B10- B17 paper 2

combined aqa biology paper 2

homeostasis

the process of your body maintaining a constant internal environment, to maintain optimum conditions in response to internal and external changes

internal conditions include

water content, body temp and blood glucose concentration

why do we need homeostasis

to maintain the optimal conditions for enzyme and cell function

automatic control systems

include a chemical or nervous response

al control systems must contain

receptors, coordination centres and effectors

nervous system path

stimuli → receptor → sensory neurone → CNS → motor neurone → effector → response

required practical: ruler drop test

* method:
* Work with a partner.
* Person A holds out their hand with a gap between their thumb and first finger.
* Person B holds the ruler with the zero at the top of person A's thumb
* Person B drops the ruler without telling Person A and they must catch it.
* The number level with the top of person A's thumb is recorded in a suitable table. Repeat this ten times with each condition (drinking cola/ coffee, talking on the phone, etc)
* Swap places, and record another ten attempts.
* variables:
* independent - the distractions that cause differing reaction times
* dependant - the reaction time
* control - the length of ruler, the person, if they were looking at the ruler

how are reflex actions different from normal reactions

they do not involve the conscious part of the brain

reflex arc neurone

sensory, relay, motor

what are examples of reflex actions

breathing, heart rate, digestion and avoiding danger

endocrine system

composed of glands that secrete chemicals called hormones into the blood stream so they can travel to the target organ

nervous system compared to endocrine

endocrine has a much slower reaction and is more long lasting

pituitary gland

a master gland that secretes multiple hormones in response to changes in body conditions, some of these hormones act on other glands to secrete their hormone

examples of endocrine glands

pituitary, thyroid, adrenal glands and pancreas, ovaries, testes

blood glucose is monitored

by the pancreas

what does the pancreas do in response to blood glucose

produces the hormone insulin which allows glucose to move from the blood into the cells and be stored as glycogen in muscles and liver

pancreas also produces glucagon which

allows glycogen to be turned back into glucose and raises the blood glucose concertation

type 1 diabetes

blood glucose levels rise too high or fall too low because the pancreas isn’t secreting insulin or glucagon, which also means cells can’t get glucose

type 2 diabetes

blood glucose levels rise too high or too low because the body stops responding to it’s own insulin and glucagon

treating type 1 diabetes

injecting insulin to replace the hormone not being produced

treating type 2 diabetes

usually treated by a carbohydrate controlled diet and exercise, but if it doesn’t work you can use drugs

negative feedback (blood glucose)

glucagon and insulin, glucagon if its too low, insulin if its too high

negative feedback (oxygen and growth)

thyroxine and TSH, TSH is produced when thyroxine levels fall and limits production when they are too high

thyroxine

it is produced by the thyroid gland in your neck and controls you basal metabolic reactions (the rate at which substances are broken down and built up in the body). Controls how much oxygen is used by tissues and brain development

adrenaline

produced by the adrenal glands in response to fear and stress, it boosts heart rate and delivers more blood to muscles and brain to prepare the body for ‘flight or fight’

difference between thyroxine and adrenaline (apart from function)

thyroxine is controlled by negative feedback, adrenaline isn’t

during puberty reproductive hormones

cause secondary sexual characteristics to develop

oestrogen

the main female reproductive hormone that is produced by the ovaries, it stimulates the build of the uterus lining, secreted in response to FSH, inhibits FSH and stimulates LH

testosterone

is the main male reproductive hormone produced by the testes and stimulates the production of sperm

