Paper 4 Review Cambridge A Level Biology

what environmental factors increase chance of mutation?

- all types of ionising radiation - chemicals like mustard gas - ultraviolet radiation

3 Different ways in which the sequence of bases in a gene may be altered?

- base substitution - base addition -base deletion

Examples of crop improvement by selective breeding is:

- disease resistant rice and wheat - inbreeding and hybridisation producing vigorous and uniform varieties -incorporation of mutant alleles for gibberellin synthesis into dwarf varieties so increasing yield by having a greater proportion of energy put into grain

Phenotypic variation can be based on

- genetics - environmental factors

ultrastructure of striated muscle

-made up of thousands of muscle fibres -each fibre is made up of an arrangement of contractile proteins in the cytoplasm surrounded by a syncytium - sarcolemma: the cell surface membrane -sarcoplasm: the cytoplasm -sarcoplasmic reticulum: endoplasmic reticulum - the cell surface membrane has many deep infoldings in the interior of the muscle fibre called T-tubules. -the membranes of the sarcoplasmic reticulum have a huge number of protein pumps that transport calcium ions into the cisternae of the SR. -The sarcoplasm contains a large number of mitochondria, packed between myofibrils. -myofibril is made of filaments. -A line known as the Z line provides attachment for actin filaments, while the M line does the same for myosin filaments. -the part of a myofibril between two Z lines is called a sarcomere

Role of hormones in menstrual cycle

. -The hormones FSH and LH are released by the anterior pituitary glands and control the the activity of the ovaries. -During the monthly ovarian cycle, follicles develop which secret the steroid hormone oestrogen -After the female gamete is released from the ovary at ovulation, the remains of the follicle secretes progesterone follicle stimulating hormone (FSH): causes the maturation of an egg in the ovary luteinising hormone (LH): stimulates the release of the egg oestrogen: is involved in repairing and thickening the uterus lining progesterone: maintains it

how do contraceptive pills work to stop pregnancy

1. Inhibits secretion of LH/FSH 2. from anterior pituitary gland 3. Inhibits follicle development 4. Inhibits ovulation 5. thickens cervical mucus to stop sperm 6. prevents implantation

How muscles contract

1. Muscle contracts; Ca2+ released from stores in SR and binds to troponin 2. Troponin molecules change shape 3. Troponin and tropomyosin move to different positions on the thin filament to expose myosin-binding sites on the actin chain; Cross-links form between the thick and thin filaments 4. Myosin heads tilt and pull actin filaments towards the sarcomere centre 5. ATP hydrolysis forces heads to let go of actin 6. Heads spring back and the process repeats so long as: troponin and tropomyosin molecules don't block the binding site muscles have a supply of ATP

How does bacterial antibiotic resistance occur?

1. There is a mutation in allele giving resistance to penicillin 2. As bacteria have one loop of DNA they only have one copy of each gene so it'll be present in the phenotype 3. Bacteria without this allele will be killed by the antibiotic but this resistant one can survive and reproduce

stimulating muscles to contract

1. action potential arrives at presynaptic neurone 2. stimulates opening of voltage-gated channels for Ca2+ to diffuse into cytoplasm 3. Ca2+ cause vesicles containing acetylcholine (ACh) to move towards the presynaptic membrane 4. Vesicle fuses with the membrane, Ach is released and diffuses across the neuromuscular junction; Ach temporarily binds to receptor proteins on the sarcolemma; causes chemically-gated ion channels for Na+ to open 5. Na+ diffuse into the sarcolemma à depolarizes membrane à generates action potential that spreads along the membrane 6. Depolarization of sarcolemma spreads down to T-tubules 7. Channel proteins open: Ca2+ diffuses out of SR 8. Ca2+ binds to troponin. Tropomyosin moves to expose myosin-binding sites on actin filament; Myosin heads form cross-bridges with thin filaments à sarcomere shortens.

What allow for genetic diversity in meiosis?

1. bivalent line up 2. independent segregation chromosomes 3. crossing over 4. random mating and fertilisation

Diploid

2 sets of chromosomes so 22 pairs + X + Y

how does a reflex arc function?

