Complete B4, B5 and B6 Notes

Notes for OCR unit 2 exam, hier tier. This should help with your revision but don't forget to try some past papers so you know what to expect :) hope this helps and good luck with your revision and your exam x

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Preview of Complete B4, B5 and B6 Notes

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Ocr Biology ­ B4, B5, B6
OCR Biology ­ B4, B5, B6
You will have already done B1, B2 and B3. These units are really just a follow up from the first
ones so make sure you have a quick read over the notes from last year to make sure you've
got the basics.
B4 ­ Homeostasis
Homeostasis it the maintenance of a constant internal environment. It's the way our body
keeps a range of factors at steady levels, which are required for cells to function properly.
Negative feedback
Allows a factor, for example temperature, to be kept very close to the ideal
There will always be slight fluctuations but negative feedback means that any
changes are reversed quickly
Many artificial systems use negative feedback. It may help to think of negative
feedback as a heater with a thermostat.
There are lots of different parts to a negative feedback system. These are...
o A stimulus
This is a change in the environment. It can occur inside or outside the
o Receptor
A sensor within the body which detects change
o Processing centre
Information from the receptor is sent here.
It co-ordinates the response
o Effector
The part that works to get the system back in balance
o Response
What happens as a result of the effectors action

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Ocr Biology ­ B4, B5, B6
Controlling body temperature
Our body temperature needs to be kept at about 37°c
There are several ways our body does this.
If we get too hot...
o Receptors in the brain detect temperature
o The information is sent to the processing centre in the brain called the
o Blood vessels near the skin relax so more heat is lost to the environment
o Sweat is produced.…read more

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Ocr Biology ­ B4, B5, B6
If the temperature is too cold the molecules don't have enough energy to collide
successfully. Even with the enzyme the reaction doesn't happen.
If the temperature is too hot the active site becomes denatured this means the
substrate no longer fits into the active site so the enzyme stops working. The same
thing happens if the Ph. is too low or too high.…read more

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Ocr Biology ­ B4, B5, B6
Exercise High Yes High
Hot day High Yes High
Urine tests can be used to diagnose diabetes and kidney disease
People with kidney failure sometimes need to be put on dialysis which works just like
the kidneys.
The fluid used in dialysis is made from water, sugar and salt
B5 ­ Growth and development
This section is all about how organisms produce new cells, how genes control growth and
development and how organisms develop from a single cell.…read more

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Ocr Biology ­ B4, B5, B6
o Chromosomes line up and spindle fibres form
o Spindle fibres pull the chromosomes apart
o The cell splits into two new cells. They are identical to the parent cell
Meiosis is a special type of cell division
It produces gametes (egg and sperm cells)
It happens in sex organs
Gametes contain half the number of chromosomes
Meiosis creates variation
This time we'll imagine a cell with c chromosomes. This is how it happens...…read more

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Ocr Biology ­ B4, B5, B6
o Chromosomes split. This creates two daughter cells
o Chromosomes line up. Spindle fibres form
o The cell splits. 4 gametes are formed.
DNA Structure
DNA is found in chromosomes in the nucleus of cells.
DNA was only recently discovered.…read more

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Ocr Biology ­ B4, B5, B6
C always pairs with G
Chromosomes are made up of long strands of DNA
DNA is instructions for making proteins. The order of the bases affects how they are
3 Bases code for one amino acid. Amino acids join together to make proteins.…read more

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Ocr Biology ­ B4, B5, B6
They are also found in adult bone marrow but they are harder to get and can't be
used for as many things
Some genes are active in every cell, for example the gene for making proteins to
transport chemicals
Some genes are only activated in particular cells, for example the insulin producing
gene is only activated in the pancreas
Plant growth
Plants have `growing points' called meristems
Meristems are found at the shoot and root tips
A meristem is…read more

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Ocr Biology ­ B4, B5, B6
Bright light being shone Cells at the back of the eyes Pupil becomes smaller
Knee being tapped The knee Knee jerk
Babies feet touching a flat
Feet Walking action
Putting your finger on a
Palm of the hand Grasping onto finger
babies palm
Spreading arms and legs ­
Baby hears a loud noise Ears
startle response
Nipple or finger in baby's
Mouth Sucking
Placing baby under water Whole body Hold breath and move limbs
The startle reflex…read more

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Ocr Biology ­ B4, B5, B6
o The bell was a secondary stimulus- it had no direct link to the response
Complex behaviours
Mammals can develop complex behaviours
As they interact with the environment new neuron pathways are formed
As they learn these pathways become more likely to transmit impulses
This is why skills are learnt through repetition
Repetition is a very effective way of learning
Start an activity
Nerve pathways formed
Repetition of a skill
Nerve pathways strengthen
Memory is the storage and retrieval…read more


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