4 hormones in the menstrual cycle

oestrogen, progesterone, FSH, LH

follicle stimulating hormone

secreted by the pituitary gland and stimulates the maturing of the egg in the ovaries, stimulates production of oestrogen

luteinising hormone

secreted by the pituitary gland and stimulate the release of a mature egg from the ovaries

progesterone

secreted by the empty follicles in the ovary after ovulation, helps maintains a pregnancy, inhibits FSH and LH, maintains the lining of the uterus ready for the fertilised egg

which hormones stimulate/ inhibit each other in the menstrual cycle

* FSH - inhibited by high levels of oestrogen and progesterone, stimulated when all levels fall due to egg no being fertilised
* LH - inhibited by high levels of oestrogen and progesterone, stimulated when oestrogen

ways of contraception + examples

* hormones based, pill, injections, patches, intrauterine device
* barrier based, condoms, diaphragm
* other, abstinence, vasectomy, sterilisation

fertility drugs to treat infertility

FSH and LH can be taken to stimulate ovulation

IVF

FSH and LH are given to stimulate ova maturing, they are collected and fertilised outside the woman and allowed to start developing, then they are replaced in the uterus

pros of IVF

* infertile couples can have a child
* single women or same sex couples can have a child

cons of IVF

* expensive
* not always successful (causing emotional and physical stress)
* risk of multiple births
* ethical issues:
* children chosen to not have specific conditions, could be interpreted by people with the condition as disrespectful
* embryos are destroyed which destroys the chance for human life

differences between sexual and asexual reproduction

* asexual has no gametes, or fusion at all
* asexual produces clones or genetically identical daughter cells while sexual shows variation and is not genetically identical to either parent
* asexual uses mitosis, sexual uses meiosis

meiosis

1. genetic material copied, one chromosome becomes two
2. cell divides twice (one into two and then two into four) to form a gamete

gamete

all genetically different cells that contain half the number of chromosomes needed, example: egg cell, sperm cell

zygote

two gametes join together in fertilisation and form a single body cell with a full number of chromosomes

genome

the entire genetic material of an organism

DNA is

a polymer found inside chromosomes and is two strands twisted into a double helix structure

gene

a small section on the DNA that has a particular sequence of amino acids to code for specific proteins

alleles

different forms of genes

phenotype

outward or physical characteristics

genotype

genetic makeup determined by the type of allele

homozygote

both of the alleles are the same type, DD or dd

heterozygote

alleles are different, dD or Dd, so the dominant allele is inherited

most characteristics are a result of

multiple genes interacting rather than one single gene

methods of understanding genetic inheritance

punnet square and family trees

an ordinary human cell contains

23 pairs of chromosomes, 22 of which control the general characteristics while the sex chromosomes which carry genes that determine sex

male vs female chromosomes

male chromosomes are XY and female are XX

examples of inheritable disorders

polydactyly and cystic fibrosis

polydactyly

a dominant phenotype caused by a dominant allele inherited from one or both parent, causes extra fingers and toes

cystic fibrosis

a recessive phenotype caused by a recessive allele that both parent must have, affects the cell membrane and produces a sticky mucus that affects the lungs and pancreas

carrier

a person you has inherited the allele but does not have to condition

screening

test done on embryos and foetuses to see if they have inherited an allele which causes a genetic disorder

cons of embryo screening

* risks a miscarriage
* may not be reliable
* results might be that they have to terminate the pregnancy, raising ethical and religious concerns
* expensive
* ethical issue of destroying living embryos

variation

the different characteristics of individuals within a population

causes of variation

the different genes that are inherited, the conditions that the organism develops in , or a combo

theory of evolution by natural selection

all living things have evolved from simple life forms that first developed over 3 billion years ago

mutations (in reference to natural selection)

they occur continuously but rarely lead to a new phenotype, however if the new phenotype is suitable for the environment it can lead to rapid changes in the species

how a new species forms

when two populations of a species become so different they can’t interbreed anymore to produce a **fertile** offspring they have formed two species

selective breeding

a process where humans breed plants or animals to achieve a desired characteristic

examples of desired characteristics

* resistant to droughts/ pests/ disease
* high yield
* gentle temperament
* colours/ scents of flowers

limitations of selective breeding

* reduces the amount of alleles in the population, reducing variation
* new disease or climate could wipe out a whole population because they are all the same
* incest, due to being bred with organisms in the same family tree it leads to more inherited defects

genetic engineering

changing the genetic make-up of an organism, done in early stages of development to achieve a desired characteristic