A sensory neurone, an intermediate neurone and a motor neurone work together to bring about a response to a stimulis. Impulses are passed from neurone to neuron. In some reflex arcs impulse passes directly from sensory neurone to the motor neurone.

Structure of thin filaments

Actin which is a globular protein. Many actins are formed together as a chain then two of these chains are linked together to make one strand on thin filament. Also twisted around a actin chain is a fibrous protein called tropomyosin. Another protein, troponin is attached to the actin chain at regular intervals.

the morning-after pill

An oral contraceptive with high levels of progesterone-like hormone. It reduces chances of the sperm reaching and fertilising and egg or prevents pregnancy by stopping the embryo implanting the uterus.

heterozygous

An organism that has two different alleles for a trait

the birth control pill

Both oestrogen and progesterone suppress the secretion of FSH and LH from the anterior pituitary gland, This is an example of the negative feedback loop. Taking this daily, keeps oestrogen and progesterone concentrations high. This suppresses the secretion of FSH and Lh, and prevents their concentrations from reaching levels that would stimulate ovulation.

describe the role of calcium in striated muscle contraction:

Calcium ions are released by the sarcoplasmic reticulum and released into the sarcoplasm (the cytoplasm of the muscle cell). There the Ca2+ ions attach to one of the three molecules of tropnine, this causes the tropomyosin to displace slightly from the actin filaments. This displacement exposes the binding sites on the actin filaments. Thus myosin heads get instantly attached to the binding sites on the actin filament and cause the contraction of muscle.

describe the structure of a neuron (sensory and motor)

Cell body: This includes a nucleus which contains the genetic material (chromosomes) of the cell. Axon: This is a long extension from the cell body. Usually has two or more branches, called collateral branches. Myelin sheath: This insulates or protects the axon from external influences that might affect transmission of the nerve impulse. Dendrite: Receives nerve impulses or signals from adjacent neurons. This is how information is passed between neurons through electrical impulses. 1. Nucleus in cell body/soma 2 (long) dendron 3 (short) axon 4 many mitochondria (in cell body) 5 many ribosomes in cell body 6 synaptic knobs 7 Schwann cells / myelin sheath 8 nodes of Ranvier

Structure of Thick Filament (Myosin)

Composed of many molecules of myosin, which is a fibrous protein with a globular head. Within the thick filament, many myosin molecules all lie together in a bundle with their globular heads all pointing away from the M line.

Disruptive selection

Conditions favour both extremes of the population, maintains different phenotypes in a population

sensory receptor cells

Cpnverts stimulus into electrical impulse. e.g. the chemoreceptor cell found in human taste buds.

chromatin

DNA and histones

Allele

Different forms/variations of a gene

role of synapses in the nervous system

Ensure one-way transmission: because neurotransmitter is released on one side and its receptors are on the other Allow integration of impulses: Each sensory neurone has many branches at the end of its axon that forms synapses with many relay neurones Allow interconnection of nerve pathways: this happens in two ways, 1. Individual sensory and relay neurones have axons that branch out to form synapses with many different neurones 2. there are many neurones that terminate on each relay and motor neurone as they have dendrites to give a large surface area for synapses. Involved in memory and learning

Speciation

Formation of new species after a population becomes separated and cannot interbreed

Homozygous

Having two identical alleles for a particular gene

Where is there competition in genes?

In alleles in that specific segment of the gene in the specific individual, there is competition for the primary allele presented. In an individual there is a mix within an allele which competition resolves

Myelin Sheath

Made of Schawnn cells which spirals around the axon enclosing its cell surface membrane. Increases the speed of conduction and nerve impulses.

how is action potencial transmitted (along sensory neurone)

Na+ is attracted to areas with resting potencial, which causes Na+ ion channels to open. There is a transmission in one direction due to hyperpolarisation. The myelin sheath insulated the axons in order to protect it. Depolarisation only occurs in the nodes of ranvier (the unmyelinated areas). This process is called the saltatory conduction because action potencial 'jumps' from node to node.

describe and explain the transmission of an action potential in myelinated neurone

Neurones transmit electrical impulses along the cell surface membrane .the signals are very brief changes in the distribution of electrical charge across the cell surface membrane called action potentials, caused by very rapid movement of sodium ions and potassium ions into and out of the axon.

