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Biology Paper 2 Cheat Sheet (DRAFT) by

All content notes from this link: https://www.youtube.com/watch?v=keUwYKQk3Ec All revision tips and mnemonics (in the separate note section at the bottom of each box) are mine

This is a draft cheat sheet. It is a work in progress and is not finished yet.

B5: HOMEOS­TASIS & RESPONSE

Homeos­tasis

Homeostasis
an organism's ability to regula­te/­control its internal conditions so crucial reactions (including those involving enzymes) can happen at optimal rates
What needs to be regulated?
- Blood glucose concen­tration
- Internal temper­ature
- Water levels

The Nervous System

CNS
Central Nervous System (brain and spinal cord)
PNS
Peripheral Nervous System (all other nerves)
Normal Response
Stimulus
Receptor
Sensory Neurone
Relay Neurone
CNS
Motor Neurone
Effector
Synapse
the gap between two neurones
- electrical messages get converted into chemical neurot­ran­smi­tters which diffuse across the synapse to the other neurone
Reflex Arc
Stimulus
Receptor
Sensory Neurone
Relay Neurone
Motor Neurone
Effector
Response
Effectors
glands or muscles
Mnemonic for Reflex Arc = SRSRMER
Remember that a reflex arc BYPASSES THE CNS. It is an UNCONS­CIOUS ACTION.

Reaction Time Practical

- drop ruler between finger and thumb
- measure distance fallen before caught
- repeat and calculate mean
Indepe­ndent Variables
- stimulant (eg coffee) which increases neurot­ran­smi­ssion
- depressant (eg alcohol) which decreases neurot­ran­smi­ssion

The Brain

Cerebral Cortex
- higher function
- memory
- speech
- proble­m-s­olving
TOP PART THAT IS FOLDED
Cerebellum
- motor skills
- movement
- balance
- coordi­nation
BACK PART THAT LOOKS LIKE A LUMP
Medulla
- unconcious actions
- heart and breating rate
- signals to adrenal glands to release adrenaline
PART THAT CONNECTS TO AND INCLUDING BRAIN STEM
MRI Scans
allow doctors to see brain activity without surgery
Issues with the brain are diffic­ult­/im­pos­sible to treat safely due to:
- limited knowledge about the brain
- delicate nature of the brain

The Eye

To view near objects, ciliary muscles CONTRACT and suspensory ligaments SLACKEN which leads to a thick lens
To view far away objects, ciliary muscles RELAX and suspensory ligaments SLACKEN which leads to a thin lens
Retina Cells
- rods only detect light intensity
- cones are sensitive to red, blue or green wavele­ngths of light and provide colour inform­ation
- these signals travel to the brain via the optic nerve
Myopia
short-­sig­hte­dness
Hyperopia
long-s­igh­tedness
To remember which way round it is for accomo­dation:
- near objects => Ciliary muscles Contract and Suspensory ligaments Slacken
and the opposite must be true for far away objects

Thermo­reg­ulation

The brain detects blood temper­ature and then sends nervous and hormonal signals to effectors
TOO HOT
- vasodi­lation
- sweating
- hairs lie flat on skin
TOO COLD
- vasoco­nst­riction
- shivering
- hairs stand up
Vasodilation/constriction
increases or decreases blood flow to the skin which leads to more or less heat dissipated to the surrou­ndings respec­tively
To remember which way round it is, think about what happens when someone has a fever (too hot) or is very very cold. Fever = hot to touch = vasodi­lation. Cold = cold to touch = vasoco­nst­riction

Endocrine System

A system of glands that secrete hormones to send signals to effectors, transp­orted via blood making it slower than the nervous system
Pituitary gland
"­master gland" which sends hormonal signals to other glands
Thyroid
controls growth and basal metabolic rate
Pancreas
secretes insulin and glucagon to control blood sugar
Adrenal Glands
release adrenaline
Ovaries
release eggs and secrete hormones
Testes
produces sperm

Menstrual Cycle

FSH
- follicle stimul­ating hormone
- produced by pituitary gland
- causes an egg to mature
- causes ovaries to produce oestrogen
Oestrogen
- produced by ovaries
- causes uterus lining to thicken
- inhibits FSH so no more eggs mature until next cycle
- causes production of LH
LH
- lutein­ising hormone
- produced by pituitary gland
- causes egg to be released
- inhibits oestrogen
- causes the production of proges­terone
Proges­terone
- produced by ovaries
- maintains uterus lining
- inhibits LH
- causes production of FSH
REMEMBER FOLP
FSH and LH are both acronyms so both produced in the same place (pitui­tary)
Oestrogen and Proges­terone sound similar so both produced in the same place. Oestrogen and progesterone so produced in ovaries

Plant Hormones

These can be used to our advantage when growing plants
Gibber­llins
- induces germin­ation
- promotes flowering
- increases fruit size
Ethene
- causes ripening
Auxins
- control root and shoot growth
- weedki­llers
- rooting powders
- promoting growth in tissue cultures
Phototropism
- auxins are destroyed by sunlight
- they gather on the shaded side of a shoot making it grow more quickly
- shoot bends towards Sun
Geotropism
- auxins gather on the bottom of roots
- inhibits growth
- causes downward growth of the roots

Adrenaline and Thyroxine

Adrenal Glands
- release adrenaline into body
- increases blood flow and breathing rate
- prepares you for fight or flight
Thyroid
- secretes thyroxine
- controls body's metabolic rate
TOO LOW
- hypoth­alamus releases TRH
- causes pituitary to releasea TSH
- causes thyroid to release more thyroxine

Fertility Treatments

FSH/LH Injections
simple and relatively cheap
IVF
- in-vitro fertil­isation
- hard and expensive
- relatively low success rate
- can cause multiple embryos to develop
Process of IVF
- eggs collected after inducing release with LH
- fertilised in a lab (in-vitro = in glass)
- viable embryos inserted back into woman's uterus