genetic engineering, making bacteria produce insulin

1. ‘cut’ out the insulin gene from a healthy human cell with an enzyme
2. remove the plasmid from a bacteria cell and cut open using an enzyme
3. insert insulin gene into plasmid using another enzyme
4. insert the plasmid back into the bacteria (or another vector, prob a virus)
5. multiply that bacteria multiple times so it can produce inulin to be used to treat diabetes, or insert the DNA into an embryonic stem cell so it will be present in every cell

pros of genetic modification

* a person can be cured of a genetic disorder
* medical drugs can be made this way
* more food can be produced cheaply
* crops can grow in multiple climates
* improves growth rate of plants and animals
* crops can have added vitamins to support poorer countries

cons of genetic modification

* crops have bigger yield but seeds need to be rebought every year since crops are infertile
* modified genes may be introduced into wildlife and disrupt an entire ecosystem (might be a cause of a declining bee population)
* insects that are not pests are affected
* insects become resistant to pesticides
* unknown effects on human health after eating gm crops

fossils

remains of organisms from millions of years ago that can be found in rock, ice and other places

ways fossils could form

* hard parts of the animal that don’t decay, shells, bones, teeth
* organisms that cannot decay because of the conditions around it, for example if it is preserved in ice
* parts of the organism being replaced by minerals as they decay
* preserved traces like footprints, burrows and rootlet traces

how is a fossil formed (skeleton bones)

1. reptile (or dino) falls on the ground and dies
2. flesh/ soft bits decay and leave the skeleton undamaged and covered by clay/ sand or soil
3. over many millions of years the skeleton becomes mineralised and turns into rock, rocks shift and fossil becomes trapped
4. eventually erosion takes place and the fossil emerges

purpose of fossils

shows how much a species has changed in the long term (over many millions of years)

causes of extinction

* new disease
* change in the environment
* new predator
* more competition
* single catastrophic event (volcanoes eruption or meteorite)
* natural change in the species

why did dinosaurs die out (theories)

* meteorite caused huge fires, earthquakes, landslides and tsunamis. Dust rose to cover the sun causing the temperatures to drop and making in very dark
* ice melted and sea temperature dropped to 9C which means there was less plankton and less food

mutations in bacterial pathogens

results in new strains

process of bacteria becoming resistant to antibiotics

1. person takes antibiotic A and kills 95% of the bacteria, leaving 5% alive through mutation
2. happens again with antibiotic B
3. and again with antibiotic C
4. and over and over

why is bacteria becoming antibiotic resistant bad

developing a new antibiotic takes a long time and is quite slow which means it can’t keep up with the spread and bacteria population grows

classification

living things are classified into groups depending on structure and characteristics described by Carl Linnaeus

Linnaeus classified them into… (keep ponds clean or frogs get sick)

kingdom, phylum, class, order, family, genus, speicies

binomial system

an animals name with the first being the genus then the species

why was a new classification system proposed

microscopes improved and biochemical processes were more understood, now there are three domains then divided into 6 kingdoms

the 3 domains

archaea (primitive forms of bacteria, includes extremophiles), bacteria, eukaryotes

why is classification important

helps us understand evolutionary and ecological relationships

ecosystem

the interaction between living communities and non-living surroundings/ environment

interdependence

within a community species depend on each other for food, shelter, pollination, seed dispersal; so if one part is removed the whole community is affected

stable community

everything is balanced and populations remain relatively constant

abiotic factors affecting a community

* light intensity
* temperature
* moisture levels
* soil pH and minerals
* wind intensity
* carbon dioxide levels
* oxygen levels (aquatic plants)

biotic factors affecting a community

* availability of food
* new predators
* new pathogens/ diseases
* new competition

quadrats

used to find abundance of a species over a large area

competition in animals is over

* food
* territories
* mates

competition in plants is over

* light
* space
* water
* mineral ions

adaption

a feature or characteristic that allows the organism to survive and live normally

extremophiles

organisms, usually microorganisms, that are adapted to live in conditions where most enzymes would denature; live in extremely salty, high/ low pressures, or high/ low pressures.

adaptions may be

behavioural, structural or functional

photosynthetic organisms

producers of biomass for life on earth