converted the data into a growth rate.

Describe and explain modifications that the student should make to improve the investigation and ensure the data collected are valid. (You may assume that full aseptic technique was used.)

I think it is a prompt for the question asked because if every 4 hours the culture is being added to the agar, it puts the previous samples at an disadvantage because they are not in their optimum condition and could affect the final data collected?

hey guys should we be practicing past paper questions other than the 2016-2021 ones on PMT, the extra topic questions? is that the old spec?

I’d say for now yes because it helps you to figure out the topics you know and the ones you don’t. It also means you are doing practice paper but at the same time are saving the newer ones for closer to the exams? - at least that’s what I’m doing! 😁

thank you for replying, and good luck! 💓

how many hours of revision are you guys doing at this point in time per day?

hey guys should we be practicing past paper questions other than the 2016-2021 ones on PMT, the extra topic questions? is that the old spec?

hiii does anyone know why the answer is A for this mcq? I think all of them happen during meiosis, so is it because only crossing over causes genetic variation in the offspring?

Meiosis is an important feature of sexual reproduction.
Which of the following processes occurs during meiosis and contributes to genetic variation in the offspring?

1 crossing over
2 gene mutation
3 random fertilisation

A 1, 2 and 3
B only 1 and 2
C only 2 and 3
D only 1