Directional selection

New environmental factor or new allele appears, then allele frequencies may change

Auxins and elongation growth

Plant growth regulator which influences aspects of growth such as elongation growth which determines the overall length of roots and shoots. Stimulates cells to pump hydrogen ions (protons) into the cell wall. This acidifies the cell walls which leads to a loosening of the bonds between cellulose microfibrils and the matrix that surround them. The cell absorb water by osmosis and the pressure potencial causes the wall to stretch so that these cells become longer, or elongate.

the Venus fly trap

Plant that obtains a supply of nitrogen compounds by trapping and digesting small animals, mostly insects. The specialised lead is divided into two lobes either side of a midrib. Inside the lobe has nectar-secreting glands around the edge to attract insects. Each lobe has three stiff sensory hairs that respond to being detected. The outer edges of the lobes have stiff hairs that interlock to trap the insect inside. They also have glands to secrete the insects. The touch of insect on the sensory hairs o the inside of the folded leaves of the plant stimulates action potencial that cause the leaf to fold over and trap the plant. The defection of a sensory hair activates calcium ion channels in cells at the base of the hair. These channels open so that the calcium ions flow in to generate a receptor potencial.

Cholinergic synapse (and the role of calcium ions)

Synapses that use Acetylcholine (ACh) as their neurotransmitter. They are an important kind of synapse because they pass on signals to muscle cells in all neuromuscular junctions. In the presynaptic neuron, the arrival of action potential causes calcium ion voltage-gated channels to open along with sodium ions into the cytoplasm of the presynaptic neurone. The calcium ions are places in the tissue surrounding the synapse, which gives a very steep electrochemical gradient for calcium ions. The influx of calcium ion stimulates vesicles containing ACh to move to the presynaptic membrane and fuse with it, emptying their contents into the synaptic cleft. The ACh diffuses across the synaptic cleft.

Gibberellin in germination of wheat or barley

The absorption of the water at the beginning of germination stimulates the embryo to produce this. These gibberellins diffuse to the aleurne layer and stimulate the cells to synthesise amylase. The amylase mobilises energy reserves by hydrolysing starch molecules in the endosperm, converting them to soluble maltose molecules.These maltose molecules are converted to glucose and transported to the embryo, providing a source of carbohydrate that can by respired to provide energy as the embryo begins to grow.

What are sex chromosomes?

X and Y chromosomes.

Nodes of Ranvier

a gap in the myelin sheath of a nerve, between adjacent Schwann cells. They are around 2-3 micrometer long.

genes have several different variants called..

alleles

in Gametogenesis in plants where are male gametes produced?

anthers

Which base altering states can be most significant?

base additions or deletion because they alter every set of 3 bases that follow in the DNA molecule. They cause 'frame shifts' and can introduce stop triplet part of the way through.

different alleles of a gene contain slightly different sequences of...

bases

What is a somatic cell?

body cell

What is the role of acetylcholinesterase?

break down acetylcholine (ACh) which Stops continuous production of action potencials.

What is fitness in the capacity of selection?

capacity of an organism to survive and transmit its genotype to offspring

What are abiotic factors in natural selection?

caused by non-living components of environment

What are biotic factors in natural selection?

caused by other living organisms

what is a gene mutation?

change in structure of DNA molecules producing a different allele of a gene

what is chromosome mutation?

changes in structure or number of whole chromosomes in a cell

Examples of biotic factors in natural selection:

competition for food predation inter species competition disease

Example of artificial selection

dairy cow highest milk yield cow enables the identification of best bulls. Cows with highest yield given egg production hormone to increase it and fertilised in vitro and put in surrogate mothers.