Contra­ception

FSH-In­hib­iting Pills
stops eggs from maturing
Proges­terone Inject­ion­/Im­plant
stops eggs from being released
Barrier Methods (eg Condom)
stops sperm entering vagina
Abstinence
not having sex
Vasect­omy­/Cl­amping Oviduct
stops egg/sperm from reaching uterus

Kidney Function

ADH
- anti-d­iuretic hormone
- produced by pituitary gland
- causes tubules in kidneys to reabsorb MORE water into bloods­tream
TOO HIGH
- less ADH made
- more water sent to bladder
- more water lost as urine (paler)
TOO LOW
- more ADH made
- more water reabsorbed (less sent to bladder)
- less water lost as urine (more yellow)
Dialysis
- blood filtered by machine
- must be done regularly due to toxic urea
- takes a 4-6 hours 2-3 times a week
- diet must be watched
- expensive
- doesn't work forever
HOWEVER
- keeps patient alive until a transplant is possible
- no shortage
- no need for drugs
Transplant
- rejection is common
- immuno­sup­pre­ssant drugs must be taken
- shortage of organ donors
- standard surgical risks
- only last 8-9 years on average
HOWEVER
- diet doesn't need to be watched
- cheaper overall

Contro­lling Water and Nitrogen Levels

Water is lost through processes like
- exhalation
- sweating
- urination
Excess water is removed from the blood by the kidneys to the bladder
Water + Urea --> Urine
Urea
- contains ammonia
- ammonia produced through the deamin­ation of digested proteins in the liver
Kidneys selectively reabsorb
- glucose
- useful minerals
- useful ions

Contro­lling Blood Sugar

TOO HIGH
- pancreas secretes insulin
- glucose moves from bloods­tream into cells to be used for respir­ation
- excess gluxose converted into glycogen as energy store in liver
TOO LOW
- pancreas secretes glucagon
- liver and muscles convert glycogen back into glucose
- this leads to a negative feedback loop
Type 1 Diabetes
- pancreas cannot produce insulin
- insulin injections needed
Type 2 Diabetes
- cells do not absorb glucose as they should
- need to watch carbs intake in diet
- exercising regularly
- obesity increases risk
Glucose comes from digestion
Glucagon (like gone) makes glycogen go away (converted into glucose)
Glycogen is just the other one
  

B6: INHERI­TANCE, VARIATION & EVOLUTION

Meiosis

Meiosis
the process by which cells that are geneti­cally different from parent cells are made, for example, gametes
Process
- chromo­somes in diploid cell copied
- similar chromo­somes pair up and genes swapped between them
- cell divides to produce two diploid cells
- these divide again to produce 4 haploid cells (gametes)
There are 46 chromo­somes (23 pairs) in a human diploid cell

Sexual and Asexual Reprod­uction

Most animals reproduce sexually, while plants can reproduce both sexually (pollen and egg) and asexually.
Asexual reprod­uction happens by MITOSIS which means that the daughter cells will be identical (cloned)
Sexual Advantage:
offspring can become better adapted to the enviro­nment
Asexual Advantage:
only one organism is needed to reproduce

DNA and Protein Synthesis

Genome
the entire genetic code in an organism
DNA
double helix polymer which stores genetic code
Gene
portion of DNA that codes for a protein
- mapping these allows us to identify causes of disorders
Genotype
an organism's specific genetic code
Phenotype
how this code is expressed in physical charac­ter­istics
Monomer
- the monomers of DNA are nucleo­tides
- they are made from a sugar/­pho­sphate group
Bases
A + T pair, C + G pair.
- every three bases code for an amino acid
Protein Synthesis
- code is copied by mRNA (trans­cri­ption)
- this is taken to the ribosomes
- ribosomes assemble amino acids into polype­ptides then proteins (trans­lation)

Inheri­tance

Charac­ter­istics are determined yb the type and quantity of proteins synthe­sised. Some are controlled by one gene; however most are a result of two or more genes intera­cting.
Alleles
different versions of the same gene
Dominant Alleles
- expressed even when the genotype contains a recessive allele (BB or Bb)
- always repres­ented by a capital letter (B)
Recessive Alleles
- only expressed when there is no dominant allele (bb)
- always repres­ented with a lowercase letter (b)
Homozygous alleles
- BB = homozygous dominant
- bb = homozygous recessive
Hetero­zygous
Bb
Polyda­ctyly is caused by a dominant allele (PP or Pp)
Cystic Fibrosis is caused by a recessive allele (only cc)
Females have XX chromo­somes
Males have XY chromo­somes
PUNNETT SQUARES ARE ALSO IN THIS SECTION

Variation, Adaptation and Evolution

Variation in offspring is a result of both genetic and enviro­nmental factors
Darwin's Theory of Evolution
- random mutations results in variation
- some organisms are better adapted to enviro­nment
- these compete in "­sur­vival of the fittes­t"
- those better adapted are more likely to survive
- over time, these desirable charac­ter­istics are more pronounced
Lamarck's Theory of Evolution
- mutati­ons­/ad­apt­ation are a result of the enviro­nment affecting charac­ter­istics inherited by offspring.
- not a random process
Antibi­otic- Resistant Bacteria
- often used as evidence for Darwinian evolution
- if not all bacteria killed, those most resistant will reproduce
Species
if two organisms can breed to produce a fertile offspring, they are of the same species
Selective Breeding
breeding organisms that have desired charac­ter­istics to produce offspring in which they are more pronounced
Darwin = taller giraffes can get more food and therefore survive to reproduce while the short ones die off, therefore giraffes are taller.
Lamarck = shorter giraffes keep stretching up to get food