Genetic bottleneck

decrease in genetic diversity which occurs when the population descends from a small number of ancestors

what are alleles?

different versions of the same gene

Natural selection

effects of selection pressures (ie: predation) on frequency of alleles in a population

When do you use Hardy- Edinburg equation?

estimate the frequency of alleles in a population and to see whether a change in allele frequency is occurring in a population over time.

what is a phenotype?

external observable characteristics down to a gene ie: brown eyes

What is oogenesis?

formation of female gametes

What is spermogenesis?

formation of male gametes

what are genes?

genes are sections of DNA coding for a specific protein

where is autosomal linkage?

genes on a chromosome other than the sex chromosomes are said to be autosomal linked

what is a genotype?

genetic makeup of an organism

Haploid

having a single set of unpaired chromosomes so 23 individual as no pairs

Where are there no variations in a gene?

in critical genes like ones involved in respiration, that if varied would result in death so they aren't carried on

Selection pressure

increase chances of some alleles being passed on and decreasing chance of others example: predation by foxes with the lemmings

Reasons for extinction of animals:

killing by humans competition (inter or intra species) habitat loss or climate change

Gene

length of DNA that codes for a particular protein or polypeptide

What is independent segregation chromosomes?

mixes up alleles that gametes form, mixes genes in child, all diff variations of alleles

what is a substance that increase chance of mutation called?

mutagen

Stabilising selection

natural selection which favours middle phenotypes not extremes

motor neurones

nerve cells that carry messages from the CNS to effectors short dendrites and long axons

How does sympatric speciation work?

new species evolve from single species when inhabiting the same geographic region, for example as a result of a chromosomal error during cell division

Autosomes

non-sex chromosomes

a gene is made up of a sequence of ....

nucleotides

founder effect (genetic drift)

occurs when a few individuals become isolated from a larger population

What is phenotypic variation?

offspring have combinations of alleles which differ from those of their parents, this genetic variation produces phenotypic variation

where does oogenesis take place?

ovary

in gametogenesis in plants where are the female gametes produced?

ovule

What is allopatric speciation?

physical barrier ie: geographical which results in speciation

What is a chiasma?

point of chromosome cross over

Discontinous variation

qualitative differences with clearly distinguishable categories like: blood group

continous variation

quantitative differences small and hard to distinguish like: height

What is genetic drift?

random change in allele frequency

Homologous chromosomes

same matching chromosome pair within an individual - in same loci on the map in each person

The more we use antibiotics, the greater the ..

selection pressure we exert on bacteria to evolve resistance from them

An example of characteristics influenced by genetics and environment (polygenic)

siamese cats hair colour gene coding for enzyme tyrosinase which darkens the fur which is active only below 31 degrees therefore only body extremities of Siamese cats are dark

base substitution can also be called

silent mutation

chromosome

single molecule of DNA 23 pairs, 46 chromosomes in total

What is crossing over?

the exchange of homologous portions of nonsister chromatids

saltatory conduction

the jumping of action potentials from node to node

What is artificial selection?

the process by which humans change a species by changing selection pressures for desired characteristics

Evolution occurs because

there are changes in allele frequency and natural selection gives some alleles a better chance of survival than others

How does meiosis stage I differ to mitosis?

they line up in order, so chromosome one is with chromosome one. Bivalence in pairs with maternal and paternal chromosomes on each side varied but for correct/same chromosomes

sensory neurons

transmit impulses from receptors to the Central nervous system have long dendrites and short axons

intermediate (relay) neurons

transmit impulses from sensory neurones to motor neurons have short dendrites and varing axons

where does spermogenesis take place?

tubules in testes

How does allopatric speciation work?

two groups become separated and reproductively isolated as a result, the gene flow is reduced. Each group experiences a different selection pressure as the environment they live in is different. Over time, frequency of alleles changes via natural selection --> two parts of the population can no longer interbreed and become separate species.

what is autosomal linkage?

two or more gene loci are on same chromosome, genes are said to be linked

what is mutation?

unpredictable change in genetic material of an organism

Examples of abiotic factors in natural selection:

water supply nutrient levels in soil

How does stage II of meiosis differ to mitosis?

with 23 individual chromosomes not pairs